ULN2803 ok to be driven by 3.3V logic?

drive

only

usual.

When it comes to circuit design I am, when it comes to beer, wine and cheese then I am not :-)

Once I had an inductor in a design and it cost something like a buck sixty. Was quite happy that I got away with that one by upping a switcher frequency. While talking with the client they asked whether there would possibly be a cheaper inductor.

Remember when some guys here thought I was nuts for suggesting that resistors other than 1% are still useful? An assembler in China once sent a formal request via my client, to identify those that could be increased from 10% to 20%. That is not a joke. 15 minutes of billed time later they had the list. Don't remember exactly but I believe it saved something like 30 bucks. Per month, and it's now 15 years and counting ...

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Regards, Joerg

http://www.analogconsultants.com/

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Thanks, Mark. However, Digikey has only DIP and stock on the first one is zero, very low on the second one. That always gives me the goose bumps.

Yep, that's right, old TTL never went much past 3V.

--
Regards, Joerg

http://www.analogconsultants.com/

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Driving ULN2803 from 3.3V might be OK for most micros and logic. Be careful with the 8051/2 as the P1 P2 and P3 outputs have very limited high drive (essentially -60uA at Vcc -1.5).

The On Semiconductor NUD31XX series 'Industrial Inductive Load Drivers' (comes in singels and duals) are especially suited for relays and other inductive loads.

The NUD31XX devices come with 5V, 12V, 24V and 60V inductive protected outputs. Continuous output current sink varies from about 500mA (5V) to 150mA (60V) depending on the Vgs available and Vds that can be tolerated. Their low threshold (2V5 fully on) FET inputs should work with most 3.3v logic and micros.

A bit pricy at +- $0.37 each per 100 for the dual devices.

For detail see:

(go to and search for NUD31 if URL wrap causes a problem) Most of these are available from Mouser. Search for 'NUD31' to see price and availability of the series.

Another option might be to look at biased transistors available at 0.03 each or less. Board populating cost might offset the low device cost. Biased transistors would however require an inductive protection diode and input drive might be a problem. (3 to 5 mA input for the 60mA output required). I often find biased transistors cost effective due to lower assembly costs.

For Joerg's application the ULN2803s seems to be the most cost effective solution.

Gerhard van den Berg CSIR