Current Mirrors

I'm looking to use a current mirror, based on a dual transistor like this:-

https://www.infineon.com/dgdl/bcv61.pdf?folderId=db3a30431441fb5d0114498f7eab01ce&fileId=db3a30431441fb5d011449d8ff720246

I can see that the current matching is specified to be between 0.7 and 1.3, but that is only at a collector voltage of 5 V.

Has anyone got any idea how I can see from the data sheet how the current will reduce as the collector voltage falls?

Unfortunately the data sheet doesn't directly show that information, which is usually given by the characteristic curves of collector current versus base current and collector voltage. The only info that refers to that is the AC open-circuit output admittance of 30µS which corresponds to a 33kΩ output impedance (a 1 volt change gives a 30µA change in current). This gives you an estimate of how the collector current will change with collector voltage. Of course, that's only defined for one condition of current and voltage, but it should give you a rough idea for what happens at other voltages and currents.

Thanks for that. I couldn't find any curves that meant anything to me. The admittance is the best clue.

Texas Instruments used to have current-mirrors that had better matching. I think I am the only person to buy some so now they are not made anymore.

Burr Brown listed some in the past too. No idea if they are still available.