12V power MOSFET for 3.3V logic?

Other Hardware General Electronics
1

Hi, I'm designing a thermostat, and I'm using some MCU (not arduino) to PWM-control a PTC heater (can be seen as a resistance heating wire).

  • The rated voltage is 12V with 10A max/5A avg
  • The PWM frequency is 1Khz.

Any recommendations for such as MOSFET?

Also: I'm terrible at hot air gun, so through-hole would be better than SMD for me. Thank you.

EDIT: Thank you everyone. In the end I just used LCSC's filter to find 3.3V MOSFETS. It's very easy: in this page: MOSFETs | Triode/MOS Tube/Transistor | LCSC
in the field for 'Drain Source On Resistance (RDS(on)@Vgs,Id)', you type in '4.5V' without pressing enter, then you will see all MOSFET that turns on at 4.5V.

The reasoning behind this is that most normal MOSFET will only give RDS(on) for 10V, but for logic mosfet they will also give RDS(on) for 4.5V. Now, if it turns on at 4.5V, it almost certain will turn on at 3.3V (with slightly higher resistance). For example, HSCE2530 is 2m ohm at 4.5V and 2.7mohm at 2.5V

2

Why would you PWM a heater, and more to the point, why would you want to use 1 kHz? :roll_eyes:

3

Sorry for being unclear, when I say heater I mean a raw PTC component, not some appliance bought from amazon with packages.

I'm using PID algorithm to control the heater, so I would want for example, "heating at 46% power". To do that, PWM would be needed. Of course, 1Khz is not necessary; maybe 100hz would be enough.

4

1Hz might be plenty in fact - thermal inertia is large. And switching less frequently will make less EMI for a high current load.

If the load is 10A, and you don't want a heatsink, that suggests an on-resistance of 5 milliohms or less - that's much more likely to be found in a large package size and non-logic level.

I suggest the way to go is use an NPN transistor level shifter or gate driver to drive such a FET, then the 3.3V thing is not going to be a problem. Gate drivers typically run from 12V supply (which you have), and accept 3 or 5V logic inputs happily.

There are thousands of MOSFETs, the way to find one is parametric search at one of the big suppliers' websites.

With a small heatsink you'll be able to relax the specifications to 10 or 15 milliohms, which may help.

1 Like
5

You will need a large MOSFET anyway. Even a SMD package should be easy to solder it with a decent soldering iron. The PCB will be your heatsink.

6

Thank you - the issue I found with SMD mosfet is that they usually have a large tab (for heat dissipation), which is impossible to solder onto PCB with full contact.

7

Thank you. Yes thermal inertia make sense. Do you mind recommending parts numbers for both gate driver and mosfet? I'm OK with heatsink and SMD. I just want to avoid purchasing wrong parts again...

8

I put a bit of paste on the tab, set the soldering iron to almost 300 degrees, and heat up the the tab and the heatsink on the PCB. The issue is always that the heatsink does exactly what it is supposed to do, so it takes quite a lot of time (10 - 15 secs) before the whole thing melts and makes full contact. Keep in mind though that full melted is not even needed.

9

I guess I just need a more powerful solder iron. Also I fried several mosfet by putting the iron on it for too long...

10

For example AO4402G is SOP8 package and meets your requirements.

11

There are thousands of MOSFETs and drivers, the way to find them is parametric search at one of the big suppliers' websites. I don't memorize these things, I go look, for instance:

https://www.mouser.co.uk/c/semiconductors/power-management-ics/gate-drivers/?orgKeyword=gate%20driver

12

Not for too long, but too hot. They break at 305 degrees normally, but most soldering tin has a melting point around 200 degrees (less for 'leaded' usually)

You need something that has a controlled temperature.

13

Thank you! That looks exactly like I need - unfortunately it's discontinued on LCSC

14

On JLCPCB you mean ? well to give you some idea, check how many mosfets they have in stock.

15

I agree that it can be easier to solder the individual leads on , say a TO220 or similar package. Attaching a heat sink is also easy. If this is a one or few off build, go for easy for you.

16

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.