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High current IL317 PSU

Discussion in 'Power Electronics' started by remzy, Feb 5, 2017.

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  1. remzy


    Jun 12, 2015
    Hello! Im making a controller for a wiper motor which I've modified to be able to pull a little crate uphill. When the crate is loaded it weights about 30 KG. But the wiper motor moves it way too fast, so I'm trying to make a regulator for it with a IL317 and a 3 or 4 2N3055 power transistors. The circuit is not very efficient but right now it is the best I've got. Here is a picture of circuit I've found on internet but I have a couple of questions. I would be using a car battery to power it so the circuit in beginning with a transformer, capacitors and a bridge rectifier would not be used, imagine there are 2 wires there coming from a battery. Now, why are there resistors on the output( on the emmiters), and why are there not any resistors on the base connector of the transistors, i mean should there be a resistor there or am I wrong?

    Also Is this circuit correct? Is this diode really necessary? It can carry 6 A

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    Last edited: Feb 5, 2017
  2. duke37


    Jan 9, 2011
    The 220R resistor could be there to reduce dissipation in the LM317, it may not be necessary with a lower input voltage.

    The diode could be there to prevent any chance of reverse current through the bases of the transistors. All bases will be at the same voltage but the emitters could be different depending on the actual transistor and its temperature. Note that a higher temperature will give higher current which will give a higher current - pop.
    The emitter resistors will tend to even out the transistor currents.

    There should be a flywheel diode across the motor since it has a significant inductance which can generate high voltages if switched quickly.
  3. Audioguru


    Sep 24, 2016
    The output voltage from the emitter-follower transistors fed from the diode will have poor voltage regulation. With a light load the voltage will be high and with a heavy load the voltage will be low.

    The datasheet of an LM317 shows how to add one or more PNP transistors "around" the LM317 so that the output has excellent voltage regulation.
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