Electronic power protection circuit and applications thereof
An electric power protection circuit connected in series to a secondary side circuit of a transformer in a switch mode power supply includes a voltage/current limiting device to get an electric power signal output from the secondary side circuit of the transformer that goes through current and voltage limitation before being output and a constant current/voltage controller to get the electric power signal which has the current and voltage limited by the voltage/current limiting device. The electric power signal further is undergone constant voltage/current control to achieve voltage overshoot protection.
1. A protection circuit coupled to a secondary side of a switched mode power supply (SMPS), the circuit comprising:
a detection circuit configured for coupling to the secondary side of the SMPS and being configured for providing a detection signal;
a feedback circuit coupled to the detection circuit for receiving the detection signal, the feedback circuit being also coupled to a primary-side control circuit for providing a feedback signal for over-voltage protection; and
a controller coupled to the secondary side of the SMPS, the controller having:
a first terminal for receiving a first output signal associated with an output of the SMPS; and
a second terminal for receiving a second output signal associated with the output of the SMPS,
wherein the controller is configured to use the first output signal to control the SMPS in a constant-voltage mode and configured to use the second output signal to control the SMPS in a constant-current mode.
2. The circuit of claim 1 , wherein the controller comprises:
a first comparator having:
a negative input end forming a constant-voltage control end;
a positive input end coupled to a voltage source;
an output end for providing a control signal; and
a second comparator having:
another negative input end forming a constant-current control end;
another positive input end coupled to the voltage source through a voltage dividing circuit, the another positive input end also coupled to a first output end of the voltage dividing circuit; and
another output end coupled to the output end of the first comparator.
3. The circuit of claim 1 , wherein the detection circuit comprises a voltage/current limiting device configured for:
coupling to the first terminal of the controller to provide over-voltage protection in the constant-current mode; and
coupling to the second terminal of the controller to provide over-voltage protection in the constant-voltage mode.
4. The circuit of claim 3 , wherein the voltage/current limiting device comprises a diode and has a negative electrode coupled to an output filter device in the switch mode power supply and a positive electrode coupled to the controller.
5. The circuit of claim 4 , wherein the diode has a positive electrode coupled to the constant-current control end of the controller to form a constant-current feedback circuit.
6. The circuit of claim 4 , wherein the diode has a positive electrode coupled to the constant-voltage control end of the controller to form a constant-voltage feedback circuit.
7. A protection circuit coupled in series with a secondary side of a switch mode power supply (SMPS), comprising:
a controller coupled to the secondary side of the SMPS, the controller having:
a first terminal for receiving a first output signal associated with an output of the SMPS; and
a second terminal for receiving a second output signal associated with the output of the SMPS,
wherein the controller is configured to use the first output signal to control the SMPS in a constant-voltage mode and configured to use the second output signal to control the SMPS in a constant-current mode; and
a detection circuit configured for coupling to the first terminal of the controller to provide over-voltage protection in the constant-voltage mode, and configured for coupling to the second terminal of the controller to provide over-voltage protection in the constant-current mode.
8. The circuit of claim 7 , wherein the controller comprises:
a first comparator having:
a negative input end forming a constant-voltage control end;
a positive input end coupled to a voltage source;
an output end for providing a control signal; and
a second comparator having:
another negative input end forming a constant-current control end;
another positive input end coupled to the voltage source through a voltage dividing circuit, the another positive input end also coupled to a first output end of the voltage dividing circuit; and
another output end coupled to the output end of the first comparator.
9. The circuit of claim 8 , wherein the first comparator includes a positive end coupled to a first reference voltage, and the second comparator includes a positive end coupled to a second reference voltage, the first reference voltage being higher than the second reference voltage.
10. The circuit of claim 7 , wherein the detection circuit comprises a voltage/current limiting device configured for;
coupling to the first terminal of the controller to provide over-voltage protection in the constant-current mode; and
coupling to the second terminal of the controller to provide over-voltage protection in the constant-voltage mode.
11. The circuit of claim 10 , wherein the voltage/current limiting device comprises a diode.
12. The circuit of claim 11 , wherein the diode has a positive electrode coupled to the constant current control end of the controller to form a constant current feedback circuit.
13. The circuit of claim 11 , wherein the diode has a positive electrode coupled to the constant voltage control end of the controller to form a constant voltage feedback circuit.
14. A switch mode power supply (SMPS), comprising:
a transformer having a primary side for coupling to a power source;
a power switch configured to the primary side of the transformer;
a controller coupled to the secondary side of the SMPS, the controller including:
a first terminal for receiving a first output signal associated with an output of the SMPS: and
a second terminal for receiving a second output signal associated with the output of the SMPS,
wherein the controller is configured to use the first output signal to control the SMPS in a constant-current mode and configured to use the second output signal to control the SMPS in a constant-voltage mode; and
a detection device configured for coupling to the first terminal of the controller to provide over-voltage protection in the constant-current mode, and configured for coupling to the second terminal of the controller to provide over-voltage protection in the constant-voltage mode; and
a PWM control device coupled to the controller through an optical coupling element, the PWM controller being configured for controlling the ON and OFF of the power switch;
wherein the detection device, the controller, the optical coupling element, and the PWM control device form a feedback circuit.
15. The switch mode power supply (SMPS) of claim 14 , wherein the controller comprises:
a first comparator having:
a negative input end forming a constant-voltage control end;
a positive input end coupled to a voltage source;
an output end for providing a control signal; and
a second comparator having:
another negative input end forming a constant-current control end;
another positive input end coupled to the voltage source through a voltage dividing circuit, the another positive input end also coupled to a first output end of the voltage dividing circuit; and another output end coupled to the output end of the first comparator.
16. The switch mode power supply (SMPS) of claim 15 , wherein the first comparator includes a positive end coupled to a first reference voltage, and the second comparator includes a positive end coupled to a second reference voltage, the first reference voltage being higher than the second reference voltage.
17. The switch mode power supply (SMPS) of claim 14 , wherein the detection circuit comprises a voltage/current limiting device configured for coupling to the first terminal of the controller to provide over-voltage protection in the constant-voltage mode, and configured for coupling to the second terminal of the controller to provide over-voltage protection in the constant-current mode.
18. The switch mode power supply (SMPS) of claim 17 , wherein the voltage/current limiting device comprises a diode.
19. The switch mode power supply (SMPS) of claim 18 , wherein the diode has a positive electrode coupled to the constant-current control end of the controller to form a constant current feedback circuit.