Help with choosing the right MOS-FETs

[205GTi]

I am trying to build this circuit, but I am stuck at choosing the right MOS-FETs for it...

Below is a list of MOS-FETs I could get hold of, which of these can replace the IRF510?

Thanks for helping in advance!

[justDIY]

what power level will you be driving the IR diode at?

i will point out the circuit isn't drawn properly ... they specify a N channel device, but have it switching the high side, which is a job for a P channel device.  move the LED above the transistor, and it'll be correct, or use a P channel fet, instead of an N ... keep in mind, this will also invert the output of 555, since a P channel is conducting (or "ON") when the gate is low and off when it's high, opposite an N channel.  the way the circuit is drawn, the mosfet will need more than 9v to switch fully on ... otherwise it will be partily conducting, and can experience thermal run away.

any mosfet you can find should work, except for those first few you listed with really small current ratings (ID), so the IRF520 would be a good replacement for the IRF510 (they're in the same family)... aside from a MOS transistor, you can use a BJT transistor as well, such as the TIP31, TIP101, heck even the humble 2222 can switch 600mA... it all boils down to how much power you need to switch?

[205GTi]

Thanks JustDIY!

I haven't got a lot of detail from this design, basically, this diagram is what I got, so I don't know what power I will need. But I would like to get as much power out from the LEDs as possible.

This circuit basically drives the IR LEDs to pulse with a frequency similar to what a laser speed gun gives out, hence, it can be used to test if laser detector are working properly or not.

Below is a list of IR LEDs I can get hold of, would CY85G be the best choice for max power output?

[205GTi]

The guy who sent me the design of the circuit also showed me the way to connect an array to give a stronger beam.... is that diagram wrong too?

What mod will I need to do to that circuit to make it work properly?

Many Thanks~!

[justDIY]

ask "the guy" why he is doing high-side switching with a low-side device, thats what I want to know... perhaps he's relying on the partial conduction of the switch to act as some sort of current limiting device, which is a bad idea too.

in terms of which led to choose, none of them are going to come close to matching the power of a LIDAR / LADAR IR laser emitter ... you're better salvaging emitters from old CD players, and cobbling together some optics... be sure to wear IR filtering goggles when messing with ir lasers.

regardless, pick the LED with the highest peak / surge / pulse rating ... one of those listed a surge current of 3a... also, you'll need something more than a 9v battery to deliver that kind of current.   Three 3v CR123a lithium cells in series might get you close, but probably not.

for that last diagram, there's no reason to use all those mosfets, one fet will do fine switching several leds.

edit: sorry, I suppose "high side" might be an unknown term...  think of anything with a postive and negative side as having "high" and "low" sides ... the low side is connected to a voltage source with a low potential ... such as an LED cathode (the negative side) connects to ground.   the high side is connected to a voltage source with a high potential, such as the postive rail +9v ... an N channel transistor is a "low side" switch, meaning it's designed to interrupt the flow of current between a device's low side and a rail with a lower potential than the high side.   So, it is incorrect to use a low-side switch to interrupt the flow of current between the positive rail and a devices high side.   In some situations, high side switching is desired, and for that the P channel transistor is needed, but you'll find P channel devices cost more and handle less current than N channel, so they're best to be avoided.