Current source "without" temp drift

Question

Hi, 
 I'd like to make a High precision current source with excellent temp drift (10 to the power of -6 or at best better than that). Current: about 0.5 Ampere 
 At the moment I have an AD624 combined with a Vishay resistor in mind. How can I go further? Is there a place for me to look up stuff like this? 
 Thanks 
 Matthias

FormerMember · Accepted Answer

Matthias, 
 Another thing that might help is whether or not it has to be 5 amps absolute, or just constant. In other words, 
 if 4.993 amps is o.k., as long as it doesn't change, then maybe the problem is a little easier. The other consideration 
 would be if you want it to be constant at some value you set, then sensing the field and opertating closed loop 
 might work. But then you have the temperature dirft of the sensing element and associated electronics. 
 To give you some appreciation for the difficulty of your problem, if you just wanted a simple voltage reference that 
 put out 5V at 1 mA with less than 1 ppm/deg C, that would be very expensive........ 
 Harry)

EZAdministrator · Answer

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ADIApproved · Answer

Hello Matthias, 
 Do you mean that you need a 0.5A current source which has less than 1ppm/C drift? That is very hard to achieve. It is a highly complex problem. Even if you have one or two very good components, you have to take into account and minimize (or control) every error source in your circuit (and pc board!). Then there is also the possibility to control the temperature so there is no temperature drift within a reasonably narrow operating temperature range. Can you provide more details of your end application? Are there additional requirements such as noise, bandwidth, etc? 
 Gustavo

ADIApproved · Answer

Matthias, 
 There are a few options and things to consider that might simplify your design. Some of those include a controlled environment and the ability of tracking the performance of your circuit. 
 1. Is this a circuit for production or a single experiment? 
 2. For how long does the circuit need to operate? 
 3. Do you have a narrow operating temperature range? Is this going to be done in a controlled environment? 
 4. Will you have the ability of tracking long-term stability of your circuit output with at least one more laboratory standard? 
 5. Is it possible to relax your requirements to say, 5ppm/K? 
 And a couple more questions about the source: 
 6. When you say "current source" do you mean an actual source or a "current sink"? 
 7. If you do mean a current source, what's the maximum voltage to which it needs to operate (a.k.a. compliance voltage)? 
 8. I assume your load is quite constant. Is that correct? 
 Gustavo

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Current source "without" temp drift