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Controlling 5V relay with 3.3V port ?

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bianchi77

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Guys,

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

Thanks
 

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.
 

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.
Click to expand...
can you show me the circuit please ?
thank you
 

bianchi77 said:
Guys,

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

Thanks
Click to expand...


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

001.png


In circuit +V should be +5V.
 

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, search circuit example with MC34063A IC. If you need 5V just to drive that relay, better is to use 3V relay and solve problem naturally.
 
Last edited:
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:
Click to expand...
great mate, thanks for the info
 

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!
 

Hi,

? - if you have a regulated 3v3 it kind of implies you must have a greater voltage supplying the 3v3 regulator.

Why don't you fit a 5v regulator to that power source for the 5v relay ?

A lot simpler and cheaper that fitting a voltage doubler/regulator.

- - - Updated - - -

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!
Click to expand...

Hi,

A bit OTT for diy hobby work - as the paper says its for industrial use.

For diy work, a simple base resistor on a npn transistors is fine.

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

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.
Click to expand...

This, I really recommend. I've faced a lot of problems with NPN transistors, the solution to which was just a simple pull down resistor on the base.
 

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