Okay, my 7808 regulator has not yet arrived, and I need one, so I want to use this guide to make one out of a 7805. I get most of it, but could someone explain it as if you were talking to a retard? I wanna make sure I fully understand it. Also, could I get the resistors needed for this project at, say, RadioShack?
Thanks,
CTFan
Help turning a 7805 into a 7808
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- CronoTriggerfan
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I'm surprised that page doesn't even mention wattage for the resistors. You could try standard 1/4 W resistors, but don't be surprised if they die.
So, wire a 470 ohm resistor between the output and the ground pin (pin 3 & pin 2) and a 220 ohm resistor between the ground pin and ground (pin 2 & gnd). Just make sure you input ~ (7.2 - 5 + = 10.2V to make sure it works (not sure if it can go lower, just computing the drop off compared to the std. 7805)
So, wire a 470 ohm resistor between the output and the ground pin (pin 3 & pin 2) and a 220 ohm resistor between the ground pin and ground (pin 2 & gnd). Just make sure you input ~ (7.2 - 5 + = 10.2V to make sure it works (not sure if it can go lower, just computing the drop off compared to the std. 7805)
It doesn't matter, its like a lm317, very little current passes through the resistors. So 1/4 watt will work. And radioshack should have them.gannon wrote:I'm surprised that page doesn't even mention wattage for the resistors. You could try standard 1/4 W resistors, but don't be surprised if they die.
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EDIT: Go <a href="http://bicostp.portablesofdoom.org/Articles/8v7805/" target="_blank">here</a>, I wrote up a page describing this better than the post does (I hope).
Make it look like this:
<img src="http://img96.imageshack.us/img96/9816/8 ... tlepv3.gif">
(the round grey things are solder)
You should get 8 volts out of the contraption if you attach the lead for whatever needs 8 volts AFTER the end of the 470 ohm resistor on the regulator's regulated power output. Connect the regulator ground to the resistor, then connect the resistor's other lead to ground.
Of course, always check it with your multimeter before you use it on anything important! (Once you biuld a couple of these it will be pretty easy, and you can make them pretty small. My latest one is barely bigger than 2 7805s)
Make it look like this:
<img src="http://img96.imageshack.us/img96/9816/8 ... tlepv3.gif">
(the round grey things are solder)
You should get 8 volts out of the contraption if you attach the lead for whatever needs 8 volts AFTER the end of the 470 ohm resistor on the regulator's regulated power output. Connect the regulator ground to the resistor, then connect the resistor's other lead to ground.
Of course, always check it with your multimeter before you use it on anything important! (Once you biuld a couple of these it will be pretty easy, and you can make them pretty small. My latest one is barely bigger than 2 7805s)
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- CronoTriggerfan
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- CronoTriggerfan
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On my lm317 they are very cool. On the lm317 voltage calcutator, it says that very lttle power goes through them. I think that the higher the resistance of the resistor, the less power it uses.CronoTriggerfan wrote:Another question; I have all the parts, and I'm getting ready to modify my 7805. I've got a heatsink for the regulator body, but will the resistors put off any substantial amount of heat I need to dissipate? Thanks!
CTFan
So to answer your question, most likely no.