DC-DC STEP UP CONVERTER SYSTEMS AND METHODS

Abstract

The present invention may be embodied as a DC-DC step-up converter assembly comprising a multiple-layer PCB and a converter circuit. The converter circuit comprising a boost controller, an inductor, a capacitor, and a resistor. The boost controller, inductor, capacitor, and resistor are all supported on one side of the multiple-layer PCB. The boost controller, inductor, capacitor, and resistor are configured to operate at a switching frequency of substantially between 50 kHz and 800 kHz

Claims

1. A DC-DC step-up converter assembly comprising: a multiple-layer PCB; a converter circuit comprising a boost controller, an inductor, a capacitor, and a resistor; wherein the boost controller, inductor, capacitor, and resistor are all supported on one side of the multiple-layer PCB; and the boost controller, inductor, capacitor, and resistor are configured to operate at a switching frequency of substantially between 50 kHz and 800 kHz; wherein the converter circuit comprises between 2 and 12 phases; the multiple-layer PCB comprises between 4 and 12 layers; and at least two layers of the multiple layer PCB are grounding layers.

2. A DC-DC step-up converter assembly as recited in claim 1, in which the switching frequency is substantially between 100 and 500 kHz.

3. A DC-DC step-up converter assembly as recited in claim 1, in which the switching frequency is substantially between 100 and 180 kHz.

4. A DC-DC step-up converter assembly as recited in claim 1, in which the switching frequency is substantially between 115 and 120 kHz.

5. A DC-DC step-up converter assembly as recited in claim 1, in which the multiple-layer PCB comprises between 4 and 6 layers.

6. A DC-DC step-up converter assembly as recited in claim 1, in which the converter circuit comprises between 2 and 4 phases.

7. A DC-DC step-up converter assembly as recited in claim 1, in which: the inductor defines an inductor value of 2-100 microhenries, the capacitor defines a capacitor value of 2000-7000 microfarads, and the resistor defines a resistor value of 0.002-22 ohms.

8. A DC-DC step-up converter assembly as recited in claim 1, in which: the inductor defines an inductor value of 1-10 microhenries, the capacitor defines a capacitor value of 100-300 microfarads, and the resistor defines a resistor value of 0.000005-0.003 ohms.

9. A DC-DC step-up converter assembly as recited in claim 1, in which: the inductor defines an inductor value of 2-50 microhenries, the capacitor defines a capacitor value of 100-10000 microfarads, and the resistor defines a resistor value of 0.0001-0.005 ohms.

10. A charger comprising: a DC-DC step-up converter assembly comprising: a multiple-layer PCB; a converter circuit comprising a boost controller, an inductor, a capacitor, and a resistor; wherein the boost controller, inductor, capacitor, and resistor are all supported on one side of the multiple-layer PCB; and the boost controller, inductor, capacitor, and resistor are configured to operate at a switching frequency of substantially between 50 kHz and 800 kHz; wherein the converter circuit comprises between 2 and 12 phases; the multiple-layer PCB comprises between 4 and 12 layers; and at least two layers of the multiple layer PCB are grounding layers.

11. A charger as recited in claim 10, in which the switching frequency is substantially between 100 and 500 kHz.

12. A charger as recited in claim 10, in which the multiple-layer PCB comprises between 4 and 12 layers.

13. A charger as recited in claim 10, in which: the inductor defines an inductor value of 2-50 microhenries, the capacitor defines a capacitor value of 100-10000 microfarads, and the resistor defines a resistor value of 0.0001-0.005 ohms.

14. A method of stepping up a first DC voltage to a second DC voltage comprising the steps of: providing a multiple-layer PCB comprising between 4 and 12 layers, where at least two layers of the multiple layer PCB are grounding layers; providing a converter circuit comprising a boost controller, an inductor, a capacitor, and a resistor, where the converter circuit comprises between 2 and 12 phases; supporting the boost controller, inductor, capacitor, and resistor all on one side of the multiple-layer PCB; and operating the boost controller, inductor, capacitor, and resistor at a switching frequency of substantially between 50 kHz and 800 kHz.

15. A method as recited in claim 14, in which: the inductor defines an inductor value of 2-100 microhenries, the capacitor defines a capacitor value of 2000-7000 microfarads, and the resistor defines a resistor value of 0.002-22 ohms.

16. A method as recited in claim 14, in which: the inductor defines an inductor value of 1-10 microhenries, the capacitor defines a capacitor value of 100-300 microfarads, and the resistor defines a resistor value of 0.000005-0.003 ohms.

17. A method as recited in claim 14, in which: the inductor defines an inductor value of 2-50 microhenries, the capacitor defines a capacitor value of 100-10000 microfarads, and the resistor defines a resistor value of 0.0001-0.005 ohms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIGS. 1A-1G contain a schematic circuit diagram of an example DC-DC step-up converter circuit of the present invention;

[0017] FIG. 2 contains a top elevation view of an example printed circuit board implementing the example DC-DC step-up converter circuit of FIG. 1;

[0018] FIG. 3 is a perspective view of an example enclosure that is used to contain the example printed circuit board of FIG. 2;

[0019] FIGS. 4A-D contain a schematic view of a converter circuit of the present invention configured to operate as a battery charger;

[0020] FIGS. 5A-5I contain a schematic view of an interface and control system for the converter circuit depicted in FIGS. 4A-D;

[0021] FIG. 6 illustrates an example waveform that may be implemented by the converter circuit of FIGS. 4 and 5;

[0022] FIG. 7 is a logic flow diagram that may be implemented by the DC-DC step-up converter of FIGS. 4 and 5;

[0023] FIGS. 8A-8C illustrate simplified circuit diagrams of a DC-DC step-up converter of the present invention;

[0024] FIG. 9 illustrates an example DC-DC step-up converter of the present invention configured for 2-phase operation; and

[0025] FIG. 10 illustrates an example DC-DC step-up converter of the present invention configured for 4-phase operation.

DETAILED DESCRIPTION

I. Introduction

[0026] We conducted a series of iterative experiments whereby we varied the capacity and placement of the capacitors and the number of layers in the printed circuit board. We also varied the switching frequency and the number of circuit board layers.

II. First Embodiment

[0027] A first embodiment of a DC-DC step-up converter of the invention was configured to employ a 2-layer 6-phase PCB. To accommodate the anticipated high currents, Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) were employed. When the board was tested at the manufacturer's suggested frequency, the MOSFETs became excessively hot. To reduce the heat dissipated by the MOSFETs, the first converter embodiment was configured to operate at a lower frequency and with larger inductors to lower the frequency. The switching capacitors were arranged as close to the main ground as possible to mitigate noise. At a switching frequency of 300-350 kHz, only 2 phases would work together, creating a maximum of 15 amps. When the current was increased to above 15 amps, the 24 volt output would drop, and when more phases were added, the wave signal was affected by the EMI and caused disruption. It was concluded that more grounding was required.

III. Second Embodiment

[0028] A second embodiment of a DC-DC step-up converter of the invention was configured to employ a 6-layer 6-phase PCB having two layers configured as ground layers to filter (e.g., reduce) noise and four layers configured to increase current carrying capacity. To dissipate heat, the current sensing path was improved. The current sensing capacitors employed were 10 mm by 10 mm 330 μF capacitors with a temperature rating of 125° C. The number of current sensing resistors was double to accommodate the higher current and the number of current sensing capacitors was also doubled.

[0029] When operated a switching frequency of 300-350 kHz, the two phase system topology of the second embodiment exhibited increased power handling of 45 amps for 37 minutes at 40° C. before capacitor failure. After adding 2 more phases, the internal heat generated was lower, but the capacitors still operated at their upper thermal limit. It was determined that further development was required because the circuitry was intended to be contained within an IP68 enclosure operating at 55° C.

IV. Third Embodiment

[0030] A third embodiment of a DC-DC step-up converter of the present invention employed a 6-layer, 4-phase PCB and is configured as shown in FIGS. 1 and 2. In this third embodiment, the capacitor physical size was increased to 18 mm×20 mm and value in Farads to 2700 μF with a higher operating temperature (150° C.). In addition, the resistor ratings in ohms were increased from 0.003Ω to 0.006Ω, and the circuit design layout was compressed. Contrary to conventional practice, all ICs and components were placed on the same side of the PCB instead of on different layers. The example third embodiment illustrated employs two LTC3787 polyphase synchronous boost controllers configured as shown in FIG. 1.

[0031] To test this third embodiment, the operating frequency was varied in 50 kHz (kilohertz) steps.

[0032] At 300 kHz, the third embodiment yielded an output current of 60 amps. However, the temperature of the MOSFET's reached 100° C. over ambient, temperature of the capacitors were 30° C. over ambient, and temperature of the inductor was 20° C. over ambient.

[0033] At 250 kHz, the third embodiment yielded an output current of 60 amps. However, the temperature of the MOSFET was 80° C. over ambient temperature, temperature of the capacitors 27° C. over ambient, temperature of the inductor 24° C. over ambient.

[0034] At 100 kHz, the third embodiment yielded an output current of 60 amps, and all components with acceptable temperature limits. In particular, the temperature of the MOSFET was 20° C. over ambient temperature, temperature of the capacitors 20° C. over ambient, temperature of the inductor 40° C. over ambient. However, the output voltage dropped to 23.2 V instead of the 24 V optimal for powering a vehicle HVAC system.

[0035] Still using the third embodiment, the operating frequency was increased in 10 kHz increments to correct the output voltage. At 120 kHz, the third embodiment yielded an output current of 60 amps, and the output voltage was 24.1V. Further, all components with acceptable temperature limits. In particular, the temperature of the MOSFET was 20° C. over ambient temperature, temperature of the capacitors 20° C. over ambient, temperature of the inductor 40° C. over ambient.

[0036] With a lower operating frequency and larger capacitors, the complexity of the board may be decreased such that only 4 phases are required to achieve the 60-amp at 24-volt target. The use of a lower operating frequency and larger capacitors also enhanced the longevity and stability of the board components.

[0037] Table IV-A below lists components, and variables associated with these components, may be combined to form a first embodiment of the third example DC-DC step-up converter of the present invention:

TABLE-US-00001 TABLE IV-A Exam- First Preferred Second Preferred Parameter ple Range Range number of layers 6 n/a n/a number of phases 4 n/a n/a inductor value (μH) 6.8  5-10  2-20 capacitor value (μF) 2700 2500-3000 2000-3500 capacitor size (mm.sup.2) 360 300-500 200-700 capacitor maximum 150 >125 >100 operating temperature (° C.) resistor value (Ω) .0015 .000005-.003   0.002-22.  sampling resistor value .0015 .001-.003 0.005-0.05  (Ω) switching frequency 120 115-125 100-180 (kHz)

[0038] Table IV-B below lists components, and variables associated with these components, may be combined to form a second embodiment of the third example DC-DC step-up converter of the present invention:

TABLE-US-00002 TABLE IV-B Exam- First Preferred Second Preferred Parameter ple Range Range number of layers 6 4-6 4-12 number of phases 4 2-4 2-12 inductor value 6.8  1-10  2-100 (μH) capacitor value 2700  100-3000 2000-7000  (μF) Capacitor size 18 × 20 .sup. .2 × 1-20 × 20  18 × 18-100 × 100 D × L (mm) capacitor size 360  1-500 200-700  (mm.sup.2) capacitor 150 >−40 >150 maximum operating tempera- ture (° C.) resistor value .0015 .000005-.003   0.002-22.   (Ω) sampling resistor .0015 .001-.003 0.005-0.05  value (Ω) switching 120  1-125 100-1000 frequency (kHz)

[0039] Table IV-C below lists components, and variables associated with these components, may be combined to form a third embodiment of the third example DC-DC step-up converter of the present invention:

TABLE-US-00003 TABLE IV-C Exam- First Preferred Second Preferred Parameter ple Range Range number of layers 6 4-6 4-12 number of phases 4 2-4 2-12 inductor value (μH) 6.8  1-10 2-50 capacitor value (μF) 2700  100-1000  100-10000 Capacitor size D × 18 × 20 16 × 20-18 × 40 12 × 20-18 × 40  L (mm) capacitor size (mm.sup.2) 360 320-720 240-720  capacitor maximum 135  85-135 85-150 operating tempera- ture (° C.) resistor value (Ω) 0.0015 0.0005-.003  0.0001-.005   switching frequency 350 100-500 50-800 (kHz)

[0040] The third example DC-DC step-up converter described herein can further configured to step up to voltages other than 24V. In particular, the third example DC-DC step-up converter described in this Section IV can be configured to convert 12V to 36V or 48V as necessary to accommodate a particular load.

V. Fourth Embodiment

[0041] A fourth embodiment of a DC-DC step-up converter of the present invention is depicted in FIGS. 4 and 5 of the drawing. The DC-DC step-up converter of the fourth embodiment is configured to function as a battery charger but otherwise operates under principles and parameters similar to that of the third example DC-DC step-up converter depicted in FIGS. 1 and 2. Like the example third embodiment illustrated above in FIG. 2, the fourth embodiment includes at least one LTC3787 polyphase synchronous boost controller, a STM32F303 microcontroller, and a MAX7219 display driver, all of which are configured as shown in FIG. 4.

[0042] FIG. 6 illustrates a waveform that may be implemented by the DC-DC step-up converter of FIGS. 4 and 5 when configured as a battery charger. FIG. 7 illustrates a logic flow diagram that may be implemented by the DC-DC step-up converter of FIGS. 4 and 5 when configured as a battery charger. In the example waveform depicted in FIG. 6, the duty-cycle varies from 5% to 90% of the total charging period, the example charging period in FIG. 6 is 200 ms.

[0043] FIGS. 6 and 7 illustrate that battery charging may controlled during charging by altering duty cycle of the converter based on factors such as supply voltage, charge voltage, and charge current. In a rest mode, supply voltage and battery voltage are measured to determine whether to continue charging or to place the DC-DC step-up converter in an idle mode in which battery charging is discontinued. During idle mode, the supply voltage and the battery voltage may be sampled to determine whether to place the DC-DC step-up converter back into charge mode. In the example depicted in FIGS. 6 and 7, the battery charging voltage is predetermined to be substantially between 26V and 28V.

VI. Converter Simplified Diagrams

[0044] FIGS. 8A-8C illustrate simplified circuit diagrams of the example DC-DC step-up converters described above. The MOSFET depicted in FIG. 8A is switched at a predetermined frequency such that the circuit is configured in a charge phase as illustrated in FIG. 8B and a discharge phase as illustrated in FIG. 8C.

[0045] Table VI-A below lists a first example of components, and variables associated with the components, of the DC-DC step-up converter of FIGS. 8A-8C when configured according to the principles of the present invention:

TABLE-US-00004 TABLE VI-A Exam- First Preferred Second Preferred Parameter ple Range Range inductor value 6.8 1-10 2-100 (μH) capacitor value 2700 100-3000 2000-7000  (μF) capacitor size 18 × 20  .2 × 1-20 × 20 18 × 18-100 × 100 D × L (mm) capacitor size 360  1-500 200-700  (mm.sup.2) capacitor 150 >−40 >150 maximum operating tempera- ture (° C.) resistor value .0015 .000005-.003   0.002-22.   (Ω) switching 120 100-125  100-1000  frequency (kHz)

[0046] Table VI-B below lists a second example of components, and variables associated with the components, of the DC-DC step-up converter of FIGS. 8A-8C when configured according to the principles of the present invention:

TABLE-US-00005 TABLE IV-B Exam- First Preferred Second Preferred Parameter ple Range Range inductor value (μH) 6.8  1-10 2-50 capacitor value (μF) 2700  100-3000  100-10000 capacitor size D × 18 × 20 16 × 20-18 × 40 12 × 20-18 × 40  L (mm) capacitor size (mm.sup.2) 360 320-720 240-720  capacitor maximum 135  85-135 85-150 operating tempera- ture (° C.) resistor value (Ω) 0.0015 0.0005-.003  0.0001-.005   switching frequency 350 100-500 50-800 (kHz)

[0047] FIGS. 9 and 10 illustrate simplified circuit diagrams of DC-DC step-up converters of the present invention configured for 2-phase operation (FIG. 9) and 4-phase operation (FIG. 10). The components of the DC-DC step-up converters of FIGS. 9 and 10, and variables associated with those components, may be the same as the examples listed in Tables IV-A and IV-B above.