Re: MOSFET abuse
OK. I have news.
I guess my assumptions about heating were "a bit" off.
I decided to use the TO-220 heatsink I bought despite the technical difficulty of placing it on a solderless breadboard (where my circuit is currently housed). The results were amazing.
Without the sink the FET would burn my finger in about 30 seconds of use. With the sink I could barely feel a difference (compared to room temprature) after 2 and 3 minutes of pumping 4A. I even touched the drain tab to make sure the FET is not getting hot without transferring it to the sink - Nadda. This is so exciting!
The shamless LM338 regulator gets hot, but the FET seems to handle it with ease.
First, I'd like to thank you, VVV, for all your help - I have learned a lot.
I am still interested in the answers to the questions I posted, if you've got the time.
And I've 3 more:
1. The FET's source is connected to 28V, and the Gate receives pulses of 0V. By all accounts it should be dead, shouldn't it? (I have yet to place the Zener to protect it - I've read somewhere that doing so can amplify gate drive problems)
2. The original design was for 3A. Assuming that the FET and regulator can take 10A of load, what inductor-capacitor combination would be necessary to support that current?
3. The circuit doesn't start by itself. I have to "jumpstart it" manually with a touch of the negative lead to its Gate.
My suspicion: In the original circuit there is a 2.2K resistor connecting the circuit's input with the output which is missing from my circuit. Now the notes for the circuit do mention a 4.7K(???) resistor that allows it to start... Could it be the 2.2K resistor they were referring to? I did try a 10K in place of the 2.2K and it did nothing to help the circuit start to oscillate.