A DIRECT CURRENT, DC, VOLTAGE SOURCE ARRANGED FOR PROVIDING A DC VOLTAGE BASED ON AN INPUT VOLTAGE AS WELL AS A CORRESPONDING METHOD

Abstract

A Direct Current, DC, voltage source arranged for providing a DC voltage based on an input voltage between two input terminals, wherein said DC voltage source comprises a transformer arranged for receiving a supply current, at a first side of the transformer, and for transforming said supply current to a circulating current at a second side of the transformer, a first and a second input terminal for receiving an input voltage for setting a DC voltage to be provided by said DC voltage source, a first diode, wherein an anode of said first diode is connected to a first end of said second side of said transformer, and wherein a cathode of said first diode is connected to said first input terminal, a current regulator circuit for assuring that an amount of current circulating current is shunted from the first diode.

Claims

1. A Direct Current, (DC), voltage source arranged for providing a DC voltage based on an input voltage between a first input terminal and a second input terminal, wherein a resistor is connectable between the first input terminal and the second input terminal, wherein said DC voltage source comprises: a transformer arranged for receiving a supply current, at a first side of the transformer, and for transforming said supply current to a circulating current at a second side of the transformer; said first and said second input terminal for receiving said input voltage for setting a DC voltage to be provided by said DC voltage source; a first diode, wherein an anode of said first diode is connected to a first end of said second side of said transformer, and wherein a cathode of said first diode is connected to said first input terminal; a branch diode, wherein an anode of said branch diode is connected to the first end of said second side of said transformer; a current regulator circuit having an input node, a cathode side and an anode side, wherein: said input node is connected to said second input terminal, said cathode side is coupled to said first end of said second side of said transformer via said branch diode and shunts said first diode as well as said first and second input terminal; said anode side is connected to a second end of said second side of said transformer, wherein the DC voltage source further comprises a current setting resistor coupled between said input node and said anode side, wherein the current setting resistor is for setting a predetermined amount of current from said circulating current, wherein said current regulator circuit is arranged for assuring that the predetermined amount of current is withdrawn from said circulating current, wherein said predetermined amount of current flows via said first diode, said first and second terminal and said current setting resistor back to said transformer, and for assuring that a remaining current of said circulating current flows via said branch diode, via said cathode side, via said anode side, back to said transformer thereby not flowing via said first diode.

2. The DC voltage source in accordance with claim 1, wherein said first and said second input terminals are arranged for receiving a resistor for setting a DC voltage to be provided by said DC voltage source.

3. The DC voltage source in accordance with claim 1, wherein a forward voltage of said branch diode is equal to or lower than a forward voltage of said first diode.

4. The DC voltage source in accordance with claim 1, wherein said current regulator circuit is arranged to maintain a reference voltage over said current setting resistor such that a resistance value of said current setting resistor defines said predetermined amount of current flowing via said input node.

5. The DC voltage source in accordance with claim 1, further comprising a low-pass output filter connected to said first side of the transformer.

6. The DC voltage source in accordance with claim 5, further comprises an output diode connected, directly or indirectly, to a first end of said first side of said transformer.

7. The DC voltage source in accordance with claim 6, wherein said output diode and said first diode have a same forward voltage drop.

8. (canceled)

9. The DC voltage source in accordance with claim 1, wherein said branch diode is a Schottky diode.

10. A method for operating a Direct Current DC voltage source, wherein said method comprises: assuring, by a current regulator circuit, that a predetermined amount of current is withdrawn from a circulating current, wherein said predetermined amount of current flows via a first diode, a first and second terminal and an input node via an anode side back to a transformer, and assuring, by said current regulator circuit, that a remaining current of said circulating current flows via a cathode side, via said anode side, back to said transformer thereby not flowing via said first diode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 discloses a Direct Current, DC, voltage source in accordance with the prior art;

[0046] FIG. 2 discloses a Direct Current, DC, voltage source in accordance with the present disclosure;

[0047] FIG. 3 discloses another Direct Current, DC, voltage source in accordance with the present disclosure.

DETAILED DESCRIPTION

[0048] FIG. 1 discloses a Direct Current, DC, voltage source 1 in accordance with the prior art. The electrical circuit shown in FIG. 1 is explained in more detail here below.

[0049] L1a is energized by at least positive pulses of current, e.g. via either C5, R5 or I5. This current magnetically couples to L1b, flows via D1, which is referred to as the first diode in accordance with the present disclosure, charges C1, and flows via Rptc, Rset and R1 back to L1b.

[0050] Here, Rset is the resistor received in between the input terminals and that sets the output voltage of the DC voltage source. The resistor R1 is the resistor that sets the predetermined amount of current. More specifically, the adjustable shunt regulator TL 431 is arranged to maintain a fixed voltage over R1, which fixed voltage, i.e. a reference voltage, is converted to a fixed, predetermined amount of current. The predetermined amount of current thus also flows through the resistor Rset.

[0051] If the voltage across R1 would exceed the TL431 reference voltage, the TL431 clamps the excess L1b current via R2, i.e. a low ohmic path, from its cathode into its anode. The R1 current is thus kept constant in this circuit, thereby ensuring that the output voltage, i.e. the voltage over R4, is based on the resistance value of Rset.

[0052] The above described excess current is thus the remaining current of the circulating current as described in the appending claims.

[0053] Rptc and Z1 are optional and if used typically, the Rptc resistance is very low compared to Rset. The voltage across L1b will therefore be equal to the D1 forward voltage, i.e. the forward voltage of the first diode, plus the voltage over Rset, plus the TL431 reference voltage across R1.

[0054] At the driver side, i.e. left from the insulation barrier provided by the transformer L1a/L1b, the L1b voltage is reflected across L1a, and is filtered by R3, C3 for the overshoot in L1a voltage due to the leakage inductance between L1a and L1b, and then rectified by D3, i.e. the output diode, into C4 in parallel with R4.

[0055] If L1a and L1b have a 1:1 turns ratio, the D3 Vbe forward voltage cancels the D1 Vbe forward voltage, and thus the driver-side voltage over R4 is a 1:1 representation of the input voltage and thus the Rset resistance, albeit it still includes an offset equal to the TL431 reference voltage.

[0056] After each positive current pulse, into the dot of L1a, the magnetization of L1 may need to be reset before the next positive current pulse, via a negative voltage, at the dot, across L1a and L1b.

[0057] D2 and Z2 provide a clamp to limit such reset voltage to a safe level. Clamping of the reverse voltage may also be done at the driver-side, or at both sides, and may be enhanced by a reverse current via C5, R5 or an optional reverse current of I5. An RC series network snubber may be provided, instead of D2, Z2.

[0058] The Rptc, Z1 circuit at the input side serves as a protection against inadvertently connecting the input terminals to the mains voltage. In such event, Z1 limits the voltage in either direction to safe levels, while Rptc rapidly becomes high-ohmic to robustly withstand the mains voltage.

[0059] It was found that, in the existing solution, the excess L1b current, which is clamped in the TL431, flows through the first diode, i.e. D1. It varies and decreases with increasing Rset, introducing a non-linearity and temperature dependency in the transfer curve, as the D1 and D3 forward voltages do no longer fully cancel.

[0060] The excess L1b current may also vary substantially with variation of the magnetizing inductance of the L1 transformer, which has a relatively large tolerance and temperature dependency. As the C5, R5 or I5 current is “fixed”, and the L1 magnetizing current varies, the excess L1b current and the D1 current can vary substantially. The variation of D1 current due to the variation in magnetizing inductance is not a systematical error and can not easily be compensated.

[0061] The present disclosure is directed to split the sensing path of the L1b current from the excess current clamping path.

[0062] The sensing path provides an accurate, constant current that flows via the first diode, i.e. D1, via Rset and R1 and determines the L1b voltage as sensed across L1a; the L1b excess current flows via a separate branch and not via D1 into the TL431 clamp.

[0063] This substantially reduces the inaccuracy, non-linearity and temperature dependency in the Rset to the provided DC output voltage transfer curve.

[0064] FIG. 2 discloses a Direct Current, DC, voltage source 11 in accordance with the present disclosure.

[0065] The DC voltage source 11 is arranged for providing a DC voltage, i.e. over R4 in parallel with C4, based on a resistance value of a resistor, i.e. Rset. It is noted that the provided DC voltage is based on a voltage between two terminals, wherein the Rset may be received between those two terminals. Another option is that an output of a voltage source is connected to those two terminals.

[0066] The DC voltage source comprises:

[0067] A transformer as indicated with the reference signs L1a and L1b, wherein the winding L1a is arranged for receiving a supply current and wherein the transformer is arranged for transforming the supply current to a circulating current at the winding L1b.

[0068] The supply current may be received from a current source as indicated with I5, or may originate from a voltage source via C5 and R5. The transformer further provides for an isolation barrier as indicated with the dotted lines for improving the safety aspects of the DC voltage source 11.

[0069] A first and a second terminal for receiving an input voltage for setting a voltage to be provided by the DC voltage source. The terminals may, for example, be suitable for receiving a resistor by screwing the resistor to the terminals, by soldering the resistor to the terminals, by plugging the resistors in the terminals, or anything alike.

[0070] A first diode, i.e. D1, wherein an anode of the first diode is connected to the first end of the second side of the transformer, and wherein a cathode of the first diode is connected to the first input terminal.

[0071] A current regulator circuit, in this example in the form of an adjustable shunt regulator TL431, having two input nodes and one output node, wherein [0072] a first of the input nodes is connected to the second input terminal; [0073] a second of the input nodes is connected to the first end of the second side of the transformer thereby shunting the first diode and the first and second input terminal; [0074] the output node is connected to a second end of the second side of the transformer.

[0075] Following the above, the current regulator circuit is arranged for assuring that a predetermined amount of current is withdrawn from said circulating current, wherein said predetermined amount of current flows via said first diode, said first and second terminal and said first of said input nodes via said output node back to said transformer, and for assuring that a remaining current of said circulating current flows via said second of said input nodes, via said output node, back to said transformer thereby not flowing via said first diode.

[0076] In this particular example, the second of the input nodes comprises a branch diode as indicated with D6, wherein the anode of the branch diode D6 is connected to the first end of the second side of the transformer.

[0077] The predetermined amount of current thus flows from the transformer via the first diode D1 and Rset and R1 back to the transformer. Resistor R1 is coupled between the first of said input nodes and the output node of the adjustable shunt regulator TL431. The remaining current, i.e. the excess current, flows from the transformer via the branch diode D6, through the optional resistor R2 and to the second input node of the adjustable shunt regulator TL431 via the output node of the adjustable shunt regulator TL431 back to the second side of the transformer.

[0078] In the circuit shown in FIG. 2, the Rptc, Rset and R1 current is constant and is the only current flowing via D1. Hence, the D1 current does not vary with Rset, the L1 magnetizing inductance or with temperature.

[0079] If the transfer curve needs to be accurate down to very low voltages, for example a near short of Rset, then the forward voltage of the branch diode D6 is preferably chosen lower than that of the first diode D1. In those cases, D1, and D3, are preferably Silicon diodes, while the branch diode D6 is then preferably a Schottky diode.

[0080] In an example, L1a is driven by a current source I5, delivering current pulses into L1a.

[0081] In an example, such I5 current source is voltage limited to a voltage level just above the voltage across L1a in case of the maximum voltage to be detected.

[0082] In a further example, the I5 current source does not extract current from L1a.

[0083] FIG. 2 depicts a driver-side detection positive with respect to the driver-side Gnd reference, and increases with increasing input voltage.

[0084] In an alternative implementation, L1a may not be referenced to Gnd, but e.g. to a low-voltage supply voltage, and the polarity of L1a may be reversed and the detected output signal across R4 decreases with increasing input voltage or Rset resistance.

[0085] FIG. 3 discloses another Direct Current, DC, voltage supply 21 in accordance with the present disclosure.

[0086] In an example, I5 extracts current from L1a and does not inject current during L1 magnetic reset. I5 may be a current source to Gnd, and may be integrated into an Integrated Circuit.

[0087] The output node as referred to in the description of the FIGS. 1, 2 and 3, is referred to as the anode side of the adjustable shunt regulator TL431. The excess amount of shunted current enters the adjustable shunt regulator via the cathode side, also referred to as the second input node, and leaves the current regulator via the anode side, also referred to as the output node, of the adjustable shunt regulator.

[0088] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “Comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.