I need to activate a 12VDC, 8A diaphragm pump with the output of a PIC16F628 (5VDC, 0.025A maximum). The standard way to do it, as I learned in college, is to saturate a transistor that will drive a relay, that will activate the pump.
Now I am wondering if I could do it with a high current darlington NPN transistor driving the pump directly, like this:
Is it possible and/or viable? What are the advantages and disadvantages of this compared to using a transistor driven relay?
Is it easy to find a transistor with the required characteristics? 10A Ice, with gain from 0.025A Ibe to about 20A Ice (needed at pump startup, before stabilizing at 8A Ice). Is there such a device? From the datasheets I find on Google, the higher the Ice, smaller the Hfe, so that I can't drive a high peak current from the PIC…
By the way, what is the voltage drop from base to emitter I must consider in order to dimension R1?