### Author Topic: Maximum transient current through a transistor?  (Read 962 times)

0 Members and 1 Guest are viewing this topic.

#### dsegel

• Contributor
• Posts: 22
• Country:
##### Maximum transient current through a transistor?
« 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

If necessary I could lower the voltage a bit.

#### Zero999

• Super Contributor
• Posts: 13404
• Country:
• 0999
##### Re: Maximum transient current through a transistor?
« Reply #1 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.

The following users thanked this post: dsegel

#### BigBoss

• Regular Contributor
• Posts: 59
• Country:
##### Re: Maximum transient current through a transistor?
« Reply #2 on: August 18, 2017, 06:05:15 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

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
It's got 4 channels.

The following users thanked this post: dsegel

#### dsegel

• Contributor
• Posts: 22
• Country:
##### Re: Maximum transient current through a transistor?
« Reply #3 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.

#### dsegel

• Contributor
• Posts: 22
• Country:
##### Re: Maximum transient current through a transistor?
« Reply #4 on: August 18, 2017, 06:21:20 pm »
Thanks, I'll check it out.

• Super Contributor
• Posts: 1875
• Country:
• Reactor Operator SSN-583, Retired EE
##### Re: Maximum transient current through a transistor?
« Reply #5 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.

Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer

Smf