System and method for charging a capacitor using a constant frequency current waveform

• US 6,417,649 B1
• Filed: 07/20/2000
• Issued: 07/09/2002
• Est. Priority Date: 07/20/2000
• Status: Expired due to Term

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Brink, Gregory D.
• Primary Examiner(s): Tso, Edward H.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/620,446
• Time in Patent Office: 719 Days
• Field of Search: 320/106, 320/166
• US Class Current: 320/166
• CPC Class Codes: A61N 1/3904 External heart defibrillators [EHD]
• CPC Class Codes: A61N 1/3981 High voltage charging circuitry

Abstract

A system and method for charging a high-voltage capacitor through the application of current having magnitude that has a fixed frequency waveform. During a charging sequence in which the current is applied to the capacitor, the duty cycle of the fixed frequency current waveform is dynamically controlled based on the voltage state of the capacitor to modify the energy transfer according to the efficiency with which energy can be delivered to the capacitor. This optimizes the capacitor charging sequence, increasing the speed with which the high voltage capacitor is charged. Generally, energy is transferred from a power source to the capacitor via a magnetic element such as a fly-back transformer. A pulsed voltage supply provides voltage pulses having a constant frequency and an adjustable duty cycle to a primary winding of the transformer. Initially, there is no energy stored in the transformer core. As a result, the duty cycle of the initial voltage pulse is of sufficient duration to accumulate stored energy in the transformer core. Once a predetermined quantity of energy is stored in the transformer, the transformer is controlled to generate a current to charge the capacitor. The magnitude of the current has a fixed frequency and variable duty cycle waveform.

Claims

1. A system for charging a high-voltage capacitor through application of a current, the magnitude of the current having a fixed frequency waveform, with a duty cycle that decreases as a charging voltage of the capacitor increases during charging.

2. A high-voltage capacitor charging system constructed and arranged to generate current pulses having a fixed frequency to a capacitor, wherein during a charging sequence in which said current pulses are repeatedly applied to the capacitor, the duty cycle of the fixed frequency current waveform is controlled dynamically based on the voltage of the high voltage capacitor.

3. A system for charging a high-voltage capacitor comprising;

a flyback transformer having a core, a primary winding and a secondary winding; and

a pulsed voltage supply for providing to said primary winding a voltage having a constant frequency, adjustable duty cycle waveform,

wherein an initial duty cycle of said voltage waveform is sufficiently long to accumulate a quantity of stored energy in said transformer core, after which a value of said duty cycle of said voltage waveform decreases during a charging sequence as a voltage of the high voltage capacitor increases.

4. A system for charging a high-voltage capacitor comprising;

a transformer having a core, a primary winding and a secondary winding wherein the high-voltage capacitor is coupled across the secondary winding; and

a pulsed voltage supply for providing to the primary winding a voltage having a constant frequency, adjustable duty cycle waveform,

wherein said duty cycle of said voltage waveform is modified dynamically such that energy is stored continually in said transformer core as the capacitor is charged.

5. The system of claim 4, wherein, during individual cycles of a charging sequence, the system transfers energy from said pulsed voltage supply to said transformer core to replace energy transferred previously from said transformer core to the high voltage capacitor.

6. A capacitor charging system comprising:

a capacitor charger connected to a capacitor, said capacitor charger constructed and arranged to charge the capacitor by generating a current having a magnitude that has a fixed frequency, variable duty cycle waveform; and

a diode electrically connected to and interposed between the capacitor and said capacitor charger, said diode having a cathode connected to the capacitor and an anode connected to said capacitor charger.

7. The capacitor charging system of claim 6, wherein said capacitor charger comprises:

a transformer having a core, a primary winding, and a secondary winding, the capacitor is coupled across the secondary winding; and

a pulsed voltage supply connected to a node of said transformer, said pulsed voltage supply constructed and arranged to provide to said core a charging voltage that transitions between a first voltage and a second voltage that is smaller than the first voltage, wherein said charging voltage having a substantially constant frequency, and a variable duty cycle.

8. The capacitor charging system of claim 7, wherein said transformer comprises a fly-back transformer.

9. The capacitor charging system of claim 8, wherein said capacitor charger further comprises:

a current sensor, connected to a second node of said primary winding, constructed and arranged to generate a current magnitude signal indicative of current flowing through said primary winding; and

a control circuit, operationally coupled to said pulsed voltage supply and said current sensor, constructed and arranged to provide a duty cycle adjust signal to said pulsed voltage supply to adjust said duty cycle of said charging voltage waveform based on said current magnitude signal.

10. The capacitor charging system of claim 9, wherein said current sensor comprises:

a current-to-voltage converter.

11. The capacitor charging system of claim 10, wherein said current-to-voltage converter includes a resistor.

12. The capacitor charging system of claim 11, wherein said current-to-voltage converter further includes an analog-to-digital converter.

13. The capacitor charging system of claim 8, wherein said pulsed voltage supply comprises:

a voltage source for providing a voltage; and

a switching element connected in series with said voltage source and said primary winding,

wherein said switching element controls said voltage applied to said primary winding.

14. The capacitor charging system of claim 13, wherein said pulsed voltage supply further comprises:

a clock generator providing a plurality of clock signal pulses, wherein a frequency of the clock signal pulses is equal to said substantially constant frequency of the pulsed voltage provided to said switching element, wherein said switching element, responsive to said clock signal pulses, provides said voltage pulses to said primary winding.

15. The capacitor charging system of claim 14, wherein said frequency of said clock signal pulses generated by said clock generator is a function of battery chemistry.

16. The capacitor charging system of claim 15, wherein said switching element comprises:

a switching transistor.

17. The capacitor charging system of claim 16, wherein said switching transistor is a MOSFET transistor.

18. The capacitor charging system of claim 14, wherein said frequency of said clock signal pulses generated by said clock generator is a function of a particular battery manufacturer.

19. The capacitor charging system of claim 14, wherein said control circuit comprises:

a bistable device connected to said current sensor, said bistable device constructed and arranged to change states of said duty cycle adjust signal when said current sensor indicates said current in said primary winding approximately equals a predetermined amount.

20. The capacitor charging system of claim 19,

wherein said current sensor comprises a current-to-voltage converter, and

wherein said reference value is a reference voltage.

21. The capacitor charging system of claim 20, wherein said current-to-voltage converter is a resistor.

22. The capacitor charging system of claim 19, wherein said control circuit further comprises:

a filter having an input from said current sensor at which said filter receives said current magnitude signal, and an output coupled to said first input of said comparator,

wherein said filter attenuates at least one frequency of said current magnitude signal.

23. The capacitor charging system of claim 22, wherein said control circuit further comprises:

control logic having a first input coupled to said output of said bistable device at which said control logic receives said duty cycle adjust signal and a second input coupled to said clock generator at which said control logic receives said clock signal, and an output coupled to said switching element for controlling said duty cycle of said voltage pulses.

24. A capacitor charger for charging a high voltage capacitor comprising:

a capacitor charging transformer including a core, a primary winding and a secondary winding, the capacitor being electrically connected across said secondary winding; and

a charging circuit connected to said primary winding, said charging circuit applying a voltage across said primary winding to cause a current to flow through said secondary winding such that said transformer continually stores energy in its core,

wherein said current flowing through said secondary winding transfers energy from said transformer core to said high voltage capacitor.

25. The capacitor charger of claim 24, wherein said circuit comprises:

a clock generator constructed and arranged to generate a clock signal having a substantially constant frequency;

a voltage supply, responsive to said clock signal, constructed and arranged to supply to said primary winding a voltage having a fixed frequency, variable duty cycle waveform;

a current sensing element providing a current magnitude signal indicative of current flowing through said primary winding; and

a controller having at least one output control signal coupled to said voltage supply for adjusting said duty cycle of said variable waveform based on said current magnitude signal.

26. The capacitor charging circuit of claim 25, wherein said voltage supply comprises:

a voltage source; and

a switching transistor coupled to said voltage source and having a control input at which said clock signal is received, said transistor providing said variable duty cycle voltage waveform at said substantially constant frequency and a voltage level substantially equal to said voltage source.

27. The capacitor charging circuit of claim 25, wherein said controller comprises:

a bistable device having an input coupled to said current sensing element and an output coupled to said voltage supply, said bistable device changing state when said current sensing element indicates said current in the primary winding is substantially equal to a predetermined value, wherein said voltage supply, responsive to said change in state, adjusts said duty cycle of said voltage waveform.

28. The capacitor charging circuit of claim 25, wherein said adjustment of said duty cycle includes setting said voltage pulse to substantially zero volts.

29. A method for charging a capacitor comprising:

providing to the capacitor a current the magnitude of which has a fixed frequency waveform.

30. The method of claim 29, further comprising:

varying the duty cycle of said fixed frequency current.

31. The method of claim 30, further comprising the steps of:

driving a primary winding of a transformer with a fixed frequency variable duty cycle voltage waveform;

sensing an electric current flowing through said primary winding;

adjusting said duty cycle of said voltage waveform when said electric current flowing in said primary winding reaches a predetermined value.

32. A capacitor charger for charging a high voltage capacitor, wherein said capacitor charger is constructed and arranged to enable said capacitor to store up to 240 joules in less than three seconds.