Ganging outputs - UDN2981A High-side driver

J

jedynakiewicz

Senior Member
I need to switch a number of outputs through a driver chip; normally I would use the ubiquitous ULN2803A but in this case I need to switch the high side. Fortunately, before they became discontinued, I bought a number of UDN2981A chips. These are really the high-side switching equivalent of the ULN2803A and have proved to very useful. The problem is that they do not quite have the same current rating and I am just getting a bit marginal at 400mA. They are specified for 500mA but 350mA is recommended deeper in the graphs within the datasheet (http://www.rapidonline.com/pdf/82-2202.pdf). I recall Hippy proposing piggy-backing ULN2803A chips in order to increase the output; also ganging up two or more lines within the chip is possible.

Do any experts foresee any problems in ganging up the outputs of the UDN2981A chips? I see no reason why I shouldn't, but it would be helpful to know if I am missing something before I waste a scarce resource and before I have to reach for discrete PNP power transistors or MOSFETs.

I would very much value your opinions and observations.
 
JimPerry

JimPerry

Senior Member
How may outputs and what voltage & curren? OK 500ma mentioned -- but how many? Is cost a big factor? :confused:
 
J

jedynakiewicz

Senior Member
Jim, I just want the output doubled. 700mA would do fine - hence the piggy-back idea or ganging up two outputs together. If you can suggest anything else (and cost is not a factor at all) I would be delighted to hear it. The simplicity of the single chips on my strip-boards is why I was choosing the DIL route; like the ULN2803s they sit so easily next to a PICAXE chip.
 
JimPerry

JimPerry

Senior Member
I use DIL P Fets (@76p each) to do trhis sort of thing 1Amp 60V - but ganging the existing chips would probably be fine :)
 
J

jedynakiewicz

Senior Member
Jim, thank you for that ... could I trouble you for a part number? Can't immediately find what you are referring to. Anything on Rapid?
 
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