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Current Limit Resistor Network

Current limiting resistor network that works quite well.

If the value of each resistor is .1 ohms at 10 watts, then this resistor network is capable of a current limit value of approximately 20 to 25 amps. Each .1 ohm resistor is an approximate current limit value of 6.5 amps.

The placement of this network is nearest to the output binding post as possible. It is in series with the positive terminal post. On each side of the resistor network we connect wires from the regulator circuit.

The current limit pin, of the 723 voltage regulator, connects on the positive power supply side of the resistor network. The current sense pin, of the 723 voltage regulator connects on the positive output side nearest to the positive binding post as possible.

Some builders put a fuse in the place of the resistor network. But I have found that we can not push the supply right up to it's maximum limits using a fuse, and hold good regulation. There is too much fluctuation in the regulation. Current limiting by way of voltage fold back occurs.

The fuse is a resistor of a sort, designed to separate or blow, when a pre-determined amount of current is drawn through it. Therefore, the fuse is changing value with the more or less current that is drawn through it. This effects the regulation dramatically. The resistor network does not seem to change value.

The ideal way to fuse the output, is to have a fuse in series with the positive lead of the equipment that is being powered by the power supply, on the outside. The author, personally, does not fuse the output of the power supply. Just in series of the positive lead to the equipment. This can be a controversial subject, but it is entirely up to the builder as to what is proper for any given application.

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