1
\$\begingroup\$

Both of the below circuits are sinking 1A of current.The TL074 has a slew rate of 13V/us and OP07 0.3V/us. Does that makes the upper circuit have s slower response time?

What other differences, advantages and disadvantages do the circuits have?

schematic

simulate this circuit – Schematic created using CircuitLab

\$\endgroup\$
4
  • 2
    \$\begingroup\$ You can save one op amp if you use the second circuit. ;) \$\endgroup\$
    – Long Pham
    Commented Sep 25, 2021 at 16:21
  • 1
    \$\begingroup\$ slew rate doesn't matter because in both cases the capacitance in the FET gate is driven by the TL074 \$\endgroup\$
    – tobalt
    Commented Sep 25, 2021 at 16:58
  • \$\begingroup\$ Is V7 correctly oriented in the second circuit? \$\endgroup\$
    – user16324
    Commented Sep 25, 2021 at 20:46
  • \$\begingroup\$ @user_1818839 Yes. \$\endgroup\$
    – ElectronSurf
    Commented Sep 26, 2021 at 0:05

1 Answer 1

Reset to default
2
\$\begingroup\$

You ask "What's the performance difference between this two differential amplifier?" but I think what you really meant to ask was "What's the performance difference between these two current sources?".

The first circuit performs better because it amplifies the sensed voltage directly. Though, the OP07 may not be the best choice. They make specialized ICs to sense the current in the positive rail: https://www.digikey.se/short/8ftfz4n0. For example, the AD8212YRMZ

\$\endgroup\$
4
  • \$\begingroup\$ If we PWM the reference voltage (V3 in above diagram and V7 in below) at 100Hz with 50% duty cycle, which circuit will perform better? \$\endgroup\$
    – ElectronSurf
    Commented Sep 25, 2021 at 17:43
  • 2
    \$\begingroup\$ Generally, neither circuit is appropriate for PWM. However, at only 100 Hz, it may work. Both circuits will perform about the same as far as the PWM is concerned, but the top one will regulate the current (DC) more accurately, especially if you get a current sense IC, as I recommended in my answer. \$\endgroup\$
    – Davide Andrea
    Commented Sep 25, 2021 at 18:09
  • \$\begingroup\$ Why the circuits are not appropriate for PWM? \$\endgroup\$
    – ElectronSurf
    Commented Sep 25, 2021 at 18:24
  • 2
    \$\begingroup\$ Short answer: because PWM is digital and OP-amps are analog. Rather than modulate the voltage source, consider also the possibility of disabling the MOSFET independently of the analog feedback loop. But, as I said, 100 Hz is slow, so you are probably going to be fine. \$\endgroup\$
    – Davide Andrea
    Commented Sep 25, 2021 at 20:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.