Enabling circuit for avoiding negative voltage transients

• US 6,756,769 B2
• Filed: 06/20/2002
• Issued: 06/29/2004
• Est. Priority Date: 06/20/2002
• Status: Expired due to Fees

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Bucur, Constantin, Niculae, Marian
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US10/176,141
• Publication Number:
  US 20030234633A1
• Time in Patent Office: 740 Days
• Field of Search: 320/134, 320/166, 320/132
• US Class Current: 320/134
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

An enabling circuit includes a comparison circuit configured to compare a feedback signal representative of a charge of an energy storage element of a regulating circuit with a reference charge and provide an output in response to the comparison to enable the regulating circuit to switch from a first state to a second state if the charge of the energy storage element is less than the reference charge. The enabling circuit may also be used to enable a synchronous rectifier converter to provide a charging current to a battery in a battery charging system of an electronic device thereby avoiding negative voltage transients that may otherwise occur at the output of the synchronous rectifier converter. Various methods are also provided.

Claims

1. An enabling circuit for enabling a synchronous rectifier converter having a capacitor coupled to an output terminal of said synchronous rectifier converter, said enabling circuit comprising:

a comparison circuit configured to compare a feedback signal representative of a charge on said capacitor with a signal representative of a reference charge and provide an output in response to said comparison;

an output decision circuit configured to receive at least said output from said comparison circuit and provide an enabling signal to enable said synchronous rectifier converter to switch from a first state to a second state if said charge on said capacitor is less than said reference charge; and

a discharge path coupled to said capacitor and said comparison circuit, wherein said discharge path is configured to discharge said charge on said capacitor if said charge is greater than said reference charge.

2. The enabling circuit of claim 1, wherein said output decision circuit is further configured to receive a condition signal, and wherein said output decision circuit provides said enabling signal in response to said condition signal.

3. The enabling circuit of claim 1, wherein said comparison circuit comprises a comparator.

4. The enabling circuit of claim 1, wherein said output decision circuit comprises a NOR gate.

5. The enabling circuit of claim 1, wherein said discharge path comprises at least one resistor, wherein said at least one resistor is configured to discharge said charge on said capacitor.

6. The circuit of claim 1, wherein said discharge path comprises a first resistor having a first resistive value and a second resistor having a second resistive value, said first resistive value higher than said second resistive value, and said first resistor connected in parallel with said second resistor, wherein said second resistor is configured to discharge said capacitor to a charge level less than said reference charge.

7. The circuit of claim 6, wherein said discharge path further comprises a first switch coupled in series with said first resistor and a second switch coupled in series with said second resistor, wherein said first switch and said second switch are configured to close if said enabling signal is not output from said output decision circuit, and wherein said first switch and said second switch are configured to open if said enabling signal is output from said output decision circuit.

8. The enabling circuit of claim 7, wherein said first switch and said second switch are closed when said synchronous rectifier converter is in said first state and open when said synchronous rectifier converter is in said second state.

9. The enabling circuit of claim 1, wherein said synchronous rectifier converter does not provide a charging current to an associated battery when said synchronous rectifier converter is in said first state and does provide a charging current to said associated battery when said synchronous rectifier converter is in said second state.

10. A battery charging system comprising:

a synchronous rectifier converter configured to accept an input power level from a power source and provide a regulated output power level to a rechargeable battery, said synchronous rectifier converter having a capacitor coupled to an output terminal of said synchronous rectifier converter; and

an enabling circuit for enabling said synchronous rectifier converter, said enabling circuit comprising;

a comparison circuit configured to compare a feedback signal representative of a charge on said capacitor with a signal representative of a reference charge and provide an output in response to said comparison; and

an output decision circuit configured to receive at least said output from said comparison circuit and provide an enabling signal to enable said synchronous rectifier converter to switch from a first state to a second state if said charge on said capacitor is less than said reference charge; and

a discharge path coupled to said capacitor and said comparison circuit, wherein said discharge path is configured to discharge said charge on said capacitor if said charge is greater than said reference charge.

11. The system of claim 10, wherein said output decision circuit is further configured to receive a condition signal, and wherein said output circuit provides said enabling signal in response to said condition signal.

12. The system of claim 10, wherein said comparison circuit comprises a comparator.

13. The system of claim 10, wherein said output decision circuit comprises a NOR gate.

14. The system of claim 10, wherein said discharge path comprises at least one resistor, wherein said at least one resistor is configured to discharge said charge on said capacitor.

15. The system of claim 10, wherein said discharge path comprises a first resistor having a first resistive value and a second resistor having a second resistive value, said first resistive value higher than said second resistive value, and said first resistor connected in parallel with said second resistor, wherein said second resistor is configured to discharge said capacitor to a charge level less than said reference charge.

16. The system of claim 15, wherein said discharge path further comprises a first switch coupled in series with said first resistor and a second switch coupled in series with said second resistor, wherein said first switch and said second switch are configured to close if said enabling signal is not output from said output decision circuit, and wherein said first switch and said second switch are configured to open if said enabling signal is output from said output decision circuit.

17. The system of claim 16, wherein said first switch and said second switch are closed when said synchronous rectifier converter is in said first state and open when said synchronous rectifier converter is in said second state.

18. The system of claim 10, wherein said synchronous rectifier converter does not provide a charging current to said rechargeable battery when said synchronous rectifier converter is in said first state and does provide said charging current to said rechargeable battery when said synchronous rectifier converter is in said second state.

19. A method of avoiding negative voltage transients at the output of a synchronous rectifier converter having a capacitor coupled to an output terminal of said synchronous rectifier converter, said method comprising:

monitoring a charge on said capacitor;

maintaining said synchronous rectifier converter in a first state if said charge is above a reference level;

switching said synchronous rectifier converter to a second state if said charge is below said reference level; and

discharging said capacitor via a discharge path of an enabling circuit if said charge is above said reference level.

20. The method of claim 19, wherein said switching step occurs if at least one non capacitor condition is satisfactory.

21. The method of claim 19, wherein said synchronous rectifier converter does not provide a charging current to an associated battery if said synchronous rectifier converter is in said first state, and wherein said synchronous rectifier converter does provide said charging current to said associated battery if said synchronous rectifier converter is in said second state.

22. A method of avoiding negative voltage transients at the output of a synchronous rectifier converter having a capacitor coupled to an output terminal of said synchronous rectifier converter, wherein said synchronous rectifier converter provides a charging current to an associated rechargeable battery, said method comprising the steps of:

monitoring a charge on said capacitor;

maintaining said synchronous rectifier converter in a first state if said charge on said capacitor is above a reference charge;

discharging said capacitor via a discharge path of an enabling circuit until said charge on said capacitor is less than said reference charge; and

enabling said charging current to flow to said associated rechargeable battery once said capacitor is discharged to a charge value less than said reference charge.

23. An enabling circuit for enabling a synchronous rectifier converter having a capacitor coupled to an output terminal of said synchronous rectifier converter, said enabling circuit comprising:

a comparison circuit configured to compare a feedback signal representative of a charge of said capacitor with a signal representative of a reference charge and provide an output in response to said comparison to enable said synchronous rectifier converter to switch from a first state to a second state if said charge of said capacitor is less than said reference charge; and

a discharge path coupled to said capacitor and said comparison circuit, wherein said discharge path is configured to discharge said charge on said capacitor if said charge is greater than said reference charge.

24. The enabling circuit of claim 23, wherein said discharge path comprises at least one resistor, wherein said at least one resistor is configured to discharge said charge on said capacitor.

25. The enabling circuit of claim 23, wherein said discharge path comprises a first resistor having a first resistive value and a second resistor having a second resistive value, said first resistive value higher than said second resistive value, and said first resistor connected in parallel with said second resistor, wherein said second resistor is configured to discharge said capacitor to a charge level less than said reference charge.

26. The enabling circuit of claim 25, wherein said discharge path further comprises a first switch coupled in series with said first resistor and a second switch coupled in series with said second resistor, wherein said first switch and said second switch are configured to close to discharge said charge on said capacitor if said charge is greater than said reference charge.

27. An enabling circuit for enabling a synchronous rectifier converter having a capacitor coupled to an output terminal of said synchronous rectifier converter, said enabling circuit comprising:

an output decision circuit configured to receive a signal representative of a comparison between a charge on said capacitor and a reference charge level and provide an enabling signal to enable said synchronous rectifier converter to switch from a first state to a second state if said charge of said capacitor is less than said reference charge; and

a discharge path coupled to said capacitor, wherein said discharge path is configured to discharge said charge on said capacitor if said charge is greater than said reference charge.

28. The enabling circuit of claim 27, wherein said output decision circuit is further configured to receive a condition signal, and wherein said output circuit provides said enabling signal in response to said condition signal.

29. The enabling circuit of claim 27, wherein said output decision circuit comprises a NOR gate.

30. The enabling circuit of claim 27, wherein said discharge path comprises at least one resistor, wherein said at least one resistor is configured to discharge said charge on said capacitor.

31. The circuit of claim 27, wherein said discharge path comprises a first resistor having a first resistive value and a second resistor having a second resistive value, said first resistive value higher than said second resistive value, and said first resistor connected in parallel with said second resistor, wherein said second resistor is configured to discharge said capacitor to a charge level less than said reference charge.

32. The circuit of claim 31, wherein said discharge path further comprises a first switch coupled in series with said first resistor and a second switch coupled in series with said second resistor, wherein said first switch and said second switch are configured to close if said enabling signal is not output from said output decision circuit, and wherein said first switch and said second switch are configured to open if said enabling signal is output from said output decision circuit.