Ib = 1/10 Ic is a good place to start from. thats where i start glen John Mitchell wrote: > On Mon, 17 May 1999, Adam Bryant wrote: > > > I recently picked up a number of 2N5192's surplus and would like to use > > them to construct an H Bridge motor controller (controlled from a PIC of > > course). The motor I will be driving will draw around 1.5A. My power > > supply is a 12v 5A battery. The problem (if I read the datasheet > > correctly) is that the "Collector-Emitter Saturation Voltage" of the 5192 > > is specified as Ic=1.5Adc, Ib=0.15Adc. As I understand this, for my > > Collector-Emitter current to be the 1.5amps I need to drive the motor, I > > need to drive the Base with 150mA. Is this correct? So my thought was to > > add another transistor between the PIC and the 2N5192's to amplify the > > signal from the 20mA the PIC can source to the 150mA needed for the > > 2N5192. Seem reasonable? Are there any other options for doing this > > using the 5192's? I would hate to have to use 8 transisitors per motor > > H-bridge. > > I'd strongly suggest ditching your 5192s and just buy a L298 or LMD18200 > to handle your motor. The 298 will do 1A, 3A peak; the LMD is heftier. > > This site has more info, theory, and a PCB: > http://www.dprg.org/hbridge_theory.html > > You can get a 298 surplus at BG Micro (http://www.bgmicro.com/) for $3.49 > US. Note: you'll need fast-blow diodes. Or, a kit from HVW Technologies > is available for $25 CDN at > http://www.hvwtech.com/robotics.htm#motor_drivers > > But if you're desperate or really cheap: yes, as far as I know, you can > use a small transistor to switch the larger transistor: the pair forms a > relative of the Darlington amplifier, for which you can search for more > info. > > I'm building a small 6-transistor H-bridge, and it's basically is a pain > in the ass. But this is my first real-world project, so it's a Valuable > Learning Experience :) I'm using a variation of this circuit: > http://www.wizard.org/schem/motor.html > > - j