Hey guys I'm designing my own guitar pedal power supply. And it needs to have 8x 9v outputs and one 15v output. The 15v output needs to have 400-500mA and the 9v outputs need to have around 6-800mA capability.
Anyway, I got lm7815 and lm7809 regulators. A 2x12v transformer with 2A capability. I was thinking of using 1n54xx diodes for the rectifier. Now first off I was going to take 24v out of the transformer and use it to power the regulators. After some research I noticed that these 24v aren't exactly 24v anymore after they've gone through the rectifier. More like 32v with regard to the 2v-ish drop of the rectifier. I didn't realize this when I bought the transformer but this high voltage is going to make the lm7809 really hot and it will probably loose current. So a friend suggested that I use the transformer in parallel, ergo 12vAC. After the rectifier that would be around 16,3vdc which is totally fine for the lm7809 but not the lm7815.
Now the datasheets claim that the lm7809 needs at least 11.5v to be able to provide steady 9 volts. and the 7815 needs 17.5 volts.
I'm not so good at reading and understanding the data sheets but as I understood it, it generates 5° celcius for each watt plus the room temperature. So if I were to use the 32v I am thinking if the formula would be something like this. (for the lm7809) 32v(voltage it gets)-11.5v(voltage it needs)= 20.5v(unused) 20.5v*1amp=20.5 watts and therefore
20.5w * 5°celcius= 102.5° plus the room temperature, am I understanding this correctly? If so it's a huuge heat generation.
Anyways
So here are a few ideas to solve this matter:
Using 24vac (around 32vdc) and using something like a voltage divider or a zener diode to drop the voltage down to say, around 18 volts. But I'm thinking, will this generate enormous heat over the two resistors or the a 18v zener diode?
Another idea: Return the 2x12v transformer and get a 2x9v transformer and use 18 volts ac( around 23v Dc) which will still be a bit hot for the lm7809. Or even using a 2x7.5v transformer ergo 15v Ac(around 19v Dc) would that be to hot for the lm7809? It is perfect for the 7815.
Yet another idea: how about those experiment transformers that give 6, 9, 12, 15, 18, 24 volts and then take the zero tap and 12v through one rectifier for the 7809 channel and the zero tap and 15v through another diode bridge. Therefore both channels are using the same ground and hopefully eliminate ground loop problems I guess. Or do those transformers just don't work like that. I'm also thinking if those transformers have isolated taps or is it maybe just the same wire making a tap and continuing to the next tap.
What do you guys think?
Anyway, I got lm7815 and lm7809 regulators. A 2x12v transformer with 2A capability. I was thinking of using 1n54xx diodes for the rectifier. Now first off I was going to take 24v out of the transformer and use it to power the regulators. After some research I noticed that these 24v aren't exactly 24v anymore after they've gone through the rectifier. More like 32v with regard to the 2v-ish drop of the rectifier. I didn't realize this when I bought the transformer but this high voltage is going to make the lm7809 really hot and it will probably loose current. So a friend suggested that I use the transformer in parallel, ergo 12vAC. After the rectifier that would be around 16,3vdc which is totally fine for the lm7809 but not the lm7815.
Now the datasheets claim that the lm7809 needs at least 11.5v to be able to provide steady 9 volts. and the 7815 needs 17.5 volts.
I'm not so good at reading and understanding the data sheets but as I understood it, it generates 5° celcius for each watt plus the room temperature. So if I were to use the 32v I am thinking if the formula would be something like this. (for the lm7809) 32v(voltage it gets)-11.5v(voltage it needs)= 20.5v(unused) 20.5v*1amp=20.5 watts and therefore
20.5w * 5°celcius= 102.5° plus the room temperature, am I understanding this correctly? If so it's a huuge heat generation.
Anyways
So here are a few ideas to solve this matter:
Using 24vac (around 32vdc) and using something like a voltage divider or a zener diode to drop the voltage down to say, around 18 volts. But I'm thinking, will this generate enormous heat over the two resistors or the a 18v zener diode?
Another idea: Return the 2x12v transformer and get a 2x9v transformer and use 18 volts ac( around 23v Dc) which will still be a bit hot for the lm7809. Or even using a 2x7.5v transformer ergo 15v Ac(around 19v Dc) would that be to hot for the lm7809? It is perfect for the 7815.
Yet another idea: how about those experiment transformers that give 6, 9, 12, 15, 18, 24 volts and then take the zero tap and 12v through one rectifier for the 7809 channel and the zero tap and 15v through another diode bridge. Therefore both channels are using the same ground and hopefully eliminate ground loop problems I guess. Or do those transformers just don't work like that. I'm also thinking if those transformers have isolated taps or is it maybe just the same wire making a tap and continuing to the next tap.
What do you guys think?