L298 and anti-phase PWM

Mickster

I have one of the Ebay-type dual H-bridge amps based on the the above. I was wondering if there is a way to configure it for anti-phase PWM where a 50% duty cycle results in zero amplifier output.

I seem to remember achieving this with a 18200 based amp (?) where I tied a pin high and applied the PWM to the Enable....I don't remember.

Cheers!

MIckster

evanh

I think the normal way is just B is always inverted A. That gives the anti-phase needed. When input signal time high equals the time low then you have your zero speed. Only detail is carrier frequency, it needs to be high enough to prevent motor vibration and large current peaks, but low enough not to add too much in losses to the amp.

Beau Schwabe

If your using the 180 Deg out of Phase for driving an H-Bridge it won't work .... at least not for very long. You need a "Trapezoid" approach where the rise and fall time of the trapezoid is the dead time or where ALL MOSFETs are allowed to turn OFF. This will prevent shoot-through and unnecessary transistor overheating and eventually the destruction of the MOSFET transistors.

evanh

Beau,
The L298 documentation shows the push-pull as internally hard-wired inversion of each other and doesn't seem to indicate any requirement for dead time on the enable signals. The functional diagram isn't any help ... presumably such details are hidden but taken care of.

EDIT: The documentation says the Enables do have to be low upon power up of the power supply. So, can't just tie those controls high. I guess a capacitor plus pullup-resisitor plus pull-down diode would be enough.