# OpAmp Infrared LED driver circuit

#### Thanos_husk

Joined Nov 6, 2018
12
Hi!
I have the following schematic , used as an infrared LED driver.
The purpose of the circuit is:
As long as the button is pressed (shown in the schematic) , the LED emits.
The "Vin" signal is a 1,5Vpp sinusoidal waveform with 37 kHz frequency.
I have to choose the values for the components so thah the AC current (IL) of the LED is 34 mA.
I can understand that the schematic is some kind of "voltage to current converter" and that the C capacitor is there for removing any DC offset from my signal but I can't find how to choose the component's values.
The OpAmp's supply voltage is 20V.
Any help would be appreciated.
Thanks a lot!

#### Alec_t

Joined Sep 17, 2013
10,429
Is this a school/college project?

#### ericgibbs

Joined Jan 29, 2010
8,848
hi Thanos,
Where did you get the circuit for the OPA IR driver.?
E

#### Thanos_husk

Joined Nov 6, 2018
12
hi Thanos,
Where did you get the circuit for the OPA IR driver.?
E
Our professor gave it to us as a template. But did not explained anything

#### TANDBERGEREN

Joined Jan 20, 2014
90
Determine what amplification You will need to drive the LED. (Ratio between RF an R)
Then it would be smart to calculate the series resistance of the LED.
The reisstors at the non-inverting input must be calculated in a manner that one ensures that the output voltage of the OP-amp is sufficient low to cut off the IR-LED when no transmission is wanted.
The R1 and R1 and R2must only be calculated to obtain the OP-Amp to allow the IR-diode to be enabled.
Somewhere near to giving about half the supply to the non-inverting input.

But beware, look out for how the IR-diode is to be driven. Rarely it is to send pure sinewawe....

#### Thanos_husk

Joined Nov 6, 2018
12
Determine what amplification You will need to drive the LED. (Ratio between RF an R)
Then it would be smart to calculate the series resistance of the LED.
The reisstors at the non-inverting input must be calculated in a manner that one ensures that the output voltage of the OP-amp is sufficient low to cut off the IR-LED when no transmission is wanted.
The R1 and R1 and R2must only be calculated to obtain the OP-Amp to allow the IR-diode to be enabled.
Somewhere near to giving about half the supply to the non-inverting input.

But beware, look out for how the IR-diode is to be driven. Rarely it is to send pure sinewawe....
Thanks a lot for the great answer!
I am 100% sure that our Vin is a sine wave .

#### TANDBERGEREN

Joined Jan 20, 2014
90
Good luck.