Dual-Switches flyback power converter with self-excited supply to power the high-side driver
View Patent ↗An exemplary embodiment of a flyback power converter includes a transformer for power transfer, a high-side transistor, a low-side transistor, two diodes, a control circuit, and a high-side drive circuit. The high-side transistor and the low-side transistor are coupled to switch the transformer. The two diodes are coupled to said transformer to circulate energy of leakage inductance of the transformer to an input power rail of the power converter. The control circuit generates a switching signal coupled to control the high-side transistor and the low-side transistor. The high-side drive circuit is coupled to receive the switching signal for driving the high-side transistor. The transformer has an auxiliary winding generating a floating power to provide power supply for said high-side drive circuit.
1. A flyback power converter comprising:
a transformer for power transfer;
a high-side transistor and a low-side transistor coupled to switch said transformer;
two diodes coupled to said transformer to circulate energy of leakage inductance of said transformer to an input power rail of said flyback power converter;
a control circuit generating a switching signal coupled to control said high-side transistor and said low-side transistor; and
a high-side drive circuit coupled to receive said switching signal for driving said high-side transistor;
wherein said transformer has an auxiliary winding generating a floating power to provide a power supply for said high-side drive circuit.
2. The flyback power converter as claimed in claim 1 further comprising:
a low-side drive circuit coupled to receive said switching signal for driving said low-side transistor;
wherein said low-side drive circuit will turn on said low-side transistor before power supply of said low-side drive circuit reaches an operating threshold.
3. The flyback power converter as claimed in claim 2 further comprising:
a floating capacitor for generating said floating power;
a floating diode coupled from said auxiliary winding to said floating capacitor; and
a bootstrap diode coupled from the power supply of said high-side drive circuit to said floating capacitor.
4. The flyback power converter as claimed in claim 2 , wherein said high-side transistor and said low-side transistor are turned on/off simultaneously after the power supply of said low-side drive circuit reaches said operating threshold.
5. The flyback power converter as claimed in claim 1 , wherein said high-side drive circuit is a differential-mode level-shift circuit.
6. The flyback power converter as claimed in claim 1 , wherein said high-side drive circuit comprises:
a pulse generation circuit generating a pulse-on signal and a pulse-off signal;
two transistors coupled to receive said pulse-on signal and said pulse-off signal for generating a level-shift-on signal and a level-shift-off signal by switching on said transistors, respectively;
a comparison circuit receiving said level-shift-on signal and said level-shift-off signal for generating a set signal and a reset signal; and
a flip-flop generating a high-side drive signal for driving said high-side transistor;
wherein said comparison circuit and said flip-flop are powered by said floating power.
7. The flyback power converter as claimed in claim 6 , in which the pulse width of said pulse-on signal and said pulse-off signal is shorter than 500 nsec.
8. The flyback power converter as claimed in claim 1 , further comprising:
a low-side drive circuit coupled to receive said switching signal for driving said low-side transistor;
wherein a low-side drive signal of the low-side drive circuit follows the switching signal when the power supply of said low-side drive circuit higher than an operating threshold.