Hi
I was trying to test my circuit. I would like to know is it possible to test my PWM IC UC2846 alone in a test bench like set up. I want to see the output waveforms (A OUT and B OUT) in my scope
to confirm my PWM out puts are ok before giving it to driver circuit. In my Test bench setup i have VCC supply and all required peripheral circuits/components for the PWM IC to function.
Thanks and regards
Nanda Kumar
Hi Nanda,
Take a look at the UC2825 datsheet, on page 8 you will see an open loop test circuit. You can setup something similar for the UC2846.
Main points are to ensure that the test board has short connections from the pins to the components to reduce noise.
Ensure Vcc is well decoupled and that the oscillator components are close to the pins.
To get the IC to operate and to be able to vary the duty cycle you will need to feed some of the oscillator signal from pin 8 into the CS amplifier. You can do this by using a simple npn transistor as a buffer, connect its collector to Vref, its base to pin 8 and connect the emitter with a resistor to pin 4, tie pin 3 to ground. Place another resistor from pin 4 to pin 3 so the two resistor act a potential divider and you can size the resistors to give you a 400mV peak signal on pin 4 at max duty cycle. the current limit value is 450mV.
You can set up the error amp in the circuit in the link above with atrim pot and that will allow you vary the COMP pin voltage and hence the duty cycle.
Regards
Peter
