Help with Voltage Regulation

[Pete Olsen]

I know how to regulate 5 and 12 volt circuits, but how would I regulate 7.8 vdc supplied by a 12 vdc source?

 

[eng1]

I know how to regulate 5 and 12 volt circuits, but how would I regulate 7.8 vdc supplied by a 12 vdc source?

Take a look at the LM317. It's probably the most common solution. However, you didn't mention the current requirements of your application.

 

[Hero999]

Use an LM7808 which gives 8V and is close enough to 7.8V for it to work.

 

[Pete Olsen]

7808 Regulator

That sounds like a good start, thanks.
Also the current load is 1.7 amps.

 

[Hero999]

That's above the current rating of the regulator which is 1A.

You can build a current booster (see datasheet) or use a higher rated regulator.

What's the minimum load current?

If the current isn't expected to drop below 700mA another trick is to connect a power resistor across the regulator.

For example the voltage difference between the input and output is 4V so connecting a 4R resistor from the input to output will allow 1A around the regulator (which will only need to pass 700mA) and will work fine providing the current used by your device is >1A As soon as the current drops below 1A then the output voltage will rise which could destroy the appliance being powered.