OP07: Is there a diffuser current reference circuit for a normal op amp?

Hi Aiwen,

is there a reason why you use a discrete design? I ask, because TI has lots of "Power OPAmps":

https://www.ti.com/amplifier-circuit/op-amps/power/products.html

Can you tell more about your application? What output current and output voltage do you need?

Kai

Hello Aiwen,

I was typing when I saw Kai had just responded. Here's my thoughts and questions about your inquiry:

It is not completely clear what kind of op amp circuit you are asking about. When I search on "diffuser current function" I find that is a very specialized type of circuit having an array of a particular op amp/bipolar transistor configuration. It is a specialized function, and we do not produce any op amp product that performs that function.

If that isn't the function you are asking about, I see the circuit schematic you have provided is that of an op amp having an added output stage used to provide increased output current over what the op alone can provide. TI does have op amps that can provide high output current without having to add an external output circuit. Some have user settable current limiting if that is a needed function. Is this the type of op amp that you need?

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi  Kai;

thanks for  your reply

our Input current is very  small and input voltage is 0-5V,  we need  the output currrent is around +/-300mA,  output  voltage  around 0-10V,   The main idea is to expand the output current, and  We have chosen the OP07，Then how to design the peripheral circuit of OP07  for expanding  the  output current , ,  Do  you  have  any  idea for this? 

Hi  Thomas；

Thanks  for  your  reply;

  We have chosen the OP07，circuit schematic I have provided just for  FYI，I want  use circuit schematic with OP07,but I think op07 did not have current restriction protection, can you  give me any advice ? The  main idea is Increase the output current up  to +/-300mA,  output  voltage up  to  10V, could you  please  give me some reference schemes ？

Hello Aiwen,

If I understand your circuit use intentions correctly, you plan to use the OP07 a the input amplifier and you intend to add the external, NPN/PNP bipolar transistor stage to obtain a +/-300 mA output current. Additionally, you you want to somehow limit the maximum current in some manner using the OP07.

The OP07, like most op amps do not a have a current limit set feature. Their output current limit at some maximum based on the output transistor saturation characteristics of the transistors. If that maximum is in the tens-of-milliamperes the external output transistors may be driven hard enough to put out more than the +/-300 mA maximum you are concerned about.

The OP07 doesn't have any provisions for limiting the current it can deliver up to its maximum. Likely, the best place to attempt to limit that current would be the external output stage you are adding after the OP07. Some possibilities include adding low-value emitter degeneration resistors to both the 2N5550 and 2N5401, or possible a single low-value resistor between the 2N5550/2N5401 common emitter connection point and where the feedback resistor connects at IOUT.

The added resistance in either case would limit the maximum current that could be delivered from the output stage. However, the voltage drop developed across the resistors when high current is flowing will very much limit how close the output can swing towards the supply rails +V and -V. In my opinion, I would forgo using the OP07 and external transistors and use a power op amp that has an externally programable output current limit.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Thomas;

1、I'm glad you have got what I meant，actually，I want to use  NPN/PNP bipolar transistor to change OP07 's  peripheral circuit to get a higher current，But i think  adding low-value emitter degeneration resistors to both the 2N5550 and 2N5401, or possible a single low-value resistor between the 2N5550/2N5401 common emitter connection point and where the feedback resistor connects at IOUT  is not enough to play the role of current limiting protection, our input  current is very small ,Probably only a few milliamps，and  I need up  to  +/-300mA output, just only    +/-300mA  output. I need to limit the current output larger than 300mA，What else do I need to add outside of the OP07，Is there a similar scheme design?

2、You said you would use a power op amp that has an externally programable output current limit instead of  the OP07, Which device you will choose？

Hello Aiwen,

What supply voltages do you plan to use for +V and -V, and what are the critical op amp parameters needed for your application? A TI power op amp that can handle up to 500 mA continuous, and has resistor programable current limiting is the OPA547:

https://www.ti.com/product/OPA547

Do keep in mind that power op amps in general do not have as high a level of dc precision as a low power op amp such as the OP07.

Regards, Thomas

Precision Amplifiers Applications Engineering

Adding to Tom's recommendation, if you do not need OPA547 max supply of 60V, please also take a look at ALM2402F-Q1 (max Vs 16V) with output current above -540mA/750mA or ALM2403-Q1 (max Vs of 24V) with max output current of -400mA/500mA, both dual op amps available at much lower cost.