Start up circuit of power converter
View Patent ↗A start up circuit of power converters is presented. It includes a first transistor, a resistive device, a second transistor, a third transistor and a diode. The first transistor is coupled to a voltage source. The third transistor is connected in serial with the first transistor to output a supply voltage to a control circuit of the power converter in response to the voltage source. The diode is connected from a transformer winding of the power converter to supply a further supply voltage to the control circuit of the power converter. The second transistor is coupled to control the first transistor and the third transistor in response to a control signal. The resistive device provides a bias voltage to turn on the first transistor and the third transistor when the second transistor is turned off. Once the second transistor is turned on, the third transistor is turned off and the first transistor is negative biased.
1. A start up circuit of power converter, comprising:
a first transistor having a first terminal, a second terminal and a third terminal, in which the first terminal is coupled to receive a voltage source;
a third transistor having a drain terminal, a source terminal and a gate terminal, in which the drain terminal of the third transistor is connected to the second terminal of the first transistor, the source terminal of the third transistor is coupled to provide a supply voltage to a control circuit of the power converter;
a diode coupled from a transformer winding of the power converter to the control circuit of the power converter for providing a further supply voltage to the control circuit;
a second transistor having a drain terminal, a source terminal and a gate terminal, in which the drain terminal of the second transistor is coupled to the gate terminal of the third transistor and the third terminal of the first transistor, the gate terminal of the second transistor is coupled to receive a control signal, and the source terminal of the second transistor is coupled to a ground; and
a resistive device connected from the third terminal of the first transistor to the second terminal of the first transistor;
wherein the resistive device provides a bias voltage to turn on the first transistor and the third transistor when the second transistor is turned off, the control signal is coupled to turn on the second transistor for switching off the third transistor, the third transistor and the second transistor being positive-threshold voltage devices.
2. The start up circuit of power converter as claimed in claim 1 , wherein the first transistor is a negative-threshold voltage device.
3. The start up circuit of power converter as claimed in claim 1 , wherein the resistive device provides a negative bias to the first transistor once the second transistor is turned on.
4. The start up circuit of power converter as claimed in claim 1 , wherein the second transistor is turned on after the control circuit of the power converter starts to operate.
5. The start up circuit of power converter as claimed in claim 1 , wherein the first transistor is a voltage controlled resistance device, the first transistor still has a current flow through the first transistor when the third transistor is turned off.
6. The start up circuit of power converter as claimed in claim 1 , wherein the resistive device can be implemented by a resistor or a transistor.
7. A start up circuit of power converter comprising:
a first transistor coupled to receive a voltage source;
a third transistor connected in serial relation with the first transistor to provide a supply voltage to a control circuit of the power converter in response to the voltage source;
a resistive device coupled to the first transistor and the third transistor to provide a bias voltage to turn on the first transistor and the third transistor; and
a second transistor coupled to the third transistor to turn off the third transistor;
wherein a control signal is coupled to the second transistor to control the second transistor, the second transistor and the third transistor being positive-threshold devices.
8. The start up circuit of power converter as claimed in claim 7 , wherein the first transistor is a negative-threshold voltage device.
9. The start up circuit of power converter as claimed in claim 7 further comprises a diode coupled from a transformer winding of the power converter to the control circuit of the power converter to provide a further supply voltage to the control circuit.
10. The start up circuit of power converter as claimed in claim 7 , wherein the second transistor provides a negative bias to the first transistor through the resistive device.
11. The start up circuit of power converter as claimed in claim 7 , wherein the first transistor is a voltage controlled resistance device, the first transistor still has a current flow through the first transistor when the third transistor is turned off.
12. The start up circuit of power converter as claimed in claim 7 , wherein the resistive device can be implemented by a resistor or a transistor.
13. A start up circuit comprising:
a first transistor having a first terminal, a second terminal and a third terminal, the first terminal coupled to receive a voltage source and the second terminal providing a supply voltage to a control circuit of a power converter;
a resistive device connected from the third terminal of the first transistor to the second terminal of the first transistor and coupled to the supply voltage to provide a bias voltage to turn on the first transistor;
a second transistor coupled to the third terminal of the first transistor and the resistive device to turn off the first transistor; and
a diode coupled from a transformer winding of the power converter to the control circuit of the power converter for providing a further supply voltage to the control circuit;
wherein a control signal is coupled to the second transistor to control the second transistor.
14. The start up circuit as claimed in claim 13 , wherein the second transistor is turned on after the control circuit of the power converter starts to operate.
15. The start up circuit as claimed in claim 13 , wherein the first transistor is a negative-threshold voltage device.
16. The start up circuit as claimed in claim 13 , wherein the second transistor provides a negative bias to the first transistor through the resistive device to turn off the first transistor.
17. A start up circuit comprising:
a first transistor having a first terminal, a second terminal and a third terminal, the first terminal coupled to receive a voltage source and the second terminal providing a supply voltage to a control circuit of a power converter;
a resistive device connected from the third terminal of the first transistor to the second terminal of the first transistor and coupled to the supply voltage to provide a bias voltage to turn on the first transistor; and
a second transistor coupled to the third terminal of the first transistor and the resistive device to turn off the first transistor;
wherein a control signal is coupled to the second transistor to control the second transistor.
18. The start up circuit as claimed in claim 17 further comprises a diode coupled from a transformer winding of the power converter to the control circuit of the power converter to provide a further supply voltage to the control circuit.
19. The start up circuit as claimed in claim 17 , wherein the second transistor is turned on after the control circuit of the power converter starts to operate.
20. The start up circuit as claimed in claim 17 , wherein the first transistor is a negative-threshold voltage device.
21. The start up circuit as claimed in claim 17 , wherein the second transistor provides a negative bias to the first transistor through the resistive device to turn off the first transistor.