Self-excitation push-pull type converter

Abstract

A self-excitation push-pull type converter with a transformer having a closed magnetic core or iron core, which formed of a main part (52) and a local part (53). The local part reaches magnetic saturation earlier than the main part under the same increasing magnetic field excitation. When the self-excitation push-pull type converter is in a light load state, the efficiency is significantly improved, and further improved in a rated load state. As the number of turns of the coil on the magnetic saturation transformer is reduced, the working frequency of the converter increases while still keeping the loss low. The probability of generating a current peak at the moments of switching on or off is reduced, thereby further improving the efficiency and reducing output ripples.

Claims

1. A self-excitation push-pull converter, comprising a first transistor and a second transistor, each with an emitter and a collector where the emitter of the first transistor is connected to the emitter of the second transistor, and a transformer with a magnetic core and two primary side coils each having a first end and a second end, wherein the first ends of the two primary side coils are connected to each other to form a voltage input and the second ends of the two primary side coils are connected to the collector of the first transistor and the collector of the second transistor, respectively, and the magnetic core has a closed magnetic path and comprises a main section and at least one partial section, said partial section reaching magnetic saturation before said main section when excited under a same increasing magnetic field, wherein said partial section has a sectional area of a size less than 80% and greater than 4% of a sectional area of said main section, wherein a length of said partial section is negatively correlated to a ratio of the sectional area of said main section to the sectional area of said partial section.

2. The self-excitation push-pull converter according to claim 1, wherein with said main section is wound with a coil, while said partial section is not wound with any coil.

3. The self-excitation push-pull converter according to claim 1, wherein said main section and said partial section are made of an identical material.

4. The self-excitation push-pull converter according to claim 1, wherein there is a plurality of said partial sections, and the sum of the lengths of said closed magnetic path, and said partial sections each has a sectional area of a size less than 80% and greater than 4% of that of said main section.

5. The self-excitation push-pull converter according to claim 3, wherein said partial section has a length of over 0.05 mm.

6. The self-excitation push-pull converter according to claim 1, wherein said main section and said partial section are made of different materials.

7. The self-excitation push-pull converter according to claim 6, wherein there is one or more said partial section and the sum of the lengths of said partial sections is less than one eighth of the length of said closed magnetic path.

8. The self-excitation push-pull converter according to claim 7, wherein feature said partial sections each has a length of over 0.02 mm.

9. The self-excitation push-pull converter according to claim 1, said magmatic core further comprises a transition section to facilitate demoulding between said main section and said partial section.

10. The self-excitation push-pull converter according to claim 1, wherein there are two or more salient points on said main section.

11. The self-excitation push-pull converter according to claim 1, wherein a proportion of the length of the partial section in a length of a total magnetic path of the magnetic core is y/(k-1), wherein y is an expected value, and k is the ratio of the sectional area of the main section to the sectional area of the partial section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1-1 is a common application circuit diagram of the Royer circuit of self-excitation push-pull converter;

(2) FIG. 1-2 is a common application circuit diagram of the Jensen circuit of self-excitation push-pull converter;

(3) FIG. 2-1 is the output side waveform diagram of the Royer circuit winding Ns in FIG. 1-1;

(4) FIG. 2-2 is the DC output voltage of the self-excitation push-pull converter superposed with the ripple waveform;

(5) FIG. 3 is the square hysteresis loop of the magnetic core of transformer B1 in the Royer circuit of FIG. 1-1;

(6) FIG. 4 shows a generally known full-wave rectifying circuit;

(7) FIG. 5 is the ring type magnetic core used by the existing self-excitation push-pull converters;

(8) FIG. 6 is the principle diagram for conversion efficiency testing in general use in this article;

(9) FIG. 7 is the working area diagram of the magnetic core in a self-excitation push-pull converter;

(10) FIG. 8 is the working area diagram of the magnetic core corresponding to the main section in this invention in a self-excitation push-pull converter;

(11) FIG. 9-1 is the front view of the magnetic core in embodiment 1 of this invention;

(12) FIG. 9-2 is the side view of the magnetic core in embodiment 1 of this invention;

(13) FIG. 9-3 is the top view of the magnetic core in embodiment 1 of this invention;

(14) FIG. 9-4 is the 3D view of the magnetic core in embodiment 1 of this invention;

(15) FIG. 10-1 is the schematic diagram of the magnetic path l.sub.w inside the main section of the magnetic core in embodiment 1 of this invention;

(16) FIG. 10-2 is the schematic diagram of the magnetic path l.sub.t inside the partial section of the magnetic core in embodiment 1 of this invention;

(17) FIG. 11-1 is the front view of the magnetic core for comparison with the existing technology;

(18) FIG. 11-2 is the side view of the magnetic core for comparison with the existing technology;

(19) FIG. 11-3 is the top view of the magnetic core for comparison with the existing technology;

(20) FIG. 12 is the efficiency comparison diagram of embodiment 1 of this invention with that of the existing technology already fitted;

(21) FIG. 13-1 is the front view of the magnetic core in embodiment 2 of this invention;

(22) FIG. 13-2 is the side view of the magnetic core in embodiment 2 of this invention;

(23) FIG. 13-3 is the top view of the magnetic core in embodiment 2 of this invention;

(24) FIG. 14 is the efficiency comparison diagram of embodiment 2 of this invention with the magnetic core of existing technology fitted into circuit;

(25) FIG. 15-1 is the front view of the magnetic core in embodiment 3 of this invention;

(26) FIG. 15-2 is the side view of the magnetic core in embodiment 3 of this invention;

(27) FIG. 15-3 is the top view of the magnetic core in embodiment 3 of this invention;

(28) FIG. 15-4 is the 3D view of the magnetic core in embodiment 3 of this invention;

(29) FIG. 16-1 is the front view of the magnetic core in embodiment 4 of this invention;

(30) FIG. 16-2 is the side view of the magnetic core in embodiment 4 of this invention;

(31) FIG. 16-3 is the top view of the magnetic core in embodiment 4 of this invention;

(32) FIG. 16-4 is the 3D view of the magnetic core in embodiment 4 of this invention;

(33) FIG. 17-1 is the front view of the magnetic core in embodiment 5 of this invention;

(34) FIG. 17-2 is the side view of the magnetic core in embodiment 5 of this invention;

(35) FIG. 17-3 is the top view of the magnetic core in embodiment 5 of this invention;

(36) FIG. 17-4 is the 3D view of the magnetic core in embodiment 5 of this invention;

(37) FIG. 18-1 is the front view of the magnetic core in embodiment 6 of this invention;

(38) FIG. 18-2 is the side view of the magnetic core in embodiment 6 of this invention;

(39) FIG. 18-3 is the top view of the magnetic core in embodiment 6 of this invention;

(40) FIG. 18-4 is the 3D view of the magnetic core in embodiment 6 of this invention;

(41) FIG. 19-1 is the front view of the magnetic core in embodiment 7 of this invention;

(42) FIG. 19-2 is the side view of the magnetic core in embodiment 7 of this invention;

(43) FIG. 19-3 is the top view of the magnetic core in embodiment 7 of this invention;

(44) FIG. 19-4 is the 3D view of the magnetic core in embodiment 7 of this invention;

(45) FIG. 20-1 is the front view of the magnetic core in embodiment 8 of this invention;

(46) FIG. 20-2 is the side view of the magnetic core in embodiment 8 of this invention;

(47) FIG. 20-3 is the top view of the magnetic core in embodiment 8 of this invention;

(48) FIG. 20-4 is the 3D view of the magnetic core in embodiment 8 of this invention.

EMBODIMENTS

Embodiment 1

(49) FIG. 9-1 to FIG. 9-4 show the magnetic core used in the transformer in the self-excitation push-pull converter of embodiment 1 of this invention, this magnetic core has a small partial section with a sectional area smaller than that of the magnetic core in the existing technology, and the length of this partial section is short. Accordingly, to clearly demonstrate the effect of this embodiment, the sectional area of the main section is set to be the same as that of the magnetic core of the existing technology.

(50) The ratio of the main section sectional area to partial section sectional area is the reciprocal of the percentage points described in the technical plan, denoted as constant k, as the reciprocal of <80% and >4% in the above technical plan, i.e., between 1.25 times and 25 times. FIG. 5 shows the ring shaped magnetic core of the existing technology, with a constant sectional area as shown and, according to the existing generally known knowledge, the inductance of the coil wound over it is:

(51) $\begin{array}{cc}L=\frac{4i\mathrm{Ae}{N}^2}{l_e}& \mathrm{Formula}\left(3\right)\end{array}$
where: i is magnetic core relative permeability, Ae is the same as S in formula (1), being the effective sectional area (cm.sup.2) of the magnetic core, N is the number of turns of the coil, l.sub.e is the magnetic path length (cm), and the perimeter of the circumference dotted line 51 in FIG. 5 is magnetic path length l.sub.e.

(52) FIG. 9-1 to FIG. 9-4 show the structural diagram of the magnetic core used in the transformer in the self-excitation push-pull converter in embodiment 1 of this invention, FIG. 9-1 is the front view of the magnetic core in embodiment 1 of this invention; FIG. 9-2 is the side view of the magnetic core in embodiment 1 of this invention; FIG. 9-3 is the top view of the magnetic core in embodiment 1 of this invention; and FIG. 9-4 is the 3D view of the magnetic core in embodiment 1 of this invention. In FIG. 9-1, the circumference dotted line 51 is the length of the physical magnetic path, which is actually divided into two sections, one is in the main section, its length is denoted as l.sub.w, being the magnetic path inside the main section 52 in FIG. 9-1. The other section of the physical magnetic path is within the partial section, its length is denoted as l.sub.t, being the magnetic path inside the partial section 53 in FIG. 9-1. FIG. 10-1 and FIG. 10-2 are respectively the schematic diagrams of the magnetic paths l.sub.w and l.sub.t in this invention, in FIG. 10-1, the dotted line 61 shows the magnetic path length l.sub.w within the main section, in FIG. 10-2, the dotted line 62 shows the magnetic path length l.sub.t within the partial section, then in embodiment 1 of this invention, the inductance of the coil wound on the thick part can be calculated using the Faraday's law, suppose the effective sectional area of the partial section is S.sub.1, then the effective sectional area of the main section is kS.sub.1, substitute them into formula (3), the inductance L.sub.1 of the N-turn coil on the main section is:

(53) $\begin{array}{cc}{L}_1=\frac{4i{\mathrm{kS}}_1{N}^2}{l_w+{\mathrm{kl}}_t}& \mathrm{Formula}\left(4\right)\end{array}$
where: i is the relative permeability of the magnetic core; S.sub.1 is the effective sectional area (cm.sup.2) of the partial section of the magnetic core, i.e. kS.sub.1 is effective sectional area of the main section, the same as S in formula (1); N is the number of turns of coil; the denominator is the total equivalent length of the magnetic path (cm), being the sum of the equivalent length of the magnetic path l.sub.w in the main section and magnetic path l.sub.t in the partial section, as the effective sectional area of the partial section is l/k that of the main section, to make equivalent the magnetic path l.sub.t within the partial section to the effective sectional area of the main section, according to the generally known theory, it should be multiplied by k, so the length is equivalent to kl.sub.t, i.e.:
L.sub.equivalent length=kl.sub.tFormula (5)

(54) FIGS. 11-1, 11-2 and 11-3 are respectively the front view, side view and top view of the magnetic core for comparison with the existing technology, to facilitate the description of the principle of this invention, the main section sizes of the magnetic core for comparison with existing technology are basically identical to those in FIG. 9-1 to FIG. 9-4, that is, the length of the physical magnetic path 51 of the magnetic core in FIG. 11-1 is equal to the length of the physical magnetic path of the circumference dotted line 51 of the magnetic core used in this invention in FIG. 9-1, that is, the two magnetic cores have the identical outer diameter, as the effective sectional area of the magnetic core for comparison with the existing technology in FIG. 11-1 is equal all over, the length of its physical magnetic path 51 is equal to the actual magnetic path length, and the effective sectional area of the magnetic core in FIG. 11-1 is equal to the effective sectional area of the main section of the magnetic core of this invention in FIG. 9-1, i.e. kS.sub.1, then we have:
l.sub.e=l.sub.w+l.sub.tFormula (6)
Ae=kS.sub.1Formula (7)

(55) By substituting the above into formula (3), the inductance L.sub.2 of the coil with the same N turns as the magnetic core for comparison with the existing technology in FIG. 11-1 is:

(56) $\begin{array}{cc}{L}_2=\frac{4i{\mathrm{kS}}_1{N}^2}{l_w+l_t}& \mathrm{Formula}\left(8\right)\end{array}$

(57) Compare formula (4) with formula (8), we obtain:

(58) $\begin{array}{cc}\frac{L_1}{L_2}=.Math.\frac{4i{\mathrm{kS}}_1{N}^2}{l_w+{\mathrm{kl}}_t}.Math.\stackrel{.}{\underset{.}{-}}.Math.\frac{4i{\mathrm{kS}}_1{N}^2}{l_w+l_t}.Math.=\frac{l_w+l_t}{l_w+{\mathrm{kl}}_t}& \mathrm{Formula}\left(9\right)\end{array}$

(59) That is, the inductance of the transformer realized with the magnetic core of this invention and the same number of turns is:

(60) $\begin{array}{cc}{L}_1=\frac{l_w+l_t}{l_w+{\mathrm{kl}}_t}{L}_2& \mathrm{Formula}\left(10\right)\end{array}$

(61) According to formula (10), as the sectional area of the main section is larger than that of the partial section, i.e. k is constantly greater than 1, the N-turn inductance L.sub.1 of the magnetic core in embodiment 1 of this invention is less than the N-turn inductance L.sub.2 of the magnetic core in the existing technology, as long as k is not taken too big, and the l.sub.t in the partial section is sufficiently short, the inductance L.sub.1 of the N-turn coil of the magnetic core in embodiment 1 of this invention can be quite close to L.sub.2, for example L.sub.1=0.99L.sub.2. With this, due to the existence of the partial section, when the magnetic core of this invention is used in a self-excitation push-pull converter, it can still trigger the push-pull oscillation in the circuit, because of the similar inductance, and the working frequency changes very little, as the magnetic saturation only occurs in the partial section, the energy loss is low, the no-load input current is small, therefore the conversion efficiency of the self-excitation push-pull converter can be substantially improved.

(62) As the magnetic path l.sub.t of the partial section is the smaller the better, so that less part is required for the magnetic ring to reach magnetic saturation, and the loss can be reduced more apparently, the lower limit of the length of the partial section is taken as 0.05 mm because 0.05 mm is the limit of the current mould forming process or cutting process for magnetic cores, in fact, the purpose of this invention can be better realized with a size below 0.05 mm.

(63) The following is the process to prove the dimensional limits in the claims, up to formula (10-10), the methods and processes in this proof are academically initials not published before:

(64) With reference to formula (6), let x be the proportion of partial section length 53 in the total magnetic path length 51, we have:
l.sub.t=x l.sub.hFormula (10-1)
l.sub.w=(lx)l.sub.eFormula (10-2)

(65) According to formula (10), the N-turn inductance L.sub.1 of the magnetic core in embodiment 1 of this invention is smaller than the N-turn inductance L.sub.2 of the existing technology, a constant k is introduced, being a percentage, as it is convenient to express it in decimals, it is required that y be less than 0.1, and it can approach zero infinitely, suppose:
L.sub.1=(1y)L.sub.2Formula (10-3)

(66) Substitute formula (6), formula (10-1), formula (10-2) and formula (10-3) into formula (10), we have:

(67) $\begin{array}{cc}\left(1-y\right)L_2=\frac{l_e}{\left(1-x\right)l_e+{\mathrm{kxl}}_c}{L}_2& \mathrm{Formula}\left(10\text{-}4\right)\end{array}$

(68) Simplify formula (10-4) by dividing out L.sub.2 on both left and right, and dividing out L.sub.e from the numerator and denominator on the right of the equation, we obtain:

(69) $\begin{array}{cc}1-y=\frac{1}{1-x+\mathrm{kx}}=\frac{1}{1+x\left(k-1\right)}& \mathrm{Formula}\left(10\text{-}5\right)\end{array}$

(70) Formula (10-5) is simplified as:

(71) 0$\begin{array}{cc}x\left(k-1\right)=\frac{1}{1-y}-1& \mathrm{Formula}\left(10\text{-}6\right)\end{array}$

(72) Because y is smaller and equal to 0.1, we have the following equations in engineering calculation:
1y.sup.21Formula (10-7)

(73) When y=0.1, formula (10-7) obtains 0.991, with an error of 1%, it has satisfied with the precision for engineering calculation, as y is smaller than and equal to 0.1, formula (10-7) can obtain:
(1y)(1+y)1Formula (10-8)

(74) That is:

(75) $\begin{array}{cc}\frac{1}{1-y}1+y& \mathrm{Formula}\left(10\text{-}9\right)\end{array}$

(76) In formula (10-9), y is taken as the maximum value 0.1, then we have:
1.11.1

(77) That is, the circulating decimal 1.1 is approximately equal to 1.1, with an error of 1%, when y drops to 0.05, or by 5%, it is 1.052631.05, with an error of 0.25%, which is already quite accurate. Substitute formula (10-9) into formula (10-6), we have:

(78) $x\left(k-1\right)=\frac{1}{1-y}-11+y-1=y$

(79) That is:
yx(k1)Formula (10-10)

(80) It can be seen from formula (10-3) that, in this invention, a smaller y value is preferable, as this will have a magnetic core inductance closer to the desired value, in this way, it is not necessary to increase the number of turns of the coil in embodiment 1 of this invention, and it is found in the experimental test that only when the sectional area of the partial section is below 80% of that of the main section, can it be ensured that no magnetic saturation will occur in the main section when magnetic saturation occurs in the partial section. As transistors have a storage time, that is, after the transistor base has received a cutting off signal, the collector current will drop with a time delay till cut-off, the storage time can occur in FIG. 3, the moving line of the magnetic core working point will be from point D to E, correspondingly, the moving line of the magnetic core working point will move from point H to A. When the moving line of the magnetic core working point moves from point D to E, it will increase the magnetic flux in the magnetic core, which will result in saturation within the main section with an area not quite different, therefore, only when the sectional area of the partial section is below 80% of that of the main section, can it be ensured that no magnetic saturation will occur in the main section when the moving line of the afore-said magnetic core working point moves from point D to E. k is the reciprocal of the afore-said 80%, being 1.25.

(81) When k is taken as 1.25, if y in formula (10-10) is not greater than 3%, then:
x=y/(k1)=0.03/(1.251)=0.12

(82) x is the proportion of the partial section length 53 in the total magnetic path length 51, and 0.12 is approximately one eighth, i.e. the partial section has a length of over 0.05 mm, less than one eighth of the total magnetic path length.

(83) Of course, it is only an example here with y as 3%, Table 2 below gives the tolerable deviation values commonly used in electronic engineering, all obtained using formula (10-10):

(84) TABLE-US-00002 TABLE 2 X obtained Percentage of partial Expected from section length in total value Y calculation magnetic path length 1% 0.04 One 25th 2% 0.08 One 12th 3% 0.12 One 8th 5% 0.2 One 5th 10% 0.4 About one 3rd

(85) It is verified in experimental test that a fairly good implementation effect can be obtained only when y is taken below 3% in this invention.

(86) In actual application, when the value k exceeds 25, i.e. the sectional area of main section is 25 times that of partial section, the partial section is likely to break as its strength cannot be guaranteed, and an air gap will form after break, making it impossible to use in a self-excitation push-pull converter. When the value k exceeds 25, as the window area that can be wound with wire in the ring center is too small, it often requires extending the length of the geometric magnetic path 51 in FIG. 9-1 to implement it, it can be seen from formula (3) that, the extension of the length of the geometric magnetic path 51 can reduce the inductance, which in turn requires increasing the number of turns, therefore reducing the implementation effect.

(87) Therefore, the value of k is required to be 1.25 to 25 times, and then the sectional area of the partial section is below 80% and above 4% of that of the main section.

(88) In the following, a set of measured data will demonstrate the actual effect of the circuit in embodiment 1. Take FIG. 1-1 as an example, the plans adopted in the existing technology and presented in background technology are identical.

(89) A circuit as shown in FIG. 1-1 is used to make a converter with input DC at 5V, output DC at 5V and output current of 200 mA, i.e. with an output power of 1 W. The downstream output of the transformer is in the circuit structure as shown in FIG. 4, which is a generally known full-wave rectifying circuit. The main parameters of the circuit are: the capacitor C is 1 uF, resistor R1 is 1 K, capacitor C1 is 0.047 uF, and TR1 and TR2 are switching transistors with magnification factor of about 200, with its maximum collector working current being 1 A. The primary side coils N.sub.P1 and N.sub.P2 have respectively 20 turns, feedback coils N.sub.B1 and N.sub.B2 respectively 3 turns, secondary side coils N.sub.S1 and N.sub.S2 respectively 23 turns, and the magnetic core is a common ferrite loop magnetic core with an outer diameter of 5 mm and sectional area of 1.5 mm.sup.2.

(90) When it is made with the above parameters, at an output of 10 mA as 5% of the full load of 200 mA of the output current, the measured parameters are as shown in Table 1 of background technology, with an efficiency of 38.03%, and ripple of 135.7 mV (peak-peak value).

(91) In the circuit of self-excitation push-pull converter in embodiment 1 of this invention, the magnetic core has an outer diameter of 5 mm, with the sectional area of main section being 1.5 mm.sup.2 and that of partial section being 0.75 mm.sup.2, i.e. the k value is 2, and the partial section has a length of 1 mm. No coil will be made on the partial section, a transformer as shown in FIG. 1-1 is made with the same number of turns, when the transformer made as per embodiment 1 of this invention is connected into the circuit, with the output current at 10 mA, or 5% of the full load 200 mA, the efficiency is tested also using the circuit in FIG. 6, and in conjunction with Table 1, the measured data are as shown in Table 3:

(92) TABLE-US-00003 TABLE 3 Input Input Output Output current voltage current voltage Output ripple Efficiency Iin Vin Iout Vout (p-p value) (Calculated value) Actually measured with 28.4 mA 5.060 V 9.96 mA 5.487 V 135.7 mV 38.03% existing technology Actually measured with 23.5 mA 5.066 V 9.95 mA 5.480 V 69.6 mV 45.80% the transformer made as per embodiment 1 of this invention in the circuit Note: the output ripple is tested with a full load of 200 mA.

(93) Obviously, after using the self-excitation push-pull converter of this invention, the efficiency of the self-excitation push-pull converter when working with low load has been substantially increased, by (45.80%-38.03%)=7.77%. Obviously, after using the self-excitation push-pull converter of this invention, the output ripple of the self-excitation push-pull converter when working with full load has been substantially reduced, by 66.1 mV, or 48.7%. Further, conversion efficiency was measured over the full range from low load to full load at steps of 5%, and at steps of 10% when the load rate is over 40%, records were made in Table 4:

(94) TABLE-US-00004 TABLE 4 Iin Vin Iout Vout Increase of Load rate Product (mA) (V) (mA) (V) Efficiency efficiency 5% Existing technology 28.4 5.060 9.96 5.487 38.03% 7.77% This invention 23.5 5.066 9.95 5.480 45.80% 10% Existing technology 40.0 5.045 20.00 5.424 53.76% 7.65% This invention 35.0 5.052 20.00 5.429 61.41% 15% Existing technology 51.1 5.031 30.10 5.381 63.00% 6.21% This invention 46.5 5.037 30.10 5.386 69.22% 20% Existing technology 62.7 5.016 40.00 5.341 67.93% 6.09% This invention 57.7 5.022 40.10 5.349 74.02% 25% Existing technology 73.7 5.002 50.00 5.305 71.95% 4.86% This invention 69.2 5.008 50.10 5.313 76.81% 30% Existing technology 85.1 4.987 59.90 5.269 74.37% 4.73% This invention 80.2 4.994 60.00 5.280 79.10% 35% Existing technology 96.3 4.973 69.90 5.236 76.42% 4.09% This invention 91.6 4.978 70.00 5.245 80.52% 40% Existing technology 107.6 4.960 79.70 5.202 77.68% 4.02% This invention 102.7 4.965 79.90 5.214 81.70% 50% Existing technology 130.1 4.931 99.70 5.138 79.85% 3.24% This invention 125.4 4.936 99.90 5.148 83.09% 60% Existing technology 153.8 4.900 120.50 5.073 81.11% 2.98% This invention 148.7 4.907 120.70 5.084 84.10% 70% Existing technology 174.9 4.873 139.40 5.013 81.99% 2.48% This invention 170.1 4.879 139.60 5.022 84.47% 80% Existing technology 199.8 4.847 161.80 4.950 82.70% 2.16% This invention 195.0 4.845 161.90 4.952 84.86% 90% Existing technology 220.0 5.030 180.00 5.131 83.46% 2.10% This invention 215.0 5.032 180.20 5.137 85.56% 100% Existing technology 242.0 5.024 198.00 5.094 82.96% 2.28% This invention 237.0 5.025 199.00 5.101 85.24%

(95) Obviously, the conversion efficiency when the self-excitation push-pull converter of this invention is used has been obviously increased in the whole range from low load and full load, a comparison chart is made using software, refer to FIG. 12, in which curve 2# is the conversion efficiency curve of the self-excitation push-pull converter after using this invention, and curve 1# is the conversion efficiency curve of the self-excitation push-pull converter with the existing technology.

(96) The no-load current of the self-excitation push-pull converter of this invention has been reduced from 18.0 mA of the existing technology to 12.0 mA, i.e. the no-load loss of the self-excitation push-pull converter of this invention has reduced from 90 mW of the existing technology to 60 mW.

Embodiment 2

(97) In embodiment 2 of this invention, the transformer used in the self-excitation push-pull converter is slightly different from that in embodiment 1, in embodiment 1, the main section has the same sectional area as that of the magnetic core of existing technology, while the sectional area of the partial section is smaller than that of the existing technology, with a ratio of l/k. To fully demonstrate the effect of this embodiment, in the transformer magnetic core used in embodiment 2 of this invention, the sectional area of the partial section is equal to that of the existing technology, that is, the sectional area of the main section is k times that of the existing technology.

(98) FIGS. 11-1, 11-2 and 11-3 are respectively the front view, side view and top view of the magnetic core for comparison of the existing technology with that in embodiment 2 of this invention, suppose the sectional area of the magnetic core of the existing technology is S.sub.2, when we substitute it into formula (3), the inductance L.sub.3 of the coil with the same N turns as the magnetic core for comparison with the existing technology in FIG. 11-1 is:

(99) $\begin{array}{cc}{L}_3=\frac{4i{S}_2{N}^2}{l_e}& \mathrm{Formula}\left(11\right)\end{array}$

(100) The transformer magnetic core used in embodiment 2 of this invention is as shown in FIG. 13-1 to FIG. 13-3, FIG. 13-1 is the front view of the transformer magnetic core used in embodiment 2 of this invention; FIG. 13-2 is the side view of the transformer magnetic core used in embodiment 2 of this invention; and FIG. 13-3 is the top view of the transformer magnetic core used in embodiment 2 of this invention. In the transformer magnetic core used in embodiment 2, there is a small partial section 53 with the same sectional area as the magnetic core for comparison with the existing technology, i.e. the sectional area of the partial section 53 of the magnetic core in FIG. 13-1 is equal to the above-mentioned S.sub.2, but its length is very short. Correspondingly, the sectional area of the main section 52 in FIG. 13-1 is larger than the sectional area of the magnetic core of the existing technology, equal to kS.sub.2, the ratio is the reciprocal of the percentage in the technical plan, denoted as constant k, for which reciprocal is taken as for the technical plan above, being 12.5 to 25 times. Accordingly, the inductance per turn of the coil on the main section increases, and the inductance L.sub.4 with the same number of turns of coil on the magnetic core of embodiment 2 of this invention is:

(101) $\begin{array}{cc}{L}_4=\frac{4i{\mathrm{kS}}_2{N}^2}{l_w+{\mathrm{kl}}_t}& \mathrm{Formula}\left(12\right)\end{array}$
where: i is the relative permeability of the magnetic core; S.sub.2 is the effective sectional area (cm.sup.2) of the partial section of the magnetic core, i.e. kS.sub.2 is effective sectional area of the main section, the same as S in formula (1); N is the number of turns of coil; the denominator is the total equivalent length of the magnetic path (cm), being the sum of the equivalent length of the magnetic path l.sub.w in the main section and magnetic path l.sub.t in the partial section, as the effective sectional area of the partial section is l/k that of the main section, to make equivalent the magnetic path l.sub.t within the partial section to the effective sectional area of the main section, it should be multiplied by k, so the length is equivalent to kl.sub.t;

(102) Compare formula (12) with formula (11), we obtain:

(103) $\begin{array}{cc}\frac{L_4}{L_3}=.Math.\frac{4i{\mathrm{kS}}_2{N}^2}{l_w+{\mathrm{kl}}_t}.Math.\stackrel{.}{\underset{.}{-}}.Math.\frac{4i{S}_2{N}^2}{l_w+l_t}.Math.=\frac{{\mathrm{kl}}_e}{l_w+{\mathrm{kl}}_t}& \mathrm{Formula}\left(13\right)\end{array}$

(104) That is, the inductance of the transformer realized with the transformer magnetic core used in embodiment 2 of this invention and the same number of turns is:

(105) $\begin{array}{cc}{L}_4=k\left(\frac{l_e}{l_w+{\mathrm{kl}}_t}{L}_3\right)& \mathrm{Formula}\left(14\right)\end{array}$

(106) According to formula (14), if the magnetic path length lt in the partial section is sufficiently short, for instance close to 0.05 mm, the sum of the product kl.sub.t and magnetic path l.sub.w in the main section will approach the magnetic path length l.sub.e of the magnetic core for comparison with the existing technology in FIG. 11-1, i.e. the inductance of the N-turn coil of the magnetic core of this invention L.sub.4kL.sub.3.

(107) With the same number of turns, the inductance can be increased by about k times, that means the number of turns can be reduced as appropriate to realize the same inductance as that with the background technology; in other words, the number of turns in this invention can be reduced as appropriate, and the ratio n of the number of turns with the existing technology to that of this invention is:

(108) $\begin{array}{cc}n=\sqrt{\frac{1}{k}}& \mathrm{Formula}\left(15\right)\end{array}$
i.e., when K is taken as 25, n=1/5=0.2, for the product with input voltage of 24V as mentioned in the background technology, a good working efficiency can be obtained with 96 turns, but in the circuit of this invention, it only requires 960.2=19.2 turns, or rounded as 20 turns, to realize the same effect. That is why in the technical requirement, the sectional area of the partial section length is below 80% and above 4% of the sectional area of the main section. In the above corresponding to embodiment 1, it is mentioned that: when the value k exceeds 25, as the window area in the magnetic ring center is too small, it often requires extending the length of the physical magnetic path 51 in FIG. 9-1 to implement it, it can be seen from formula (3) that, the extension of the physical magnetic path 51 can reduce the inductance, which in turn requires increasing the number of turns, therefore reducing the implementation effect.

(109) Similarly, when k is taken as 16, n=1/4=0.25, the number of turns can be reduced to of the original, making it easy to wind it. For the product with input voltage of 24V as mentioned in the background technology, a good working efficiency can be obtained with 96 turns, but in the circuit of this invention, it only requires 960.25=24 turns, thus increasing the working efficiency in winding transformers.

(110) In FIG. 13-1, due to the existence of the partial section 53, with the self-excitation push-pull converter of this invention, it can still trigger the push-pull oscillation in the circuit, as the magnetic saturation only occurs in the partial section 53, which is fairly short, the energy loss is low, i.e. the no-load input current of the circuit of self-excitation push-pull converter is small, therefore the conversion efficiency of the self-excitation push-pull converter can be substantially improved. As the energy loss is low, the working frequency of the self-excitation push-pull converter can be further increased, and the resulted benefit is: the number of turns wound on the magnetic core of embodiment 2 of this invention can be further reduced. In the following, a set of measured data will demonstrate the actual effect of the magnetic core in embodiment 2.

(111) In the plan for comparison with existing technology, the plan adopted is the same as that in the background technology and presented in embodiment 1, and it is quoted below for convenience in comparison:

(112) A circuit as shown in FIG. 1-1 is used to make a converter with input DC at 5V, output DC at 5V and output current of 200 mA, i.e. with an output power of 1 W. The downstream output of the transformer is in the circuit structure as shown in FIG. 4, which is a generally known full-wave rectifying circuit. The main parameters of the circuit are: the capacitor C is 1 uF, resistor R1 is 1 K, capacitor C1 is 0.047 uF, and TR1 and TR2 are switching transistors with magnification factor of about 200, with its maximum collector working current being 1 A. The primary side coils N.sub.P1 and N.sub.P2 have respectively 20 turns, feedback coils N.sub.B1 and N.sub.B2 respectively 3 turns, secondary side coils N.sub.S1 and N.sub.S2 respectively 23 turns, and the magnetic core is a common ferrite loop magnetic core with an outer diameter of 5 mm and sectional area of 1.5 mm.sup.2.

(113) With the above parameters set, at an output of 10 mA as 5% of the full load of 200 mA of the output current, the measured parameters are as shown in Table 1 of background technology, with an efficiency of 38.03%. For other parameters, refer to the part of corresponding existing technology in Tables 3 and 4.

(114) In the self-excitation push-pull converter in embodiment 2 of this invention, the magnetic core has an outer diameter of 5 mm, with the sectional area of main section being 3 mm.sup.2 and that of partial section being 1.5 mm.sup.2, i.e. the k value is 2, and the partial section has a length of 0.5 mm. No coil will be made on the partial section, the primary side coils N.sub.P1 and N.sub.P2 have respectively 7 turns, the feedback coils N.sub.B1 and N.sub.B2 respectively 2 turns, and the secondary side coils N.sub.S1 and N.sub.S2 respectively 8 turns, when the transformer made as per embodiment 2 of this invention is connected into the circuit, the measured working frequency of the circuit is 139 kHz, with a no-load input current of 6.9 mA.

(115) When the output current is 5% of the full load 200 mA, or 10 mA, the efficiency is tested also using the circuit in FIG. 6, and in conjunction with Table 1, the measured data are as shown in Table 5:

(116) TABLE-US-00005 TABLE 5 Input Input Output Output current voltage current voltage Output ripple Efficiency Iin Vin Iout Vout (p-p value) (Calculated value) Actually measured with 28.4 mA 5.060 V 9.96 mA 5.487 V 135.7 mV 38.03% existing technology Actually measured with 17.5 mA 5.066 V 9.95 mA 5.478 V 54.3 mV 61.48% the transformer made as per embodiment 2 of this invention in the circuit Note: the output ripple is tested with a full load of 200 mA.

(117) Obviously, after using this invention, the efficiency of the self-excitation push-pull converter when working with low load has been substantially increased, by (61.48%-38.03%)=23.45%.

(118) Obviously, after using the self-excitation push-pull converter of this invention, the output ripple of the self-excitation push-pull converter when working with light load has been substantially reduced, by 81.4 mV, or 59.9%.

(119) Further, tests were made over the full range from low load to full load at steps of 5%, and at steps of 10% when the load rate is over 40%, records were made in Table 6:

(120) TABLE-US-00006 TABLE 6 Iin Vin Iout Vout Increase of Load rate Product (mA) (V) (mA) (V) Efficiency efficiency 5% Existing technology 28.4 5.060 9.96 5.487 38.03% 23.45% This invention 17.5 5.066 9.95 5.478 61.48% 10% Existing technology 40.0 5.045 20.00 5.424 53.76% 20.58% This invention 28.9 5.052 20.00 5.427 74.34% 15% Existing technology 51.1 5.031 30.10 5.381 63.00% 16.83% This invention 40.3 5.037 30.10 5.384 79.84% 20% Existing technology 62.7 5.016 40.00 5.341 67.93% 15.12% This invention 51.4 5.022 40.10 5.346 83.05% 25% Existing technology 73.7 5.002 50.00 5.305 71.95% 12.70% This invention 62.8 5.008 50.10 5.314 84.65% 30% Existing technology 85.1 4.987 59.90 5.269 74.37% 11.67% This invention 73.7 4.994 60.00 5.278 86.04% 35% Existing technology 96.3 4.973 69.90 5.236 76.42% 10.31% This invention 85.0 4.978 70.00 5.243 86.74% 40% Existing technology 107.6 4.960 79.70 5.202 77.68% 9.58% This invention 96.1 4.965 79.90 5.211 87.26% 50% Existing technology 130.1 4.931 99.70 5.138 79.85% 8.02% This invention 118.5 4.936 99.90 5.145 87.87% 60% Existing technology 153.8 4.900 120.50 5.073 81.11% 7.21% This invention 141.5 4.907 120.70 5.081 88.33% 70% Existing technology 174.9 4.873 139.40 5.013 81.99% 6.31% This invention 162.7 4.879 139.60 5.021 88.30% 80% Existing technology 199.8 4.847 161.80 4.950 82.70% 5.60% This invention 187.4 4.845 161.90 4.952 88.30% 90% Existing technology 220.0 5.030 180.00 5.131 83.46% 4.84% This invention 208.2 5.032 180.20 5.134 88.31% 100% Existing technology 242.0 5.024 198.00 5.094 82.96% 5.04% This invention 229.1 5.025 199.00 5.091 88.00%

(121) Obviously, the conversion efficiency when the self-excitation push-pull converter of this invention is used has been obviously increased in the whole range from low load and full load, a comparison chart is made using software, refer to FIG. 14, in which 2# is the conversion efficiency curve of the self-excitation push-pull converter after using this invention, and curve 1# is the conversion efficiency curve of the self-excitation push-pull converter with the existing technology.

(122) The no-load current of the self-excitation push-pull converter has also been reduced from 18.0 mA of the existing technology to 6.9 mA of the self-excitation push-pull converter of this invention, i.e. the no-load loss has reduced from 90 mW of the existing technology to 34.5 mW of this invention. At the same time, the working frequency has increased from 97.3 kHz with the existing technology to 139 kHz in embodiment 2 of this invention. The resulted benefit is reducing the number of turns of the primary side coils N.sub.P1 and N.sub.P2 respectively from 20 to 7, reducing the work time in winding, and also avoiding mistakes in memorizing.

(123) It can be seen from Table 6 that, at a load of 10%, i.e. an output current of 20 mA, this invention still has an efficiency of 74%, if the magnetic core size is reduced to design a specific micro power DC/DC converter, the efficiency can be further improved.

Embodiment 3

(124) FIG. 15-1 to FIG. 15-3 show the transformer magnetic core used in the self-excitation push-pull converter of embodiment 3 of this invention, FIG. 15-1 is the front view of the transformer magnetic core used in embodiment 3 of this invention; FIG. 15-2 is the side view of the transformer magnetic core used in embodiment 3 of this invention; FIG. 15-3 is the top view of the transformer magnetic core used in embodiment 3 of this invention; and FIG. 15-4 is the 3D view of the transformer magnetic core used in embodiment 3 of this invention. There is also a small partial section 53 with a small area of the magnetic core, the main section 52, and the length of the partial section is very short. The working principle is identical to that in the above description of the invention and in embodiments 1 to 2, so it will not be repeated here.

Embodiment 4

(125) FIG. 16-1 to FIG. 16-4 show the transformer magnetic core used in the self-excitation push-pull converter in embodiment 4 of this invention, FIG. 16-1 is the front view of the magnetic core in embodiment 4 of this invention; FIG. 16-2 is the side view of the magnetic core in embodiment 4 of this invention; FIG. 16-3 is the top view of the magnetic core in embodiment 4 of this invention; and FIG. 16-4 is the 3D view of the magnetic core in embodiment 4 of this invention. As there is also a small partial section 53 with smaller sectional area of magnetic core, the main section 52, and the feature of further improvement of embodiment 4: a transition section 54 exists between the main section and partial section, the transition section 54 can be equivalent as part of the partial section, the transition section 54 is provided to facilitate demoulding of the magnetic core after magnetic powder moulding, and actually it is a further improvement to embodiment 1 in FIGS. 9-1 to 9-4.

(126) Similarly, it is required that the length of the partial section and the transition section 54 be short. The working principle of the whole power flow is identical to that in the above description of the invention and in embodiments 1 to 2, so it will not be repeated here. Due to the presence of transition section 54, the length of partial section 53 can be zero, and in this case, there is still a section with the minimum sectional area, with a length close to zero, but the purpose of the invention can still be realized.

Embodiment 5

(127) FIG. 17-1 to FIG. 17-4 show the transformer magnetic core used in the self-excitation push-pull converter in embodiment 5 of this invention, FIG. 17-1 is the front view of the magnetic core in embodiment 5 of this invention; FIG. 17-2 is the side view of the magnetic core in embodiment 5 of this invention; FIG. 17-3 is the top view of the magnetic core in embodiment 5 of this invention; and FIG. 17-4 is the 3D view of the magnetic core in embodiment 5 of this invention.

(128) The improvement feature of embodiment 5 of this invention is: on the basis of embodiment 4, two or more salient points 55 are added on the main section, to prevent the wire on the main section from sliding to the partial section, and salient points 55 can be at any position on the main section. Another function of salient points 55 is to determine the zone of different windings, to prevent their mutual intersection.

(129) As there is also a small partial section 53 with smaller sectional area of magnetic core, the main section 52, and the transition section 54 between the main section and partial section, the transition section 54 can be equivalent as part of the partial section, the transition section 54 is provided to facilitate demoulding of the magnetic core after magnetic powder moulding, and actually it is a further improvement to embodiment 4 in FIGS. 16-1 to 16-4.

(130) Similarly, it is required that the length of the partial section and the transition section 54 be short. The working principle of the whole power flow is identical to that in the above description of the invention and in embodiments 1 to 2, so it will not be repeated here. Due to the presence of transition section 54, the length of partial section 53 can be zero, and the purpose of the invention can still be realized.

Embodiment 6

(131) FIG. 18-1 to FIG. 18-4 show the transformer magnetic core used in the self-excitation push-pull converter of embodiment 6 of this invention, FIG. 18-1 is the front view of the magnetic core used in embodiment 6 of this invention; FIG. 18-2 is the side view of the magnetic core used in embodiment 6 of this invention; FIG. 18-3 is the top view of the magnetic core used in embodiment 6 of this invention; and FIG. 18-4 is the 3D view of the magnetic core used in embodiment 6 of this invention. There is also a small partial section 53 with a small area of the magnetic core, the main section 52, and the length of the partial section is very short. The working principle of the circuit of the whole self-excitation push-pull converter is identical to that in the above description of the invention and in embodiments 1 to 2, so it will not be repeated here.

Embodiment 7

(132) FIG. 19-1 to FIG. 19-4 show the transformer magnetic core used in the self-excitation push-pull converter of embodiment 7 of this invention, FIG. 19-1 is the front view of the magnetic core used in embodiment 7 of this invention; FIG. 19-2 is the side view of the magnetic core used in embodiment 7 of this invention; FIG. 19-3 is the top view of the magnetic core used in embodiment 7 of this invention; and FIG. 19-4 is the 3D view of the magnetic core used in embodiment 7 of this invention. There is also a small partial section 53 with a small area of the magnetic core, and the main section 52.

(133) The technical feature of the magnetic core used in embodiment 7: a transition section 54 exists between the main section and partial section, the transition section 54 can be equivalent as part of the partial section, the transition section 54 is provided to facilitate demoulding of the magnetic core after magnetic powder moulding, and actually it is a further improvement to embodiment 6 in FIGS. 18-1 to 18-4. Due to the presence of transition section 54, the length of partial section 53 can be zero, and the purpose of the invention can still be realized.

(134) The working principle of the self-excitation push-pull converter is identical to that in the above description of the invention and in embodiments 1 to 2, so it will not be repeated here.

(135) Similarly, when the magnetic core adopted in the above-mentioned 7 embodiments is used in transformer B1 in the Jensen circuit as shown in FIG. 1-2, it can also increase the conversion efficiency of the Jensen circuit in the whole range from light load to full load, reduce the number of winding turns of the transformer B1 and increase the working frequency of the circuit.

Embodiment 8

(136) FIG. 20-1 to FIG. 20-4 show the transformer magnetic core used in the self-excitation push-pull converter in embodiment 8 of this invention, FIG. 20-1 is the front view of the magnetic core in embodiment 8 of this invention; FIG. 20-2 is the side view of the magnetic core in embodiment 8 of this invention; FIG. 20-3 is the top view of the magnetic core in embodiment 8 of this invention; and FIG. 20-4 is the 3D view of the magnetic core in embodiment 8 of this invention. There is a magnetic column of an equal sectional area and made of a different material, with a length less than one eighth of the total magnetic path length, and a sectional area below 80% and above 4% of the sectional area of the main section but over 0.02 mm, taken as part of 0.5 mm. Actually, it is a circular magnetic chip because it is very thin, is pressed to a ring base in the mould to make magnetic rings, and then sintered into a magnetic core as shown in FIG. 20-4. A circular magnetic chip of 0.02 mm represents the limit of the current machining process, in fact, the purpose of this invention can be better realized with a size below 0.02 mm.

(137) When excited by the same magnetic field, the magnetic column 53 is more likely to become saturated than the main section 52, so the magnetic column 53 is the partial section, as shown in the shadow part in FIG. 20-1 to FIG. 20-4. The working principle of the self-excitation push-pull converter in embodiment 8 is identical to that in the above description of the invention and in embodiments 1 to 2, and it can also realize the purpose of this invention, so it will not be repeated here.

(138) Similarly, when the magnetic core adopted in the above-mentioned 8 embodiments is used in transformer B1 in the Jensen circuit as shown in FIG. 1-2 and the magnetic saturation transformers in Jensen circuit in different literatures, it can also increase the conversion efficiency of the Jensen circuit in the whole range from light load to full load. And it can also reduce the number of turns of the transformer B1 and increase the working frequency of the circuit.

(139) The above are only preferable embodiments of this invention, and it should be pointed out that, the preferable embodiments above should not be regarded as restrictions to this invention, and the scope of protection for this invention shall be that defined by the claims. For ordinary technical personnel in this technological field, within the essence and scope of this invention, some improvements and decorations can be made, and such improvements and decorations shall also be covered in the scope of protection of this invention. For example, the partial section and main section can be embodied by using magnetic rings of sectional area in different geometric shapes, or the profile of the whole magnetic core as aforesaid can be embodied with a square or elliptic magnetic ring.