Tool/software:
Explanation of circuit specifications and requirements
We are currently developing an application where we need to power, using a PFC, an inverter that drives a motor.
Therefore, we are currently evaluating for this application TI’s UCC28056 PFC controller.
We would like to have two different working modes:
- The PFC is active and powers the inverter
- The PFC is disabled (the converter MOSFET is turned off and doesn’t switch), but the inverter is still powered through the boost diode although the output voltage is unregulated.
To do this, we need to be able to enable and disable the PFC during operation (we change mode of operation only when the motor isn’t moving to avoid dangerous transients).
The important thing for us is that when the PFC is re-enabled the UCC28056 correctly performs its Soft Start function to avoid dangerous transients.
Questions regarding the behavior of TI’s UCC28056 PFC controller
Our questions concerning the PFC controller UCC28056 are the following:
- Is there a way to enable/disable the UCC28056 to get the behavior that we have described above?
- Is it possible to do so by acting directly on the IC’s pins?
- If it’s not possible to act directly on the IC’s pins are there any workarounds to get the behavior that we want?
Possible ideas that we thought could solve our problem
- By lowering the value of Ros1 by switching in parallel a low value resistor R, as show in the picture below, we could make the IC think that an Over-Voltage event has occurred and thus shut down the PFC.
- By controlling a PMOS as shown in the figure below we can pull-down Vcc to 0V and thus disable the entire IC and therefore even the PFC.
Are these ideas safe or can they lead to the arise of problems during the operation of the circuit?
