Help with Voltage Regulation - Electronic Circuits Projects Diagrams Free

Pete Olsen · 8th December 2008, 07:25 PM

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 · 8th December 2008, 07:38 PM

Quote:

Originally Posted by 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?

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 · 8th December 2008, 09:15 PM

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

Pete Olsen · 9th December 2008, 02:39 AM

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

Hero999 · 9th December 2008, 01:10 PM

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.

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8th December 2008, 07:25 PM	#1
Pete Olsen	Help with Voltage Regulation I know how to regulate 5 and 12 volt circuits, but how would I regulate 7.8 vdc supplied by a 12 vdc source?

8th December 2008, 09:15 PM	#3
Hero999	Use an LM7808 which gives 8V and is close enough to 7.8V for it to work. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

9th December 2008, 02:39 AM	#4
Pete Olsen	7808 Regulator That sounds like a good start, thanks. Also the current load is 1.7 amps.

9th December 2008, 01:10 PM	#5
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. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.