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  • Author Author: Robert Peter Oakes
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The Modular Bench Power Supply ++ - Power Output Stages

Robert Peter Oakes

In previous videos we have looked at the different modules that make up a typical bench power supply, in this post we will continue that trend and look at the Power Stage of typical power supply, evaluating different components (NPN, PNP, N Chan and P Chan MOSFETs), how there controlled and a bit of practical how-to

 

This is a link back to the main PSU blog : http://www.element14.com/community/groups/test-and-measurement/blog/2014/09/15/the-modular-bench-power-system-the-essential-diy-build-for-every-ee-student-and-old-timer-alike

 

Sorry its long (I did shorten it... honest image ) and is the first of two, this one covers a basic intro to the devices and detail of the NPN and PNP BJTs

 

and here is the next video covering the MOSFETS

  • in reply to jw0752

    so the + input to the op amp should swing from 0 - 5V and based on (4.7+1)/1 for gain should give a swing on the emitter of 0 - 28.5 volts or the limit of the supply rail less about 2V ish which matches your 23V seen on the emitter, but you should be able to set an output below 4V, where are you measuring the control voltage, it should always be above the emitter voltage by a few volts atleast

     

    and good work by the way

     

    Peter

  • Hi Peter, The ISL28218 40 Volt R to R Op Amps came in and so I tested one out using your designs. Using a REF02 I varied the input to non-inverting input of the ISL28218. I found that with a 25 volt supply I was able to control the voltage on the Emitter of the TIP102 Darlington. The control voltage began at 0.7 volts and went (with effect) as high as 4 volts, while the voltage at the TIP102 Emitter went from 4.6 volts all the way to 23 volts. I varied the load on the TIP 102 from 25 mA to 300 mA without a noticeable drop in voltage. My ratio of output voltage to control voltage matched almost exactly to the ratio of the resistances in my feedback voltage divider. Fun stuff.

     

    John

     

    Here is a schematic of the circuit I tested:

     

    image

  • in reply to Robert Peter Oakes

    Thanks for checking it over. Newark did not have them in stock but I found a supplier that does stock them and you are right the duals are the way to go.

    John

  • in reply to jw0752

    On quick glance it looks like a great choice, 40V, Rail to rail, target use includes power supply control

     

    Might be worth getting the dual version as we will need 2 op-amps at least in the circuit (One for Current and One for Volts), there will be more as we add more functionality and this will probably save a little on the cost,

     

    Great find, I may well order a few for myself too

  • Hi Peter, I did some digging last night and I came up with a candidate for an op amp to use to experiment with the ideas that you have been teaching. It is the Intersil ISL28218. Here is the data sheet:  http://www.newark.com/intersil/isl28218fbz-t7a/ic-op-amp/dp/99R4767?ost=99R4767.  If you don't see any problems with it covering the needs of this project let me know and I will get two or three for my experimentation. I did some work already using the 741 but since it isn't rail to rail it required a bias voltage and was difficult to integrate with a MOSFET and the REF02 that you talked about earlier.

    Thanks John