Controlling 5V relay with 3.3V port ?

Tahmid said:

Use the 3.3V output to drive an NPN transistor that drives the relay. Make sure you connect a freewheel diode in anti-parallel across the relay coil.

Hope this helps.
Tahmid.

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bianchi77 said:

Guys,

Any idea on how to controll 5V relay with 3.3V output from port ?
Is it possible with optocoupler ?

Thanks

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tpetar said:

This relay coil should get 5V not 3,3V. I have impression that you want to power 3,3V to relay coil.

In circuit +V should be +5V.

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tpetar said:

You can use relay or reed relay on 3V for coil, or if you have more 5V parts you can make 3,3V to 5V converter, see this simple example with MC34063A :

3.3V-5V Voltage Regulator Board

**broken link removed**

https://www.mikroe.com/add-on-boards/power-supply/3-3v-5v-voltage-regulator/

Circuit : **broken link removed**



Here you can see 3V relays:

https://www.tme.eu/en/katalog/#id_c...14,915,925,938,693,936&used_params=925:24791;



If you need 5V just to drive that relay, better is to use 3V relay and solve problem naturally. :wink:

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HTA said:

After reset a microcontroller I/O-port is usually in a high impedance state. Thus attached external actuators(transitors/relays etc) will see this floating state and could cause malfunction( more on IO-interfacing and level shifting see https://www.ichaus.biz/wp1_mcu_interface ).

Enjoy your design work!

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wp100 said:

To really avoid any chance of such a problem then a pull down resistor on the npn transistors base is all thats needed.

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XiaoTaoMCU said:

Light coupling or NPN transistor is ok

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