Hi .. Good afternoon to every one.
I want to design a AC constant current source with the following parameters
1mA current
50KHz frequency
Load variable upto 100 kilo ohms.
Please help me which circuit is helpfull for me

 

Welcome to AAC.
Is 1mA an RMS or peak value?
What tolerance?
Is a square-wave output satisfactory or must it be sinusoidal?
If sinusoidal, what harmonic distortion level can be tolerated?
What will power this (since 1mA through 100k implies at least 100V somewhere)?
What is the lower limit on the load resistance?

 

Hey thanks for reply
Current is 1mA peak value
with +/_ 5% tolerance and the output should be sinusoidal
And lower resistance is 5k

 

Hi,

What does the voltage compliance have to be on this?

 

What devices will this 1mA drive?
Is this for some medical/health treatment/monitoring gizmo? If so, safety features would be necessary.

 

Sounds like a classic requirement for impedance measurement such as in EIT (electrical impedance tomography).
Google Howland constant current source.

http://www.edn.com/design/analog/4430167/Op-Amp-Current-Sources--The-Howland-Current-Pump

 

For example here is a source of constant current in DC:

This it offers constant current with a value given by the resistance R2.

You make that R2 resistance to be something dynamic, to say a tranzistior.
This second transistor will be drived by sinusoidal signal.

It's just an idea, not negative current value.

 

Hello,

Here is a discussion about the use of an opamp as current source:
https://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/f/18/t/278637

Bertus

 

I tested the following circuit in simulation and it looks like it works:
R1 is the load.( a constant maximum value sinusoidal current will pass through R1, whatever the value of R1 will be. Of course within certain limits)
R2 should be a resistor with resistance as small as possible which is used to read current (few ohms or milli ohms).

It works as long as the output signal remains sinusoidal.
It works as a current source (alternating signal).
It is actually negative feedback operational amplifier, modified to respond in current, not in voltage.


1mA at 100Kohm it means 100V half the of minimum supply voltage.This is strange.

I want to design a AC constant current source with the following parameters
1mA current
50KHz frequency
Load variable upto 100 kilo ohms.

 

I don't think you can buy an op-amp with a power supply range of +/- 100 volts. You're going to have to put a driver circuit on the output of that amp in post #9 and the slew rate is 31.4 v/usec. Again, not an off-the-shelf product. This looks like a job for a high frequency transformer, or an imaginary solution to a problem that should be solved in a different way.

 

OPA454 can run on ±50V.

 

Burr Brown used to have some HV op-amps used for piezoelectric devices.

 

High Voltage Power Operational Amplifiers
Apex introduces PA34x series high voltage monolithic MOSFET OP AMPs

+/- 350v available

 

I want to design a AC constant current source with the following parameters

take one of those voltage controlled CCS and apply an ac signal to the control voltage.

 

Because this application is a constant frequency and sinusoidal, can this be done with a L-C filter circuit? Or at least approximated.
I am thinking of a series resonant circuit where the voltage at the junction of the capacitor and inductor is a very high impedance at resonance and generates a very high voltage when not loaded.
Basically, a constant current source has a very high output impedance (ideally infinite).

I am thinking of a fairly low voltage but reasonably low impedance source (a small integrated power amplifier, say) driving this series resonant circuit, perhaps with some kind of feedback to regulate the drive amplitude.

 

Thanks every one for your reply

 

For example here is a source of constant current in DC:

This it offers constant current with a value given by the resistance R2.

You make that R2 resistance to be something dynamic, to say a tranzistior.
This second transistor will be drived by sinusoidal signal.

It's just an idea, not negative current value.

Put it inside a bridge to make it AC.