That's the method I would (and have) used and recommend. But it is possible to use a single LM317, you just need to refer it to the negative rail instead of the 0 V reference.The LM317 is for positive voltages only.
Do you actually need adjustment from -7V to +7V or could you use two supplies with one being a 0 to -7V supply and the other being a 0 to +7V supply instead?
If you really need -7V to +7V you could use an op amp driving a complementary transistor output stage powered from plus and minus unregulated voltages.
How much current do you need?Hi every one,
I want to design a new variable voltage supply(-7 to +7vollts ) using lm317. what is the relation between the input and output voltage. i want to use digipot. is there any other way to do this. please reply me
But how will that source +7V or sink -7V from one LM317 (which appears to be what the OP wants)?That's the method I would (and have) used and recommend. But it is possible to use a single LM317, you just need to refer it to the negative rail instead of the 0 V reference.
What if the OP had said that he had power rails of 0V and 20 V and wanted to use an LM317 to provide an output from +3 V to +17 V? Would that have cause any heartache?But how will that source +7V or sink -7V from one LM317 (which appears to be what the OP wants)?
Just a starting point ... adjustable +7V to - 7V, 1 Amp or so, as simple as possible.HI EVERY ONE,
I WANT TO DESIGN A NEW VARIABLE VOLTAGE SUPPLY(-7 TO +7VOLLTS ) USING LM317. WHAT IS THE RELATION BETWEEN THE INPUT AND OUTPUT VOLTAGE. I WANT TO USE DIGIPOT. IS THERE ANY OTHER WAY TO DO THIS. PLEASE REPLY ME
The 741 pin 4 and Q2's collector should go to the -10V, and the junction of the two transistor emitters and 741-pin 2 should not be connected to -10V.
Good comments.One problem you are going to have with that is that it is going to be hard, if not impossible, to get an output of +/- 7 V. To get 7 V at the output, you need about 8.4 V at the output of the opamp. But a 741 can generally only get to within 2 V of the rail and most are only spec'ed to get within 3 V, so you can't count on it getting anything above about 7 V, meaning that your output might not be able to go any higher than about 5.4 V.
One trick I came up with (though I now know that I was far from the first) was to put a resistor between the output of the opamp (I used the LM384 for my application) and the circuit output. This allowed the first bit of current to be sourced by the opamp and made the transition region between push and pull much gentler.
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