jsolarski 94 Posted September 28, 2010 Share Posted September 28, 2010 Types of transistors(basics) type BJT, JFET, IGFET (MOSFET), IGBT most common transistors are BJT or MOSFET(FETs) we will be just going into BJTs, FETs should be discussed another time Bipolar junction transistors(BJT) are used to amplify current, but a side effect is they can be used as a switch. If you would like to know exactly how they work you may want to consult Wikipedia or your local libray or google. *transistor = BJT transistor for this document/post* transistors come in 2 common polarities, NPN and PNP, they both function on the same property but are biased differently NPN - voltage/current flows from the emitter to the collector and is controlled by the base current/voltage when the base current is applied to the base, more current flows from E to C PNP - current/voltage flows from the collector to the emitter and is also controlled by the base current/voltage when the base current is 0v current flows from C to E, but when voltage is applied, the current will be limited *the arrow on the symbol is the way the current flows Pins on the Transistors, some power transistors have 2 pins and one connected to the housing/case collector - think of it as a label, but refers to how the transistor works base - your control current/voltage emitter - think of it as a label, but refers to how the transistor works some sample circuits to get you started Basic use NPN switch Sensors LDR/photo-transistor an LDR or photo-resister or CDS cell can be substituted for photo-transistors sample 1 - when dark, more current flows through sample 2 - when light, more current will flow through R2 = is your gain, you can substitute a Potentiometer for the resister to adjust the gain amp Darlington pair + Szikai pair darlington is more useful then the szikai. I like to use darlingtons for touch sensors or anything else that has a low voltage, that needs to be read. also you can buy darlington arrays, in a DIP package, single TO92 packages or build your own. personally i have never used the szikia in a project. Its just a reference, usually used in audio amps. Ignore my BCE labels on the darlington i had mess it up........the E and the C are just reversed, sorry. values to consider IC max. - max collector current VCE max. maximum voltage collector to emitter hFE min. minimum gain When using s switched load like a Coil, solenoid, motor, relay - add a diode across(parallel to) the load to prevent voltage spikes when the load is switched off (IE the diode should be opposite of current flow\) sources http://www.kpsec.freeuk.com/trancirc.htm http://en.wikipedia.org/wiki/Transistor http://en.wikipedia.org/wiki/Bipolar_junction_transistor http://en.wikipedia.org/wiki/Baker_clamp http://www.bcae1.com/trnsistr.htm http://letsmakerobots.com/node/2907 http://www.ampslab.com/c200cfp.htm Quote Link to post Share on other sites
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