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I am trying to understand the working of this Darlington transistor array. I am using it for inductive loads and for driving the loads of my relays, but now I am trying to understand the part of its ability to drive high loads.

What for the high current drive is needed, if the use of the load driving is just to have a current path and to energize the inductor by the COM supply?

For my relays (min switching power 5V, 100mA,) I am using AC/DC power adaptor + buck converter, so the output power is around 5V, 3A load.

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ What voltages are you using for com and in? \$\endgroup\$
    – José Manuel Ramos
    Commented Jan 24, 2020 at 9:35
  • \$\begingroup\$ IN voltage is around 5V (MCP23017 I/O expander) and maximum current sunk from this pin is 25mA. COM voltage is 5V, max current 400mA. Need to mention that there are cases where I use two relays at the same time. \$\endgroup\$
    – Gabriel
    Commented Jan 24, 2020 at 9:51
  • \$\begingroup\$ Good for providing a schematic, but please rotate it through 90 degrees anticlockwise, so +ve to the top of the page, ground to the bottom. It's how 100% of the engineering population draws schematics. \$\endgroup\$
    – Neil_UK
    Commented Jan 24, 2020 at 9:51
  • \$\begingroup\$ See this discussion also electronics.stackexchange.com/questions/235668/… As you are only sinking 400mA, I would suggest a low Rds, logic level gate N-channel MOSFET so there is less voltage drop across the switch and more voltage available to the load. AOD508, AOD514 are two very good examples digikey.com/products/en/discrete-semiconductor-products/… \$\endgroup\$
    – CrossRoads
    Commented Jan 24, 2020 at 15:14

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