Input current control method, switch control circuit and power supply including the switch control circuit

• US 9,467,137 B2
• Filed: 11/18/2014
• Issued: 10/11/2016
• Est. Priority Date: 11/18/2013
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Korea Semiconductor Limited (ON Semiconductor Corporation)
• Inventors: Kim, Young-Jong, Eum, Hyun-Chul
• Primary Examiner(s): Puentes, Daniel
• Application Number:
  US14/546,624
• Publication Number:
  US 20150137859A1
• Time in Patent Office: 693 Days
• US Class Current: 1/1
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop
• CPC Class Codes: H03K 17/16 Modifications for eliminating interference voltages or currents
• CPC Class Codes: H03K 2217/0027 Measuring means of, e.g. currents through or voltages across the switch

Abstract

A switch control circuit that controls a switching operation of a power switch includes: an input current calculator generating an input sense voltage by integrating a sense voltage that indicates a switching current flowing to the power switch for a switching period unit of the power switch; and an input current comparator generating a gate-off signal according to a result of comparison between the input sense voltage and a predetermined input reference voltage, wherein the power switch is turned off according to the gate-off signal.

Claims

1. An input current control method of a power supply including a power switch, comprising:

generating an input sense voltage by integrating a sense voltage that indicates a switch current flowing to the power switch for a switching period of the power switch;

comparing the input sense voltage with a predetermined input reference voltage, wherein the input reference voltage is based on the switching period and a predetermined reference voltage; and

controlling a switching operation of the power switch according to a result of the comparison.

2. The input current control method of claim 1, wherein generating the input sense voltage comprises:

converting the sense voltage to a sense current; and

charging a first capacitor using the sense current, wherein the input sense voltage is a voltage charged in the first capacitor.

3. The input current control method of claim 2, wherein the charging the first capacitor with the sense current is performed until the input sense voltage reaches the input reference voltage.

4. The input current control method of claim 1, wherein controlling the switching operation comprises turning off the power switch at a time that the input sense voltage reaches the input reference voltage.

5. The input current control method of claim 1, wherein generating the input reference voltage further comprises:

converting the reference voltage to a reference current;

charging a second capacitor for the switching period using the reference current; and

generating the input reference voltage by sampling and holding a peak of a switching period voltage charged in the second capacitor for each switching period.

6. The input current control method of claim 5, wherein the voltage charged in the second capacitor is reset by being synchronized at a turn-on time of the power switch.

7. The input current control method of claim 5, wherein the charging of the second capacitor is performed for a predetermined period while a switching enable signal is an enable level.

8. The input current control method of claim 7, further comprising:

generating a first output according to a level of a switching enable signal that controls the switching enable period by being synchronized with an oscillator signal that determines a switching frequency of the power switch;

generating a second output according to a level of the first output by being synchronized with the oscillator signal; and

performing an OR operation on the first output and the second output, and generating a gate voltage for driving the power switch according to a result of the OR operation.

9. The input current control method of claim 1, further comprising generating the reference voltage using an information corresponding to an input voltage of the power supply and a comparison voltage generated by amplifying a difference between a voltage that corresponds to an output current of the power supply and a first reference voltage.

10. The input current control method of claim 9, wherein generating the input reference voltage comprises generating the input reference voltage by multiplying the reference voltage and the switching period.

11. The input current control method of claim 9, wherein generating the reference voltage comprises multiplying the comparison voltage and the information corresponding to an input voltage.

12. A switch control circuit to control a switching operation of a power switch, comprising:

an input current calculator configured to generate an input sense voltage by integrating a sense voltage that indicates a switching current flowing to the power switch for each switching period of the power switch;

an input current comparator configured to generate a gate-off signal according to a result of comparison between the input sense voltage and a predetermined input reference voltage, wherein the power switch is turned off according to the gate-off signal; and

a multiplier configured to generate an input reference voltage using a predetermined reference voltage and the switching period.

13. The switch control circuit of claim 12, wherein the input current calculator comprises:

a first voltage-current converter configured to receive the sense voltage and generate a sense current that depends on the sense voltage; and

a first charging unit configured to generate the input sense voltage by charging a first capacitor for a turn-on period of the power switch with a current that corresponds to the sense current.

14. The switch control circuit of claim 13, wherein the first voltage-current converter comprises:

a first error amplifier configured to generate an output that controls a voltage of a first input end to which the sense voltage is input and a voltage of a second input terminal to be equivalent to each other;

a first BJT including a base to which an output of the first error amplifier is input; and

a first resistor including a first terminal connected to an emitter of the first BJT and the second input terminal, wherein the sense current flows to a ground through the first BJT and the first resistor.

15. The switch control circuit of claim 14, wherein the input current calculator further comprises a first current mirror circuit connected to a collector of the first BJT and is configured to supply a current to the first capacitor by mirroring the sense current.

16. The switch control circuit of claim 13, wherein the first charging unit comprises a first transistor connected in parallel with the first capacitor, wherein the first transistor is turned off during a turn-on period of the power switch.

17. The switch control circuit of claim 12, wherein the multiplier comprises:

a second voltage-current converter configured to receive the reference voltage and generate a reference current that depends on the reference voltage;

a second charging unit configured to generate a switching period voltage by charging a second capacitor with a current that corresponds to the reference current for the switching period; and

a sampling/holding unit configured to generate the input reference voltage by sampling and holding a peak of the switching period voltage for each switching period.

18. The switch control circuit of claim 17, wherein the second voltage-current converter comprises:

a second error amplifier configured to generate an output that controls a voltage of a first input end to which the reference voltage is input and a voltage of a second input terminal to be equivalent to each other;

a second BJT including a base to which an output of the second error amplifier is input; and

a second resistor including a first terminal connected to an emitter of the second BJT and the second input terminal, wherein the reference current flows to the ground through the second BJT and the second resistor.

19. The switch control circuit of claim 18, wherein the multiplier further comprises a second current mirror circuit connected to a collector of the second BJT and configured to supply a current to the second capacitor by mirroring the reference current.

20. The switch control circuit of claim 17, wherein the second charging unit comprises a second transistor connected in parallel with the second capacitor, wherein the second transistor is turned on by being synchronized at a turn-on time of the power switch.

21. The switch control circuit of claim 17, wherein the multiplier further comprises an enable switch to control a current supplied to the second capacitor, wherein the enable switch is to perform a switching operation according to a switching enable signal and the switching enable signal controls a switching operation period of the power switch.

22. The switch control circuit of claim 21, further comprising a gate enable unit configured to determine whether or not to output a gate voltage that switches the power switch based on the switching enable signal and an oscillator signal that determines the switching frequency.

23. The switch control circuit of claim 22, wherein the gate enable unit comprises:

a first D-flip-flop unit having a clock terminal to which the oscillator signal that determines the switching frequency of the power switch is input and an input terminal to which the switching enable signal is input, and is to output a first output according to the switching enable signal by being synchronized with the oscillator signal;

a second D-flip-flop having a clock terminal to which the oscillator signal is input and an input terminal to which the first output is input, and is to generate a second output according to a level of the first output by being synchronized with the oscillator signal; and

an OR gate that performs an OR operation on the first output and the second output.

24. The switch control circuit of claim 12, wherein the input current calculator comprises a first resistor to which the sense voltage is applied and a first capacitor to be charged with a current that corresponds to a sense current flowing to the first resistor, wherein

the multiplier comprises a second resistor to which the reference voltage is input and a second capacitor charged with a current that corresponds to a reference current flowing to the second resistor, and further wherein

the input current is proportional to a result acquired by dividing a value of multiplication of resistance of the first resistor and capacitance of the first capacitor with a value of multiplication of resistance of the second resistor and capacitance of the second capacitor.

25. The switch control circuit of claim 12, further comprising:

a first multiplier configured to generate the reference voltage using information on an input voltage of the power supply and a comparison voltage generated by amplifying a difference between a voltage corresponding to an output current controlled according to the switching operation of the power switch and a first reference voltage; and

a second multiplier configured to generate the input reference voltage by multiplying a reference voltage and a switching period of the power switch.

26. A power supply, comprising:

a power switch electrically connected with an input voltage; and

a switch control circuit to generate an input sense voltage by integrating a sense voltage corresponding to a switching current flowing to the power switch for each switching period of the power switch, and controlling a switching operation of the power switch according to a result of comparison between the input sense voltage and a predetermined input reference voltage, wherein the switch control circuit comprises;

a first multiplier to generate the reference voltage using information on the input voltage of the power supply and a comparison voltage generated by amplifying a difference between a voltage corresponding to an output current of the power supply and a first reference voltage; and

a second multiplier to generate the input reference voltage by multiplying the reference voltage and the switching period of the power switch.

27. The power supply of claim 26, wherein the switch control circuit is to generate a switching period voltage by charging a capacitor using a predetermined reference voltage for each switching period, and is to generate the input reference voltage by sampling and holding the switching period voltage for each switching period.

28. The power supply of claim 26, wherein the switch control circuit is to determine whether or not to output a gate voltage that switches the power switch based on a switching enable signal that controls a predetermined switching enable period and an oscillator signal that determines a switching frequency of the power switch.

29. The power supply of claim 28, wherein the switching enable period is a predetermined period in a period during which the input voltage is generated.