Hello majenko and dc42. Sorry for this delay, had to travel to work and no internet there (I swear
I'm not very experienced with transistors and electronics in general. I'm taking some time to understand the transistor's world and all the info are very welcome, thanks for all the tips and information about the matter.
Actually my small led array works just great feeding it with the same +5v used to power Arduino, had just to adjust resistors for the optimal bright. Point is that I’m using this actual circuit to test other conditions, looking forward to projects I may want to execute, like a wider display to be powered into car’s 12v VCC. From the answers you guys provided I have now some residual questions about the subject:
Discovered that PNP BJT’s aren’t good to load voltages higher than the microcontroller’s supply voltage, used for the logic control wired directly into microcontroller. NPN ones are OK in this situation? For the information I could read looks like they are OK for this, so just a confirmation here.
For darlington pairs the above problem of different voltage loads doesn’t happen as it does for BJT’s? By the circuit diagram for darligtons sounds like this isn’t a problem but I’m still not sure about it.
I can’t understand well. I was reading materials about MOSFETS and seems that bipolar transistors are good in the task of amplifying current and MOSFETS are good in the task of amplifying voltages. What confuses me after reading stuff like http://ww1.microchip.com/downloads/en/AppNotes/00898a.pdf
and others is that seems that MOSFETS are used to switch high loads so I can just ignore such comparison and fix only on the part datasheet for whatever plan I have? A point I see about MOSFETS is that they are voltage dependent do get saturate and this can be a problem while interfacing it from the logical part of the circuit, more like using intermediate transistors are needed to drive MOSFETS, so well yeah maybe this is a good point about avoiding MOSFETS if possible.
The UDN2981A is a good option but the PNP world is much more restrict than NPN one (I mean, parts are more difficult to find on regular market etc), so I may be using what I can find more easily that’s plain transistors or FETS or whatever easier to buy.
Steeping down the voltage and keeping things simpler sounds really a nice idea, the only problem I see on this is that all circuit possibilities (current), are subjected to the regulator limits.