Originally posted by John_Bedini
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The way I understand this, is that the capacitor charges up to the diode's bias voltage (about 0.6V) when switching the power tor on. Then, when you want to switch it off, you intend to push the base of the power tor down to -0.6V in order to quickly switch it off, right?
However, if there is no pull-down resistor somewhere, who's pulling the base of the power tor down?
This reminds me of a problem we found some 10 years ago in PLC backplanes I was developing units for. There was one reset signal on that backplane that had an open collector driver without a pull-up resistor. In practice, this was no problem. It worked just fine, ..., most of the time.
However, it was a hell of a problem once you started ESD testing, i.e. firing sparks onto the external connectors of the modules you built for the backplane in order to simulate static discharging. Then, this signal would be raised by the ESD, causing your modules to reset when they were not supposed to. The obvious solution would be to add a pull-up resistor to the backplanes, where they should be, but these things had been in production for several years. So, that was not an option. So, we eventually solved the problem by adding metal shields inside the modules.
So, it appears to me that without a pull-down resistor, the circuit might be pretty sensitive to disturbances....
Another point is that with the introduction of a diode in your base line, you create an additional voltage drop of 0.6V, which will also appear over your power tor, resulting in unneccesary power loss and unneccessary heating of your power tor.
However, with this, I'm not taking any reverse potentials into account here, so I might be totally wrong for at least some of the switches.... OTOH, these might be some points that can be taken into consideration at some point.
Anyway, I'm definately going to order some stuff to experiment myself. I'm thinking about using 9V 150 mAH NiMh batteries, and TIP41 transistors. These are cheap and then I should at least be able to make a proof of concept lighting a small light-bulb or something.
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