In one of my first days in electronics training they told us to do our testing with one hand in a pocket. One of the first things I learned is that theory sounds a lot better then actual practice. The problem with a auto-transformer is that you aren't isolated from ground, meaning anytime you touch any part of the circuit, you complete the path to ground. That's always a bad thing. Now, having said that, and if you are very careful not to switch the hot and neutral wires coming in to the transformer, you should be ok. Use a three prong plug.
I don't know if you are using a full wave or half wave bridge rectifier, or what the current draw is that you want, or even what voltage you want. However the capacitor is indeed storing the charge. The current can't go backwards against the diodes and has nowhere else to go, except as dissipating as leakage current thru the capacitor's insulation. That's what a bleeder resistor does, act like a controlled short to ground.
Without really knowing what voltage and current you are after I hesitate to go further, but there are several ways to go about it. The problem with the 1 K Ω 8 watt resistor is that it is there all the time, causing heat and sucking energy. Again, I don't know how fancy you want to get but you could put a relay in circuit so that when it's energized, it puts power out to the circuit and when it's de-enerzied, it shorts to ground thru the resistor. Or you could go with a higher resistance, which would take longer to discharge, but a whole lot easier to implement.
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Bill K.  |