# 12v to 5v

Discussion in 'General Electronics Discussion' started by spike47, Oct 18, 2015.

1. ### spike47

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0
Aug 11, 2009
Hi

I am making a simple voltage regulator using a TS7805 , as per the diagram attached , to light up some led's in a PC Gaming machine I am building , can I fit another spec of capacitor instead of the ones shown :

1x TS7805 5 volt regulator
2x 1uf capacitor
1x power plug (or other connector)
1x 220 ohm resistor
1x Blue LED (I used a diffused one)

I have plenty 16v 22μf capacitors ! , I have seen simular voltage reducers using a TS7805 and using different spec capacitors .

question : how do you work out in that simple circuet what size capacitors to use .

cheers

spike

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Sep 5, 2009
3. ### Colin Mitchell

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Aug 31, 2014
The minimum is 1,000u per amp.

4. ### dorke

2,342
665
Jun 20, 2015
spike,
If all you need is TO light a LED(s) you don't need to step-down the voltage!
Connect the LED directly to 12V with a series resistor(just like you do with 5v).
The resistor value will be different that is all.

For the LED you used above with 220 Ohm Calculate R for 12V:

R=220+7000/i ; i=LED current in mA

for 5ma ---> R=1.6k
for 10ma ---> R=910
for 20ma ---> R=560

5. ### spike47

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Aug 11, 2009
Hi davenn

12 v feed is from the PC's power supply , as per my first post ! .

6. ### spike47

11
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Aug 11, 2009
Hi dorke

the LED in the pic is only to show power is there .

7. ### spike47

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Aug 11, 2009
Hi Colin

I have about 12 led's to light inside the PC , I have no idea what there load is to work out what Capacitors I would use , I think I will go for a resister instead of the TS7805 , i was only going that route because I have a spare TS7805 .

spike

8. ### spike47

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Aug 11, 2009
Hi dorke

I have no idea what amperage the led's draw ! .

9. ### BobK

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Jan 5, 2010
Then you have little hope of driving them correctly.

Using the 12V power is actually more efficient than reducing it to 5V because you can put several LEDs in series and reduce the total current you draw.

You need to determine the forward voltage and current that the LEDs are designed to operate at.

Bob

10. ### davennModerator

13,671
1,892
Sep 5, 2009
that was very unclear as the power source
My answer could have been very different

Colin's comment ONLY applies if you are supplying from an unregulated source

if it is indeed a reasonably standard PC supply ??
then his comments are spot on use the 12V rail as he said, or if you want to, just use the existing 5V rail
there no need to have another 5V reg line

If they are standard 5mm LED's then around 20 -30mA,

Dave

11. ### dorke

2,342
665
Jun 20, 2015
Well you can easily measure it .
Connect like you intended ( 5v, led,resistor).
use a resistor =1k potentiometer in series with 100 ohm.
Get the correct luminescence you need from the led
-important start with the pot. at max value and lower the resistance!

VF==> measure the voltage on the led.
IF ==> measure the voltage on the 100 ohm and calculate the current through it.

Last edited by a moderator: Oct 18, 2015
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