# Regulate voltage using op amp

Joined Sep 28, 2021
181

I am doing an Op Amp voltage regulation of voltage drop across load. As you can see from diagram, I have a fluctuating_Vin (0V to 50V) and I want the voltage drop at load (100 Ohms) to be the same (14V) at all times no matter whether input voltage is 20V or 30V or 50V?
Note: I believe that the voltage drop across load can be controlled by changing duty cycle inputed into the transistor. The change in the V_in of op-amp will change the duty cycle which in turns affect the voltage drop of load. How to relate both of this together in a circuit ?

Question: Is there a way to regulate the voltage drop at load?

Thank you for reading . Have a nice day

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#### Papabravo

Joined Feb 24, 2006
18,070
Transistor Q1 says "OUCH!"

#### MrSalts

Joined Apr 2, 2020
1,506
use your op amp to create a 140mA constant current source and feed that through your 100ohm load.

#### dl324

Joined Mar 30, 2015
14,305
I have a fluctuating_Vin (0V to 50V) and I want the voltage drop at load (100 Ohms) to be the same (14V) at all times
You can't get 140mA from a 0V input. What is a more realistic minimum input voltage?

#### crutschow

Joined Mar 14, 2008
29,466
I have a fluctuating_Vin (0V to 50V)
What is the frequency of the fluctuations?

#### Ian0

Joined Aug 7, 2020
4,823
If you want exactly 14V across the load at all times, then PWM isn't going to do it unless you also add an inductor, a diode and a capacitor. Then you will have built a buck regulator, and there are plenty of ICs that will do that for you, but you can probably achieve it with an op-amp and a 555 (or other methods) if you really want to.
If you simply want the same heating effect in the load as if it had 14V DC across it, then it can be achieved, but you will need more parts than an op-amp.