2N3772 equivalent in TO-218 package

Discussion in 'The Projects Forum' started by recklessrog, Sep 17, 2015.

  1. recklessrog

    Thread Starter Member

    May 23, 2013
    Hi, I'm building another variable power supply to replace one I built ten years ago which is very similar to the one described by Tony Van Roon (bench top power supply 0-6/1-30 0-1/1-10amp) using the LM723 and 2n3772 series pass transistors.
    My original is very large and heavy, and I don't really need 10amps. Looking through my over 50 years worth of "useful" acquired junk, I have a lovely 42v rms toroidal mains TX and a very nice super efficient heat sink (from a scrap plasma tv) The whole lot will fit in a redundant midi desktop computer case so it will end up much neater than the original.
    My problem is that the heatsink is designed for TO218 style or similar power transistors and it is not possible to fit TO-3 type devices. I don't want to use TIP3055's as they have a nasty habit of going s/c due to secondary breakdown. There is room for four transistors which will be adequate to supply 5 amps at any o/p voltage without too much stress.
    What I am looking for is a TO-218 style transistor with good resistance to secondary breakdown that can come somewhere close to the original 2N3772. I have trolled through miles of data and there are many that seem suitable, What I'm hoping is that someone here has had a similar problem and found a suitable device that has proved to be reliable. Any suggestions will be appreciated.

    One thing I learned when I built my original, is that if the output is connected to equipment that has a large value capacitor, then if the voltage control is lowered faster than the capacitor discharges, then the E/B junctions can be over stressed and fail. I put a 1N1004 anode to emitter, cathode to base, between the E/B junction of each series pass transistor, also another, reverse biased from the junction of the emitter resistors to the collector junction. after doing this, in ten years, despite the sometimes awful abuse I put it through, I never had a single failure of any component.