EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: dsegel on August 18, 2017, 05:14:10 pm

Title: Maximum transient current through a transistor?
Post by: dsegel on August 18, 2017, 05:14:10 pm

I have an application where I want to switch a path through a transistor that will be +/-20V and may go up to 2A. The current will only be flowing for about 100ms, with at least 1 second in between. I'm currently planning on using a ULQ2003A transistor array because I need 6 of them to control 6 devices independently.

My question is, how do I know if this will work, or if I'm going to blow up the transistors? The datasheet for the ULQ2003A is here: http://www.mouser.com/ds/2/389/ulq2001-957368.pdf (http://www.mouser.com/ds/2/389/ulq2001-957368.pdf)

If necessary I could lower the voltage a bit.

Title: Re: Maximum transient current through a transistor?
Post by: Zero999 on August 18, 2017, 05:51:21 pm

The data sheet specifies a peak current of 600mA.

Another issue you may have is that the Hfe of the transistors might not be high enough to give a low enough on voltage. The transistor might operate in its linear region acting like a current sink, dropping most of the voltage, leaving very little for the load.

Title: Re: Maximum transient current through a transistor?
Post by: BigBoss on August 18, 2017, 06:05:15 pm

Quote from: dsegel on August 18, 2017, 05:14:10 pm

I have an application where I want to switch a path through a transistor that will be +/-20V and may go up to 2A. The current will only be flowing for about 100ms, with at least 1 second in between. I'm currently planning on using a ULQ2003A transistor array because I need 6 of them to control 6 devices independently.

My question is, how do I know if this will work, or if I'm going to blow up the transistors? The datasheet for the ULQ2003A is here: http://www.mouser.com/ds/2/389/ulq2001-957368.pdf (http://www.mouser.com/ds/2/389/ulq2001-957368.pdf)

If necessary I could lower the voltage a bit.

If you application is purely to switch a signal during 100ms, I recommend you to use Switching MOS Transistors.They have more current carrying capability and higher dissipation capacity on them.
http://www.onsemi.com/PowerSolutions/product.do?id=FDMQ8403 (http://www.onsemi.com/PowerSolutions/product.do?id=FDMQ8403)
It's got 4 channels.

Title: Re: Maximum transient current through a transistor?
Post by: dsegel on August 18, 2017, 06:19:21 pm

Yeah, i just read up on Hfe and realized it might be a problem.

I saw the 600mA spec, but didn't know if that applied to transient events.

Title: Re: Maximum transient current through a transistor?
Post by: dsegel on August 18, 2017, 06:21:20 pm

Thanks, I'll check it out.

Title: Re: Maximum transient current through a transistor?
Post by: danadak on August 21, 2017, 12:14:31 am

Google "octal power driver", a number of alternatives. Darlingtons suck because they
have such high Vcesat.


Regards, Dana.