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Topic: Darlington array selection (Read 920 times) previous topic - next topic

Sean Wagner

I'm using an Arduino Mini Pro to soft-PWM currents up to 1.1A at 5V (and max about 1.5W per) via individual transistors. This works.

Now I'd like to see if substituting Darlington arrays might make sense, and have selected the following to experiment with:

STMICROELECTRONICS - ULN2064B - DARLINGTON ARRAY 4NPN, 2064, DIP16 <- 5V logic family
http://www.st.com/internet/analog/product/65562.jsp

STMICROELECTRONICS - ULN2068B - DARLINGTON ARRAY 4NPN, 2068, DIP16 <- TTL, CMOS 5V
http://www.st.com/internet/analog/product/65566.jsp

STMICROELECTRONICS - ULN2074B - ARRAY, DARLINGTON
http://www.st.com/internet/analog/product/65568.jsp

I take it the TTL logic isn't compatible with Arduinos? Can I solder them directly, or is using a DIP socket mandatory? Do I need resistors too?

Any advice and pointers to good tutorials are highly welcome - I've obviously searched the forums old and new, and done some googling, but the specifics elude me.

RuggedCircuits

Not recommended. At 1.1A each Darlington driver will be dissipating a significant amount of power (>1W) due to its internal saturation voltage (the VCE(SAT) number in the datasheet on page 6). This will cause the chip to be destroyed. Yes, it says "up to 1.5A for each Darlington" but that is marketing-speak and assumes you are aggressively heat-sinking the device, and does not say anything about 1.5A for ALL 4 Darlington's at the same time (no way!)

Never trust a number on the front page of a datasheet :)

I'd stick with the discrete transistors at these current levels.

I'm not sure what you mean by "TTL logic isn't compatible with Arduino", indeed it is and the three devices you picked out can be driven from an Arduino.

--
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Sean Wagner

Thank you, that's very helpful! I looked up the VCE(SAT) in the datasheet to at least learn something by osmosis. :)

MarkT

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I'm not sure what you mean by "TTL logic isn't compatible with Arduino", indeed it is and the three devices you picked out can be driven from an Arduino.


Suspect this is a reference to CMOS in general not being drivable from TTL levels unless specifically designed to have a low enough threshold(high is 2.4V in TTL).  This is why there are HCT as well as HC CMOS logic family.  Its a non-issue here because we are talking about CMOS outputs driving TTL levels which isnt the problem.  Also the darlington arrays don't have a TTL input circuit anyhow!

So if you are using TTL chips to drive Arduino inputs you need pull-up resistors to ensure correct operation.
[ I won't respond to messages, use the forum please ]

Grumpy_Mike

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So if you are using TTL chips to drive Arduino inputs you need pull-up resistors to ensure correct operation.

As we say in my part of the world..... give over.

You can connect a TTL output directly to an arduino input. I always do it, it always works.
The maximum high of 2.4V for TTL is only applicable at the maxium current loading from the device.

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