Hi I'm new to using transistors

I saw a post for the same transistor and same current(1.5A) needed however I am using 5v instead of 12v. I'm asking what base resistor I need and maybe if you could tell me how much the voltage would drop. Thanks in advance.

 

Hi I'm new to using transistors

I saw a post for the same transistor and same current(1.5A) needed however I am using 5v instead of 12v. I'm asking what base resistor I need and maybe if you could tell me how much the voltage would drop. Thanks in advance.

We cannot tell you anything useful without seeing your proposed schematic; please post a copy.

 

Hi I'm new to using transistors

I saw a post for the same transistor and same current(1.5A) needed however I am using 5v instead of 12v. I'm asking what base resistor I need and maybe if you could tell me how much the voltage would drop. Thanks in advance.

What resistor? How is the transistor connected?
Can you post a clear schematic please (hand drawn is fine)?

 

Sorry

 

What resistor? How is the transistor connected?
Can you post a clear schematic please (hand drawn is fine)?

Sorry, is this ok? I haven't put a resistor value as that is what I'm trying to find out.

 

What transistor are you using?

 

Looks like you're switching the load posative lead with a Pnp, you can use a 1 to 4.7K resistor, ideally what type of transistor are you using will help...

 

Looks like you're switching the load Negative lead with a Pnp

Switching the positive lead.

 

Sorry, is this ok? I haven't put a resistor value as that is what I'm trying to find out.View attachment 190965

What is the load?

Maybe you can try this

 

Looks like you're switching the load Negative lead with a Pnp, you can use a 1 to 4.7K resistor, ideally what type of transistor are you using will help...

Thanks for the replies. Should I be switching the positive side with a PNP transistor. Also, would there be any difference with 1k to 4.7k resistor or would they do the exact same thing? Thanks

 

What transistor are you using?
The necessary value of the resistor depends on the gain of the transistor. To determine that we need to look up its datasheet.

 

See. The diode may not be used, but with a weaker load, it limits the saturation and speeds up the shutdown of the powerful transistor.

 

What transistor are you using?
The necessary value of the resistor depends on the gain of the transistor. To determine that we need to look up its datasheet.

It's a bd140 transistor. Isn't the transistor on the positive side?

 

It's a bd140 transistor. Isn't the transistor on the positive side?

Yes, the transistor is on the positive side and that is fine.
The maximum rated collector durrent for the BD140 is 1.5A so you would be pushing your luck using it with a 1.5A load as your diagram says. You really need to leave a safety margin, perhaps using a transistor with maximum current rating of at least 3A. Also the gain would be rather low at that current requiring lots of current from the arduino pin.

[EDIT] If you look at @Bordodynov circuit you will see an extra transistor to get around the low gain problem.

 

Yes, the transistor is on the positive side and that is fine.
The maximum rated collector durrent for the BD140 is 1.5A so you would be pushing your luck using it with a 1.5A load as your diagram says. You really need to leave a safety margin, perhaps using a transistor with maximum current rating of at least 3A. Also the gain would be rather low at that current requiring lots of current from the arduino pin.

The 1.5A is only used for a few seconds, so it should be ok. I used these resistors as I had them lying around and I want to make the project as soon as possible. Someone send use a resistor of 1k to 4.7k, do you know which resistor would require the least base current from the Arduino. Thanks so much!

 

If the maximum possible current is 1.5A then the resistor must supply sufficient base current for that. From the datasheet the typical gain may be just 30. So the base current would need to be 50mA which is above the maximum for the arduino. If you want to use the BD140 then you need the extra transistor as in post #12.

 

You will need 150 mA. The Arduino cannot supply that, so you need another transistor to raise the base current to that level.

Bob

 

If the maximum possible current is 1.5A then the resistor must supply sufficient base current for that. From the datasheet the typical gain may be just 30. So the base current would need to be 50mA which is above the maximum for the arduino. If you want to use the BD140 then you need the extra transistor as in post #12.
View attachment 190970

That's a bummer. Do you know of any transistors that can be turned on with Arduino and can handle 5v and 1.5A. thanks!

 

I would recommend a P-channel MOSFET for the job.
This would be good: https://www.digikey.com/product-detail/en/NDP6020P/NDP6020P-ND/1055922

 

That's a bummer. Do you know of any transistors that can be turned on with Arduino and can handle 5v and 1.5A. thanks!

TIP126 darlington transistor PnP.. 5A @ hfe 2500

Or a Pfet like IRF9540N...