I am trying to wire six IR LEDS with three parallel sets of two IR LEDS in series. Each set has its own current limiting resistor and they all share a common 5V line at their anode and are connected together to a Mosfet at the cathode. Is there something wrong with this implementation or can it be improved in any way?enter image description here

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  • \$\begingroup\$ You've forgotten to tell us the supply voltage. Add it into the question using the edit link ... \$\endgroup\$ – Transistor Jul 8 '20 at 5:40
  • \$\begingroup\$ @Transistor Thanks for the feedback. I have made the necessary changes \$\endgroup\$ – adnan Jul 8 '20 at 5:44
  • \$\begingroup\$ It can be improved with design specs , Temp Range. Tolerance analysis. And temp rise \$\endgroup\$ – Tony Stewart EE75 Jul 8 '20 at 5:51

There's nothing wrong with your circuit (assuming it works out thermally). Plenty of voltage across the dropping resistors so the current is reasonably constant. The MOSFET is 'okay', a beefier one wouldn't hurt, xx2302 for example, which is usually not much different in price.

Maybe it could be improved by dumping the resistor droppers and using a LED boost chip such as the AP3031. There are other options which might be better under your particular conditions, maybe there are fancier ones which replace the diode with a synchronous MOSFET for better efficiency, for example.

That plus one small (4.7uH) inductor, a Schottky diode, a current-setting resistor, and a couple ceramic capacitors yield constant current control about 80% efficiency. All your LEDs can go in series, since that only adds up to about 8V. It also has a control voltage input so you can get rid of the MOSFET.

80% efficiency means ~200mA from the 5V supply rather than 300mA.

But really there's nothing wrong with your circuit as-is, and it won't contribute electrical noise like a 1MHz switcher might.

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    \$\begingroup\$ Wonderful answer, I think. Covers a lot of bases, quickly. I'd have written far too much with less effect. Thanks! \$\endgroup\$ – jonk Jul 8 '20 at 8:08

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