shift register "74HC595" output to open relay module

Hi there, I want to use the output of a shift register "74HC595" as signal for a relay module. is this possible? I read in a thread that it isn't possible because the low voltage/current and that it may damage the register. if isn't what should I add to get the required voltage/current? What is good for such a register if doesn't allow to control a set of relays? i think there is some solution around that.

Thank you!

What relay module? Do you have a link to the specs?

Most relay coils require too much current (and often more than 5V), but a “relay module” usually includes a driver of some sort to take the “load” off whatever’s driving it.

A "normal" shift register like the 74HC595 has max. current of 20 mA per output (and ± 75 mA continuous current through VCC or GND) so this may not be enough to drive relays directly.

You can use a "Power Logic Shift Register" like the TPIC6A595 (350 mA per output) or the TPIC6B595 (150 mA per Output). That are shift registers with MOSFETs integrated. They have switching capability up to 50 Volts. You could use one of these parts to drive relays directly.

74HC595, 70mA absolute max.
IO pins much less - 6-8mA.

TPIC6B595 very good as you noted.

74HC595 is a logic part, designed for using with computer logic, sending data to other logic chips.
Wasn’t intended for LEDs & such.

There are plenty of 5V relays, but they usually need higher higher current.
12V relays need less current - but you have to deal with 12V.
TPIC6B595 usually good for either.

There are some 5V telecon relays that only need like 16mA drive current, '328P can drive those directly. Be sure to add diode across the coil. They switch less than 2A.

I used G5T-1A, 5V coil relays with 5A contact rating, on these shields. The Uno shield uses TPIC6C595 for the coils, the Mega shield uses discrete transistors:


DVDdoug: What relay module? Do you have a link to the specs?

Most relay coils require too much current (and often more than 5V), but a "relay module" usually includes a driver of some sort to take the "load" off whatever's driving it.

it is a 5v HIGH ACTIVE http://image.dhgate.com/desc_307111468_00.jpg

Thank you all that was helpful an so clear. but I still have a question... do the transistors that appear on the relay card do the work for me? http://image.dhgate.com/desc_307111468_00.jpg

I didn't tested it yet because I wasn't sure the register or the board won't burn.

bilald:
Thank you all that was helpful an so clear.
but I still have a question… do the transistors that appear on the relay card do the work for me?

That is precisely what they are put there for. :grinning:

Paul__B: That is precisely what they are put there for. :grinning:

Wonderful life :D Plug & play