Arduino PNP transistor wiring

Hi all, I'm an electronic newby and I'm not sure how to wire the analog out of the arduino board to a PNP transistor. Here are the connection of the circuit I'd like to realize:

arduino pin 3-> resistor Rb -> transistor E +12Vcc external power source -> transistor E transistor B -> arduino GND -> external power source GND transistor C -> Rc -> external power source GND

Beside the value of the resistors and transistor, I'm confusing about the connection to the ground. Are them correct? The main issue for me is the fact that in another portion of the circuit the external power source and the Arduino GND are already connect. Thank you in advance,

arduino pin 3-> resistor Rb → transistor E

More usual to wire the output pin to the base of the transistor.
What are you trying to do?

I've understand that in PNP transistor the current flow into the base. Due to the fact that the pin3 output is a positive voltage I've attached it to the emitter. I've found a lot of examples in the web with the two positive poles connect to the emitter of PNP transistor. What is confusing me is the connection of GND. No one of the examples on the web had both the positive poles and the GND connected together.

In my project I'm trying just to modulate the power of the resistor Rc.

No one of the examples on the web had both the positive poles and the GND connected together.

That's what we call a short circuit, so it's understandable you didn't find any examples.

I'm not sure how to wire the analog out of the arduino board to a PNP transistor.

Well there is no analogue output of the arduino board so you will struggle. Do you mean the PWM output, this is a digital output not an analogue one.

Due to the fact that the pin3 output is a positive voltage I've attached it to the emitter.

Very faulty logic, it is just plane wrong.

Output to base through a resistor. Emitter to +5V, collector to your load resistor, the other end of the resistor to ground.

I mean: 1) the positive poles of the arduino and external power source connected 2) the GND of Arduino and external power source connected

Thats what is called parallel connection, I suppose. What do you think about:

arduino pin 3-> resistor Rb -> transistor E +12Vcc external power source -> transistor E transistor B -> arduino GND -> external power source GND transistor C -> Rc -> external power source GND

How it works?

arduino pin 3-> resistor Rb → transistor E

When did we decide it a good idea to wire the output to the emitter?

  1. the positive poles of the arduino and external power source connected

That would probably be a Bad Thingtm

1) the positive poles of the arduino and external power source connected

No don't do this ever.

2) the GND of Arduino and external power source connected

Yes always do this.

Quote arduino pin 3-> resistor Rb -> transistor E +12Vcc external power source -> transistor E transistor B -> arduino GND -> external power source GND transistor C -> Rc -> external power source GND

How it works?

It works not at all and will damage your arduino if you try.

When did we decide it a good idea to wire the output to the emitter?

Well you can in a common base amplifier configuration but this is not the place to do this.

Says:-

This arrangement is not very common in low-frequency circuits, where it is usually employed for amplifiers that require an unusually low input impedance, for example to act as a preamplifier for moving-coil microphones. However, it is popular in high-frequency amplifiers, for example for VHF and UHF, because its input capacitance does not suffer from the Miller effect, which degrades the bandwidth of the common-emitter configuration, and because of the relatively high isolation between the input and output. This high isolation means that there is little feedback from the output back to the input, leading to high stability.

Grumpy_Mike 1) Where should I connect the 12Vcc external power source?

AWOL Ok, I will connect the PWM output to the transistor base. How can I control the current flowing into the pin 3?

It would help enormously if you tell us what you are trying to do, and what load you are trying to drive and why you want to use a PNP transistor and not an NPN.

1) I'm trying to change the load of the resistor Rc, that is just an heater, about 45W. The external power source feed 12Vcc and max 3.8A. 2) I'm using a PNP transistor because I've already buy it

  1. I’m trying to change the load of the resistor Rc, that is just an heater, about 45W. The external power source feed 12Vcc and max 3.8A.
  2. I’m using a PNP transistor because I’ve already buy it

I am guessing : 12 V = Automotive or Tailer or RV application

PNP to control from a PWM = Bad idea.

Use a Power MOSFET - logic type ← accepting a 0 to 5 V signal. <— Best

A NPN Power transistor ← OK

Just curious here… What the part number of the transistor in question ?

So if you want to switch 12V through a PNP transistor you will have to drive it with an NPN transistor. What is the gain of your PNP?

So arduino output to resistor -> to base of an NPN , emitter to ground, collector to resistor -> 12V Collector of the NPN to another resistor which connects into the base of the PNP. Emitter of the PNP to 12V, collector of the PNP to your load. The other end of the load to ground.

About my project:
12Vcc: recycled power source
PNP transistor: I’d like to understand how it works.
Transistor Part number TIP36C

Sorry about my reply… is it possible to wire the load to the emitter?
The connections:

  1. +12V → Rc (the load, about 3 ohm) → transistor emitter
  2. arduino pin3 → resistor → transistor base
  3. transistor collector, arduino GND → external power GND

How it works?

Sorry about my reply... is it possible to wire the load to the emitter?

What part of the word NO are you having trouble with?

1) +12V -> Rc (the load, about 3 ohm) -> transistor emitter 2) arduino pin3 -> resistor -> transistor base 3) transistor collector, arduino GND -> external power GND

How it works?

Again this does not work at all. I suggest if you can't understand English don't post in the English section.

About the TIP36C.

Here the link of the datasheet : http://www.datasheetcatalog.org/datasheet/motorola/TIP35B.pdf

The NPN version is TIP35B.

I agree with Grumpy_Mike here. Use the NPN version, if you CAN NOT have that option - Automotive - you will have no choise to use a relay ( connect to +12 V or No connection ) A relay solution is MUCH better in my opinion. Specially controlling a 45 Watt load - 12 V Heater. You still need to use a NPN - like a 2N4401 to control the relay.

Here a link about transistors use to turn on / off - switch mode http://www.kpsec.freeuk.com/trancirc.htm

A relay control schematic is on that site. I hope you know to understand a schematic.