# Current sources

Discussion in 'Electronic Design' started by john, Jan 13, 2006.

1. ### johnGuest

Hello,
Please look at the following data sheet of an instrumentation amplifier

INA2133.

I am using it as a constant current source ( figure 16, page 13 ). I
made the following changes in the circuit

1. I put a capcitor in series with the load for AC coupling reason.
2. The power supply of the circuit is +/- 15 volts.

I have a following questions about the circuit.

1. For example, if the circuit is producing 100microA and the load
resistance is 1mega ohm then the complaince voltage will be +/- 10
volts or the voltage across the load will be +/- 10 volts. How can I
keep the complaince voltage or voltage across the load equal to +/-
0.7 volts with the current of 100microA without changing the power
supply which is +/-15 volts?

Thanks
John

2. ### Rich GriseGuest

.
Well, what load resistance would develop 0.7V with 100 uA through it?

What's the reactance of the cap at the frequency in question?

Good Luck!
Rich

3. ### johnGuest

Hi,

I am using a iridium oxide material as a load. when voltage exceeds the
+/- o.7voltage limit, the material breaks down. I need to protect the
material.

Thanks
John

Hi.

Thanks
John

5. ### Spehro PefhanyGuest

How close to 0.7V do you have to go? Would (say) 0.5V compliance be
enough, or do you need 0.699V?

Best regards,
Spehro Pefhany

6. ### Rich GriseGuest

What, exactly, is the specification of the load? Are you sure that
what you want to use on it is a "current source", when the load is

What is it you're trying to accomplish? Please give an overall overview,
like, "I'm trying to do so-and-so with such-and-such a thing, and the
thing looks like this..." that sort of thing. (redundancy unintended,
apologies to the pedant contingent ;-).)

Thanks!
Rich

7. ### Ian StirlingGuest

If 0.6V (about) would do, then a couple of standard diodes across it
will work.
For 0.7V, two shocketty(sp?) diodes in series may work.
If the sole aim is protecting the device.