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I've a strange issue. I wired everything up like that: enter image description here

The ATTiny13 changes, for test purposes, every 10 seconds between HIGH and LOW. Since the IRF3708 needs 2.8V to switch state, I use the 5V "power line" with a transistor to get over the threshold.

FYI: This is not my whole project; but it must work as a single component. After all, some may think "he doesn't need this part at all" - I do :)

This setup works - even the 10s cycle etc. But when I measure between source of IRF3708 and GND - there is only 3V on my multimeter.

When I measure between Drain and GND, it is my 24V. So it seems that the IRF3708 is "swallowing" 21V while running through it.

I hope the problem is clear and you can help me.

Thanks a lot already!

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    \$\begingroup\$ You are high-side switching with an N-channel device. Similarly, you are using an NPN transistor with a 10k resistor on the emitter. Either change for P-channel and PNP devices or reconfigure the circuit to keep emitter/sources at or close to ground and see how it works. \$\endgroup\$
    – vir
    Jan 25, 2021 at 16:12
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    \$\begingroup\$ So I just have to place the Mofset AFTER the Fogger? \$\endgroup\$
    – dessi
    Jan 25, 2021 at 16:36
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    \$\begingroup\$ Okay I just tried my comment. Now it works. THANK you very much! \$\endgroup\$
    – dessi
    Jan 25, 2021 at 16:41

1 Answer 1

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That's a N type FET. It can't be used for high side switching. Or it can, but you'd need gate higher than supply then. Either change to P type FET, or better yet, simply use low side switching.

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