I would like to commute a 12V siren with an ESP01. I thought to use NPN or PNP transistors TO-92 that I have since a long time in my drawers.

The ESP01 has 3.3V maximum at the output, and the siren work at 12V and drive a current about 300 mA.

I found for example a NPN transistor S8050 which can draw up to 700 mA. The power dissipation is about 0.625W, whereas the siren consume about 3.6W. I don't know if it is a problem or not...

Is this NPN transistor is ok for my application, or should I use a MOSFET ?


  • \$\begingroup\$ Have you considered using a low power relay? Drive an optocoupler which is connected to a 3V relay. The relay then switches the 12V for the siren. ex: i.imgur.com/CRgcmv5.jpg \$\endgroup\$ – Natsu Kage Feb 11 at 16:13
  • \$\begingroup\$ you could make a darlington pair if your ESP can't push out enough current from a GPIO; the siren should still work at ~10.5V.. \$\endgroup\$ – dandavis Feb 11 at 17:26
  • \$\begingroup\$ This transistor would lose close to 1V with an hFE3=40 min as a poor switch \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 12 at 0:53

You need the transistor to be a saturated switch. The datasheet for your transistor and nearly every other transistor shows that its base current should be 1/10th its collector current for it to saturate well. Then the base current must be 300mA/10= 30mA. Can the ESP01 output 30mA at a reasonable voltage?

The saturation voltage loss is shown as a max of 0.5V at 500mA so might be 0.4V at 300mA. Then the transistor heats with 0.4V x 300mA= 0.12W and it will be warm but not hot.

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  • \$\begingroup\$ Thanks, after watching some YouTube vidéo, I think that I will buy some FET / MOSFET which are more suitable for this use. \$\endgroup\$ – RomainD2 Feb 12 at 7:07
  • \$\begingroup\$ Most Mosfets need a gate-source voltage of 10V to fully turn on but some need only 5V. Can your ESP01 output 5V or 10V? \$\endgroup\$ – Audioguru Feb 13 at 14:37
  • \$\begingroup\$ No, just 3.3v, but it is ok with some MOSFET \$\endgroup\$ – RomainD2 Feb 13 at 18:36

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