5.2 Isolated Input Voltage Sense Circuit (PIC16F Based)

The dsPIC33C main power controller is sitting at the secondary low voltage side (i.e., 12V LV Battery. 4 kilo-Volt Isolation is requirement between primary and secondary stages for safety). This galvanic isolation is implemented through the main SMPS transformer and by use of isolated gate drivers and gate driver supplies for powering and controlling Phase-Shifted Full-Bridge SiC MOSFETs.

Monitoring the 800 VDC bus voltage is important for protecting and controlling the Power stage. Input side overvoltage and undervoltage protections are implemented in firmware. Additionally, adaptive gain control may also be used. This introduces the need to have an isolated voltage sensing method. This is done by having a PIC16F sitting on the high-voltage side, powered through auxiliary gate driver supply.

The PIC16F measures the HV DC-Bus via its on-board ADC. This value is encoded into a PWM at 31 kHz and is transferred across the isolation barrier via an opto-coupler. On the low-voltage side, this PWM is passed through a low-pass filter with a corner frequency of 2kHz and then read by an ADC on the main dsPIC33C power controller.