Power Digital Potentiometer

[djnik1362]

hi

I need a digital potentiometer that can operate at 28V 400Hz.
There is a AM signal which fed to this potentiometer.
I need a power digital potentiometer for handling this signal .

Thanks for your support.

 

[FvM]

As you said power rather than high voltage, I guess you want to supply a load with a variable AC voltage.
Most likely, it doesn't work with a potentiometer (neither "analog" nor "digital"). But you can caculate, how the circuit
performs for specific potentiometer resistance values and see, if it's feasible. Generally you should think about a servo
motor operated transformer (or power resistor, if a potentiometer does, though).

 

[djnik1362]

As you said power rather than high voltage, I guess you want to supply a load with a variable AC voltage.
Most likely, it doesn't work with a potentiometer (neither "analog" nor "digital"). But you can caculate, how the circuit
performs for specific potentiometer resistance values and see, if it's feasible. Generally you should think about a servo
motor operated transformer (or power resistor, if a potentiometer does, though).

My problem is :

I want to attenuate a signal with this specification :

10V AM signal + 20 VDC

Do you have any idea what type of digital potentiometers can i use...?

thanks for your response.

 

[FvM]

Usual digital potentiometers have e.g. +/- 5V voltage range. You can attenuate the input signal,
send it to the potentiometer and amplify it to the original level.

 

[djnik1362]

Usual digital potentiometers have e.g. +/- 5V voltage range. You can attenuate the input signal,
send it to the potentiometer and amplify it to the original level.

This signal must be real-time and we don't any right to add
noise on it. We must fed this signal directly to potentiometer and
attenuate this signal with calculated parameters.

I think Analog Device potentiometers with +30V range can be used but
i am not sure.

Is there any idea...?

 

[FvM]

I think Analog Device potentiometers with +30V range can be used but
i am not sure.
Is there any idea...?

You didn't give a clear signal specification, how can we know? If the signal fit's the device's voltage range, hopefully yes.
But the minimum potentiometer resistance is 10 or 20k, maximum continuous current 5 mA, so the output is not
a power signal, just high voltage.

 

[djnik1362]

hi
As i mentioned the input signal is a 20V DC plus an AM sine with 10V amp and
400 HZ frequency.

So our input signal have a maximum amp at 30V and minimum at 10V.

In circuit i have +15V and -15V so i must change input level
without any distortion .

I think using an op-amp adder circuit seems to be good but i am not sure.

By adder i add input signal with -15V so my input signal level become in range
of my digital potentiometer (AD5291)

If it works please help me to choosing proper op-amp .

If there is better circuit please tell me.

Thanks for your support.

Added after 4 minutes:

I think Analog Device potentiometers with +30V range can be used but
i am not sure.
Is there any idea...?

You didn't give a clear signal specification, how can we know? If the signal fit's the device's voltage range, hopefully yes.
But the minimum potentiometer resistance is 10 or 20k, maximum continuous current 5 mA, so the output is not
a power signal, just high voltage.

If i reduce input signal by adding -15V to it then max of input signal become +15V.
Then it seems there is no current problem...

Am i true...?

 

[FvM]

It can basically work. I would try to use standard supply voltages (+/- 15 V) as far as possible. The "adder" circuit must be able to process the voltage signal range, an inverting adder is the most simple way to achieve it. A shift of 15 V still causes saturation of the amplifier, even with rail-to-rail OP.

If you intend to restore the original signal range at the output, you'll need non-standard supply voltages for the output amplifier. But I didn't hear a specification yet.

 

[djnik1362]

It can basically work. I would try to use standard supply voltages (+/- 15 V) as far as possible. The "adder" circuit must be able to process the voltage signal range, an inverting adder is the most simple way to achieve it. A shift of 15 V still causes saturation of the amplifier, 20 V would be better. A DC shift also implies a variation of DC bias depending on the potentiometer ratio.

If you intend to restore the original signal range at the output, you'll need non-standard supply voltages for the output amplifier. But I didn't hear a specification yet.

How can i shift down input signal to 20V ?
I have only +15V and -15V...

 

[FvM]

Sorry, I edited my previous post in betweeen. I guess you shoudln't shift by 20V, because it won't achieve the intended potentiometer effect.

It's most likely better to apply a small attenuation in the adder to allow operation with +/- 15 V supply. It can be compensated in the output amplifier.

Otherwise you would need higher supply voltages.