Adjusting for conductor loss to regulate constant output voltage in a primary feedback converter
A lower-cost and more precise control methodology of regulating the output voltage of a flyback converter from the primary side is provided, which works accurately in either continuous voltage mode (CCM) and discontinuous mode (DCM), and can be applied to most small, medium and high power applications such cell phone chargers, power management in desktop computers and networking equipment, and, generally, to a wide spectrum of power management applications. Two highly integrated semiconductor chips based on this control methodology are also described that require very few components to build a constant voltage flyback converter.
1. A method comprising:
receiving a feedback voltage indicative of a voltage across a winding on a primary side of a transformer of a switching regulator;
comparing the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off;
storing a current signal that is based on a current flowing through the power switch;
adjusting the comparing based on the current signal to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer; and
controlling the power switch based on the adjusted comparing of the feedback voltage to the reference voltage.
2. The method of claim 1 , further comprising:
sampling the feedback voltage when the power switch is off.
3. The method of claim 1 , further comprising:
determining a magnitude of the current flowing through the power switch by sensing a voltage across a current sense resistor.
4. A method comprising:
receiving a feedback voltage indicative of a voltage across a winding on a primary side of a transformer of a switching regulator;
comparing the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off;
adjusting the comparing based on a current flowing through the power switch to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer;
controlling the power switch based on the adjusted comparing of the feedback voltage to the reference voltage, wherein the feedback voltage is present in a feedback signal; and
generating a triggering signal by sensing a negative-going edge of the feedback signal.
5. The method of claim 1 , wherein the switching regulator has a primary winding, a secondary winding and an auxiliary winding, and wherein the feedback voltage is indicative of a voltage across the auxiliary winding.
6. The method of claim 1 , wherein the switching regulator does not include an optical coupler.
7. A method comprising:
receiving a feedback voltage indicative of a voltage across a winding on a primary side of a transformer of a switching regulator;
comparing the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off;
holding a current sense voltage based on a current flowing through the power switch;
adjusting the comparing based on the current sense voltage so as to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer; and
controlling a voltage on a switch terminal so as to switch the power switch based on the adjusted comparing of the feedback voltage to the reference voltage.
8. The method of claim 7 , further comprising:
sampling the feedback voltage when the power switch is off.
9. The method of claim 7 , further comprising:
determining a magnitude of a current flowing through the power switch by sensing a voltage across a current sense resistor.
10. The method of claim 7 , wherein the switching regulator has a primary winding, a secondary winding and an auxiliary winding, and wherein the feedback voltage is indicative of a voltage across the auxiliary winding.
11. The method of claim 7 , wherein the switching regulator does not include an optical coupler.
12. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit stores a current signal that is based on a current flowing through the power switch, wherein the control circuit adjusts the comparison based on the current signal to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer, and wherein the control circuit uses the adjusted comparison to control the power switch.
13. The integrated circuit of claim 12 , further comprising:
a switch terminal that is coupled to the power switch;
a power terminal through which power is provided to the integrated circuit; and
a ground terminal through which the integrated circuit is grounded, wherein the integrated circuit includes no terminals other than the feedback terminal, the switch terminal, the power terminal and the ground terminal.
14. The integrated circuit of claim 12 , further comprising:
a sample-and-hold circuit that samples and holds a signal derived from the feedback voltage when the power switch is off.
15. The integrated circuit of claim 12 , wherein the transformer has a primary winding, and wherein the power switch is connected directly to the primary winding.
16. The integrated circuit of claim 12 , wherein the transformer has a primary winding and an auxiliary winding, and wherein a voltage across the auxiliary winding is fed back to the feedback terminal via voltage divider resistors.
17. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit adjusts the comparison based on a current flowing through the power switch to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer, wherein the control circuit uses the adjusted comparison to control the power switch, and wherein the power switch is connected to an emitter of an external bipolar transistor of the switching regulator.
18. The integrated circuit of claim 17 , wherein the external bipolar transistor turns on in response to the power switch turning on.
19. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit adjusts the comparison based on a current flowing through the power switch to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer, wherein the control circuit uses the adjusted comparison to control the power switch, and wherein the power switch is connected to an external field effect transistor of the switching regulator.
20. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit holds a current sense voltage based on a current flowing through the power switch, wherein the control circuit adjusts the comparison based on the current sense voltage so as to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer, and wherein the control circuit controls a voltage on a switch terminal so as to switch the power switch based on the adjusted comparing of the feedback voltage to the reference voltage.
21. The integrated circuit of claim 20 , further comprising:
a power terminal through which power is provided to the integrated circuit, wherein the switch terminal that is coupled to the power switch; and
a ground terminal through which the integrated circuit is grounded, wherein the integrated circuit includes no terminals other than the feedback terminal, the current sense terminal, the switch terminal, the power terminal and the ground terminal.
22. The integrated circuit of claim 20 , further comprising:
a sample-and-hold circuit that samples and holds a signal derived from the feedback voltage when the power switch is off.
23. The integrated circuit of claim 20 , wherein the transformer has a primary winding, and wherein the power switch is connected directly to the primary winding.
24. The integrated circuit of claim 20 , wherein the transformer has a primary winding and an auxiliary winding, and wherein a voltage across the auxiliary winding is fed back to the feedback terminal via voltage divider resistors.
25. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit adjusts the comparison based on a voltage present on a current sense terminal so as to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer, wherein the control circuit controls a voltage on a switch terminal so as to switch the power switch based on the adjusted comparing of the feedback voltage to the reference voltage, and wherein the power switch is connected to an emitter of an external bipolar transistor of the switching regulator.
26. The integrated circuit of claim 25 , wherein the external bipolar transistor turns on in response to the power switch turning on.
27. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit adjusts the comparison based on a voltage present on a current sense terminal so as to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a winding on a secondary side of the transformer, wherein the control circuit controls a voltage on a switch terminal so as to switch the power switch based on the adjusted comparing of the feedback voltage to the reference voltage, and wherein the power switch is connected to an external field effect transistor of the switching regulator.
28. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit stores a current signal that is indicative of a magnitude of current flowing through a primary winding of the transformer, wherein the control circuit adjusts the comparison based on the current signal so as to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a secondary winding of the transformer, and wherein the control circuit controls a voltage on a switch terminal so as to switch the power switch based on the adjusted comparison of the feedback voltage to the reference voltage.
29. The integrated circuit of claim 28 , further comprising:
a power terminal through which power is provided to the integrated circuit, wherein the switch terminal that is coupled to the power switch; and
a ground terminal through which the integrated circuit is grounded, wherein the integrated circuit includes no terminals other than the feedback terminal, the switch terminal, the power terminal and the ground terminal.
30. The integrated circuit of claim 28 , further comprising:
a sample-and-hold circuit that samples and holds a signal derived from the feedback voltage when the power switch is off.
31. The integrated circuit of claim 28 , wherein the power switch is connected directly to the primary winding.
32. The integrated circuit of claim 28 , wherein the transformer has an auxiliary winding, and wherein a voltage across the auxiliary winding is fed back to the feedback terminal via voltage divider resistors.
33. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit adjusts the comparison based on a signal indicative of a magnitude of current flowing through a primary winding of the transformer so as to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a secondary winding of the transformer, wherein the control circuit controls a voltage on a switch terminal so as to switch the power switch based on the adjusted comparison of the feedback voltage to the reference voltage, wherein the switching regulator comprises an external bipolar transistor, and wherein the external bipolar transistor turns on in response to the power switch turning on.
34. The integrated circuit of claim 33 , wherein the power switch is connected to an emitter of the external bipolar transistor.
35. An integrated circuit, comprising:
a feedback terminal on which a feedback voltage is present, wherein the feedback voltage depends on a voltage across a winding on a primary side of a transformer of a switching regulator; and
a control circuit that compares the feedback voltage to a reference voltage at a time point during which a power switch of the switching regulator is off, wherein the control circuit adjusts the comparison based on a signal indicative of a magnitude of current flowing through a primary winding of the transformer so as to compensate for a change in a voltage output by the switching regulator caused by conductor loss in a current loop through a secondary winding of the transformer, wherein the control circuit controls a voltage on a switch terminal so as to switch the power switch based on the adjusted comparison of the feedback voltage to the reference voltage, and wherein the power switch is connected to an external field effect transistor of the switching regulator.