I've been working on a simple FET/NPN constant current driver. It should use an NPN transistor, but instead, I have accidentally ordered and soldered in a PNP.
Please see attached image. The left circuit is how it should be. The right circuit is how it is on my board. Surprisingly it works and I only noticed when I went to reorder the components to build more!
I can't quite get my head around the theory. Does the PNP play a part in the circuit? Or is the circuit equivalent to it not being there?
If it's not playing a part, then I'm very surprised that the current flow through the LED (approx 2A instead of 700mA) didn't fry it!
Many thanks.
Please see attached image. The left circuit is how it should be. The right circuit is how it is on my board. Surprisingly it works and I only noticed when I went to reorder the components to build more!
I can't quite get my head around the theory. Does the PNP play a part in the circuit? Or is the circuit equivalent to it not being there?
If it's not playing a part, then I'm very surprised that the current flow through the LED (approx 2A instead of 700mA) didn't fry it!
Many thanks.
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