KA7808 Voltage Regulator

[dj_ricoh]

hy guys

still learning, so stupid Q incoming

i got this crap *&&%&* cd player i wanna fix(won`t power) and PSu i think its ok.

i just try to find thinks that i don`t know and i wanna know how it works.

So, i put this regulator on the PSU and see how it outputs

everything its ok until i pass 8V, i get stuck on 7.85V



ups sry for the side pics

[tom66]

Re: KA7808 Voltage Regulator

That would appear to be working, it is an 8V device.

[dj_ricoh]

Re: KA7808 Voltage Regulator

ty tom

Back to testing crap caps

[tom66]

Re: KA7808 Voltage Regulator

Crap caps would be unexpected, and would probably only cause poor audio quality, digital skipping, etc. Does CD player have a track number display? If so, focus on the controller chip for that (probably surface mount, bottom of board) -- if you can find a datasheet for it, check the VDD etc supply voltages.

[mariushm]

Re: KA7808 Voltage Regulator

The 7808 is a linear regulator.
Like any linear regulator, it has a specific voltage drop. In the 78xx family this voltage drop is 2v, but it can be slightly less if there's nothing connected at the output or something that uses very little power (like a led for example).

So if you want to make sure it works fine and outputs 8v, you need to give an input voltage of at least 10v. If you give it less than 10v, it will output Vin - ~ 2v.

So you got 7.85v - this is a bit outside the tolerance, a bit far away from 8v. But, I don't know what input voltage you used. Ah nevermind, I see 15.4v on the power supply. It's a bit low to see 7.85v but I wouldn't consider the regulator bad right away.

[tom66]

Re: KA7808 Voltage Regulator

7.85V is within 2%, regulator like that is typically 5% tolerance.

[PeteS in CA]

Re: KA7808 Voltage Regulator

One convenient thing about the part numbering of uA78xx and uA79xx type parts (and LM340-xx and LM320-xx parts) is that the "xx" is the output voltage. How +8V and -8V came to be standard voltages (and for what), I don't know.