Hi Team,
Our customer is looking for an amplifier with an integrated NPN transistor at the output which he will use to build a 0A to 11mA current source. I found some amplifiers such as OPA548, OPA549 and TLE2301 but it is not clear if these devices have NPN transistor. Can you please confirm?
Regards,
Danilo
Hi Danilo,
to build a 0A to 11mA current source
Do you mean that the output current of the the power amplifier may source or sink up to 10Apk? Please confirm. If the output current source is designed for 0-11mA, most of our op amp will meet the output requirements.
such as OPA548, OPA549 and TLE2301 but it is not clear if these devices have NPN transistor. Can you please confirm?
OPA549 is based on Bipolar technology in design.
OPA548 is similar to OPA549, which bipolar technology is used.
TLE2301 should be in bipolar technology design as well, based on the equivalent block diagram.
Please let us know why does the customer will require an integrated NPN transistors at the output stage. If you are able to provide us the design requirements, I can simulate one for you.
BTW, does the current output require source or sink or both source/sink capability?
Best,
Raymond
Hi Raymond,
Thank you for your response and I apologize for the delay. Please see the response of our customer below.
I search for an OP where the transistor is integrated to save space on the pcb!
Regards,
Danilo
Hi Danilo,
he transistor is integrated to save space on the pcb!
This is V-to-I converter, where I_load in R2 may be controlled from 1V/Rsens to 5VRsens or 10mA to 50mA, if the OA1 is capable to operate in a linear region.
There is a typo in the diagram, where V1 should connect to non-inverting input or Vin+ for NPN transistor. It can also use NPN transistor, then the negative feedback should be configured from top.
I believe that this may be for a low constant current application, which you mentioned from 0-11mA previously. If you want to use BJT, then you can configure the op amp as follows. This circuit is only able to source current.
If the constant current source is from 0-11mA, then the BJT is not required, since the most of op amp is capable to source/sink approx. 0-40mA without issues. You may try the following, which it will provide you with the same result per the lower current application.
OPA391 Current Source 06152023.TSC
If this is for higher constant current application, the original V-to-I circuit is more applicable.
If you have additional questions, please let me know.
Best,
Raymond
There is no opamp with such a separate transistor.
You could use the opamp's output transistor and sense at the supply, if the supply current is very small relative to the output current (e.g., TLV9041):
Hi Bernd,
Rload is outside the circuit board, which is connected by the customer with long cables.
ok, the following circuit should work and be stable with longer external cable at the Rload, which the loop gain has approx. 66 degrees of phase margin.
BTW, the Rload < 100Ω, otherwise the Rload will be the current limiting resistor and V-to-I conversion will not work.
Here is the transient step responses of the circuit. Both OPA391 (SC70) and 2N2222 are available in tiny package and the PCB can be constructed in a small area.
OPA391 V2I Step Response 06162023.TSC
You may use other op amps, such as TLV9041 and low voltage, lower cost op amp as Clemens suggested, but you should check out the loop stability whatever you are using.
Best,
Raymond
Hi Bernd,
There is no opamp with such a separate transistor.
As Clemens pointed out, no op amps are configured with a separate transistor among op amp manufactures.
becaues I need to save space on the PCB
SC70 op amp is very small, approx. 1.7mm x 2.2mm + MMBT2222 or MMBT3904T-7-F or similar NPN with small package, SOT-523-3 or SC-70-3 packages etc., which are occupied very small space.
If you have additional questions, please let me know.
Best,
Raymond
