Somoene Explain in Stupid Talk what a darlington driver is for?

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Digisapien

Member
Just building my own pcb for my project.... now switching to a 20m2 built my own board with upload/download stuff....its working fine the project board that is for the 20M2 has a darlington driver chip... but I cant find any real info as to what purpose a darlington driver serves?:confused:
 
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Rick100

Senior Member
Hello Digisapien,

Look in manual 3: pages 6, 7, 15, and 16. They are used to drive loads the Picaxe can't drive directly from it's pins. The uln2803 and uln2003 are commonly used in the microcontroller world to operate relays, lightbulbs, and small stepper motors.

Rick
 
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MartinM57

Moderator
In simple terms:

Darlington driver = a high gain pair of transistors where you don't need much current on the input side to control large currents on the output side

Often come as sets of 7 or 8 in a single IC package e.g. ULN2003/ULN2008 - as in the project board - often also called a "darlington driver", but actually they are multiple darlington drivers in one package


The most important thing is that they are normally "low side switches":
http://www.opencircuits.com/Basic_Circuits_and_Circuit_Building_Blocks#Transistor_Low_Side_Switch

So they act like a switch in the ground lead of your load (LED, motor, relay etc) and they are like...
...an open circuit/switch when the input to them is low - so LED, motor etc will be off
...a short circuit/closed switch when the input to them is high - so LED, motor etc will be on

They do not "produce" or "source" current themselves, they just switch your load on or off

However, they are not "perfect switches" and have/suffer from having a voltage across them when "on" - maybe 0.6 to 2 volts or so - and in some circumstances you need to be aware of that
 
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AllyCat

Senior Member
Hi,

Perhaps it's also worth mentioning that a "classic" Darlington Transistor consists just two transistors (connected with common collectors and one emitter to the other's base). However, the "Darlington Driver" integrated circuit packages not only contain several (7 - 8) Darlingtons but a number of "extra" components.

Typically, the ics have a resistor in series with each (input) base, "pull-down" resistors from each base to its emitter and a "catching" diode from each collector to the supply rail pin (if it's connected ! ).

So the ics can be a very easy "plug and play" component, but beware (as Martin says) they do have significantly higher voltage drops (Vbe and Vce) than a single transistor. So in some cases a simple BC548 or BC337 (or many others) can be a better choice.

Cheers, Alan.
 
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g6ejd

Senior Member
In days of yore when transistors first came out, their gain was low and so two transistors were used, one to drive another - known as a Darlington pair. Treat them as a single transistor and although the characteristics are different this can be ignored for most applications.
 
techElder

techElder

Well-known member
Along the lines of the ULN2003/ULN2008 packages of darlington drivers, is there a commonly used package of "FET" type switches for similar use? I've always just used individual "FET" packages.
 
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