Switch on/off 18ohm load with a pnp transistor

Thread Starter

doctor spot

Joined Nov 26, 2018
5
Hello guys,
I need to switch on/off a load which consumes 280 mA with a 5V supply using Arduino. But in this case I am only allowed to use a PNP transistor not an NPN transistor. Which transistor should I choose for this circuit? I need some help with the design diagram.

Thank You
 

Thread Starter

doctor spot

Joined Nov 26, 2018
5
Do you know how a transistor works, and what is required to turn on a PNP transistor as a switch to power the load?
Yes, I know how a transistor works. I have used NPN transistor as well. But I never used a PNP transistor. I dont know how to use a PNP transistor as a switch.
 

ScottWang

Joined Aug 23, 2012
6,873
But in this case I am only allowed to use a PNP transistor not an NPN transistor.
Why you have that limitation, is this a school homework or project?

The better choice is to use an npn stage with one P ch MOSFET or an N ch MOSFET with one P ch MOSFET, both N or P ch MOSFET all use the logic level Vgs MOSFET.
 

Thread Starter

doctor spot

Joined Nov 26, 2018
5
Why you have that limitation, is this a school homework or project?

The better choice is to use an npn stage with one P ch MOSFET or an N ch MOSFET with one P ch MOSFET, both N or P ch MOSFET all use the logic level Vgs MOSFET.
No, Its not a school homework. I want the negative polarity of my load to be grounded whenever the transistor is turned off, thats why I choose an PNP transistor. I cant achieve this with a NPN.
 

ScottWang

Joined Aug 23, 2012
6,873
If the control is just normal high and low then the values of R2 can be use like 20K~47K, if the control is more active or the frequency is more higher then you can use the values shown below, the difference is that the Ic1 draw current of Q1(2N3904) and the reactive speed (response frequency), normally you don't need the R4, but you may need it when you want to turn off the Q1 fast and you can adjust the values of R4 to suit your need.

When you use BJT to drive the 280mA load then you should consider the power dissipation, you still can use one N ch MOSFET as IRF540 to drive the load when the control speed is very slow.

Arduino To Control a 280mA Load_ScottWang.png

IRF9540_Pch_100V19A_Vgs10V_20mΩ_with IRF540.
FDT434P_Pch_20V5.5A_Vgs±8V3W_Vgs_4.5V_50mΩ_Vgs2.5V_70mΩ.
 
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