Capacitor charging apparatus

• US 20080061746A1
• Filed: 03/06/2007
• Published: 03/13/2008
• Est. Priority Date: 03/07/2006
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Yamamichi, Yoshifumi, Kobayashi, Shinya
• Granted Patent: US 7,710,080 B2
• Time in Patent Office: Days
• US Class Current: 320/166
• CPC Class Codes: H01F 29/02 with tappings on coil or winding; with provision for rearrangement or interconnection of windings
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

A capacitor charging apparatus includes a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, and charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer. A switching control unit controls on and off of the switching transistor. A voltage detector monitors a voltage at a tap provided in the secondary coil of the transformer. The switching control unit regards the voltage detected by the voltage detector as an output voltage of the capacitor charging apparatus, and controls the on and off of the switching transistor.

Claims

1. A control circuit of a capacitor charging apparatus, the capacitor charging apparatus including a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, which charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer, the control circuit comprising:

a switching control unit which controls on and off of the switching transistor; and

a voltage detector which monitors a voltage at a tap provided on the secondary coil of the transformer,

wherein said switching control unit controls the on and off of the switching transistor by taking the voltage detected by said voltage detector as an output voltage of the capacitor charging apparatus.

2. A control circuit according to claim 1, wherein said switching control unit includes a charging completion detector which detects completion of charging by comparing the voltage detected by said voltage detector with a predetermined threshold voltage, and

when a completion of charging is detected, said switching control unit stops the on and off of the switching transistor.

3. A control circuit according to claim 1, wherein said switching control unit repeats an operation of turning on the switching transistor until current flowing through the primary coil of the transformer has reached a predetermined peak current and of then turning off the switching transistor during an off-time, and

said switching control unit varies the off-time in response to the voltage detected by said voltage detector.

4. A control circuit according to claim 3, wherein said switching control unit sets the off-time in such a manner that the higher the voltage detected by said voltage detector is, the shorter the off-time becomes.

5. A control circuit according to claim 3, said switching control unit including:

a primary-current detection circuit which detects a primary current flowing through the primary coil of the transformer;

a comparator which compares the primary current detected by the primary-current detection circuit with a predetermined peak current value and outputs a comparison signal of a predetermined level when the primary current exceeds the predetermined peak current value;

an off-time setting circuit which begins to count an off-time when the comparison signal outputted from the comparator becomes the predetermined level; and

a driver circuit which repeats an operation of turning off the switching transistor during a period of time in which the off-time is counted and turning on the switching transistor after the off-time has elapsed,

wherein the off-time setting circuit varies the off-time in accordance with the voltage detected by said voltage detector.

6. A control circuit according to claim 5, wherein the off-time setting circuit sets the off-time in such a manner that the higher the voltage detected by said voltage detector is, the shorter the off-time is.

7. A control circuit according to claim 1, wherein said control circuit is integrated on a single semiconductor substrate.

8. A capacitor charging apparatus, comprising:

a transformer, including a primary coil and a secondary coil, wherein an input voltage is applied to one end of the primary coil and a switching transistor is connected to other end thereof;

an output capacitor one end of which is grounded;

a diode having an anode thereof connected to a second coil side of said transformer and a cathode thereof connected to the other-end side of said output capacitor; and

a control circuit, according to claim 1, which controls on and off of the switching transistor.

9. A light emitting apparatus, comprising:

a capacitor charging apparatus according to claim 8;

and

a light-emitting element driven by an output voltage appearing at the output capacitor in said capacitor charging apparatus.

10. An electronic apparatus, comprising:

a light emitting apparatus according to claim 9;

and

a control unit which controls an emitting state of said light emitting apparatus.

11. A method for controlling a capacitor charging apparatus, the capacitor charging apparatus including a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, which charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer, the method comprising:

repeating;

a first step of detecting a primary current flowing through the primary coil of the transformer;

a second step of turning on the switching transistor until the detected primary current reaches a predetermined peak current; and

a third step of turning off the switching transistor during an off-time wherein the third step comes after the second step; and

a fourth step of detecting that a voltage at a tap provided in the secondary coil of the transformer has reached a predetermined threshold voltage,

wherein when the voltage at the tap has exceeded the predetermined threshold voltage, said repeating the first to the third step is stopped.

12. A control method according to claim 11, wherein in the third step the off-time is set in accordance with the voltage at the tap provided on the secondary coil of the transformer.

36. A control method according to claim 11, wherein when the off signal of the predetermined level is generated, said switching step turns off the switching transistor, and

wherein said switching step turns on the switching transistor according to the on signal, whichever first goes to the predetermined level, of either the first on signal or the second on signal.

13. A control circuit of a capacitor charging apparatus, the capacitor charging apparatus including a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, which charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer, the control circuit comprising:

a primary-current detection circuit which detects a primary current flowing through the primary coil of the transformer; and

a switching control unit which monitors at least the primary current detected by said primary-current detection circuit and outputs to a control terminal of the switching transistor a switching signal for specifying ON to the switching transistor until the primary current reaches a predetermined peak current value and then specifying OFF to the switching transistor during an off-time,

wherein said switching control unit adjusts the switching signal outputted to the control terminal of the switching transistor, according to the predetermined peak current value.

14. A control circuit according to claim 13, wherein the switching transistor is a bipolar transistor, and

wherein said switching control unit adjusts a current value of a base current, which is supplied to a base of the bipolar transistor as the switching signal, in accordance with the predetermined peak current value.

15. A control circuit according to claim 14, wherein said switching control unit sets the current value of a base current in such a manner that the larger the predetermined peak current value is, the larger the current value of a base current becomes.

16. A control circuit according to claim 15, wherein said switching control unit sets the current value of a base current in such a manner the current value of a base current is proportional to the predetermined peak current value.

17. A control circuit according to claim 14, wherein said switching control unit includes a current generator which receives a current adjustment signal specifying the predetermined peak current value and generates a current in accordance with the current adjustment signal, and

wherein the current generated by the current generator is supplied to a base of the switching transistor as a switching signal in a period during which the switching transistor is to turn on.

18. A control circuit according to claim 17, wherein the current adjustment signal is inputted to a charge current control terminal provided in said control circuit, from outside said control circuit.

21. A control circuit according to claim 13, wherein said control circuit is integrated onto a single semiconductor substrate.

22. A capacitor charging apparatus, comprising:

a transformer, including a primary coil and a secondary coil, wherein an input voltage is applied to one end of the primary coil and a switching transistor is connected to other end thereof;

an output capacitor one end of which is grounded;

a diode having an anode thereof connected to a secondary coil side of said transformer and a cathode thereof connected to the other-end side of said output capacitor; and

a control circuit, according to claim 13, which controls on and off of the switching transistor.

23. A light emitting apparatus, comprising:

a capacitor charging apparatus according to claim 22;

and

a light-emitting element driven by an output voltage appearing at the output capacitor in said capacitor charging apparatus.

24. An electronic apparatus, comprising:

a light emitting apparatus according to claim 23;

and

a control unit which controls an emitting state of said light emitting apparatus.

19. A control circuit of a capacitor charging apparatus, the capacitor charging apparatus including a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, which charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer, the control circuit comprising:

a current generator which generates a current according to the amount of a charging current for the output capacitor; and

a driver circuit which supplies the current generated by said current generator as a base current of a bipolar transistor serving as the switching transistor, in a period during which the switching transistor is to turn on.

20. A control circuit according to claim 19, wherein said current generator sets the current value of a base current in accordance with a peak value of the charging current.

25. A method for controlling a capacitor charging apparatus, including a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, which charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer, the method comprising:

detecting a primary current flowing through the primary coil of the transformer; and

outputting to a control terminal of the switching transistor a switching signal for specifying ON to the switching transistor until the primary current reaches a predetermined peak current value and then specifying OFF to the switching transistor during an off-time; and

adjusting the switching signal outputted to the control terminal of the switching transistor, according to the predetermined peak current value.

26. A control circuit of a capacitor charging apparatus, the capacitor charging apparatus including a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, which charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer, the control circuit comprising:

an off-signal generator which monitors current flowing through the primary coil of the transformer and which outputs an off signal of a predetermined level when the current rises up to a predetermined peak current;

a first on-signal generator which monitors voltage across the primary coil of the transformer and which outputs a first on signal of a predetermined level when the voltage across the primary coil thereof drops down to a first predetermined threshold voltage;

a second on-signal generator which monitors a monitoring voltage corresponding to an output voltage appearing at the output capacitor and sets an off-time based on the monitoring voltage and which outputs a second on signal of a predetermined level after the off signal of the predetermined level has been outputted from said off-signal generator and then the off-time has elapsed; and

a switching control unit which receives the off signal from said off-signal generator and receives the first and the second on signal from said first and said second on-signal generator and which turns off the switching transistor according to the off signal and turns on the switching transistor according to the first and the second on signal.

27. A control circuit according to claim 26, wherein when the off signal of the predetermined level is outputted from said off-signal generator, said switching control unit turns off the switching transistor, and

wherein said switching control unit turns on the switching transistor according to the on signal, whichever first goes to the predetermined level, of either the first on signal outputted from said first on-signal generator or the second on signal outputted from said second on-signal generator.

28. A control circuit according to claim 26, wherein said switching control unit is configured in a manner that a mode of operation is selectable between a first mode that operates according to the first on signal and the off signal and a second mode that operates according to the second on signal and the second off signal.

29. A control circuit according to claim 26, wherein when the monitoring voltage is less than or equal to a second predetermined threshold voltage, said switching control unit turns on the switching transistor according to the second on signal.

30. A control circuit according to claim 26, wherein said second on-signal generator sets the off-time in a manner that a voltage corresponding to a voltage appearing at a tap provided in the secondary coil of the transformer is taken as the monitoring voltage.

31. A control circuit according to claim 26, wherein said switching control unit includes a flip-flop which is set by the off signal and reset by either the first on signal or the second on signal, and

wherein said switching control unit controls on and off of the switching transistor according to an output signal of the flip-flop.

32. A control circuit according to claim 26, wherein said on-signal generator unit sets the off-time in such a manner that the larger the monitoring voltage is, the shorter the off-time becomes.

33. A control circuit according to claim 26, wherein said control circuit is integrated on a single semiconductor substrate.

34. A capacitor charging apparatus, comprising:

a transformer, including a primary coil and a secondary coil, wherein an input voltage is applied to one end of the primary coil and a switching transistor is connected to other end thereof;

an output capacitor one end of which is grounded;

a diode having an anode thereof connected to a secondary coil side of said transformer and a cathode thereof connected to the other-end side of said output capacitor; and

a control circuit, according to claim 26, which controls on and off of the switching transistor.

45. A light emitting apparatus, comprising:

a capacitor charging apparatus according to claim 34;

and

a light-emitting element driven by an output voltage appearing at the output capacitor in said capacitor charging apparatus.

47. An electronic apparatus, comprising:

a light emitting apparatus according to claim 45;

and

a control unit which controls an emitting state of said light emitting apparatus.

35. A method for controlling a capacitor charging apparatus, including a transformer and an output capacitor charged with current flowing through a secondary coil of the transformer, which charges the output capacitor by performing a switching control of a switching transistor provided on a path leading to a primary coil of the transformer, the method comprising:

an off-signal generating step of monitoring current flowing through the primary coil of the transformer and generating an off signal of a predetermined level when the current rises up to a predetermined peak current;

a first on-signal generating step of monitoring voltage across the primary coil of the transformer and generating a first on signal of a predetermined level when the voltage across the primary coil thereof drops down to a first predetermined threshold voltage;

a second on-signal generating step of monitoring a monitoring voltage corresponding to an output voltage appearing at the output capacitor, setting an off-time based on the monitoring voltage, and generating a second on signal of a predetermined level after the off signal of the predetermined level has been outputted and then the off-time has elapsed; and

a switching step of turning off the switching transistor according to the off signal and turns on the switching transistor according to the first and the second on signal.

37. A capacitor charging apparatus, comprising:

a transformer, including a primary coil and a secondary coil, wherein one end of the primary coil is connected in common with one end of the secondary coil and an input voltage is applied to a common connection point thereof;

a switching transistor connected to the other-end side of the primary coil;

a diode having an anode thereof connected to other end of the secondary coil;

an output capacitor provided between a cathode of said diode and ground; and

a control circuit which controls on and off of said switching transistor.

38. A capacitor charging apparatus according to claim 37, wherein a tap is provided in the secondary coil of said transformer, and

wherein said control circuit performs at least part of on-off control of said switching transistor, based on a voltage corresponding to a voltage appearing at the tap.

39. A capacitor charging apparatus according to claim 38, said control circuit detects completion of charging of said output capacitor by comparing the voltage corresponding to a voltage appearing at the tap with a predetermined threshold voltage.

40. A capacitor charging apparatus according to claim 39, wherein the predetermined threshold voltage is varied according to the input voltage.

41. A capacitor charging apparatus according to claim 38, said control circuit including:

a difference voltage generation circuit which generates a voltage corresponding to a difference voltage between the voltage appearing at the tap and a voltage obtained by multiplying the input voltage by a predetermined constant; and

a comparator which compares an output voltage of the difference voltage generation circuit with a predetermined threshold voltage,

wherein when the output voltage of the difference voltage generation circuit exceeds the predetermined threshold voltage, completion of charging is detected by said control circuit.

42. A capacitor charging apparatus according to claim 37, said control circuit including:

an off-signal generator which monitors current flowing through the primary coil of said transformer and which outputs an off signal of a predetermined level when the current rises up to a predetermined peak current;

a first on-signal generator which monitors voltage across the primary coil of said transformer and which outputs a first on signal of a predetermined level when the voltage across the primary coil thereof drops down to a first predetermined threshold voltage;

a second on-signal generator which monitors a monitoring voltage corresponding to an output voltage appearing at said output capacitor and sets an off-time based on the monitoring voltage and which outputs a second on signal of a predetermined level after the off signal of the predetermined level has been outputted from the off-signal generator and then the off-time has elapsed; and

a switching control unit which receives the off signal from the off-signal generator and receives the first and the second on signal from the first and the second on-signal generator and which turns off said switching transistor according to the off signal and turns on said switching transistor according to the first and the second on signal.

43. A capacitor charging apparatus according to claim 42, wherein a tap is provided on the secondary coil of said transformer, and

wherein the second on-signal generator monitors a voltage corresponding to a voltage appearing at the tap, as the monitoring voltage.

46. A light emitting apparatus, comprising:

a capacitor charging apparatus according to claim 37;

and

a light-emitting element driven by an output voltage appearing at the output capacitor in said capacitor charging apparatus.

48. An electronic apparatus, comprising:

a light emitting apparatus according to claim 46;

and

a control unit which controls an emitting state of said light emitting apparatus.

44. A transformer including a primary coil and a secondary coil, wherein one end of the primary coil is connected in common with one end of the secondary coil and a terminal is provided for a common connection point thereof, and terminals are further provided for the primary coil and the secondary coil, respectively.