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Author Topic: How Can I make my own regulated and filtered 9VDC Power Supply?  (Read 8745 times)


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How Can I make my own regulated and filtered 9VDC Power Supply?
« on: September 12, 2008, 09:09:09 PM »

I was given a large digital LED wall clock and the place that gave it to me was getting new branded clocks with their logo. to put it short they cut off the AC adapter and lost it so I don't know the volt/Amp requirements (I think it's 9VDC at around 300-450MA) I used a mufti voltage wall wort (Available Voltages are 1.5 - 3.0 - 4.5 - 6.0 - 7.5 - 9.0 - 12VDC)to find this out at anything less then 9V it will not light up any more any the LEDS start to get hot, the LEDS get warm at 9VDC but not hot) I want a filtered supply to totally isolate from the 120VAC line (If possible) because with the adapter I'm using now I get a 60HZ flicker on the clock which is annoying, A friend gave me an old Dell Pentium 100 MHZ and as I was pulling out the cards I noticed the sound card has a L7809CV regulator which I can probably solderer and use so I looked it up and it appears to be a positive 9VDC regulator
Is there any way to use this to create a Regulated and filtered 9VDC power supply for my giant clock?

Here are some parts I already have in my electronics bin
Proto board
A variety of resistors
0.01UF Cap
22 Gauge hookup wire
plenty of extra wall worts and DC jacks (Is feeding the circuit 14 VDC OK, All of my good 12VDC ones are in permanent use)
The regulator IC itself
Soldering Iron

Any other parts I need to buy to complete the unknown circuit?

Thanks and sorry for the super long post :D
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Re: How Can I make my own regulated and filtered 9VDC Power Supply?
« Reply #1 on: September 13, 2008, 05:00:29 PM »

This is a pretty good beginner project actually.

Bill of materials:
1A fuse and holder
1 12V transformer, 500mA or higher (they get big in a hurry above 500mA)
1 bridge rectifier
1 1000uF* electrolytic cap, 16V or higher
1 7809 voltage regulator. (TO220) and heatsink

More or less, you hook these components up in the order they are listed.
1) connect the mains supply to the primary windings of the xformer. Put a 1A fuse in series there, safety is key.
2) the secondary side of the xformer connects to the AC terminals on your bridge rectifier (usually labeled ~). Polarity is not significant.
3) the electrolytic cap connects across the DC terminals of the bridge rectifier (usually labeled + and -). Polarity must be observed.
4) the same output terminals of the rectifier get connected to Vin and gnd of the 7809.
5) your regulated 9VDC out is available between Vout and gnd on the regulator.

Hardest part is shopping for all the components.

*In all likelihood, anything down to 220uf or so will work fine--I don't feel like doing all the calculations. Just know that as the size of this cap goes up, the amount of ripple in the input to the regulator will go down. The only tradeoff is that your inrush current goes up at start, so making it absurdly large is a bad idea, since you will run a lot of current through those transformer windings. Pick a cap in this range out of your junk drawer or use a couple in parallel to get to a value between 220-1000uF.

Here's some pics of a 5V one I built ages ago:

I swear there was a fuse in the thing. I think it got scavenged when I removed the lighted power switch (you can see the hole in the project box)
« Last Edit: September 13, 2008, 05:07:08 PM by linear »
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