I'm trying to create a constant current LED driver. I have found and read information about the miller effect and came up with the schematic below.

What are the most important parameters for choosing the Opamp? Is this the Slew Rate, Gain Bandwidth Product, or any of the other specifications?

I was looking at an Opamp and power it with ±15 Volt since the MOSFET has a maximum VGS of ±20 Volt.

UPDATE: I was thinking of a opamp like this one BA4580YFVM-MGTR

  • Frequency: 1-100 Hz
  • Pulse duration: 100-300 us
  • If: 1A during pulse


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ There are so many opamps available that selecting "the best" will be difficult. My approach would be to go on sites like Mouser or Farnell, enter your "must have" requirements like maximum voltages en then sort on increasing price. I'd then look at the datasheet of the cheapest opamp and see if I think it can "do the job". I would pay attention to the opamp's driving capability, if it can source/sink at least 10 mA that would be good enough for me. For the rest in this circuit almost any opamp would work as it does not need to be very fast nor have a very low offset. \$\endgroup\$ Mar 19 '19 at 11:03
  • \$\begingroup\$ For this circuit, you can take a general purpose opamp. The critical component is the MOSFET transistor which need to have a low leakage current. If the leakage current is to high, the LED will light when they need to be off. \$\endgroup\$
    – Foxrider83
    Mar 19 '19 at 12:07
  • 1
    \$\begingroup\$ Depending on the current through the sense resistor, you should probably look into rail2rail op amps, and low offset input depending on the tolerance of the current though the LEDs. \$\endgroup\$
    – Linkyyy
    Mar 19 '19 at 12:44
  • 1
    \$\begingroup\$ Why would you use op amps when you can buy the entire circuit in a single chip? \$\endgroup\$ May 9 '19 at 21:36

I would pick something like the LT1056 with specified low output impedance since you're only isolating the output with 10\$\Omega\$. It's not particularly cheap. If you want to reduce cost, you can put the work in to search for your important parameters (30V operating voltage, relatively high slew rate and GBW etc.)

enter image description here

Depending on the polarity of the offset voltage of the op-amp you happen to get, the output could rail at the negative supply and then take a long time to slew back to 0V, so you can put a 1N4148 across the feedback capacitor. Speaking of which, you probably want to reduce that to maybe 1nF to speed up the response.


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