Main supply zero crossing detection for PFC converter
A fault mode of a PWM module embedded in a microcontroller is used to detect main supply zero crossings for regulating output voltage of a PFC converter operating in BCM, without using an external detecting element or a comparator, ADC or other specialized component internal to the microcontroller. In some implementations, the end of decrease current flow in the energy storage inductor of the converter is used to reinitialize a PWM timer or counter (counting-up or counting-down timer). The current goes to zero for a time period when the main supply voltage goes to zero, resulting in the PWM timer or counter not being reinitialized prior to the end of the current PWM cycle. The failure to reinitialize the timer or counter can be used to generate a signal indicative of a zero voltage crossing of the main supply voltage.
1. A power-factor-correction (PFC) converter circuit, comprising:
a rectifier circuit;
an energy storage device coupled to the rectifier circuit and configured to receive an input voltage from the rectifier circuit;
a switch coupled to the energy storage device, the switch configurable to provide a path for removing energy from the energy storage device;
a microcontroller coupled to the energy storage device and the switch; and
an analog-to-digital converter (ADC) coupled to an output of the power-factor-correction (PFC) converter circuit and to the microcontroller, where the microcontroller includes a pulse width modulation (PWM) module coupled to the energy storage device, the PWM module being configured to enable the ADC to sample an output voltage of the power-factor-correction (PFC) converter circuit by detecting a zero voltage crossing point of the input voltage received from the rectifier circuit based on an absence of a trigger event that occurs external to the microcontroller, the absence of the trigger event being based on an end of decrease current flow in the energy storage device.
2. The circuit of claim 1 , where the PWM module indirectly detects the zero voltage crossing point of the input voltage by detecting when a timer or counter for controlling the PWM module in the power-factor-correction (PFC) converter circuit is not reinitialized by the trigger event prior to an end of a programmed PWM cycle period of the PWM module, and
where the timer or counter is reinitialized by the trigger event before the end of the programming PWM cycle period to start a new programming PWM cycle when the input voltage is not at the zero voltage crossing point.
3. The circuit of claim 1 , where the rectifier circuit is a diode bridge.
4. The circuit of claim 1 , where the sampled output voltage is used in a voltage regulation loop of the power-factor-correction (PFC) converter circuit.
5. The circuit of claim 1 , where the energy storage device includes first and second inductors, and where the first inductor is coupled to the rectifier circuit and the second inductor is magnetically coupled to the first inductor and connected to the PWM module for generating the trigger event.
6. The circuit of claim 1 , where the PWM module is configured to perform operations comprising:
in response to detecting that the input voltage has reached the zero voltage crossing point, generating a trigger signal; and
providing the trigger signal to the ADC, the trigger signal causing the ADC to sample the output voltage of the converter circuit.
7. The circuit of claim 2 , where the PWM module includes a retriggerable counting-down timer and the zero voltage crossing point is detected when the retriggerable counting-down timer reaches its bottom value.
8. The circuit of claim 2 , where the PWM module includes a retriggerable counting-up timer and the zero voltage crossing point is detected when the retriggerable counting-up timer reaches its top value.
9. The circuit of claim 2 , where the energy storage device includes an inductor and the external trigger event is based on the end of decrease current flow in the inductor.
10. The circuit of claim 9 , where the inductor does not receive any current during a time window Δ given by
Δ
=
T
π
*
(
2
*
v
th
)
v
max
where V max is the maximum voltage of a main supply voltage, V ac , V th is the threshold voltages of diodes in a diode bridge, and T is the period of the main supply voltage V ac .
11. The circuit of claim 10 , where the PWM module includes a retriggerable counting-down timer, and the retriggerable counting-down timer uses a compare value cmp that is used to adjust conduction time of the switch and complies with a constraint
(
top
-
cmp
)
F
timer
<
Δ
where top is the top value of the retriggerable counting-down timer and F timer is timer frequency.
12. The circuit of claim 10 , where the PWM module includes a retriggerable counting-up timer, and the retriggerable counting-up timer uses a compare value cmp that is used to adjust conduction time of the switch and complies with a constraint
cmp
F
timer
<
Δ
,
where F timer is timer frequency.
13. The circuit of claim 10 , where the external trigger event that did not occur during the time window Δ failed to reinitialize the timer or counter.
14. A method performed by a power-factor-correction (PFC) converter circuit, the method comprising:
receiving an input voltage generated by a supply voltage;
storing energy in an energy storage device of the power-factor-correction (PFC) converter circuit generated by the input voltage;
configuring a switch of the power-factor-correction (PFC) converter circuit coupled to the energy storage device, where the switch is configured by an output of a pulse width modulation (PWM) module of the power-factor-correction (PFC) converter circuit;
determining that the input voltage has reached a zero voltage crossing point based on a fault mode of the PWM module, where the fault mode of the PWM module is based on an absence of a trigger event, and the absence of the trigger event is based on an end of decrease current flow in the energy storage device, and where the fault mode includes determining that a timer or counter of the PWM module has not been reinitialized by the trigger event prior to an end of a current PWM cycle of the PWM module, and where the timer or counter is reinitialized by the trigger event before the end of the current PWM cycle to start a new current PWM cycle when the input voltage is not at the zero voltage crossing point; and
in response to determining that the input voltage has reached the zero voltage crossing point, enabling, by the PWM module, an analog-to-digital converter (ADC) of the power-factor-correction (PFC) converter circuit to sample an output voltage of the power-factor-correction (PFC) converter circuit.
15. The method of claim 14 , where enabling, by the PWM module, an analog-to-digital converter (ADC) of the power-factor-correction (PFC) converter circuit to sample an output voltage of the power-factor-correction (PFC) converter circuit includes:
providing a trigger command to the analog-digital converter (ADC) during the current PWM cycle; and
causing the ADC to sample the output voltage of the power-factor-correction (PFC) converter circuit, where the sampled output voltage is used in a voltage regulation loop of the power-factor-correction (PFC) converter circuit.
16. The method of claim 14 , where the PWM module includes a retriggerable counting-down timer and the zero voltage crossing point is detected when the retriggerable counting-down timer reaches its bottom value.
17. The method of claim 14 , where the PWM module includes a retriggerable counting-up timer and the zero voltage crossing point is detected when the retriggerable counting-up timer reaches its top value.
18. The method of claim 14 , where the energy storage device includes first and second inductors, and where the first inductor receives the input voltage and the second inductor is magnetically coupled to the first inductor and connected to the PWM module for generating the trigger event.
19. The method of claim 14 , where enabling, by the PWM module, an analog-to-digital converter (ADC) of the power-factor-correction (PFC) converter circuit to sample an output voltage of the power-factor-correction (PFC) converter circuit comprises:
in response to determining that the input voltage has reached the zero voltage crossing point, generating a trigger signal; and
providing the trigger signal to the ADC, the trigger signal causing the ADC to sample the output voltage of the power-factor-correction (PFC) converter circuit.