I've been playing around developing a "toy controller" to gain experience to jump to higher dreams later on. This controller is an h-bridge for a 250W dc-brushed motor. I developed the whole thing from the ground up and assembled the first prototype in a perf-board (I know, not such a good choice, but is part of the learning path anyway; 2nd prototype will have a custom PCB). The bridge uses both N and P MOSFETs; only the N-MOSFETs do PWM switching. Which half-bridge has 2 N-MOSFETs paralleled with 10 Ohm gate resistors and 1 P-MOSFET.
I started by testing with a car lamp and then a small DC-motor from a wireless vacuum cleaner. What I'm showing below doesn't change with being the lamp or motor, with current nor with more capacitance at the power rails. This is what I see at the input of the N-MOSFETs driver and at the N-MOSFET's drain (load: 21W 12Vcar lamp):
The MOSFETs are ON when the yellow line is low. Directly at one of the N-MOSFETs gate I see this:
The PWM frequency is 10KHz and the duty cycle on these pics is very very small (some 2%; that's how I'm limiting current while not implemented in the firmware).
From where exactly are these bounces coming from? This is where the MOSFETs turn on/off. I have 35cm thick long wires from battery (2 series gel lead-acid 7Ah) to controller, another 20cm from controller to load. I see this with currents from 1A to 12A or 13A, current changes very little the effect. Circuit routing is not good, I have some thick 5 - 6cm wires to distribute power to the half-bridges, I have also a shunt on the GND line, from GND to the N-MOSFETs' source; don't know exactly the value but should be some 6-7 mOhm max. Are the drivers too fast? I see the same bouncing on the GND line. What's your opinion?
Update: Here's the schematics of the power section, just one half-bridge, the full circuit has 2 of these and an extra micro-controller based circuit as brain. Pins from the micro-controller (AVR) connect directly to HB1_L (scope yellow traces are taken here) and HB1_H. MGND is GND through the shunt. The blue trace on the 1st waveform was taken at HB1_OUT (only HB1_L taking the PWM, and the P-MOSFET on the other half-bridge is constantly on).
I started by testing with a car lamp and then a small DC-motor from a wireless vacuum cleaner. What I'm showing below doesn't change with being the lamp or motor, with current nor with more capacitance at the power rails. This is what I see at the input of the N-MOSFETs driver and at the N-MOSFET's drain (load: 21W 12Vcar lamp):
The MOSFETs are ON when the yellow line is low. Directly at one of the N-MOSFETs gate I see this:
The PWM frequency is 10KHz and the duty cycle on these pics is very very small (some 2%; that's how I'm limiting current while not implemented in the firmware).
From where exactly are these bounces coming from? This is where the MOSFETs turn on/off. I have 35cm thick long wires from battery (2 series gel lead-acid 7Ah) to controller, another 20cm from controller to load. I see this with currents from 1A to 12A or 13A, current changes very little the effect. Circuit routing is not good, I have some thick 5 - 6cm wires to distribute power to the half-bridges, I have also a shunt on the GND line, from GND to the N-MOSFETs' source; don't know exactly the value but should be some 6-7 mOhm max. Are the drivers too fast? I see the same bouncing on the GND line. What's your opinion?
Update: Here's the schematics of the power section, just one half-bridge, the full circuit has 2 of these and an extra micro-controller based circuit as brain. Pins from the micro-controller (AVR) connect directly to HB1_L (scope yellow traces are taken here) and HB1_H. MGND is GND through the shunt. The blue trace on the 1st waveform was taken at HB1_OUT (only HB1_L taking the PWM, and the P-MOSFET on the other half-bridge is constantly on).