AO3400 Super Transistor!

[@amitmeyuhas6216]

hello, you need a back emf diode (reverse) between the +5v and the drain in order to protect the AO3400 from high voltage while turning off the fan

[@onecircuit-as]

@@amitmeyuhas6216 Good point - I’ll add it for the final version! 👍😀

[@ColinMcCormack]

Doesn't the mosfet body diode do that?

[@BLOCKsignallingUK]

@@ColinMcCormack The body diode allows current to flow in the direction from the ground rail to the drain of the mosfet. That's not what will happen when the mosfet turns off and the fan is still running. In that case, the fan motor negative lead will become more positive than the positive rail. A diode across the fan will prevent this voltage from rising significantly. A 1N4140 of 1N4001 would be fine.

[@onecircuit-as]

Diode installed (1N4001], leads shortened, all of it fits comfortably in the case.👍😀

[@AndersNielsenAA]

Fan should indeed be blowing on the heat sink :) Also - I’m happy to see it didn’t fry the GPIO when you hooked it straight to it in the beginning. I don’t think a Raspberry Pi would’ve been that forgiving with trying that much current. The internal reverse diode might be enough for back EMF?

[@onecircuit-as]

The fan is now blowing back into the case and I did install a flyback diode in the final version. 👍😀

[@paulwojcik1856]

Hi, yes fan should blow onto heat sinks. The air flow when sucking comes via the least resistance path and so although will flow some air over heat sinks, most air movement will travel from sideways into the fan (as path of least resistance). Pushing the air onto the heat sinks will provide much moor cooling capacity as it will force air across the surface of the heat sink.

[@onecircuit-as]

Thanks Paul my thoughts as well! 👍😀

[@ChrisSmith-tc4df]

The BS170/2N7000 were really aimed at 5V gate drive switching applications, so their maximum gate threshold can be problematic unless one is hand testing and binning for lower threshold specimens. That combined with their lower transconductance can be problematic in 3.3V circuits - especially at colder temperatures.

[@onecircuit-as]

Yes I think the AO series looks like the goods for IoT logic level applications. 👍😀

[@ChrisSmith-tc4df]

@@onecircuit-as I thought so too, so 10 years ago I bought factory sealed 3000 each reels of AO3400A and its complement AO3401A. They only cost 4c each back then.

[@onecircuit-as]

@@ChrisSmith-tc4df Wow good pickup - I'm happy if I find 100 pcs relatively cheap!

[@frankowalker4662]

I'd have the fan blowing into the case. But the size of those components gets me. I've read books with bigger full stops.

[@onecircuit-as]

I lost a few 603s along the way due to breathing. The fan is now blowing into the case, plus I installed a flyback diode and shortened the leads. 👍😀

[@frankowalker4662]

@@onecircuit-as One sneeze and your project is gone. LOL Nice one. I did'nt think of the back EMF diode. 👍

[@Steve_Coates]

You can buy them in SOT-23 format which is much easier to solder.

[@frankowalker4662]

@@Steve_Coates With my eyesight and tremors, SMD is just a myth. LOL.

[@Steve_Coates]

@@frankowalker4662 Join the club although on good days I can manage SOT-23.

[@bonnome2]

I used this transistor for a 10 watt led. It's able to strobe at like 1mhz.

[@onecircuit-as]

Amazing little guy! 😮

[@GnuReligion]

Those Alpha-Omega 34xx series mosfets are ubiquitous!

[@GnuReligion]

Have you ever used an Airpax temp-activated passive switch? They have models that will close at 40C/50C/60C, etc.

[@onecircuit-as]

Interesting! I’ll look into that - thanks! 👍😀

[@Rtube-b1l]

It has all the right things to run a pulse laser except the watts is to low. If I use an arduino to create a PWM , need 75w 12v 2.5-30a . Any ideas how to drive a 75w 905nm pulse laser diode with an arduino ? Pulse Drvers cost upward of $1500.

[@onecircuit-as]

Use something like this circuit to trigger a larger fet like the IRFZ44?

[@Rtube-b1l]

@@onecircuit-as I will look at the data. I freaked myself out and got the laser diode to light up with a PWM and then I fried the PWM module. I tried with a Arduino and found that it is easy to use the simple blink code but I couldn’t get any light using a TIP31c. I might have killed the laser diode ? 4 days and nights of studying now , trying to get a 75w 12.8v 30a 100ns max pwm . I thought when I bought the diode for $20 it would be as easy as connecting to a buck converter not realising it needed a PWM. Thankyou for your quick reply.

[@onecircuit-as]

Good luck with the project, sounds like good fun! 👍😀

[@Rtube-b1l]

@@onecircuit-as I want to know how cheap I can drive a pulse laser diode ? The $2000 drivers look like cheap circuits so why are they so expensive ?

[@onecircuit-as]

🤷🏻‍♂️ This is often the case with electronics. Commercial WiFi extender AU$60. ESP8266 version? AU$1.50 😂

[@GWorxOz]

Always good.👍 👍 👍 👍

[@onecircuit-as]

Thank you 👍😀