Activate 12v pnp via arduino

i have 4 NPN (bd679) and 4 PNP (bd680) transistors

I want to use them as matrix 4x4 so i can control/switch on off 16 devices that use 12v voltage

I can control NPN just by connecting pin from arduino to base of transistor but how can i control 12v PNP transistor

through an optocoupler

or with a signal level N-MOS

The base-emitter voltage has to be zero to turn it off. So it takes 12V on the base to turn-off the PNP.

You might add a npn driver transistor... bc547.

Is it beter to use bd679 or bc547

Here is a typical schematic for a PNP "high side switch", low current design. For your particular application, follow the basic design rules for saturated bipolar transistor switches. Good textbook: The Art of Electronics, by Horowitz and Hill.

See schematic in post #7.
NPN transistor can be almost any general NPN transistor.
BD679 is a power transistor. It is not made for this purpose, but I guess it would work.
Usually BD transistors have lower amplification factors, but here that does not really matter, as even a factor 10 would be sufficient in this schematic....
What are the devices you want to control???
Given the fact you are using BD transistors, it seems that your load might be far lower than the 4 kOhm shown in post#7.
If so, you would need to reduce all resistors in the schematic accordingly... It will be important to drive your power transistor into saturation, so the base resistor to your BD PNP would need to be order of magnitude 100 Ohm if you have a 10 Ohm load (I see @jremington already warned you for this)...

a resistor between the base and emitter of transistor Q2 will not be superfluous

BJT transistors are current driven.
No curent into the base = no collector current.
Different story for (voltage driven) fets.

So why R2.. :slight_smile:
Leo..

What about power transients? )))
without this resistor, when power is applied, the relay may spontaneously turn on for a while
PS we live in an imperfect world and components from China are no exception

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