This shematic shuld give me +15 vdc, but that is to high for me i ant it down to +8Vdc
I guess bacaus i realy dont have a clue, that i gota change R5 and maybe R3 to fix the voltage down to 8V, hope someone can help me whit this one
Changing R3 or R5 won't do anything as the final ouput voltage is controlled by the pass transistor and op-amp. I suggest you contact the circuit originator.
richie00boy said:
I did trye to, but no luck.. i got it from ebay and the seller cant help mutch .
have been searching on www.diyzone.net and i cant find anything there
What do you want 8V for and at what current? It's a bit strange voltage and that circuit is a bit esoteric. There may be an easier way depending on the answer to the first question.
Planing to build my second diy cd transport, and i dont want to use an LM7808 as reg this time.. not sure about the current but less than 1A
The resisitve divider R10 / R11 after the pass transistor Q1 sets the output voltage. If You swap the resistors R10 and R11 this should give You about 7,5V out. With a standard resistor value of 390R for R10, Vout should be something slightly over 8V.
Another option might be to change the LM336-5.0 voltage reference for a LM336-2.5 type and to adjust the existing voltage divider only slightly (increase R10 to about 680R, leave R11 as it is).
Anyway, with the lower output voltage You should keep an eye on the temperature of Q1. Depending on the magnitude of the load current it can get hot (as now it has to burn about more than double the power with the lower output voltage). Good heatsinking helps here.
Just want to add that I`m not an expert in this things and maybe You should still wait for some other advice. Maybe I´ve overlooked something.
Another option might be to change the LM336-5.0 voltage reference for a LM336-2.5 type and to adjust the existing voltage divider only slightly (increase R10 to about 680R, leave R11 as it is).
Anyway, with the lower output voltage You should keep an eye on the temperature of Q1. Depending on the magnitude of the load current it can get hot (as now it has to burn about more than double the power with the lower output voltage). Good heatsinking helps here.
Just want to add that I`m not an expert in this things and maybe You should still wait for some other advice. Maybe I´ve overlooked something.
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