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Transistor help

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guitardenver

New Member
I need to amplify 2.7v supply from a light up to a 9v battery. So I need a transistor that will open around the 2.7v voltage and will handle the amp draw from a geared up 6Ω motor from a cdrom.

I=v/r
I= 9/6
I=1.5Amps

What transistor will handle the 9v 1.5amp through the emitter collector. And will open the gate around 2.7v.

I am tired of blowing transistors!!!
 

crutschow

Well-Known Member
Most Helpful Member
A 2N3055 will readily handle the voltage and current if you place a clamp diode (1N4001-1N4007) in parallel with the motor (cathode to plus).

To get about a 2.7V threshold voltage you could add 3 diodes, such as the 1N4148 in series with the base resistor.
 

guitardenver

New Member
Great, could you explain the theory of why that would work I like to know it so I can use it for another project if i can use it. And that way I can uderstand it if I run into problems.

Is a clamp diode different than a regular pn junction rectifying diode or is it different like a zener diode?

I have a bunch of 2n2222, 2n3904, and 2n4401 transistors could I use one of them?

Also probably should mention that there will be two lights if one lights up it amplifies and makes the motor go one way and if the other lights up it amplifies and the motor goes the other way. Same motor oposite polarities so will the clamp diode work with both polarities?
 
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crutschow

Well-Known Member
Most Helpful Member
A clamp diode is just a regular pn junction diode such as the 1N4001 I suggested.

Those transistors are low current and can not drive the motor. If you look up their data sheets you will see their maximum ratings. You can't design without looking at data sheets (I know many of you try).

If you reverse the motor by reversing the voltage polarity, then you need to put the clamp in that part of the circuit that is reversing the polarity. Without seeing the circuit, I can't be more specific.
 

i_build_stuff

New Member
So, you have a 2.7V signal that you want to control the transistor (on if input = 2.7V, off if input = 0)?


With a 2N3055, you could do this:

(+9V)----(motor)------------------------------(collector)
(2.7V input) -----(20 ohm resistor)--------(base)
(ground)----------------------------------------(emitter)

Just don't do it without that resistor, or your circuit will smoke! The circuit may work a bit better with a 10 ohm resistor, but it will have to be rated at about 1W instead of the usual 1/4W.
 

Roff

Well-Known Member
So, you have a 2.7V signal that you want to control the transistor (on if input = 2.7V, off if input = 0)?


With a 2N3055, you could do this:

(+9V)----(motor)------------------------------(collector)
(2.7V input) -----(20 ohm resistor)--------(base)
(ground)----------------------------------------(emitter)

Just don't do it without that resistor, or your circuit will smoke! The circuit may work a bit better with a 10 ohm resistor, but it will have to be rated at about 1W instead of the usual 1/4W.
I agree that a resistor is needed.
2N3055 is probably overkill for this application. He doesn't need a TO-3 package to dissipate a few hundred milliwatts. There are plenty of transistors in TO-220 that will handle 1.5A, like TIP-31 or TIP41.
Having said all that, I would probably try to get a MOSFET with Rds(on) specified at 2.7V. Fairchild has lots of them.

Don't forget the diode across the motor, which crutschow mentioned.
 

guitardenver

New Member
I'm still confused on why the diode is there, and in my second post i explained that there where two of those lights with a 2.7v output. If one turns on makes the motor go one way and if the other one turnes on it makes the motor go the other way. So is the diode configuration across the motor the same? Or will I just put two of them just the oposite way. The lights will not be on at the same time so that should work right?

So if I use the tip31 which I looked up the data sheet for and will handle 3A. what resistor should I use on the base and why and how did you come up with that. thanks for that suggestion I want this to be as compact as possible.

sorry for typing so much.:eek:
 

Roff

Well-Known Member
I'm still confused on why the diode is there, and in my second post i explained that there where two of those lights with a 2.7v output. If one turns on makes the motor go one way and if the other one turnes on it makes the motor go the other way. So is the diode configuration across the motor the same? Or will I just put two of them just the oposite way. The lights will not be on at the same time so that should work right?

So if I use the tip31 which I looked up the data sheet for and will handle 3A. what resistor should I use on the base and why and how did you come up with that. thanks for that suggestion I want this to be as compact as possible.

sorry for typing so much.:eek:
What kind of lights do you have? Are they LEDs? If so, you probably won't have enough current available to drive a bipolar transistor like a TIP31. How are you going to reverse the motor? You normally need an H-bridge or a DPDT relay to do this.
 

Sceadwian

Banned
You buy parts from radioshack and you think Digikey sucks??

Digi-Key - DIP05-1A72-11D-ND (Meder Electronic Inc - DIP05-1A72-11D)
is the first one I found. Half the price of the Radio shack one. It's coil voltage is 3.3 volts but all you need is a series resistor for 5 volt operation. It's also significantly smaller and rated for a higher contact voltage.
 

be80be

Well-Known Member
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Sceadwian

Banned
Yaeh it is a little silly.
Like I searched for 5V coil 125VAC 1amp relays, they don't sell any. But they sell several 3.3V coil 200VAC 1 amp relays. It's a reed relay too they switch pretty fast.
 

be80be

Well-Known Member
I like Google it a very powerful tool if you use it right you can find out what your old lady or man is doing on the net. Now I don't think it hard for it to find a part. It's the only way to find what you need
 

Sceadwian

Banned
Most people don't know that google can be used to search a single domain.
 

audioguru

Well-Known Member
Most Helpful Member
The OP forgot to say how much current is available at 2.7V. The 2N3055 or TIP31 transistor needs an input current of 150mA to saturate properly.
 
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