Thyristor powered pulse motor
Oops – BT169D, not DT169D Description – Having little idea of these before this evening, one was found on an old PC monitor circuit board. I thought it was a transistor, though the numbering looked odd. Looked it up and it’s a thyristor. The thing is about these, they are used as latches. A small current comes in at what would be a transistor Base and the unit switches on….and doesn’t stop conducting. I’ve found out that there is a mode where they shut down once the input current goes below a certain level and, presumably, that is what’s happening here, hundreds of times per second. I don’t really know 🙂 There is a 1K resistor on the middle triggering leg. The Negative supply comes in on leg 1 and leaves on leg 3. I would think it’s a bit like a MOSFET, but again have no real idea.