I've built a very simple H-bridge N-channel motor driver (using IRF3205) with 10K pull down resistors. The bridge is optically isolated from the driving circuit using an ILQ74.
All works perfectly apart from one thing.
Even without the motor connected, I seem to be getting spikes (on the oscilloscope) when the bridge changes from forward to reverse very quickly.
It even causes the power supply to throw a current warning. So I'm assuming it's a very quick short as the first pair of mosfets switch off and the others on, these voltage spikes are so quick, it barely shows on the oscilloscope but it's enough to cause problems. I can drive one side of the bridge as fast as 20 KHz without any significant degrade in signal. Drive both sides and the signal degrades even at 30Hz.
What would people recommend? Lower the pull down resistor resistances?
The application for it is to make a servo motor, But the servo driving circuit does cause these spikes to occur. I'll be driving some considerable current, and the last thing I want to do is start popping mosfets.
All works perfectly apart from one thing.
Even without the motor connected, I seem to be getting spikes (on the oscilloscope) when the bridge changes from forward to reverse very quickly.
It even causes the power supply to throw a current warning. So I'm assuming it's a very quick short as the first pair of mosfets switch off and the others on, these voltage spikes are so quick, it barely shows on the oscilloscope but it's enough to cause problems. I can drive one side of the bridge as fast as 20 KHz without any significant degrade in signal. Drive both sides and the signal degrades even at 30Hz.
What would people recommend? Lower the pull down resistor resistances?
The application for it is to make a servo motor, But the servo driving circuit does cause these spikes to occur. I'll be driving some considerable current, and the last thing I want to do is start popping mosfets.