Question for electrical circuit geeks

[slackerisme]

I am looking at two different transistors. Am I right in assuming the only difference that matters to me (using it as a switch to prevent dc burnout) is the C to E voltage allowable. These are the two data sheets 1 & 2.

I am trying to use a 5v dc source to run a 12-48vdc motor at a predictable (i.e. slower than max) speed. TIA

 

[snowrs]

What is the amperage draw of your motor?

 

[Mr. Habib]

What is the current draw of your motor? The TIP 120s are only rated for 5A continuous. The 2N64... series are rated at 15A continuous.

 

[slackerisme]

Not that high for now I think. Going to use a CD motor for playing with circuit. I will get the higher max ones so I don't need to upgrade later. Thanks

 

[Mr Evilwrench]

You can definitely do that, but yeah, we need to know more. Then you get into heat sinking and all that. Do you need variable speed, or are you setting a fixed voltage?

 

[Mr Evilwrench]

Oh, and you'll want a reverse biased rectifier in parallel with the C-E connections. A motor is an inductive load, and upon interrupting the current you can get hella voltage spikes which will demise your transistor.

 

[slackerisme]

Fixed voltage supplying the motor. I plan on using the transistor to control speed, by controlling the speed at which it allows power to the motor.

 

[slackerisme]

Oh, and you'll want a reverse biased rectifier in parallel with the C-E connections. A motor is an inductive load, and upon interrupting the current you can get hella voltage spikes which will demise your transistor.

Diode, check.

 

[snowrs]

PWM controllers are designed to do exactly this and are much better at it.

 

[x10]

Let me jump the shark here, your not mentioning your drive circuit, I'm assuming your going to do it with a PWM not a linear type control, forget those 2nxxxx Transistors and go with a VN920

http://www.alliedelec.com/Images/Pr...OELECTRONICS_ACTIVES-AND-PASSIVES_2480120.PDF

I'm assuming your trying to use a 555 timer for your pwm, I would ditch that also but thats your choice.

 

[slackerisme]

Physical computing, already have the programmable portion, Arduino based.

 

[Mr Evilwrench]

That should be able to do the PWM, which is indeed the mode you would want for speed control. I always use MOSFETs for this kind of thing myself. Now, you said CD motor. What do you mean by CD motor? How many wires come out of it? This will only work for one with two wires. If it's some kind of brushless motor, you're into different circuitry.

 

[slackerisme]

The Arduino has a 5v PWM built in, but that is no fun. Its just a small motor taken from an old 4x cd rom drive. Yes its two wire.

 

[Mr Evilwrench]

Oh come on, if you have too much fun, your head will explode, then where would you be? PWM for speed control. Does it just need to go one direction? It's possible to do both