MC3PHAC PWM

[driftboat]

Had just found out about the MC3PHAC chip yesterday, and did as much reading as I could.  I need some help/advice on identifying the PWM (pulse Width Modulation).  Is it consisting of Triac's or some other type of a modular device.

Thank you in advance

[driftboat]

Thanks rocco,

I've done some more research and purchased some low priced IGBT,s ( IRGPH20M 6.9 Amp, 1200 Volt, n-channel Insulated Gate Bipolar Transistors). My problem now is coming up with the value of the external high speed switch diode that would be parallel with IGBT's. The ones that I purchased do not have the internal diode.  My project is to operate a 3-phase motor, probably 1/3hp to 3/4hp from a single phase source, the IGBT are limited in current.  Any help would be appreciated.

Thanks again in advance

[rocco]

Hi Driftboat,

A few things to consider:

Heat dissipation:

If you are only pushing 7 amps, MosFets might be more appropriate. You control a MosFet the same way as an IGBT, but the power-dissipation operates differently. An IGBT will have approximately .6 volts across it when ON, whereas a Mosfet will have a voltage based on its ON resistance (ohm's law). So at lower currents, the dissipation in the switch will be lower in a MosFet than in an IGBT, and at higher currents, the dissipation will be lower in an IGBT than in a MosFet. Also, as the current increases, dissipation increases linearly in an IGBT and exponentially in a MosFet.

Radiated noise:

You will get switching noise with any high-power PWM topology. How much you (and your neighbors) can tolerate will dictate many design parameters. You can minimize EMI by switching your drive-stage slower, but that will generate more heat as the switches will spend more time in their linear (unsaturated) region. With PWM, there has always been that heat/noise trade-off. Be prepared to add chokes, for controlling both noise and current-ripple (which will heat the motor), if your motor does not have high-inductance.

Bus voltage:

You do not mention where your single-phase is from. Is it 110 or 220? This will proportionately influence both noise and current-ripple, but will mainly influence cost. Unless I'm designing for 400 volts or more, I stick with 600 volt Mosfets or IGBTs. Of course, the reverse-recovery diodes are important to keep the switching transients from exceeding that voltage. Faster is better, with a current-rating better than your peak motor current. Keeping the transients low in amplitude helps with reducing EMI.

Keep in mind that driving a motor is no trivial task. Be prepared to do multiple iterations of your power circuit.

[rocco]

Hi Driftboat,

Welcome to the forum.

The MC3PHAC is a controller only, it has no power stage. Some of the drawings in the datasheet show the PWM outputs driving six IGBTs, but they could just as easily been MosFets. It all depends on your requirements. I doubt it would be able to drive triacs, as the triacs would latch on and the PWM would not work.