just because I happen to have one around: TDA2040 as voltage reg !

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Thunderchild

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I'm out of money and need to regulate voltage from 14 V to about 11, I've got a TDA2040 (22 w power op amp 4 A output), I might as well fix this up as a non inverting amp and use it to provide me output ....

ok i know its not the most logical solution except that I have it and will never use it an an amp. anything again my using it ?
 
how do you mean the voltage drop ? if i set up an op am supplied by 12 V and give it a gain on 2 and an input of 5 V it will give an output of 10 V ! its only for 1.6 A just out of reach a 78xx
 
Thunderchild said:
how do you mean the voltage drop ? if i set up an op am supplied by 12 V and give it a gain on 2 and an input of 5 V it will give an output of 10 V ! its only for 1.6 A just out of reach a 78xx
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I think it is just a little more complicated than that. A normal voltage regulator is sensing the output voltgage, comparing it to a reference and making an internal adjustment to compensate for a change in load.
Perhaps the attached circuit will work. The resistors chosen to give 5V to the inverting input. I would make sure the amp is on a heatsink.
 

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that was my intention
 
I have a scope but what sort of instability will there be ? the load will be constant i forgot to say so should not be a problem
 
Audio amp ICs have internal frequency compensation so that they do not oscillate. The TDA2040 is designed for a gain of 33. If you make the gain lower by adding more negative feedback then it will be unstable and will oscillate at a fairly high frequency.
as an audio amplifier it has a DC gain of 1 so use it as a voltage follower if your reference voltage has no AC ripple.

Look at the datasheet for the LM386 little power amplifier. It has a gain of 20 and the datasheet says that it becomes unstable if you reduce its gain below 9.
 
well I csn put a potential divider on the input to ajust the 78L05 output voltage to one suitable, not sure if I have the neccesary stable voltage at 10-11 volts, oh what the hec maybe I can use the BD237 transistor as a constant current generator using the 78l05 to supply the base resistor with a constant current
 
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