AC/DC converter with control circuit that receives rectified voltage at input detection terminal

• US 9,112,419 B2
• Filed: 07/10/2014
• Issued: 08/18/2015
• Est. Priority Date: 07/16/2013
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Nate, Satoru
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): AHMED, YUSEF A
• Application Number:
  US14/328,064
• Publication Number:
  US 20150023070A1
• Time in Patent Office: 404 Days
• Field of Search: 363/16, 363/17, 363/20, 363 2101- 2118
• US Class Current: 1/1
• 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 first rectified voltage obtained by rectifying an AC voltage is input to an input detection terminal of a control circuit. A first NMOS transistor configured as a depletion-type high-voltage element, and its drain is connected to the input detection terminal, and its gate is connected to its source. An AC voltage detection circuit detects the amplitude of the AC voltage based on a current that flows through the first NMOS transistor.

Claims

1. A control circuit used for an AC/DC converter configured to convert an AC voltage into a first DC voltage, wherein the AC/DC converter comprises:

a first rectifier circuit configured to rectify and smooth the AC voltage so as to convert the AC voltage into a second DC voltage;

an insulating DC/DC converter configured to step up or otherwise step down the second DC voltage; and

a feedback circuit configured to generate a feedback voltage that corresponds to the first DC voltage,

wherein the control circuit comprises;

an input detection terminal coupled to receive a first rectified voltage obtained by performing full-wave rectification of the AC voltage is input;

a power supply terminal connected to an external capacitor, and coupled to receive a third DC voltage generated on a primary side of a transformer of the DC/DC converter in an operating state of the DC/DC converter;

a feedback terminal coupled to receive the feedback voltage;

a depletion-type high-voltage first NMOS transistor having its drain connected to the input detection terminal and its gate connected to its source;

an AC voltage detection circuit configured to detect an amplitude of the AC voltage based on a current that flows through the first NMOS transistor;

a starter circuit arranged between the input detection terminal and the power supply terminal, and configured to charge the capacitor connected to the power supply terminal using the first rectified voltage in a startup operation of the AC/DC converter; and

a driving circuit configured to receive a voltage at the power supply terminal as its operating voltage, and to drive a switching transistor of the DC/DC converter according to the feedback voltage,

and wherein the control circuit is monolithically integrated on a single semiconductor substrate.

2. The control circuit according to claim 1, wherein the AC voltage detection circuit is configured to convert a current that flows through the first NMOS transistor into a voltage, and to detect the amplitude of the AC voltage based on the aforementioned voltage.

3. The control circuit according to claim 2, wherein the AC voltage detection circuit comprises:

a current mirror circuit comprising a third transistor arranged between the source of the first NMOS transistor and a ground line, and a fourth transistor configured to generate a current having a current value obtained by multiplying a current that flows through the third transistor by a predetermined coefficient; and

a converter resistor arranged on a current path of a current that flows through the fourth transistor such that its one end is set to a fixed electric potential,

and wherein the AC voltage detection circuit is configured to detect the amplitude of the AC voltage based on an inverted rectified voltage that occurs at the other end of the converter resistor.

4. The control circuit according to claim 1, further comprising a third resistor arranged between the source of the first NMOS transistor and the AC voltage detection circuit,

wherein the gate of the first NMOS transistor is connected to a connection node that connects the source and the AC voltage detection circuit.

5. The control circuit according to claim 1, further comprising a discharge transistor arranged between the power supply terminal and a ground line.

6. The control circuit according to claim 1, wherein the starter circuit comprises a second NMOS transistor configured as a high-voltage transistor.

7. The control circuit according to claim 6, wherein the second NMOS transistor is configured as a depletion-type transistor, and has its source and its back gate connected together.

8. The control circuit according to claim 3, wherein the AC voltage detection circuit comprises:

a comparator configured to compare the inverted rectified voltage with a predetermined threshold voltage, and to generate a comparison signal which indicates a comparison result; and

a logic unit configured to judge, based on the comparison signal, a magnitude relation between the amplitude of the AC voltage and a threshold amplitude that corresponds to the threshold voltage.

9. The control circuit according to claim 8, wherein, when the comparison signal remains at a constant level over a predetermined number of cycles of the AC voltage, the logic unit judges that the amplitude of the AC voltage is greater than the threshold amplitude.

10. The control circuit according to claim 1, wherein, when the amplitude of the AC voltage is smaller than the threshold amplitude, which is set to a value that is lower than a rated amplitude, the AC voltage detection circuit suspends the operation of the DC/DC converter.

11. The control circuit according to claim 3, wherein the size of the first NMOS transistor and the size of the third transistor are determined such that the first NMOS transistor operates in a saturation range when the amplitude of the AC voltage is within a detection range.

12. The control circuit according to claim 10, wherein the threshold voltage is provided with hysteresis.

13. An AC/DC converter configured to convert an AC voltage into a first DC voltage, wherein the AC/DC converter comprises:

a first rectifier circuit configured to rectify and smooth the AC voltage so as to convert the AC voltage into a second DC voltage;

an insulating DC/DC converter configured to step up or otherwise step down the second DC voltage;

a second rectifier circuit configured to rectify the AC voltage so as to generate a first rectified voltage;

a transformer comprising a primary winding and an auxiliary winding provided on its primary side, and a secondary winding provided on its secondary side;

a switching transistor connected to the primary winding of the transformer;

a first diode having its anode connected to the secondary winding;

a first output capacitor having its one end grounded and its other end connected to a cathode of the first diode;

a second diode having its anode connected to the auxiliary winding;

a second output capacitor having its one end grounded, and its other end connected to a cathode of the second diode;

a feedback circuit configured to generate a feedback voltage that corresponds to the first DC voltage generated at the first output capacitor; and

a control circuit comprising;

an input detection terminal coupled to receive a first rectified voltage obtained by performing full-wave rectification of the AC voltage is input;

a power supply terminal connected to an external capacitor, and coupled to receive a third DC voltage generated on a primary side of a transformer of the DC/DC converter in an operating state of the DC/DC converter;

a feedback terminal coupled to receive the feedback voltage;

a depletion-type high-voltage first NMOS transistor having its drain connected to the input detection terminal and its gate connected to its source;

an AC voltage detection circuit configured to detect an amplitude of the AC voltage based on a current that flows through the first NMOS transistor;

a starter circuit arranged between the input detection terminal and the power supply terminal, and configured to charge the capacitor connected to the power supply terminal using the first rectified voltage in a startup operation of the AC/DC converter; and

a driving circuit configured to receive a voltage at the power supply terminal as its operating voltage, and to drive a switching transistor of the DC/DC converter according to the feedback voltage, and wherein the control circuit is monolithically integrated on a single semiconductor substrate, wherein the control circuit is arranged such that the second DC voltage is input to its input detection terminal, the second DC voltage generated at the second output capacitor is supplied to its power supply terminal, and the feedback voltage is input to its feedback terminal.

14. The AC/DC converter according to claim 13, wherein the feedback circuit comprises:

a shunt regulator configured to generate a feedback signal having a level adjusted such that the difference between a voltage obtained by dividing the first DC voltage and a predetermined target value becomes zero; and

a photocoupler comprising a light-emitting element provided on its primary side, configured to be controlled according to the feedback signal,

and wherein a signal generated by a light-emitting element provided on the secondary side of the photocoupler is supplied to the control circuit as the feedback voltage.

15. The AC/DC converter according to claim 13, further comprising a filter configured to perform filtering of the AC voltage,

wherein the second rectifier circuit is configured to rectify the AC voltage after the AC voltage is subjected to the filtering.

16. An electronic device comprising:

a load; and

the AC/DC converter according to claim 13, configured to supply the first DC voltage to the load.

17. A power supply adapter comprising the AC/DC converter according to claim 13.

18. A control circuit used for an AC/DC converter configured to convert an AC voltage into a first DC voltage, wherein the AC/DC converter comprises:

a first rectifier circuit configured to rectify and smooth the AC voltage so as to convert the AC voltage into a second DC voltage;

an insulating DC/DC converter configured to step up or otherwise step down the second DC voltage; and

a feedback circuit configured to generate a feedback voltage that corresponds to the first DC voltage,

wherein the control circuit comprises;

an input detection terminal via which a first rectified voltage obtained by rectifying the AC voltage is input;

a power supply terminal connected to an external capacitor, and configured to receive a third DC voltage generated on a primary side of a transformer of the DC/DC converter in an operating state of the DC/DC converter;

a feedback terminal coupled to receive the feedback voltage;

a first NMOS transistor configured as a depletion-type high-voltage transistor having its drain connected to the input detection terminal and its gate connected to its source;

an AC voltage detection circuit comprising a first resistor and a second resistor arranged in series between the source of the first NMOS transistor and a ground line, and configured to detect the amplitude of the AC voltage based on a second rectified voltage that develops at a connection node that connects the first resistor and the second resistor;

a starter circuit arranged between the input detection terminal and the power supply terminal, and comprising a path which allows the capacitor connected to the power supply terminal to be charged using the first rectified voltage; and

a driving circuit configured to receive a voltage at the power supply terminal as its operating voltage, and to drive a switching transistor of the DC/DC converter according to the feedback voltage,

and wherein the control circuit is monolithically integrated on a single semiconductor substrate.

19. The control circuit according to claim 18, further comprising a third resistor arranged between the source of the first NMOS transistor and the first resistor,

wherein the gate of the first NMOS transistor is connected to a connection node that connects the source and the first resistor.

20. The control circuit according to claim 18, further comprising a discharge transistor arranged between the power supply terminal and the ground line.

21. The control circuit according to claim 18, wherein the starter circuit comprises a second NMOS transistor configured as a high-voltage transistor.

22. The control circuit according to claim 21, wherein the second NMOS transistor is configured as a depletion-type transistor, and has its source and its back gate connected together.

23. The control circuit according to claim 18, wherein the AC voltage detection circuit comprises:

a comparator configured to compare the second rectified voltage with a predetermined threshold voltage, and to generate a comparison signal which indicates a comparison result; and

a logic unit configured to judge a magnitude relation between the amplitude of the AC voltage and a threshold amplitude that corresponds to the threshold voltage.

24. The control circuit according to claim 23, wherein, when the comparison signal remains at a constant level over a predetermined number of cycles of the AC voltage, the logic unit judges that the amplitude of the AC voltage is smaller than the threshold amplitude.

25. The control circuit according to claim 18, wherein, when the amplitude of the AC voltage is smaller than a threshold amplitude, which is determined to be lower than its rated amplitude, the AC voltage detection circuit suspends the operation of the DC/DC converter.

26. The control circuit according to claim 25, wherein the size of the first NMOS transistor and the resistance values of the first resistor and the second resistor are determined such that the first NMOS transistor operates in a linear range when the amplitude of the AC voltage is within a detection range.

27. The control circuit according to claim 25, wherein the threshold voltage is configured to have hysteresis.

28. An AC/DC converter configured to convert an AC voltage into a first DC voltage, comprising:

a first rectifier circuit configured to rectify and smooth the AC voltage so as to convert the AC voltage into a second DC voltage;

an insulating DC/DC converter configured to step up or otherwise step down the second DC voltage;

a second rectifier circuit configured to rectify the AC voltage so as to generate a first rectified voltage;

a transformer comprising a primary winding and an auxiliary winding provided on its primary side, and a secondary winding provided on its secondary side;

a switching transistor connected to the primary winding of the transformer;

a first diode having its anode connected to the secondary winding;

a first output capacitor having its one end grounded and its other end connected to a cathode of the first diode;

a second diode having its anode connected to the auxiliary winding;

a second output capacitor having its one end grounded and its other end connected to a cathode of the second diode;

a feedback circuit configured to generate a feedback voltage that corresponds to the first DC voltage generated at the first output capacitor; and

a control circuit comprising;

an input detection terminal coupled to receive a first rectified voltage obtained by performing full-wave rectification of the AC voltage is input;

a power supply terminal connected to an external capacitor, and coupled to receive a third DC voltage generated on a primary side of a transformer of the DC/DC converter in an operating state of the DC/DC converter;

a feedback terminal coupled to receive the feedback voltage;

a depletion-type high-voltage first NMOS transistor having its drain connected to the input detection terminal and its gate connected to its source;

an AC voltage detection circuit configured to detect an amplitude of the AC voltage based on a current that flows through the first NMOS transistor;

a starter circuit arranged between the input detection terminal and the power supply terminal, and configured to charge the capacitor connected to the power supply terminal using the first rectified voltage in a startup operation of the AC/DC converter; and

a driving circuit configured to receive a voltage at the power supply terminal as its operating voltage, and to drive a switching transistor of the DC/DC converter according to the feedback voltage, and wherein the control circuit is monolithically integrated on a single semiconductor substrate, wherein the control circuit is arranged such that the second DC voltage is input to its input detection terminal, the second DC voltage generated at the second output capacitor is supplied to its power supply terminal, and the feedback voltage is input to its feedback terminal.

29. The AC/DC converter according to claim 28, wherein the feedback circuit comprises:

a shunt regulator configured to generate a feedback signal having a level adjusted such that the difference between a voltage obtained by dividing the first DC voltage and a predetermined target value becomes zero; and

a photocoupler comprising a light-emitting element provided on its primary side, configured to be controlled according to the feedback signal,

and wherein a signal generated by a light-emitting element provided on the secondary side of the photocoupler is supplied to the control circuit as the feedback voltage.

30. The AC/DC converter according to claim 28, further comprising a filter configured to perform filtering of the AC voltage,

wherein the second rectifier circuit is configured to rectify the AC voltage after the AC voltage is subjected to the filtering.

31. An electronic device comprising:

a load; and

the AC/DC converter according to claim 28, configured to supply the first DC voltage to the load.

32. A power supply adapter comprising the AC/DC converter according to claim 28.