I'm making an 8-channel mosfet array with a 74hc595 shift register to switch on IRLB8721 mosfets. This is meant to provide power to electromagnets, solenoids, and other 12v components. If I want an LED per output to indicate when the mosfet is "on", where in the circuit should it be placed? Between the shift register and mosfet? After the mosfet to be switched on by the 12v? If the former, should it be in series with the output pin going from the shift register to the gate of the mosfet? I want the light to be as dim as possible so that it's visible but draws little current.
Place the LED (with resistor) in parallel with the MOSFET load.
Make sure you have a series resistor on each LED.
Adjust the value of these resistors to get the LED brightness needed.
You might want to investigate using a TPIC6B595 if the load is small enough.
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Cool, thank you. Seems like the TPIC6B595 wouldn't provide quite enough current for my current needs (har har), but I will keep that part in mind.
There's also TPIC6595 (250mA per channel) and TPIC6A595 (350mA per channel).
That would probably cover some of my use cases, actually. Aside from the slight inconvenience of not operating at 3.3V. It says it has an absolute maximum source-drain of 1A, so an array of 8 electromagnets would be a bit much, but that's not a particularly common scenario for me. Looking at the pins, I can't quite understand where the higher voltage comes in? If all 8 drain pins need 12 volts (and I'm assuming I can't have varying voltage levels here?), what pin do I connect to 12V? Or are these all low side switches?
Yes, unfortunately, not only does it need min 4.5V supply but also the input signals need to be 0.85 x Vcc, so 3.3V data signals would need a boost, in theory.
Yes. The high voltage doesn't connect to the chip directly, and so yes, you could have varying voltages across the channels.
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