Transistor Components

When used as amplifiers:

See also:

• The Electronics Companion - Lecture 5. "Transistor"
• The Intel Museum - How Transistors Work

Difference between transisters and fets and why you might want a fet instead Mark Willis says:

Transistors are current amplifiers, a FET is more like a voltage-controlled switch or (non-inductive) relay. I like HexFETs, just a quirk maybe. The logic gated ones have really been convenient in some packages I've made in the past. With a FET instead of a bipolar, you do have to make sure you saturate the FET (the logic gated FETs handle this for you.) The advantage is that, when switching a 1A 12V load (for example), instead of dissipating base drive * base current + Vce * Ice i.e (0.7V*(1A/hFE)) + (0.3V*1A) or about 0.31 watts in that transistor, you dissipate (1A^2*0R01) or 0.01W in that FET, if you're running off a battery pack that can make a big difference. (The 1A is the real killer, of course, in this case that was just the startup surge, and you need to saturate the transistor/FET for THAT; the sensor's supply current then dropped down to about 30mA - no use dissipating 20mA into that transistor, to keep a 30mA load switched on, the HexFET made a big difference here. Net savings, about 35% of the power budget, for one project.)

Russell McMahon [apptech at CLEAR.NET.NZ] says

• A transistor with opposite to normal voltage applied to C-E and base open will breakdown at some voltage - typically around 9 volts or so
• Adding a base to emitter resistor greatly reduces this voltage and softens the knee.
• Adding instead a collector - base resistor does similar but with somewhat less severity.
• IT MUST NOT BE ASSUMED THAT A REVERSE BIASED BIPOLAR TRANSISTOR WILL NOT CONDUCT THROUGH A REVERSE BIASED JUNCTION !!!!!!!!!!!!!
• Adding a series diode in series with the transistor's collector is a good idea when reverse biased C-E junction will occur if well defined operation is desired,

see PICList Thread %analog design challenge% for more.

Archive:

• List post "Lists of complementary transistors?" +
• PICList post "The Answer :-) - Analog Design Challenge - explain this" +
• PICList post "Semiconductor tester" identifying and testing MOSFETs

See:

• /techref/piclist/projects.htm
• /techref/piclist/jal/bitsandbytes.htm
• /techref/piclist/burdetteswitcher.htm
• /techref/microchip/devices.htm
• /techref/piclist/jal/drivingbipolarsteppermotors.htm
• /techref/microchip/power.htm

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