Current amplifier circuit?

[pacmann]

A current transformer for my project uses a current output that I want to 2x amplify. The current is bidirectional between +100ma and -100ma. Can I use a current mirror?

[moffy]

You would need at least two, one for each direction, npn and pnp, and probably some level shifting transistors as well.

[guenthert]

A current mirror won't yield exactly the same current.  Such a scheme will introduce gain errors, perhaps non-linearity and temperature dependency.  Why not use a different CT with the output current you actually desire?  Or a 2nd one with the desired 1:2 ratio?

[pacmann]

A current mirror won't yield exactly the same current.  Such a scheme will introduce gain errors, perhaps non-linearity and temperature dependency.  Why not use a different CT with the output current you actually desire?  Or a 2nd one with the desired 1:2 ratio?

Cheers. The ct is in an existing project thus cant be changed easily

[moffy]

A current mirror won't yield exactly the same current.  Such a scheme will introduce gain errors, perhaps non-linearity and temperature dependency.  Why not use a different CT with the output current you actually desire?  Or a 2nd one with the desired 1:2 ratio?

You can probably hold it to 1% of fullscale, but what sort of bandwidth and voltage range out are you looking at, also what output impedance is needed for the current.

[magic]

Maybe something could be done with a handful of transistors.

What power supplies are available and what will happen to the doubled current?

[Terry Bites]

You will need to use the recomended load resistor (burden resistor) for the CT.

Add an amplifier and use it to drive a bipolar current source.
Vin is the voltage across the burden resistor. Set Rg accordingly. Most inst amps should work in circuit 1.
You might get away with 3904 and 3906 type transistors at 100mA.  But...  If they get too hot use the Zetex parts.

The second circuit is simpler (cheaper) but needs good resistor matching and or tweaking. Set the gain to suit.
Use a low Vos dual opamp for best results.
Ref https://ez.analog.com/amplifiers/operational-amplifiers/f/q-a/559321/op177-improved-howland-current-source---how-to-increase-current-output
Watch out for ouput voltage complance limits at low supply voltages and with high impedance loads.

[Terry Bites]

This circuit is a current mirror propper:

The tighter the resistor match and the better the opamp, the higher the accuracy.
Again supply voltage limits output compliance.  The bipolar transistors can be repaced with small signal (logic level) mosfets.
There is a price to be paid for this in lost compliance. At higher supply voltages this is less of a problem.
Add C1 if the mirror starts oscillating. Igain=Rbdn/Rset. I'd choose Rbdn to give 0.1-1V full scale at the input.
Get a 100 10k's and sort them for the best match or spend a couple of bucks a piece on 0.01% resistors eg RNCF1206TKW10K0
A low cost precision amp will improve performance, eg OPA4991

[tszaboo]

Just to avoid the XY problem:
Why would you like to have twice the current?

[mawyatt]

Here's similar looking Bipolar Current Source to Terry's used for the Base Current in a Curve Tracer Fixture we developed awhile back, but never had time to build even tho PCBs are finished 

Best,