Transistors

I have the following circuit and for some reason it does not work. Any ideas why or what i can do to fix it ??

transistors.fzz (4.1 KB)

You will get more replies if you post your circuit as an image and explain what you mean by "does not work".

Hi, by the look of the circuit you are trying to activate a coil using two transistors from the output of the arduino.
Can you tell us if this is the case?
Really you only need one transistor and a couple of extra components.
Also tell us what output pins you are using and what is base emitter and collector on the transistors and their part number.
Tom.. :slight_smile:

Thank you both for your replies !

I am trying to activate both transistors (BU2525DW power transistor, pins B C E) with the arduino mega 2560 output (pwm pins 9,8) and then the coils (connected to an external power source) should be activated. However, when I activate both transitors the coil is not switched on. Current flows through the pins on the tranistors but it does not flow through the coil. I am aware that it takes one transistor to switch a coil but the whole circuit is too complex to design. This is a part of the circuit.

I hope I gave all the information neccessary !

alex_poupakis:
Thank you both for your replies !

I am trying to activate both transistors (BU2525DW power transistor, pins B C E) with the arduino mega 2560 output (pwm pins 9,8) and then the coils (connected to an external power source) should be activated. However, when I activate both transitors the coil is not switched on. Current flows through the pins on the tranistors but it does not flow through the coil. I am aware that it takes one transistor to switch a coil but the whole circuit is too complex to design. This is a part of the circuit.

I hope I gave all the information neccessary !

no you didn't :wink:
do yourself a favor, and draw the schematics of your circuit, take a photo, resize it 900x600 and post it here .
looking at your fritzing file, it seems that the coil has one side connected to the collector of Tr1, and the other side to GND
The +5V is connected to the collector of TR2, which emitter is connected to..... GND ! imagine what happens when the output connected to base is HIGH !!

Drawing the schematics will help you to wire it on the breadboard

I hope I gave all the information neccessary !

Not really.

It looks like you have HALF an H-Bridge with a wiring error... but that's just a wild guess.

Here is the circuit.

look at the schematic that corresponds to a part of your wiring (only the 2 transistors on the left), but applies to the 3rd and fourth too :

what happens when TR2 base is HIGH ??

you really don't want to draw a schematics ?
I'm sure it would help you to wire it right !

PS : please, stop sending these fritzing breadboard circuits . We have to draw a schematics from it etc....

alex_poupakis:
Here is the circuit.

No it is not the circuit - it is a physical layout diagram and is only of any use to the brain dead.

If you can't draw a schematic then you can't make one.

look at the schematic

The photo is very small but I think you have connected the tr1 collector to the tr2 emitter right ?

When tr1 and tr2 bases are HIGH the coil is stil switched off.

No it is not the circuit

you really don't want to draw a schematics ?

Misunderstanding ! I will post a schematic as soon as it is ready !

alex_poupakis:

look at the schematic

The photo is very small but I think you have connected the tr1 collector to the tr2 emitter right ?

When tr1 and tr2 bases are HIGH the coil is stil switched off.

No it is not the circuit

you really don't want to draw a schematics ?

Misunderstanding ! I will post a schematic as soon as it is ready !

No, I didn't connect anything :grin: I just draw the schematics from your wiring. YOU have the TR1 collector connected to the coil, which other side is connected to TR2 emitter and GND !
TR2 collector is connected to +V ,emitter to GND ! When the base is HIGH, then TR2 saturates and there is a short between +V and GND !!
edit : and the arduino output is almost shortened to GND (via TR2 Base-Emitter junction ) , I doubt arduino will like it very long :grin:

Here is what I have done

Could you tell me how I can efficiently and safely connect this to arduino ?

Could you tell me how I can efficiently and safely connect this to arduino ?

There is no way in the current universe of the laws of physics that that circuit can do anything.

Can you say again what you are hoping to do and why.

I have 12 coils which I need to switch on and off with 8 transistors.
Two of the transistors (when switched on) connect six coils each with the negative pole of the power supply. The rest 6 transistors control two coils (one of the first six and another of the second six) and when switched on they connect these two coils with the positive pole.

Could you explain why it cannot work ?

I have 12 coils

good

which I need to switch on and off with 8 transistors.

Why the restriction?

Two of the transistors (when switched on) connect six coils each with the negative pole of the power supply.

I am just about with you.

The rest 6 transistors control two coils (one of the first six and another of the second six) and when switched on they connect these two coils with the positive pole.

Now you have lost me.

It might help if you say why you think you want to do this. You are dealing with a micro controller so if each coil is connected to a transistor you can turn any combination of coils on at any time. What advantage do you see in this seemingly complex arrangement?

alex_poupakis:
Here is what I have done

Could you tell me how I can efficiently and safely connect this to arduino ?

Agreed with Mike ....

but there are 2 or 3 things I'd like to add :

  • no, it is not what you have done, it is what you wanted to do.
  • in your...."schematics" , there are at least 2 things that could damage your arduino :
  • there are no resistor on the transistor bases -> the outputs go to GND via base-emitter junction -> too much current for arduino outputs
  • there are no protection diodes in // with the coils -> high peaks when the coil switches off . OK, they will more likely impact the transistors, but......

Do you know the resistance value of the coils ?

Now you have lost me.

It is a bit confusing I know but it might help if you take another look at my schematic.

What advantage do you see in this seemingly complex arrangement?

  1. I cannot spare more than 8 pwm pins(cannot do it with digital and all the analog pins are in use)
  2. There is not much room on the breadboard for an additional 4 transistors.

Do you know the resistance value of the coils ?

I calculated it as 3.8 Ohms.

  1. I cannot spare more than 8 pwm pins(cannot do it with digital and all the analog pins are in use)

Nothing like being up front with all the relevant information is there?
so what is the voltage you are trying to drive the coils with, you will not get more than 4.3V on the output of the top switching transistor if it is NPN.

So we know you are trying to PWM the coils but why, and to what end and why will this arrangement be any advantage to you?

The more you can cooperate the more help we can give you.

Let me explain the whole situation again and see whether we can find a solution to my problem.

I have 12 coils which I need to switch on and off whenever I need and they are connected to a 19V power supply. In order to do this I am using transistors. Unfortunately I can use only 8 transistors because there is no more room and I have only 8 pwm pins left (there are no more pins of any type to drive the transistors). I have come up with a more complex arrangment to drive those 12 coils with 8 transistors but from what I have seen and what you have told me, it does not work.

Given the above situation I hope you could tell me how (if there is a way) I could fix my circuit or how else to arrange it in order to work.

You haven't even explained it once before and sorry but you failed that time.

Eight PWM pins, what arduino?

Why do you need PWM pins anyway. How do you want the coilsto be controlled.
A power of 19V at a resistance of 3.8R gives you 5 Amps per coil.

The replies can only be as good as your questions and so far both have been unsatisfactory.