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Driving bistable relays with a 74HC541

  1. Oct 30, 2013 #1
    I'm currently considering my options for driving a bunch of single-coil bistable (latching) 5V/250Ω relays which set and reset at 3.75V.

    The solution I'm leaning on atm is one 74HC541 octal buffer/driver per four relays. The 74HC541 is rated at ±25mA per output, and if each output pair (four total) is grounded between pulses, I'm thinking there would be no need for any kickback protection either as the inductor would be shorted out at the end of the pulse.

    Timing/speed is not really a factor—I'm just switching in/out some low-level stuff once in a while. I know H-bridges is normally the right tool for the job, but the lack of google hits for this particular solution made me wonder if I've missed something obvious here? Thanks.

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  2. jcsd
  3. Nov 1, 2013 #2

    meBigGuy

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    Gold Member

    I thought I posted an answer to this already ---- strange

    There is nothing fundamentally wrong from building your own H bridge this way. But you are probably wrong about leaving off protection diodes (4 of them). Imagine what happens during any time when both buffers switch off while there is current in the coil, even for short transients. If both drivers turn off you will severly test the ESD diodes and anti-latchup protection of the chip (probably destroy it or progressively destroy it). There are faster versions that would have shorter transients.

    The short delays matter, like the inverter that is probably between the inputs. One mistake and the chip is likely toast if there are no diodes. And they need to be fast diodes.
     
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