I'd like to use PBSS4350SS transistors for driving multiple low power solenoids, but looking at the datasheet I can't figure out what value the base resistor (R1) should be?


simulate this circuit – Schematic created using CircuitLab


Work out the current through L1, roughly 12V divided by its resistance.

Divide this by the minimum transistor gain from the data sheet, this gives you a minimum value for the base current.

The voltage across R1 is 3.3V-transistor VBE or about 2.6V.

Divide this by the base current to give you the maximum value of R1, in practice you need lower this by about 10% to ensure the transistor is driven into saturation.

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