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PNP transistor switching voltage
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danners430:
Hey guys, couple of questions regarding PNP transistors.

I'm planning on using a PNP device to switch a 12V system using a 5V MCU - as far as I can tell, I'd need some additional circuitry to make this work, as the PNP device would need 12V to the base to switch off completely?

Also, related question - what would I need for Vce?

Cheers guys :-)

Sent from my ONEPLUS A3003 using Tapatalk

iMo:
Transistors are not voltage driven devices but current driven devices.
You have to ask how much current would you need in order to switch a load with a PNP transistor.

And yes, you would need an another transistor to drive the PNP properly. For example:
EDIT: fixed the missing 1k resistor in Q2's base.
danners430:

--- Quote from: imo on August 13, 2018, 12:07:23 pm ---Transistors are not voltage driven devices but current driven devices.
You have to ask how much current would you need in order to switch a load with a PNP transistor.

--- End quote ---
I'm afraid you've completely lost me there... Certainly destroyed any idea I previously had regarding their operation [emoji23] could you expand?

Sent from my ONEPLUS A3003 using Tapatalk

iMo:

--- Quote from: danners430 on August 13, 2018, 12:10:08 pm ---
--- Quote from: imo on August 13, 2018, 12:07:23 pm ---Transistors are not voltage driven devices but current driven devices.
You have to ask how much current would you need in order to switch a load with a PNP transistor.

--- End quote ---
I'm afraid you've completely lost me there... Certainly destroyed any idea I previously had regarding their operation [emoji23] could you expand?

Sent from my ONEPLUS A3003 using Tapatalk

--- End quote ---
See above a schematics.
You are lost as you have not looked at the basics.. :)

Mind you have to specify how much current/how_fast you want to switch the LOAD on/off with the high-side PNP transistor, as you have to do some calculations as well.
danners430:

--- Quote from: imo on August 13, 2018, 12:21:45 pm ---
--- Quote from: danners430 on August 13, 2018, 12:10:08 pm ---
--- Quote from: imo on August 13, 2018, 12:07:23 pm ---Transistors are not voltage driven devices but current driven devices.
You have to ask how much current would you need in order to switch a load with a PNP transistor.

--- End quote ---
I'm afraid you've completely lost me there... Certainly destroyed any idea I previously had regarding their operation [emoji23] could you expand?

Sent from my ONEPLUS A3003 using Tapatalk

--- End quote ---
See above a schematics.
You are lost as you have not looked at the basics.. :)

Mind you have to specify how much current/how_fast you want to switch the LOAD on/off with the high-side PNP transistor, as you have to do some calculations as well.

--- End quote ---
Ah, gotcha.

Transistors have never been a strong point with me at all - I like to think I can work with most circuits, but for some reason transistors have always eluded me :-)

As long as I have some kind of functional diagram, I'm happy - it's literally just to switch LEDs as the micro can't supply sufficient current, speed etc isn't important :-)

Cheers for the help!

Sent from my ONEPLUS A3003 using Tapatalk

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