Driver circuit for 8 LED in series


Joined Oct 29, 2009
I wouldn't use a Lm317, better to use the 7805, it will power all the circuit both leds and receivers,
If the OP is driving this with a 9V battery and is worried about power consumption then both the 7805 and LM317 are the wrong way to go.

That 7805 is going to need to drop 4V. That is a lot of wasted energy in heat.

There is no need to regulate voltage when using a 9V battery to drive LEDs. It is already regulated. That needs to be done is limit current. OP might as well just add the appropriate size current limiting resistors and forget voltage regulation. But that is a waste of energy too.


Joined Jun 22, 2012
The battery isn't going to last long with leds transmitting all day, why not use constant current led drivers, or a Lm2596 buck regulator.


Joined Nov 12, 2008
thank a million sir,one more help how to include 8 photo darlington in same circuit op560a.pdf

is it possible to use all 8 PD in same circuit or if using 9v battery is not suitable i will go for 12v adapter
12 volt adapter would be much better.
Why do you need 5 volts for the darlingtons? Are they driving some logic that doesn't already use 5 volts?

Thread Starter

medic mad

Joined Oct 10, 2015
finally i bought two buck stepdown cc-cv regulator to drive LED(ife93) and Photodarlington (op560)

i am going to use 8 photo darlington in parallel 5v and 400ma and the v1 to v8 output given to 8 channel to amplify the signal using National instruments and to plot output response of the PD [the response of the PD low in my particular wavelength. so, i planned to amplify the signal using NI or OPamp since op560 the only PD available in lab used to couple with fiberoptic]

for 8 LED i use 15v and 40ma to drive it.

View attachment 95380 op560 PD
View attachment 95374 ife93 LED