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Driving a pmos using MCU

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Amr Wael

Amr Wael

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Hello,
I thought about using a pmos as a high side driver for a relay. however my mcu (smt32) could only provide 3.3V
I heard about Logic Level Mosfets that could be drived using MCU.
Any recommendations for Part numbers for PMOS logic level mosfets?
Thank you very much in advance!
 

Hi,

I assume you are aiming to control a relay with a rated voltage higher than 3.3 V, e.g. 12 V. If so, you would need an additional n-channel MOSFET or a npn BJT to control the PMOS, by means of its Gate-Source voltage. Have a look at Fig. 3 in [1]. Keep in mind, to turn the PMOS completely off (non-conductive), the Gate-Source voltage difference has to be 0 V. So for a 12 V voltage source (used to control the relay) which is connected to the source of the PMOS, also the Gate voltage has to be 12 V to turn the PMOS off.

https://www.onsemi.cn/PowerSolutions/document/AND9093-D.PDF

BR
 

stenzer said:
Hi,

I assume you are aiming to control a relay with a rated voltage higher than 3.3 V, e.g. 12 V. If so, you would need an additional n-channel MOSFET or a npn BJT to control the PMOS, by means of its Gate-Source voltage. Have a look at Fig. 3 in [1]. Keep in mind, to turn the PMOS completely off (non-conductive), the Gate-Source voltage difference has to be 0 V. So for a 12 V voltage source (used to control the relay) which is connected to the source of the PMOS, also the Gate voltage has to be 12 V to turn the PMOS off.

https://www.onsemi.cn/PowerSolutions/document/AND9093-D.PDF

BR
Click to expand...
Actually my problem isn't with the relay voltage but it's with the required current. I dont want to use ULN2003 because I want the circuit to be easily integrated with different loads (of a pre-defined current range) without the need of an external supply connected directly to the load thats why I am going for a high side.
Thank you for your suggestion ,the solution of adding NPN is cool but will increase the area of my PCB as it contains a dozen of pmos.
I wonder if there exists a more compact solution.
 

5V to 5V driver can be perfectly implemented with logic level PMOS. 3.3V to 3.3V is still good if your load can work with only 3.3V. 3.3 to 5V or higher can't be implemented with a single active device.
 
Last edited:
Hi,

Distributors have selection guides.
This is the way I'd go.

Klaus
 
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