Driving higher current on pins with transistors?!

Official Hardware Classic UNO R4 Minima
1

Given the 8 mA max of the Maxima R4 Minima and R4 WiFi and reading Maximum Pin current!, Is there a generic way workaround R4's 8 mA current limit and not having to worry about what type of current <= 50mA I may connect to any given pin, is a transistor (like a BC337) the best way forward?

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Here a 540 Ohm resistor would lead to a ten time increase of the provided base current (of 8 mA).

Rb = (Vdd - 0.7) / Ib

If so, I would then build a board with say 16 channels and link it to the pin that drives a standard LED.

Or are there better, more contemporary solutions?

2

That is a fine solution. For multiple channels, you can buy ICs that have several bipolar transistors (e.g. CA3250F with 8 NPN).

The ULN2003 is an example of a Darlington array, suitable for driving high impedance unipolar stepper motors or relays.

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4

@MaxG
Your circuit only sinks current.
Do you also want to source current?

5

UNO R4 Maxima... oops, my apologies, I mean Minima, and somehow thought the R4 WiFi is a Maxima :smiley:

Yes...

No... but I could add jumpers when designing the PCB to use either. :slight_smile:

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Well, you asked for a generic workaround so I assumed source/sink.

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Not wanting to be a smart-ar$e... if both, sink and source, what do you suggest is being done differently?

I may not understand the difference. I thought sink vs. source relates to what is being switched; with source is what I showed in the O.P., and sink with the load being below the transistor (emitter to ground)?!

8

A circuit that would source current would use a PNP transistor and the load would be connected to ground.
That is how the ICs work (except with MOSFETs rother than BJT), they have both a PMOS and NMOS circuit connected to the pin, so it can source and sink current

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