1. Added a 2N3904 transistor off the AVR PWM. This allows the pulse off my PWM pin to actually drop to zero. Instead of having a nominal 5V.
2. Swapped out wimpy inductors for high amp versions. I'm using 220uH and 1000uH still, but these can take over 3A each. They are bigger and more expensive, but show no signs of overheating.
3. Reversed firmware from being 95% duty cycle down to 5%. As usual I had reversed the counter idea which was another reason I was blowing up parts. I'm probably going to drive the pulser at a higher duty cycle, but I'll wait for the printed circuit boards to arrive before experimenting with firmware again.
3 comments:
hey mikey -- can you describe the purpose of the new 2N3904 transistor in a bit more detail? i'm not real clear on what's going on after scratching my head at the schematic for a bit.
The 2n3904 provides switching on the gate of the mosfet. A P-channel mosfet needs to have voltage above or equal to it's supply voltage applied at the gate in order to turn off. The AVR can only supply 5V. If the voltage is too low, it will conduct, and generate a LOT of heat in some cases.
I suspect that the larger inductors limit the change in current a bit, probably also helping reduce the heat in the circuit.
I set up a webpage about the transitor set up as well at 2n3904.net
Post a Comment