Trying to replace this blown transistor from a dc motor speed controller. Looks like you can see the bulge of where it puffed up when it blew. Is my new replacement close enough?
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The code underneath is a Date Code.Just realized because of the bulge in the one on the left you might not be able to read it, but they both say D635. It's what is underneath that makes me not too sure if they are the same.
It's with the circuit open. To be more exact, I'm getting .906 volts with circuit open and .897 when it's hooked up to the transistor.The transistor base is current based. Not voltage.
Is the controller putting out 0.9 volts with the transistor in place or with the circuit open?
As I said before, there may be more problems with the circuit than you're aware of.Since the original transistor blew, there may be more problems with the circuit you're repairing than you are aware of.
At least now I know there is probably no transistor with enough gain to do that. Seems like there is a resistor that brings power to the source then there are 3 little transistors and a resistor that bleed off voltage from the source. Maybe I should see what happens to the source voltage when I remove one of them?It's sounding to me like the source (where the 0.906V comes from) may have been hurt when the original Tx'r blew. You need sufficient current to turn that transistor on. If your source is not capable of doing that then you're putting new shoes on a lame horse. I'm not the expert on this, but I would expect to see a higher voltage from the source.
As I said before, there may be more problems with the circuit than you're aware of.
Working from post #3 this is your transistor.which seems logical for your mentioned application. Just about anything you could want to know, including saturation data is in the data sheet. With a proper heat sink this darlington can drive 7 amps with a base current of 0.7 amp.
@slashmaster2 , And that's the key - base current, not voltage, is what turns a transistor on. Also notice the ratio; 10/1. It's a typical ratio and basic rule of thumb. But as Ron said, everything you need to know is in the data sheet.With a proper heat sink this darlington can drive 7 amps with a base current of 0.7 amp.
If you want to know the base current then yes, but keep in mind that when we measure current the meter is placed in series with the load. You do not want to setup a meter to measure current and place it between ground (for example) and in this case the transistor base.Thanks Ron! Thanks Tony! I'm not too good at understanding those charts yet. So in other words I should be using the DC Amps part of my multimeter to measure that transistors base?
Yeah I sure do agree!. I should have mentioned earlier that this motor controller worked perfectly fine before then it shorted out on it's own chassis and popped a transistor when I plugged it in. All because I didn't bother to put in all the screws for a test. Then I blew out 2 more transistors while messing with it. But the good news is I've studied all the paths of the circuit and think I know how it works now. There is that main transistor we talked about, a little transistor that bleeds off voltage from its base and 2 other transistors that bleed off voltage from the same base in 2 stages. So it's all about taking away voltage and not adding to it. I should ignore all capacitors in the circuit because they just prevent electrical noise don't they?If you want to know the base current then yes, but keep in mind that when we measure current the meter is placed in series with the load. You do not want to setup a meter to measure current and place it between ground (for example) and in this case the transistor base.
Since you are just looking to replace a transistor which has failed I guess I don't understand why all this measuring? The more you try tinkering around the greater the chances something else can go wrong or very wrong.
Ron
by Jake Hertz
by Jake Hertz
by Duane Benson