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How to switch load using radio controlled module if it switches the ground?
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ghostbanana34:
I had old broken toy car. I wanted to use it's RC module to switch 12V fan. I measured original circuit, found the output, saw 3V there (fig. A). Then I assumed that RC module switches the 3V and designed my circuit accordingly (fig. B). It was always on. Only then I start analyzing it more deeply and to my surprise I found out that RC module output is permanently connected to 3V and only switches second output to the ground (fig. C).

I used NPN transistor in TO220 package from old PC power supply, as that was only power transistor I had. Is it possible to modify this circuit so that switching to the ground would switch it?
capt bullshot:
Add a small PNP transistor like this
Zero999:
Yes, it's very common to switch the 0V. It's often much easier, because N-channel MOSFETs have a lower on resistance than P-devices.

If the RF module can switch enough current for the 12V fan, then add another transistor, forming a cascode with the internal transistor inside the module.



If the module isn't rated to switch the current required by the fan, another option is to switch the motor's 12V with a PNP transistor.
ghostbanana34:
Thanks. The RC module isn't rated for such current, so I will have to add PNP.
spec:
Hi ghostbanana34

Attached below is a schematic for another version:
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