AZL Book: Electrical Math - 75V PS & HV Relay

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75V PS
Adjust as needed to produce different voltage outputs. I used this for a specific application and the documentation followed, but this can be changed to suit different purposes.

The little plots in red attempt to show what is happening with the input AC voltage at various stages of rectification.

This circuit uses a rectifier bridge (that’s the diamond-shaped part), then has a capacitor to smooth the output, and finally a divider/zener diode combination to change the voltage level. That last part is what you would modify to suit different applications.

HV Relay
For the same project, I needed to use optical isolation modules as relays in order to fit within the required envelope. The only thing special here is the part number, which is an isolator IC designed to work at higher voltage levels.

I believe this unit can handle a variety of inputs up to a specified threshold, but of course, you should always do your own DD when it comes to hardware selection. In general, optical isolator IC’s can be found for a wide range of voltage inputs.

One thing I think is most important for modifying this circuit is to remember that the excitation voltage going into your optical isolator IC is basically just triggering an LED that’s detected by a photocoupler. As such, remember to spec the external resistor (R) such that the internal LED will see a current of 15-25mA. Some people get more specific that that, or go as high as 30mA, but for the applications I’ve used these on, anything in the 15-25 range is good, and often times I determine the current based on what resistors I have lying around.

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