This is a multi-part message in MIME format. ------=_NextPart_000_018E_01C57D87.BE7FCA30 Content-Type: text/plain; format=flowed; charset="Windows-1252"; reply-type=original Content-Transfer-Encoding: 7bit > This is a simple design I've used before. An excellent start at improving the original circy=uit. > The resistor count is quite high as I tend to play safe and always > have pullups/pulldowns on transistor bases to ensure they are > totally switched off, /> Usually wise. Here R2 & R3 can be eliminated if drive is active high or low (as a PIC pin is) as R4 and R5 deal with leakage currents. I'd say that 4 resistors was the sensible minimum except in special cases (R4, R5, R9, R10) This is similar to my redesigned circuit but I have added additional complexity to better meet some of the desied attributes. eg your circuit, which is fine as a basic driver, varies drive substantially with applied V+ (here Vcc). Even at a fixed Vcc it is always full on when driving meaning motor woyld have to be matched to supply. In many cases this is fine. > however I have seen this implemented with only two resistors in > total; limiting current to the outer NPN drivers base. /> That would mean an undefinedly high current through where R9 & R10 now are. Not nice but would work for certain range of supply voltages. > It's not a particularly clever circuit, but it does use the main > transistor in a common emitter configuration to ensure the lowest > Vce drop. /> It is cleverer than it could be. By having Q5 driving bases of Q2 and Q4 at once it improves the current gain of drive to upper and lower stages but does so with a single drive transistor. The 'cost" is that input drive needs to be 2 x Vbe plus drop across R5. OK at all but the lowest of drive voltages. Fine where you have 5v drive as I have. A good first candidate. 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