PFC controller add-on circuit to stabilize THDi performance
A total harmonic distortion (THDi) reduction circuit for a power factor correction (PFC) controller to control a PFC stage. The THDi reduction circuit determines whether an input signal, such as an alternating current (AC) line voltage is a high voltage or low voltage signal. For a high voltage input signal, the THDi reduction circuit may limit the duty cycle of a control signal to a PFC stage to minimize a voltage spike at the zero-crossing point of the input signal and thereby minimize THDi. For a low voltage input signal, the THDi reduction circuit may extend the duty cycle of the control signal to the PFC stage, while ensuring that the control signal has at least a predetermined off-time, i.e. the duty cycle is less than 100 percent. Extending the control signal duty cycle, especially for low voltage input signals under high load, may minimize THDi.
1. A circuit comprising a maximum duty cycle (DMAX) extension element; and a rising edge blanking element operatively coupled to the DMAX extension element, wherein:
the DMAX extension element is configured to adjust a duty cycle of a first switching cycle of a control signal, and
the rising edge blanking element is configured to blank the rising edge of a second switching cycle of the control signal, wherein:
the second switching cycle is a next switching cycle subsequent to the first switching cycle, and
the rising edge blanking element causes the control signal to include at least a predetermined off-time.
2. The circuit of claim 1 , further comprising a high line detect element operatively coupled to the DMAX extension element, the rising edge blanking element and an alternating current (AC) input signal, wherein the high line detection element:
is configured to determine whether a voltage in the AC input signal exceed a voltage threshold, and
in response to determining that the voltage in the AC input signal exceeds the voltage threshold, the high line detection element causes the rising edge blanking element to adjust the duty cycle by limiting the duty cycle of the first switching cycle and the second switching cycle.
3. The circuit of claim 2 , wherein in response to determining that the voltage in the AC input signal does not exceed the voltage threshold, the high line detection element causes the DMAX extension element to adjust the duty cycle by extending the duty cycle of the first switching cycle and the second switching cycle.
4. The circuit of claim 3 , wherein a predetermined off-time is configured to start at substantially the same time as an end of the first switching cycle.
5. The circuit of claim 1 , wherein the off-time is a logical low signal.
6. The circuit of claim 1 , wherein the DMAX extension element and the rising edge blanking element are implemented using analog circuit components.
7. The circuit of claim 1 , wherein the DMAX extension element and the rising edge blanking element are implemented using a microcontroller.
8. The circuit of claim 1 , wherein the DMAX extension element and the rising edge blanking element are implemented using digital processing circuitry.
9. The circuit of claim 8 , wherein the circuit further comprises non-transient computer-readable storage medium, wherein the digital processing circuitry is operatively coupled to the computer-readable storage medium and wherein the computer-readable storage medium comprises instructions for the digital processing circuitry.
10. A circuit comprising:
a driver circuit, wherein the driver circuit is configured to output a signal to a power factor correction (PFC) stage; and
a total harmonic distortion (THDi) reduction circuit operatively coupled to the driver circuit, wherein the output of the THDi circuit is configured to regulate the signal output by the driver circuit, the THDi reduction circuit comprising:
a maximum duty cycle (DMAX) extension element configured to adjust a duty cycle of a first switching cycle of a control signal; and
a rising edge blanking element operatively coupled to the DMAX extension element, wherein:
the rising edge blanking element is configured to blank the rising edge of a second switching cycle of the control signal, wherein:
the second switching cycle is a next switching cycle subsequent to the first switching cycle, and
the rising edge blanking element causes the control signal to include at least a predetermined off-time.
11. The circuit of claim 10 , further comprising a digital PFC stage controller configured to output the control signal.
12. The circuit of claim 10 , further comprising a THDi timer element operatively coupled to the DMAX extension element and the rising edge blanking element, wherein the THDi timer element is configured to set an amount of extension time for the DMAX extension element to extend the duty cycle of the first switching cycle and is configured to set an amount of blanking time for the rising edge blanking element to blank the rising edge of the second switching cycle.
13. The circuit of claim 10 , further comprising a PFC controller operatively coupled to the THDi reduction circuit and configured to output the control signal.
14. The circuit of claim 10 , further comprising a high line detect element operatively coupled to the DMAX extension element, the rising edge blanking element and an alternating current (AC) input signal, wherein the high line detection element:
is configured to determine whether a voltage in the AC input signal exceeds a voltage threshold, and
in response to determining that the voltage in the AC input signal exceeds the voltage threshold, the high line detection element causes the rising edge blanking element to limit the duty cycle of the first switching cycle and the second switching cycle.
15. The circuit of claim 14 , wherein in response to determining that the voltage in the AC input signal does not exceed the voltage threshold, the high line detection element causes the DMAX extension element to adjust the duty cycle by extending the duty cycle of the first switching cycle.
16. The circuit of claim 10 , wherein the DMAX extension element and the rising edge blanking element are implemented using analog circuit components.
17. A method comprising:
determining whether a voltage of an alternating current (AC) input signal exceeds a voltage threshold;
in response to determining that the voltage of the AC input signal exceeds the voltage threshold, adjusting a duty cycle of a control signal by setting an on-time of the control signal to be no more than a threshold on-time;
in response to determining that the AC input signal does not exceed the voltage threshold, adjusting the duty cycle of the control signal by extending the on-time of the control signal by a predetermined amount of on-time, wherein the duty cycle of the control signal includes at least a predetermined off-time.
18. The method of claim 17 , wherein the AC input signal and the control signal is received at power factor correction (PFC) stage and a PFC controller generates the control signal.
19. The method of claim 17 , wherein voltage threshold is 180 volts.
20. The method of claim 17 , wherein the predetermined off-time is configured to start at substantially the same time as the end the predetermined amount of on-time.