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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

JRE
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Gabriel
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  • What voltages are you using for `com` and `in`? – José Manuel Ramos Jan 24 '20 at 09:35
  • 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. – Gabriel Jan 24 '20 at 09:51
  • 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. – Neil_UK Jan 24 '20 at 09:51
  • See this discussion also https://electronics.stackexchange.com/questions/235668/is-there-any-reason-to-use-junction-or-darlington-transistors-for-power-applicat/235686 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 https://www.digikey.com/products/en/discrete-semiconductor-products/transistors-fets-mosfets-single/278?k=aod5 – CrossRoads Jan 24 '20 at 15:14

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