Constant Current Source Resources

[lemosam]

Hello everyone,

I would like recommendations on books or other resources that describe and give examples of constant current sources.

I have a load that varies from 100 ohm to 2M ohm. Is it possible to build a practical constant current source that would be relatively stable at delivering a constant 1 mA over such a wide resistance range?

Any information, books, or other resources would be greatly appreciated.

Thanks in advance

 

[gabi49]

Hi

I know a bit about current injection instruments for testing circuit breakers, but this is not suitable for you as you need 1 mA (small compared with their ratings I guess).

May I ask about the nature of this load?

Gabi

 

[cbarn24050]

Hi, that would be achievable if you dont need much bandwidth.

 

[pebe]

I doubt it can be done easily. You would need 2KV to get 1mA through 2Mohms.

 

[Kido]

you could use something like an lm334, current regulator, i dont know what its upper voltage rating is but i doubt it would to 2kv, or you could use a voltage regulator of the biggest value you can lay your hands on, just connect the gnd pin to the output via a resistor, your load then comes off the gnd pin, your regulated current is I=Vreg/R
the bigger the regulated voltage the more bandwidth you will have

 

[lemosam]

Thanks everyone,

I was mistaken about the load resistance. It should be 100 ohm to 200k ohm. And by the way, I'm experimenting with electroplating with a constant current source where I can set the current to 1mA to 10mA.

I'm still interested in resources that describe different approaches to building constant current sources.

Thanks again

 

[dhwilliams]

I strongly recommend that you do not try to get 10mA through a 200K ohm load - see warning below.

For low resistance loads you should be able to make a simple constant current circuit which may be stable enough for your application using a single transistor with its base held at a constant voltage and an emitter resistor. The voltage across the emitter resistor will be the constant base voltage minus 0.7V (approx) so the current through the emitter resistor will be constant. To a first approximation, the same current will flow through the load to the collector for a wide range of load resistance as long as your supply voltage is high enough.

For example, set base voltage to 1.7V and use 100 ohm emitter resistor. Voltage across resistor = 1V, current through resistor = 10mA so current through load = 10mA.

I have used a red LED driven at 10mA to give a constant voltage of about 1.8V - just adjust the emitter resistor to set the required current.

The lower resistance and lower current ones should be very easy to implement but you will have more difficulty with the high resistance and high current versions. To get 10mA through 200K would require 2000V - I wouldn't like to attempt it in a dry and enclosed environment. Using it in an open and wet environment (which sounds likely for electroplating) you're likely to kill someone! DON'T TRY IT!!

Dave