You can get a voltmeter that requires a lot less than 0.1A for power.I wanted to add a digital voltmeter to a remote end of a 90v DC supply.
No, and the image is too small for comfortable reading, and I can't find a datasheet or part for A78HV.Can you understand how this switching regulator (from a Signetics applications manual) works?
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You can use LM7812. D1 drops the voltage to the regulator to an acceptable level.I found some on ebay, but nothing on Digikey.
You can also put a resistor in series with the collector of the transistor to shift the power dissipation from your active transistor to a passive component that is less picky about operating hot. It can also provide current limiting.At such high input voltage, a series of Zener diode is not easy to get optimal.
With 90 Volt Input Voltage and A 75 Volt, 5% Zener, the 7812 could get an input voltage between 11 Volt and almost 19 Volt.
If there is to be linear regulation, I would suggest re-arranging the circuit to a series controller as the pre-regulator:
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Z1 can be either a 16 or 18 volt type.
Also, take a look at @crutschow thoughts about power and voltage.
by Jake Hertz
by Jake Hertz
by Aaron Carman
by Jake Hertz