Enabling circuit for avoiding negative voltage transients

• US 6,949,912 B2
• Filed: 01/15/2004
• Issued: 09/27/2005
• Est. Priority Date: 06/20/2002
• Status: Active Grant

• 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:
  US10/757,870
• Publication Number:
  US 20040207378A1
• Time in Patent Office: 621 Days
• Field of Search: 320/134, 320/166, 320/132, 323/222
• 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: H02J 7/0029 with safety or protection devices or circuits
• 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 including a comparison circuit, a switching circuit, and an output decision circuit. The comparison circuit compares a first comparison signal representative of a charge on a capacitor of a DC to DC converter with a second comparison signal representative of a reference charge and provides a comparison output signal in response to the comparison. In response to the comparison output signal, the switching circuit provides a first switching signal in a first state if the charge on the capacitor is less than said reference charge. Finally, the output decision circuit accepts at least the first switching signal and provides an enabling signal to enable the DC to DC converter to be controlled by a control signal in response to the first switching signal in the first state.

Claims

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

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

a switching circuit configured to accept said comparison output signal, and in response to at least said comparison output signal provide a first switching signal in a first state if said charge on said capacitor is less than said reference charge; and

an output decision circuit configured to accept at least said first switching signal and provide an enabling signal to enable said DC to DC converter to be controlled by a control signal in response to said first switching signal in said first state.

2. The enabling circuit of claim 1, wherein said output decision circuit is further configured to accept a condition signal and wherein said output decision circuit provides said enabling signal if said first switching signal is in said first state and said condition signal is in a state representative of a desired charging state.

3. The enabling circuit of claim 2, wherein said output decision circuit comprises an AND gate, said AND gate accepting said first switching signal and said condition signal.

4. The enabling circuit of claim 1, wherein said switching circuit further provides a second switching signal in a first state if said charge on said capacitor is greater than said reference charge and in a second state if said charge on said capacitor is less than said reference charge, and wherein said enabling circuit further comprises a discharge path responsive to said second switching signal to discharge said capacitor if said second switching signal is in said first state.

5. The enabling circuit of claim 4, wherein said discharge path comprises a switch, said switch responsive to said second switching signal to close if said second switching signal is in said first state and to open if said second switching signal is in said second state.

6. The enabling circuit of claim 1, wherein said switching circuit comprises an RS flip flop.

7. A battery charging system comprising:

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

an enabling circuit for enabling said DC to DC converter to be controlled by a control signal, said enabling circuit comprising;

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

a switching circuit configured to accept said comparison output signal, and in response to at least said comparison output signal provide a first switching signal in a first state if said charge on said capacitor is less than said reference charge; and

an output decision circuit configured to accept at least said first switching signal and provide an enabling signal to enable said DC to DC converter to be controlled by said control signal in response to said first switching signal in said first state.

8. The system of claim 7, wherein said output decision circuit is further configured to accept a condition signal and wherein said output decision circuit provides said enabling signal if said first switching signal is in said first state and said condition signal is in a state representative of a desired charging state.

9. The system of claim 8, wherein said output decision circuit comprises an AND gate, said AND gate accepting said first switching signal and said condition signal.

10. The system of claim 7, wherein said switching circuit further provides a second switching signal in a first state if said charge on said capacitor is greater than said reference charge and in a second state if said charge on said capacitor is less than said reference charge, and wherein said enabling circuit further comprises a discharge path responsive to said second switching signal to discharge said capacitor if said second switching signal is in said first state.

11. The system of claim 10, wherein said discharge path comprises a switch, said switch responsive to said second switching signal to close if said second switching signal is in said first state and to open if said second switching signal is in said second state.

12. The system of claim 7, wherein said switching circuit comprises an RS flip flop.

13. The system of claim 7, wherein said control signal comprises a pulse width modulated (PWM) signal.