Go Down

Topic: does uln2003 needs base resistor ?  (Read 934 times) previous topic - next topic

tautau123

I want to control several LEDs that work on 12V using arduino.

Instead of using NPN transistor, I'm using ULN2003.

I know that in regular transistors I need to use base resistor, do I need to do the same for the ULN2003 ?

raschemmel

#1
Nov 15, 2019, 09:49 pm Last Edit: Nov 15, 2019, 09:49 pm by raschemmel
If you Googled ULN2003 example circuit you would get this:


ULN 2003 example circuit
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Grumpy_Mike

Quote
I know that in regular transistors I need to use base resistor, do I need to do the same for the ULN2003
No.

DrAzzy

#3
Nov 15, 2019, 10:13 pm Last Edit: Nov 15, 2019, 10:15 pm by DrAzzy
No, the resistors are built-in.

Note that the ULN2003 is a pretty crappy part - they give the headline spec of 500mA, but in practice, the outputs only go down to like 1.4v or so even with low current, and the total current that you can have passing through the ULN2003 at any given time (based on its' thermal limits) is much lower than a naive reading of the datasheet suggests. I got a real shock (figuratively speaking) when I tried to use these for some (what I considered) light duty switching - they ain't nearly as good as you'd think based on a quick read of the datasheet by someone who isn't used to spotting how manufacturers spin their specs.

The TBD62003 is a pin-compatible, drop-in replacement that uses superior MOSFET switching elements instead of darlingtons; unless your load and/or duty cycle is really light, I suggest considering using the TBD62003 instead (there's also an 8-channel version to replace the '2803, and a P-channel version to replace... whatever the PNP version of the '2003 is called).
ATTinyCore for x4/x5/x61/x7/x8/x41/1634/828/x313 megaTinyCore for the megaavr ATtinies - Board Manager:
http://drazzy.com/package_drazzy.com_index.json
ATtiny breakouts, mosfets, awesome prototyping board in my store http://tindie.com/stores/DrAzzy

gilshultz

They will work just fine.  No resistor is needed it would only cause problems.  The information on the data sheet will tell you what they will do. They are silicon transistors in a darlington configuration.  A silicon transistor typically has a forward voltage base to emitter of 0.7 volts. When connecting in a darlington configuration you have two base emitters in series so you have forward voltage base to emitter 1.4 volts, this is reflected on the collector in a common emitter configuration. This is a good part and performs to its specification (assuming you understand the data sheet). There are a lot of different manufacturers of this part and they are not all the same you need to check there data sheets to be sure if you start loading them. They have thermal limits so you cannot turn all outputs on currently at full load but that is in the data sheet. The data sheets from reptrutable manufactures are correct for there parts, which meet or exceed there specifications. They cannot afford to cheat on the data sheets as most large customers test to them.
Good Luck & Have Fun!
Gil

Wawa

#5
Nov 17, 2019, 01:47 am Last Edit: Nov 17, 2019, 01:50 am by Wawa
The data sheets from reptrutable manufactures are correct for there parts.
Except for the polished bullshit on the first page of the datasheet.
That page is designed to trick unwary customers.
Leo..

larryd

The data sheets tells the story.

See equivalent circuit.





No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

Paul__B

The TBD62003 is a pin-compatible, drop-in replacement that uses superior MOSFET switching elements instead of darlingtons; unless your load and/or duty cycle is really light, I suggest considering using the TBD62003 instead (there's also an 8-channel version to replace the '2803, and a P-channel version to replace... whatever the PNP version of the '2003 is called).
According to the datasheet - it is actually crap!  Very poor performance, limited to 170 mA per output at 50% duty cycle with a 3.2 Ohm "on" resistance!  :smiley-eek:

There is a vastly better one somewhere.

wvmarle

There is a vastly better one somewhere.
I would hope so, haven't been able to find a good alternative yet mysefl.

Something that could handle 7-8 inductive loads of 2-3A each would be awesome. Saves a lot of parts.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Go Up