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10-10-2009, 06:25 PM #1
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FireMyLaser
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Transistor Problem

I have a bc337 transistor that I think fail to saturate. The voltage-drop between collector and emitter is 2V in the circuit below. I calculated the resistor for it many months ago and it seemed to work at the time, but not now. The transistor gets very hot at 450mA!

Anyone knows what's wrong?

Here is the specs:

collector-emitter voltage : 45V
collector current (DC): 500 mA
peak collector current: 1A
DC current gain IC = 100 mA: 100 - 250

Thanks for any help!

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10-10-2009, 09:36 PM #2
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FireMyLaser
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Re: Transistor Problem

I think I figured it out, it is a high side circuit, so no resistor should be used. If I'm wrong you're free to slap me in the back of the head LOL!
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10-10-2009, 10:03 PM #3
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Hemlock_Mike
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Re: Transistor Problem

I'm not sure here but in emitter load condition, (emitter follower), The emitter voltage is controlled by the load resistance. If you could saturate the base with no resistor, you would have a CE drop of ~0.7 volts but we don't know the curve I/R of the load.
Try dropping the input voltage a bit. Why saturate the transistor? Just use a diode as a .7 volt dropping device.

HMike
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10-10-2009, 10:24 PM #4
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Cyparagon
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Re: Transistor Problem

For what are you using it?

10-10-2009, 10:33 PM #5
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FireMyLaser
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Re: Transistor Problem

I'm using it in the RGV driver. I want the transistor to act like a switch.

What are you saying, Mike? I should replace the resistor with a rectifier diode?
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10-11-2009, 03:15 PM #6
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Cyparagon
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Re: Transistor Problem

Quote:
 Originally Posted by FireMyLaser I want the transistor to act like a switch.
So why can't you replace the transistor with a... switch?

10-11-2009, 03:32 PM #7
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nikokapo
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Re: Transistor Problem

Quote:
 Originally Posted by Cyparagon So why can't you replace the transistor with a... switch?
Not the same, I'm in a hurry but I'll explain later, or shoot me a PM.

FML, have you tried lowering the resistor value (or using a 1/2W one?) I support HMike's idea too, any diode should drop 0,7v.

10-11-2009, 03:36 PM #8
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FireMyLaser
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Re: Transistor Problem

Because they can't be switched several hundred times per second.. and allot of other reasons.

I tested it with no base-resistor through the night and the transistor was just warm.
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