OPA227: Constant current source application with opa227

Hi Cunxu, 

li cunxu said:

The simulation result is that the circuit stability is a bit problematic, please see how to modify the resistance and capacity of the loop, so that the whole loop is stable,

We had a day off in Labor day here. 

Without much significant changes, I modify the circuit. This is V-to-I circuit. Since the load is 4ohm, you can not use the Rsense > 4 ohm --> so I changed to 1ohm instead. In addition, the delta voltage at Vp has to be 1.5V= reference. So the difference amplifier has to have gain in order to establish the linear operation (0.375V*4= 1.5Vrev).  

OPA227 V-toI converter 09022025.TSC

For step transient performance, here it is.

OPA227 Step Transient 09022025.TSC

Here is another way to do the V2I converter, and it will only use one op amp instead. 

https://www.ti.com/lit/an/sboa327a/sboa327a.pdf?ts=1756831173914&ref_url=https%253A%252F%252Fwww.google.com%252F

Please let us know if you have other questions. 

Best,

Raymond

Hi Cunxu,

The circuit is V-to-I converter, see the previous attached application note. Per the "conventional" circuit, the feedback voltage is generated by Iout*I_load, where I_load = 4ohm. In the conventional circuit and feedback topology, Vin --> Iout --> Iout*I_load is the voltage feedback.  

Your circuit is fed back from differential op amp, where Iout*Rsese is the feedback voltage delta. 0.375A*1 = 0.375V, In order to operate linearly, the difference voltage has to be gained up to 1.5V, so that the controlled circuit is operating linearly. Here I assume that the controlled current is 0.375A. It can be any other load current, as long as the OPA227 is able to operate linearly and NMOSFET is able to operate in saturation region. Anyway, in this case, I changed the gain of the difference amplifier from 1V/V to 4V/V (1.5/0.375). So Rsense may be much smaller than 1ohm, if you want to minimize the heat dissipation (it is your choice, and so the difference amplifier's gain).  

The Rsense should not be greater than R_load, otherwise, Rsense will limit the Iout current in the V-to-I branch.

If you have other questions, please let me know. 

Best,

Raymond