Howland Current Pump

Thread Starter

anoopak

Joined Nov 24, 2023
36
Is it possible to build a Howland current pump circuit for 60mA current through a 400 Ohm load?. During a search in internet i haven't seen any circuits for such current values. Presently I am using LM317 based current source circuit.
 

joeyd999

Joined Jun 6, 2011
5,287
Why Howland?

You'd need an amp capable of > 60 mA at a higher voltage than your required compliance voltage (which you didn't state), and lots of extra dissipation in the resistor network.

I don't think I'd go this route. What are your real requirements, and why is the 317 not working for you?
 

Thread Starter

anoopak

Joined Nov 24, 2023
36
Why Howland?

You'd need an amp capable of > 60 mA at a higher voltage than your required compliance voltage (which you didn't state), and lots of extra dissipation in the resistor network.

I don't think I'd go this route. What are your real requirements, and why is the 317 not working for you?
Ok. The only limitation with LM317 based circuit is that it generates fixed current. I was not able to find high precision low TCR pots so I went for high precision low TCR fixed resistors which result in a fixed current source.
I wonder whether any VCCC can be made for such high current [Compliance voltage ~20V]. Precision required for current source is +-0.02mA for a 10 degree variation in ambient.
 

joeyd999

Joined Jun 6, 2011
5,287
You said nothing in your original post about voltage control.

Now you say nothing about the range of current you wish to control, nor any specifics about the voltage with which you wish to control the current, nor any other specifics about your "system", including supply voltage.

I cannot proceed to guess about what you want. Fill in all the details first.
 

tonyStewart

Joined May 8, 2012
131
Yes there are many ways to implement a CC of 60 mA to many amps and also limit Vmax no-load which is undefined.
60mA*400R= 24V

1. What CV supply do you have? 24? or more?
2. What stable Vref do you have?
3. Do have any OpAmps that can input down to 0V? or that can sink 60 mA?
4. What lower Vcc do you have?
5. Is the load linear?
 
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MisterBill2

Joined Jan 23, 2018
18,609
OK, so now there are a bunch of additional requirements. And we know that the load is not a constant 400.000 ohms. AND the supply voltage will need to be more than 24 volts to push 60.000 milli-amps thru 400 ohms.
This post is fairly similar to another one with the TS not being able to make it work with an inductance in series with the feedback loop..

So use an opamp to drive an emitter follower NPN transistor to deliver the current. Use a series resistor to monitor the current and provide feedback to the opamp inverting input. To avoid the need for an extremely expensive opamp, add a negative supply to the negative side of the load. Then the positive collector supply will only need to handle the compliance voltage variations.
 
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