In the publications that describe several variable DC power supply (regulated, variable or fixed voltage, for bench or hobby type stuff) are also described several overvoltage protection schemes. Some of them use an MC3423P to fire an SCR to blow a fuse. The nice thing about this IC is that it fires at about 2.5 volts so to use it a voltage divider is needed - in that voltage divider is a potentiometer that allows adjustment of the trip setting. The publications recommend the use to protect against pass transistor failure - so it doesnt' ruin whatever you have connected to the power supply. I might use it to set an upper limit if I were experimenting with a variable supply - just in case I screw up and go too far.

The MC34223P has been around a while. Any better ICs or similar adjustable schemes available??

Thanks.

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stevez

 

If you are looking to protect a series element by triggering an scr......why not just use a zener diode?

Connect the cathode of said zener to the output rail, anode to gate of scr,the scr is connected anode cathode between the supply rails before the transistor...zener voltage determines when the scr triggers......so for a 5v supply use a 5.6/6.2 zener......there are other ideas to consider if this dont suit 8)

 

Thanks for the idea. A friend of mine made that suggestion too and offered that it was simpler. I like simple but if I want to put something in place that's adjustable then it would seem that the 3423 is one choice. I suspect that there are other ways to implement something variable with a zener and transistors but the self contained IC is easy. The 3423 is cheap and still available. I was wondering if there wasn't a newer IC that did the same thing with possibly more features.

I have a lot of ham radio publications and while some projects use components that are up-to-date many other projects require the use of components that are obsolete or nearly so.

Thanks and I'd welcome more thoughts.

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stevez

 

Thing is, the ic still needs an adjustment to monitor a variable supply....so, why not use a comparator such as a 311, again its got an open collector output that could be used to trigger an scr again......

I think that " how easy " you want to achieve this, needs to be looked at and then decide which way to go