Help me in This Circuit

Thread Starter

khanz

Joined Mar 24, 2008
21
Hi All,
I am posting my circuit here on this website for some help. I am not using op amp for voltage addition. Please help me in adding these two voltages. The maximum output voltage is 10V.
If you have any question after looking at the circuit please post it.

Thanks
 

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SgtWookie

Joined Jul 17, 2007
22,230
As you have drawn the circuit, the output measured from the lone 10k resistor to ground will be 12v.

That is because there is no ground reference supplied to the lower end of the two 10k potentiometers.

Once you connect the ground to the lower end of the two 10k pots, you will get the AVERAGE of the two output voltages.

Resistors are current limiters. If you use pairs of resistors in series, they are voltage dividers. You are summing the two voltages, but then dividing them by two using resistors.

You will need to use an opamp to multiply by two to get the sum.
 

Thread Starter

khanz

Joined Mar 24, 2008
21
Thanks for the suggestions. But the problem is this that I don't have any plus and minus voltages, and also I am not fully aware of op-amp funcationality. I have just studied it, so please if you help in building the circuit without using op-amp, it would be much appreciated.

Thanks once again
 

thingmaker3

Joined May 16, 2005
5,083
For signal processing, a single supply op-amp adder would indeed be a better solution. Be sure the op-amp runs on a voltage greater than the expected sum of the inputs, since most op-amps do not run rail-to-rail.

If you are dead-set against op amps in this application, perhaps this will work for you:
rider.jpg
I've used a similar circuit to drive high-side MOSFETS. (I prefer charge pumps, though.)
 

SgtWookie

Joined Jul 17, 2007
22,230
Thingmaker, that would definitely work - however, there would be quite a loss of power in the resistors. If there were any load on the output, regulation would be nonexistant.

Seems that a pair of LM117/LM317s would be a more "clean" solution; it would also keep the supply impedance the same as that of the LM117/LM317. Make the ADJ ground reference for the upper LM117/LM317 the output of the lower LM317.

Of course, bypass caps are still needed on the output of both Vregs to keep them well-regulated.

But, we don't know what Khanzs' application is.
 
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