NPN BC547 AND PNP TIP127

[koolguy]

Hello,
I have question how to use BC547 At 12V from 5V micro controller in reverse biased, and tip 127 base from micro i.e. 5V and emitter at 12V?
thanks

 

[MikeMl]

We usually describe this as a low-side switch or a high-side switch, based on where the switching transistor is placed.
There are four possible combinations, NPN, PNP either high-side or low-side. Which do you think you need?

What are you trying to switch? Resistive? Inductive? How much current? How much loss can you tolerate?

Can the 12V power supply negative be tied to the 5V power supply negative? Should it?

 

[Nigel Goodwin]

Hello,
I have question how to use BC547 At 12V from 5V micro controller in reverse biased, and tip 127 base from micro i.e. 5V and emitter at 12V?
thanks

Check my PIC tutorials, specifically the Hardware Extras section.

 

[audioguru]

We usually describe this as a low-side switch or a high-side switch, based on where the switching transistor is placed.
There are four possible combinations, NPN, PNP either high-side or low-side.

But 3 of your 4 circuits DO NOT WORK:

 

[MikeMl]

Off course they all work. All four have some values of V(b) where the respective transistor is either fully turned ON or fully turned OFF. I made no claim that all four of these circuits could be switched directly by a micro-controller port pin.

When you understand what it takes to switch each of the circuits, your level of understanding is becoming useful...

 

[Nigel Goodwin]

Off course they all work. All four have some values of V(b) where the respective transistor is either fully turned ON or fully turned OFF. I made no claim that all four of these circuits could be switched directly by a micro-controller port pin.

Not 'exactly', only 1 and 4 are 'switches', 2 and 3 act in a very poor analogue fashion rather than 'switching' - and are very poor examples, often used by people who don't understand what they are doing.

 

[MikeMl]

Not 'exactly', only 1 and 4 are 'switches', 2 and 3 act in a very poor analogue fashion rather than 'switching' - and are very poor examples, often used by people who don't understand what they are doing.

Or used by people who know exactly what they are doing, and why 2 and 3 have an advantage over 1 and 4 for certain applications...

 

[upand_at_them]

Or used by people who know exactly what they are doing, and why 2 and 3 have an advantage over 1 and 4 for certain applications...

Such as?

 

[koolguy]

But 3 of your 4 circuits DO NOT WORK:

Hello,
I agree with AG 5v switching from micro to 12V load will not supply.
NPN i.e. low side is working , but when i work at PNP with hide side it not turning OFF the PNP when base is ties up to 12V from pull up 10K it is OFF and for PNP the micro 0V and 5V remain it in ON position!
so, there should extra combination to drive it!

 

[koolguy]

But 3 of your 4 circuits DO NOT WORK:

Hello,
I agree with AG 5v switching from micro to 12V load will not supply.
NPN i.e. low side is working , but when i work at PNP with hide side it not turning OFF the PNP when base is ties up to 12V from pull up 10K it is OFF and for PNP the micro 0V and 5V remain it in ON position!
so, there should extra combination to drive it!

 

[koolguy]

Check my PIC tutorials, specifically the Hardware Extras section.

Please link i have 7 segment display working 8.8V which has 4 chip per segments!

 

[Ian Rogers]

Do you need a totem pole setup... ie.. a NPN driving a PNP ...



Or just to drive a 12v component from a pic..


These are the images off Nigel's Hardware Extras page...

 

[koolguy]

Or just to drive a 12v component from a pic..

Hello,
1st fig is fine, because the display is common anode!

 

[upand_at_them]

NPN i.e. low side is working , but when i work at PNP with hide side it not turning OFF the PNP when base is ties up to 12V from pull up 10K it is OFF and for PNP the micro 0V and 5V remain it in ON position!
so, there should extra combination to drive it!

Tie the base to 12V via pullup resistor (10K or whatever). The micro then switches it by pulling it low (0V) and closes it by setting the pin to INPUT. 5V at the base will likely not turn it off.

 

[audioguru]

I showed why it didn't work. Here it is with an explanation: