DC to DC converter current pump

• US 4,868,730 A
• Filed: 12/11/1987
• Issued: 09/19/1989
• Est. Priority Date: 07/15/1986
• Status: Expired due to Fees

• Current Assignee: Combustion Electromagnetics Incorporated
• Original Assignee: Combustion Electromagnetics Incorporated
• Inventors: Ward, Michael A. V.
• Primary Examiner(s): Wong, Peter S.
• Application Number:
  US07/179,953
• Time in Patent Office: 648 Days
• Field of Search: 323/222, 323/224, 363/16, 363/20, 363/21, 363/59, 363/60, 363/61, 363/97, 320/1, 307/109, 307/110, 123/596, 123/597, 123/604, 123/605, 123/650, 123/652-656
• US Class Current: 363/21.12
• CPC Class Codes: F02P 3/0884 Closing the discharge circuit of the storage capacitor with semiconductor devices
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer

Abstract

A DC to DC power converter designated a synchronous current pump (13) and operated in the preferred mode in synchronization with a discharge circuit (11) and using a capacitor (28) as the energy storage element, and in the preferred embodiment has in series with said capacitor the battery supply (10), an inductor (30), a diode (27a), and the primary winding (31a) of a transformer (31); and across said storage capacitor is an energy transfer FET switch (33) which is used for discharging said capacitor and transferring it stored energy to a output load capacitor (4) connected through a diode (32) to the secondary winding of said transformer. In operation, the current pump supplies power efficiently and smoothly to a load discharge capacitor in synchronization with operation of the discharge circuit.

Claims

1. A Simplified Current Pump (or SCP) DC--DC power converter which includes in series with a voltage power supply (PS) operating at a voltage Vo the following:

(a) at least one electrical current controlling and/or limiting means (ECC),

(b) energy storage and switching capacitor of a selected value of capacitance (CO),

(c) electrical transformer means (T) with at least one secondary winding (TS) and with a primary winding (TP) with a selected secondary winding (TS) to primary winding (TP) turns ratio (N),

(d) means defining a shunt switch (SS) to ground with shunt diode means across it, wherein said shunt switch (SS) is connected from ground to a point (P) between said ECC means and said capacitor CO, and

(e) output diode means comprising at least one diode defined as the charging diode connected between a high side point (S) of said secondary winding TS of the transformer means T and an electrical load in a direction which allows said charging diode to conduct current to said load when said shunt switch (SS) is switched ON

the foregoing apparatus being constructed and arranged such that during the conduction time (t-on) of the shunt switch the current in that switch first rises and then decays due to a reasonant process involving said capacitor of selected capacitance value and the leakage inductance of said transformer means, and such that the shunt switch is turned off only when (i) the current in it becomes substantially smaller than its peak current or (ii) when the polarity of the current, in the combination of said shunt switch and said shunt diode across it, reverses polarity,

whereby voltage spikes and turn-off switching losses in said switch are essentially eliminated or reduced to tolerable levels without the use of snubbing or clamping means across the shunt switch.

2. The system defined in claim 1 wherein said current controlling means ECC comprises in series an inductor (LO) and an input diode means which are located between said power supply (PS) and said point P with the input diode means oriented in a direction to allow passage of current from said power supply (PS), and wherein voltage input power from said power supply (PS) is converted to a higher voltage output power by sequentially turning said shunt switch ON for a time (t-ON) and OFF for a time (t-OFF) - where the sum of the times T-ON and T-OFF is equal to the total time (t-TOT), and wherein the foregoing apparatus is constructed and arranged such that the magnetic sense of said transformer T for like and input/output voltage polarities has an opposite sense between its said primary (TP) and said secondary (TS) windings in that a positive voltage appears on the high or ungrounded side (S) of said secondary winding when a negative voltage is on the high side of the primary winding (defined as point PP), and wherein said magnetic sense is reversed for reversed input or output voltage polarities, but not both, and remains the same when both input and output voltage polarities are reversed.

3. The system defined in claim 2 wherein the time period t-ON corresponds a first time period plus a fraction between zero and less than one half second time (T-SH2) where T-SH1 is a time equal to approximately the first half discharge cycle of switching capacitor CO discharging through primary winding TP via shunt switch SS, and T-SH2 is the secnd half of the discharge cycle, or capacitor CO recharge half-cycle, which recharges CO through said winding TP via said shunt diode when energy is available for such recharge, and wherein said inductor of inductance LO has a resistance RO comprising inductive time constant (T1) defined by LO/RO which is greater than time t-ON, and t-TOT is approximately equal to or less than the charge time Tch required to charge CO from said power supply PS through LO with zero initial current.

4. the system defined in claim 3 wherein said total time t-TOT is approximately equal t two times the time period t-SH1.

5. The system defined in claim 3 wherein said output diode means comprises an electrical energy delivery output rectifier stage selected from the class consisting of single charging diode halfwave rectifier stage, two diode full-wave rectifier stage comprising center tapped secondary winding of said transformer T, and four diode full-wave bridge rectifier stage, and wherein the end of time period t-ON is between the time of initial and maximum current through said shunt diode if current flows through the shunt diode, or approximately equal to the time of the first minimum current through shunt switch SS following turn-ON of switch SS if essentially no current flows through the shunt diode.

6. The system defined in claim 5 wherein said output diode means rectifier stage is said half-wave rectifier stage comprising said single diode, the latter constituting said charging diode with a high voltage capacitor (C2) connected in parallel immediatey across said secondary winding TS of said transformer T between said high side of said transformer point S and ground.

7. The system defined in claim 5 wherein said output diode means rectifier stage is said center tapped full-wave rectifier stage comprising said two diodes connected in series with each half of said center tapped secondary winding of said transformer T with diodes in turn connected together to said load, wherein one of said two diodes is said charging diode and the other is defined as the recharging/charging diode.

8. The system defined in claim 7 wherein the two secondary windings defined by the said center tapped secondary winding are of unequal number of turns.

9. The system defined in claim 5 wherein said output diode means rectifier stage is said full-wave bridge comprising said four diodes with each pair of diodes connected to each end of the secondary winding TS of said transformer T to form a full wave bridge comprising charging and recharging diode pairs.

10. The system defined in claim 5 wherein said shunt switch SS comprises one or more parallel FET switches with integral or separate diodes across them, defined as shunt FET switch (SSFET), and wherein load connected to output of said transformer T is at least one load capacitor with a capacitance value of C1.

11. The system defined in claim 10 wherein C1 is a capacitor of a capacitor discharge circuit including a transformer or ignition coil (TC) and high voltage switch (SHV) for producing and delivering very high voltage to a high voltage output circuit (HVOC).

12. The system defined in claim 11 wherein switch SHV is an SCR and HVOC is an ignition circuit including at least one spark plug defining at least one spark gap for producing ignition sparks.

13. The system defined in claim 12 wherein said SCR is fired sequentially to produce multiple spark pulses per ignition firing.

14. The system defined in claim 13 wherein the SCR turn-ON moment following the first spark plug corresponds essentially to the FET switch SSFET turn-OFF moment during the period of the multiple spark pulses.

15. The system defined in claim 14 wherein said switching of FET switch SSFET is in phase with the multiple spark pulse firing so that during the time period between the SCR turn-OFF and the SCR turn-ON, excluding any delay time in restarting said current pump SCP after the SCR turn-OFF, there occurs essentially an integer number (NTON) of time periods t-ON and essentially an integer number (NOFF) of time periods t-OFF where NTOFF is one less than (NTON).

16. The system defined in claim 15 wherein time SCR is ON corresponds to between one and three time periods of said SSFET OFF time t-OFF and wherein time t-OFF is approximately equal to between two thirds and one times the SSFET OFF time required to fully charge said capacitor CO.

17. The system defined in claim 15 wherein SCR ON-time is between 80 and 120 usecs and time between SCR firing pulses is between 200 and 300 usecs, and current pump time t-TOT is between 30 and 120 usecs, so that NTON is essentially either two, three, or four and NTOFF is essentially either one, two, or three respectively.

18. The system defined in claim 11 wherein VO is voltage from a twelve volt battery and CO is between 2 and 20 microfarads, LO is between 20 and 200 microhenries, C1 is in the range of 2 to 20 uFarads, transformer turns ratio N is between 15 and 30, and the energy storage factor (EO) of the system is in the range of 1 to 50 millijoules, where EO is defined as EO=1/2*CO*((2*VO)**2).

19. The system defined in claim 18 wherein said input diode means is a Schottky type diode, said FET switch SSFET is one or more inparallel FETs of the type BUZ11, MTP45NO5E, MTP5ONO5E, CO is in the range of 3 to 10 ufarads, primary leakage inductance (Le) of said transformer T is between 4 and 20 uHenries obtained by purposely reducing coupling between windings of said transformer T, such that when capacitor C oscillates with said leakage inductance Le, as occurs in operation of said current pump SCP, the period of said oscillation is in the range of 40 to 200 usecs.

20. The system defined in claim 11 wherein VO is voltage from a twenty four volt battery CO is between 1 and 20 ufarads.

21. The system defined in claim 5 wherein a capacitor of capacitance value C2 is placed immediately across said secondary winding TS except in said center tapped secondary winding case where it is placed immediately across said secondary half winding containing the non charging diode or recharge/charging diode.

22. The system defined in claim 21 wherein the transformed capacitance TrC2 of said capacitor C2, defined by TrC2=(N**2)*C2, is approximately equal to or less than C and selected such that period t-SH1 is greater than one and less than four times the half oscillation period T22 corresponding to capacitor C2 discharging through secondary TS of transformer T with primary winding TP conducting current through capacitor CO and said shunt switch SS or shunt diode, and wherein said time period t-ON corresponds to aproximately the maximum current through said shunt diode.

23. The system defined in claim 22 wherein TrC2 is between 0.3 and 0.6 of CO and t-SH1 is between 3/2 and about 2 times the half oscillation period T22 corresponding to value of capacitor C2.

24. The system defined in claim 22 wherein said shunt switch SS is one or more in parallel FETs and wherein total operating cycle time t-TOT is equal to between two and six times said period T22, and wherein values of said current pump SCP and time periods t-ON and t-OFF are chosen such that the current IOO through inductance LO after the time period t-ON, given by (VO)*(t-ON)/LO, is approximately equal to the maximum current Im which would flow through the series circuit defined by L0, C0, and the primary winding TP when the initial current through LO is zero.

25. The system defined in claim 21 wherein the value of capacitor C2 is approximately equal to or less than CO/(N**2), and wherein the system is further constructed and arranged to produce three simultaneous electrical events when said shunt switch is turned ON and OFF for said time period t-TOT, 1) a charging event wherein initial current IOO builds up through LO and said shunt switch during time t-ON to be then steered to charge capacitance CO and C2 during period t-OFF, 2) an event wherein capacitor CO discharges and recharges through said shunt switch and shunt diode and primary TP of transformer T, and 3) event wherein capacitor C2 oscillates through secondary TS and delivers current to CO through said shunt diode after C2 has completed its first half cycle to feed back energy to CO delivered to C2 during the charging event.

26. The system defined in claim 23 wherein said time period t-ON is approximately equal to T-SH1,and C2 is approximately equal to [0.5]*[CO/(N**2)], providing for a t-ON time period approximately equal to two times a time period (T22), where T22 is the half oscillation period corresponding to discharging of capacitor C2 through a secondary winding of transformer T with primary winding TP of transformer T conducting current through capacitor CO and through either said shunt switch or said shunt diode.

27. The system defined in claim 26 wherein said shunt switch is one or more in-parallel FETs defined as SSFET and shunt diode is integral or external to said FETs, and wherein the total operating cycle time t-TOT is approximately equal to twice the ON time t-ON.

28. The system defined in claim 27 wherein said inductance LO and ON-time period t-ON are chosen such that the current (IOO) through inductance LO after the time period t-ON, given by VO*(t-ON)/LO, is approximately equal to the maximum current (Im) which would flow through the series circuit defined by LO, CO and the primary winding TP when the initial current through LO is zero, providing a maximum charge voltage (VCO) to capacitor CO approximately equal to 2.5 times VO, where VO is voltage of said power supply.

29. The system defined in claim 28 wherein current IOO is greater than Im and said turns ratio N is chosen to equal a value (NO) according to a higher value of VCO produced by the higher value of IOO, where NO is given approximately by NO=2*VC1/VCO, where VC1 is the value to which a capacitor C1 representing said load is normally charged to for a normally fully charged battery power supply PS.

30. The system defined in claim 27 wherein said load connected to output said transformer T is a 400 volt capacitor with a capacitance value (C1) between 1 and 20 uFarads, and capacitance CO has a value also between 2 and 20 uFarads, turns ratio N is between 20 and 30 for a twelve volt car battery providing power to the current pump, inductance LO is between 20 and 200 uHenrys, and the number of primary winding turns (Np) is between 10 and 30 turns.

31. The system defined in claim 30 wherein transformer T primary winding leakage inductance Le is between 2 and 20 uHenries and is selected to provide in combination with CO a source impedance Z12 between 0.3 and 3 ohms, and said time T-TOT is between 30 and 120 usecs, and said SCP provides varying power output into discharged capacitor C1 of about 100 watts during the first few miliseconds and dropping to less than 20 watts after 10 milliseconds, charging capacitor C1 to about 300 volts in about 5 milliseconds when VO is approximately 12 volts and C1 is between 3 and 20 uFarads.

32. The system defined in claim 28 wherein said output diode means is four diode full-wave bridge rectifier stage and capacitor C2 is further adjusted to the value C2-optimum.

33. The system defined in claim 26 wherein ideal turns ratio NO of transformer T is selected according to the formula NO=2*VC1/VCO, where VC1 is the voltage to which capacitor C1 must be charged when said power supply PS is providing a voltage V which charges capacitor CO to a voltage VCO at the end of the charging stage.

34. Ths system defined in claim 33 wherein said supply PS is a battery used in conjunction with automotive engine and said ideal turns ratio NO is based on voltage VCO arising from voltage VO of said battery when said engine is operating in its normal mode.

35. The system of claim 34 wherein VC1 is approximately 350 volts, VO is approximately 12 volts which is taken as the typical loaded voltage at the point connecting said input diode means and said inductor, VCO is approximately 30 volts, and NO is accordingly approximately equal to a turns ratio of 24, and primary winding turns Np of primary TP of said transformer is between 15 and 30, and is capable of providing an average power output of about 100 watts during the first few milliseconds of charging when capacitor C1 is initially charged at 80 volts.

36. The system of claim 35 wherein said shunt switch is one or more in parallel low voltage, low RDS FETs, Motorola and containing integral diodes which may be of the zener type which limit voltage in the range of 50 to 70 volts to sustain short duration overvoltages and tens of amps of high avalanche currents through the internal zener.

37. The system defined in claim 33 wherein said output diode means is four diode full-wave bridge rectifier stage and capacitor is further adjusted to the value C2-optimum.

38. The system defined in claim 26 wherein said shunt switch SS is a high speed semiconductor switch with low saturation voltage of the class of bipolar power transistors, with an external shunt diode placed across it.

39. The system defined in claim 26 wherein said output diode means is four diode full-wave bridge rectifier stage and wherein said capacitor C2 is further adjusted to a value C2-optimum to give an oscillation period T22 such that at the end of the time period t-ON it provides a well defined but low amplitude current peak through said shunt diode of about 1/10 of the maximum current through said shunt switch, and at the end of time period t-OFF it provides charging current to capacitor CO such that the voltage on CO at the end of t-OFF is approximately at a peak value.

40. The system defined in claim 1 wherein an additional speed-up switch is connected across primary winding TP of said transformer T between intersection of capacitor CO and high side of primary of transformer, point PP, and ground, said speed-up switch being unidirectional power semiconductor device from the class of SCRs and bipolar power transistors.

41. The system defined in claim 1 wherein said electrical current controlling and/or limiting means ECC includes a semiconductor switch which is switched on at least during the time when said shunt switch is in the OFF condition during operation of said current pump.

42. The system defined in claim 5 wherein said electrical load includes an electric circuit further including capacitor means of capacitance C1 of at least 2 uFarads connected to ignition coil and at least one switch for discharging capacitor C1 into the primary of said coil for producing both high ignition voltage greater than 20 kilovolts and high ignition current discharge greater than 200 milliamps, said circuit further comprising:

(a) a low turns ratio high efficiency ignition coil with low primary and secondary resistance and turns ratio less than sixty for voltage rating of 400 volts of capacitor C1;

(b) high voltage capacitor of capacitance value between 0.05 and 0.4 uFarads connected directly across primary windings of said ignition coil;

(c) spark plug means for producing sparks from said coil.

43. Electric circuit of claim 42 wherein said SCP DC to DC power converter includes one or more parallel FET switches for said shunt switch SS, capacitance CO is between 2 and 20 ufarads, said low volage power supply PS is a 12 volt car battery, and said transformer of said SCP has a turns ratio N between 15 and 30.

44. Electric circuit of claim 43 wherein said spark plug has a spark gap of width of at least 0.06" connected across secondary of said spark coil for producing spark current discharges.

45. In a power delivery system comprising a DC power supply PS and a DC to DC power converter SCP for converting low voltage input energy of voltage VO from the power supply PS to a higher output voltage V1 delivered to an electrical load by means of a step-up transformer means T, the improvement comprising:

(1) an energy storage capacitor means of value CO as the main transformer primary side energy storage means,

(2) an inductor LO in series with said supply PS to store as magnetic energy an amount of energy equal to a fraction of the energy stored in capacitor CO,

(3) a shunt switch means with a shunt diode across it for shunting current derived from the power supply PS and energy storage means, said shunt switch being sequentially switched ON and OFF and constructed and arranged to produce several results;

(i) during switch ON to simultaneously enable storage of energy in said inductor LO and to enable transfer of energy from said capacitor CO to a load connected to the output of said transformer T,

(ii) during switch OFF to enable delivery of energy stored in said inductor LO and from said supply PS to charge up capacitor CO to a value VCO greater than VO,

(iii) and to perform the functions (i) and (ii) such that the current through said shunt switch is zero during normal operation during the instant of shunt switch turn-OFF,

(4) a capacitor of capacitance C2 connected across the output of said transformer T and of a selected value such that it can store high voltage energy during part or all of the shunt switch OFF time when capacitor CO has energy being stored on it, and then delivers its stored high voltage energy through transformer T to capacitor CO in such a way and phasing that as it delivers the energy to C it also reinforces the current zero condition at the shunt switch turn-OFF and helps maximize the voltage on CO at the end of the shunt switch OFF time, and

(5) means for directing current flow,

the improved system as a whole being constructed and arranged such that it is able to operate essentially without current sensing or spike suppessor means (snubbers or clamps) across the shunt switch over the widely varying range of input voltages, e.g., from 7 to 14 volts, as is typical of automotive applications.

46. The system defined in claim 45 wherein said DC to DC converter includes input diode and output diode means wherein said input diode means is a Schottky diode in series with said inductor L0, and said shunt switch SS is one or more in-parallel FETs, and said capacitor C2 has a capacitance value given approximately by [0.5]*[CO/(N**2)], where N is the secondary winding to primary winding turns ratio of said transformer T.

47. The system defined in claim 46 wherein said FET device making up said shunt switch has an internal diode integral to the device, such as devices selected from very high efficiency, low RDS FETs such as the BUZ11, and MTP45NO5E and MTP5ONO5E, wherein said internal diode may also behave as a zener diode with the capabiltiy of shunting tens of amps of avalanche current when the voltage exceeds the specified 50 to 70 volts of the device.

48. The system defined in claim 46 wherein said electrical load comprises a main capacitor means CO1 of a capacitive discharge system.

49. The system defined in claim 48 wherein said capacitive discharge system is part of an internal combustion engine ignition system.

50. The system defined in claim 48 wherein capacitor means CO1 in turn comprises energy storage capacitor of a second of said DC to DC converter designated (SCP1) wherein SCP1 is used to provide further raising of output voltage from V1 to V2.