Resonant converter with variable frequency controlled by phase comparison

• US 8,036,001 B2
• Filed: 04/02/2009
• Issued: 10/11/2011
• Est. Priority Date: 04/02/2008
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Korea Semiconductor Limited (ON Semiconductor Corporation)
• Inventors: Choi, Hang-Seok
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US12/417,168
• Publication Number:
  US 20090251929A1
• Time in Patent Office: 922 Days
• Field of Search: 363/21.02, 363/97
• US Class Current: 363/21.02
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 3/3378 in a push-pull configuration of the parallel type H02M3/3374 takes precedence
• 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

A converter and a driving method thereof are provided. The converter includes first and second switches, and generates a square wave signal according to operations of the first and second switches. The converter includes a first capacitor and a primary coil, and resonates a driving voltage by using a driving voltage with the first capacitor and the primary coil so as to generate a driving current. The converter includes a secondary coil that forms the primary coil and the transformer, and generates output power by rectifying a current and a voltage generated in the secondary coil. In addition, the converter detects the phase of the driving current, and increases switching frequencies of the first and second switches if a phase difference of the phase of the driving current and that of the driving voltage is smaller than a predetermined value.

Claims

1. A converter comprising:

a square wave generator having first and second switches, and configured to generate a square wave signal according to switching operations of the first and second switches;

a resonant network unit having a first capacitor and a primary coil of a transformer, and configured to resonate a driving voltage by using the first capacitor and the primary coil so as to generate a driving current;

a rectifier network unit having a secondary coil that is configured to be magnetically coupled to the primary coil of a transformer, and configured to generate output voltage by rectifying a current and a voltage generated in the secondary coil; and

a switch controller configured to detect the phase of the driving current, and to increase switching frequencies of the first and second switches when a phase difference between the phase of the driving current and that of the driving voltage is smaller than a predetermined value.

2. The converter of claim 1, wherein a current that is the same as the driving current flows to the first switch during a turn-on state, and the switch controller is configured to measure a current flowing through first switch before the first switch is turned off and to detect the phase difference between the phase of the driving current and that of the driving voltage.

3. The converter of claim 2, wherein the switch controller is configured to generate a triangle wave signal having a cycle that is the same as that of the switching frequency of the first switch, turn off the first switch when a voltage of the triangle wave signal reaches a predetermined first reference voltage, and detect the phase of the driving current by detecting the current flowing to the first switch when the voltage of the triangle wave signal reaches a second reference voltage, and the second reference voltage is lower than the first reference voltage.

4. The converter of claim 3, wherein the switch controller is configured to increase a slope of the triangle wave signal when the current measured before the first switch is turned off is smaller than the first reference value, and the first reference value is greater than zero.

5. The converter of claim 4, wherein the switch controller includes a switch that is turned on when the current that is measured before the first switch is turned off is smaller than the first reference value, and the slope of the triangle wave signal is increased in accordance with a current flowing through the turned-on switch.

6. The converter of claim 5, further comprising:

a capacitor having a first terminal connected to a first terminal of the switch and a second terminal that is grounded; and

a first resistor having a first terminal connected to the first terminal of the switch and the first terminal of the capacitor and a second terminal that is maintained at a predetermined voltage,

wherein when the switch is turned on, the capacitor is discharged so that a voltage of the first terminal of the first resistor is reduced.

7. The converter of claim 6, further comprising a second resistor having a first terminal connected to the first switch and a second terminal that is grounded,

wherein the switch controller comprises:

a first comparator that is configured to compare a voltage across the second resistor with a first threshold voltage that corresponds to the first reference value;

a second comparator that is configured to compare the triangle wave signal with the second reference voltage;

a first logical operator that is configured to generate a first sampling signal corresponding to an output signal of the second comparator;

a second logical operator that is configured to receive the first sampling signal and generate a second sampling signal corresponding to an output signal of the first comparator; and

an SR flipflop having a set terminal to which the second sampling signal is input, and an output signal of the SR flipflop controls turn-on/off of the switch.

8. The converter of claim 7, wherein a first threshold voltage is input to a non-inversion terminal of the first comparator, a voltage across the second resistor is input to an inversion terminal of the first comparator, the triangle wave signal is input to a non-inversion terminal of the second comparator, the second reference voltage is input to an inversion terminal of the second comparator, and the first and second logical operators are configured to perform an AND operation.

9. The converter of claim 5, wherein the switch controller is configured to turn off the turned-on switch when the current measured before the first switch is turned off is greater than a second reference value, and the second reference value is greater than the first reference value.

10. The converter of claim 9, further comprising:

a capacitor having a first terminal connected to a first terminal of the switch, and a second terminal that is grounded; and

a first resistor having a first terminal connected to the first terminal of the switch, and a second terminal maintained at a predetermined voltage,

wherein when the switch is turned on, the capacitor is discharged so that a voltage of the first terminal of the first resistor is reduced.

11. The converter of claim 10, further comprising a second resistor having a first terminal connected to the first terminal of the first switch, and a second terminal that is grounded,

wherein the switch controller comprises:

a first comparator that is configured to compare voltages across the second resistor with a first threshold voltage that corresponds to the first reference value;

a second comparator that is configured to compare a voltage across the second resistor with a second threshold voltage that corresponds to the second reference value;

a third comparator that is configured to compare the triangle wave signal with the second reference voltage;

a first logical operator that is configured to generate a first sampling signal corresponding to an output signal of the third comparator;

a second logical operator that is configured to receive the first sampling signal and generate a second sampling signal corresponding to an output signal of the first comparator;

a third logical operator that is configured to receive the first sampling signal and generate a third sampling signal corresponding to an output signal of the second comparator; and

an SR flipflop having a set terminal to which the second sampling signal is input and a reset terminal to which the third sampling signal is input, and configured to control turn-on/off of the switch by using an output signal thereof.

12. The converter of claim 11, wherein a first threshold voltage is input to a non-inversion terminal of the first comparator, a voltage across the second resistor is input to an inversion terminal of the first comparator, a second threshold voltage is input to a non-inversion terminal of the second comparator, the voltage across the second resistor is input to an inversion terminal of the second comparator, the triangle wave signal is input to a non-inversion terminal of the third comparator, the second reference voltage is input to an inversion terminal of the third comparator, and the first to third logical operators are configured to perform an AND operation.

13. The converter of claim 5, wherein the switch controller further comprises a protection unit that is configured to count the number of times that a current flowing through the first switch before the first switch is turned off is smaller than the first reference value, and allow no more the switching operation of first and second switches when the counted number of times reaches a predetermined number of times.

14. The converter of claim 13, wherein the switch controller is configured to turn off the turned-on switch when the current measured before the first switch is turned off is greater than a second reference value, and the second reference value is greater than the first reference value.

15. The converter of claim 14, wherein the protection unit is configured to reset the counted number of times when the current flowing through the first switch before the first switch is turned off is greater than the second reference value before the counted number of times reaches the predetermined number of times.

16. The converter of claim 1, wherein the first capacitor and the primary coil are connected in series, a voltage signal across the serially connected first capacitor and the primary coil is the driving voltage, and a current flowing to the first capacitor and the primary coil is the driving current.

17. A driving method of a converter, comprising:

generating a driving voltage according to switching operations of first and second switches;

generating a driving current according to a resonance generated in a capacitor and a primary coil that are serially connected between terminals of the first and second switches;

detecting the driving current before the first switch is turned off;

comparing the detected current with a first reference value that is greater than zero, and increasing switching frequencies of the first and second switches when the detected current is smaller than the first reference value; and

stopping the increase of the switching frequencies of the first and second switches when the detected current is greater than a second reference value that is greater than the first reference value.

18. The driving method of claim 17, wherein the increasing of the switching frequency of each of the first and second switches comprises:

generating a triangle wave having a cycle that is the same as that of a switching operation of each of the first and second switches;

increasing a slope of the triangle wave of the detected driving current is smaller than the first reference value; and

turning off the first switch when the triangle wave reaches the maximum value.

19. The driving method of claim 18, wherein the generating of the triangle wave comprises:

charging a first capacitor according with a first current source; and

discharging the first capacitor with a second current source,

wherein the triangle wave is a voltage signal of the capacitor.

20. The driving method of claim 19, wherein the increasing of the slope of the triangle wave comprises discharging charges charged in a second capacitor having a first terminal and a second terminal that is grounded, the first terminal connected to a second terminal of a resistor having a first terminal to which a predetermined voltage is applied, and the first and second current sources are increased or decreased corresponding to a current flowing to the resistor.

21. The driving method of claim 17, comprising:

counting the number of times that the detected driving current is smaller than the first reference value; and

allowing no more switching operation of the first and second switches when the counted number of times reaches a predetermined number of times.

22. The driving method of claim 21, wherein the counted number of times is reset when the detected driving current is greater than the second reference value before the counted number of times reaches the predetermined number of times.