Secondary side post regulator of flyback power converter with multile outputs

• US 20110032732A1
• Filed: 08/04/2009
• Published: 02/10/2011
• Est. Priority Date: 08/04/2009
• Status: Active Grant

• Current Assignee: Niko Semiconductor Co., Ltd
• Original Assignee: Niko Semiconductor Co., Ltd
• Inventors: Hsu, Ta-Ching
• Granted Patent: US 8,310,847 B2
• Time in Patent Office: Days
• US Class Current: 363/21.14
• CPC Class Codes: H02M 3/33561 having more than one ouput with independent control

Abstract

A flyback power converter with multiple outputs has a transformer, a low-voltage output circuit, a high-voltage output circuit, and a secondary side post regulator circuit is provided. The transformer has a first secondary winding and a second secondary winding. The low-voltage output circuit has a low-voltage output capacitor and a rectifier unit, and is coupled to the first secondary winding to generate a low voltage output. The high-voltage output circuit has a high-voltage output switch and a high-voltage output capacitor, and is coupled to the second secondary winding to generate a high voltage output. The secondary side post regulator circuit adjusts on-time of the high-voltage output switch according to a feedback signal to have the energy stored in the high-voltage capacitor transmitted to the low-voltage capacitor to lower down the voltage level of the high output voltage.

Claims

1. A flyback power converter with multiple outputs comprising:

a transformer, having a primary winding, a first secondary winding, and a second secondary winding;

a primary side circuit, having a main switch coupled to the primary winding;

a low-voltage output circuit, which is coupled to the first secondary winding, having a low-voltage output capacitor and a rectifier unit to generate a low output voltage;

a high-voltage output circuit, which is coupled to the second secondary winding, having a high-voltage output switch and a high-voltage output capacitor to generate a high output voltage; and

a secondary side post regulator circuit, adjusting an on-time of the high-voltage output switch according to a feedback signal respective to the high output voltage to have energy stored in the high-voltage capacitor transferred to the low-voltage output capacitor for reducing a level of the high output voltage.

2. The flyback power converter with multiple outputs of claim 1, wherein the secondary side post regulator circuit decides an upper limit of the on-time of the high-voltage output switch according to a detecting signal from the low-voltage output circuit.

3. The flyback power converter with multiple outputs of claim 2, wherein the rectifier unit has a diode and the detecting signal represents a voltage drop across the diode.

4. The flyback power converter with multiple outputs of claim 2, wherein the rectifier unit has a low-voltage output switch and the detecting signal represents a gate voltage of the low-voltage output switch.

5. The flyback power converter with multiple outputs of claim 1, further comprising a feedback circuit, utilized for detecting the low output voltage to control an on-time of the main switch.

6. The flyback power converter with multiple outputs of claim 2, wherein the secondary side post regulator circuit has:

a ramp generator, generating a ramp signal according to the detecting signal; and

a comparator, receiving the ramp signal and a feedback voltage corresponding to the feedback signal to generate an on-time signal for adjusting the on-time of the high-voltage output switch;

wherein a level of the feedback voltage is positively related to that of the feedback signal and a length of the on-time signal at high level is positively related to the level of the feedback voltage.

7. The flyback power converter with multiple outputs of claim 6, wherein the secondary side post regulator circuit further has an AND gate, which generates a conduction signal according to the detecting signal and the on-time signal to control the high-voltage output switch.

8. The flyback power converter with multiple outputs of claim 6, wherein the secondary side post regulator circuit further has a transforming circuit, and the transforming circuit has an error amplifier for receiving the feedback signal and a reference voltage to generate the feedback voltage.

9. The flyback power converter with multiple outputs of claim 8, wherein the transforming circuit has two error amplifiers, one of the two error amplifiers receives the feedback signal to generate a comparing voltage, and the other one of the two error amplifiers receives the comparing voltage to generate the feedback voltage.

10. The flyback power converter with multiple outputs of claim 8, wherein the transforming circuit has a current mirror and a resistor, an input current of the current mirror is decided by an output voltage of the error amplifier, and the resistor is utilized for transforming a respective output current of the current mirror into the feedback voltage.

11. The flyback power converter with multiple outputs of claim 1, wherein the on-time of the high-voltage output switch is positively related to a level of the high output voltage.

12. The flyback power converter with multiple outputs of claim 6, wherein the ramp generator has a current source, a capacitor, and a switch, the current source is utilized for charging the capacitor, the switch, which is controlled by the detecting signal, has one end connected to a ground and the other end connected to the capacitor for establishing a discharging path to release energy stored in the capacitor.

13. The flyback power converter with multiple outputs of claim 1, further comprising a diode connected to the high-voltage switch in parallel, wherein when the high-voltage switch is turned off, the diode forms a conduction path for the second secondary winding to charge the high-voltage output capacitor.

14. A secondary side post regulator circuit applied in a flyback power converter with multiple outputs, which has a transformer, a low-voltage output circuit for generating a low output voltage, and a high-voltage output circuit for generating a high output voltage, wherein the low-voltage output circuit has a low-voltage output capacitor and a rectifier unit and is coupled to a first secondary winding of the transformer, and the high-voltage output circuit has a high-voltage output capacitor and a high-voltage output switch and is coupled to a second secondary winding of the transformer, the secondary side post regulator circuit comprising:

a ramp generator, generating a ramp signal according to a detecting signal from the low-voltage output circuit; and

a comparator, generating an on-time signal to control an on-time of the high-voltage output switch according to the ramp signal and a feedback signal from the high-voltage output circuit to have energy stored in the high-voltage output capacitor transferred to the low-voltage output capacitor through the conducted high-voltage output switch.

15. The secondary side post regulator circuit of claim 14, further comprising an AND gate, receiving the detecting signal and the on-time signal and generating a conduction signal accordingly to control the high-voltage output switch.

16. The secondary side post regulator circuit of claim 14, further comprising a transforming circuit, utilized for transforming the feedback signal into a feedback voltage, which has a level positively related to that of the feedback signal, and the comparator receiving the ramp signal and the feedback voltage to generate the on-time signal.

17. The secondary side post regulator circuit of claim 16, wherein a length of the on-time signal at high level is positively related to the level of the feedback voltage.

18. The secondary side post regulator circuit of claim 16, wherein the transforming circuit has an error amplifier, which compares the feedback signal with a reference voltage to generate the feedback voltage.

19. The secondary side post regulator circuit of claim 18, wherein the transforming circuit further has a current mirror and a resistor, an input current of the current mirror is decided according to an output voltage of the error amplifier, and the resistor is utilized for transforming a respective output current of the current mirror into the feedback voltage.

20. The secondary side post regulator circuit of claim 18, wherein the transforming circuit has two error amplifiers, one of the two error amplifiers receives the feedback signal to generate a comparing voltage, and the other one of the two error amplifiers receives the comparing voltage to generate the feedback voltage.

21. The secondary side post regulator circuit of claim 14, wherein a level of the feedback signal is positively related to that of the high output voltage.

22. The secondary side post regulator circuit of claim 14, wherein the rectifier unit has a diode and the detecting signal represents a voltage drop across the diode.

23. The secondary side post regulator circuit of claim 14, wherein the rectifier unit has a low-voltage output switch and the detecting signal represents a gate voltage of the low-voltage output switch.

24. The secondary side post regulator of claim 14, wherein a level of the low output voltage is controlled through a primary side of the flyback power converter with multiple outputs.

25. The secondary side post regulator circuit of claim 14, wherein the ramp generator has a current source, a capacitor, and a switch, the switch is controlled by the detecting signal and has one end connected to a ground and the other end connected to the capacitor for establishing a discharging path to release energy stored in the capacitor.