# Op-Amp circuit to supply constant power

• Engineering
• JeeebeZ
In summary, using two different circuits, one with a resistor in series and one without, it is possible to get 10mW out of the 100k ohm and 100ohm resistors.
JeeebeZ

see image

## The Attempt at a Solution

I can make 2 different circuits to solve this. However, Using just op amps and resistors I am not sure how to make a single circuit that could do this

I am not sure if that is intended, but if power just has to be the same for those two specific resistance values, there is an easy solution: Add a specific resistor in series, and find a pair (voltage, resistance) where both resistors get the same power.

I would consider an op amp circuit set up so that the op amp output voltage is Vo. Then I would run a resistor R from Vo to each of your loads, one at a time of course.

Given the 10 mW for each load, compute the voltage needed across each load.

You now have 2 equations and 2 unknowns: R and Vo. Solve for both.

(You will obviously need about 31.6V across the 100K resistor so figure on an op amp that can handle about 40V between its power supply pins.)

It is really easy to do with 2 difference circuits. But using one circuit I don't see how changing one resistor could allow it to get 10mW just on the one resistor that has been changed.

In order for the 100k ohm, it needs ~31V, while the 100 ohm only needs 1V.

JeeebeZ said:
It is really easy to do with 2 difference circuits. But using one circuit I don't see how changing one resistor could allow it to get 10mW just on the one resistor that has been changed.

In order for the 100k ohm, it needs ~31V, while the 100 ohm only needs 1V.

That's what the series resistor is there for! It puts ~ 31V across the 100K but only 1V across the 100 ohm.

Have you considered doing what I suggested?

h... and I got it to work.

https://www.circuitlab.com/circuit/283w8y/screenshot/1024x768/

JeeebeZ said:
h... and I got it to work.

https://www.circuitlab.com/circuit/283w8y/screenshot/1024x768/

Can't access the link. What did you come up with?

32.62 gain, 3162 R
That way you have 1V over the 100ohm = 10mW
and 32.62(100000/(3162+100000)=31.62V -> 31.62^2 / 100000 = 9.998mW

JeeebeZ said:
32.62 gain, 3162 R
That way you have 1V over the 100ohm = 10mW
and 32.62(100000/(3162+100000)=31.62V -> 31.62^2 / 100000 = 9.998mW

Superb! Congrats!

JeeebeZ said:
h... and I got it to work.

https://www.circuitlab.com/circuit/283w8y/screenshot/1024x768/

## 1. What is an Op-Amp circuit used for?

An Op-Amp (Operational Amplifier) circuit is a type of electronic circuit that is used to amplify an input signal to a higher output voltage. It is commonly used in audio and signal processing applications.

## 2. How does an Op-Amp circuit supply constant power?

An Op-Amp circuit can supply constant power by using feedback mechanisms to adjust the output voltage in response to changes in the input signal. This allows for a stable output despite variations in the input signal.

## 3. What are the advantages of using an Op-Amp circuit for constant power supply?

Some advantages of using an Op-Amp circuit for constant power supply include high precision, low noise, and the ability to amplify signals without significant distortion. It also allows for a compact and efficient design.

## 4. What are the key components of an Op-Amp circuit?

The key components of an Op-Amp circuit include the Op-Amp itself, resistors, capacitors, and power supply. Depending on the specific circuit design, other components such as diodes and transistors may also be used.

## 5. How can I design an Op-Amp circuit for constant power supply?

To design an Op-Amp circuit for constant power supply, you will need to understand the principles of feedback control and the specifications of your power supply and input signal. You can then use these to determine the appropriate values for the components in your circuit and simulate or test the circuit to ensure it meets your requirements.

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