Transistor current source circuits

140

01:27:55

Art of Electronics 3rd ed. Figure 2.32

Left: 
Load is the collector resistor (NPN current sink)
Stiff (R1||R2<<βRe) voltage divider gives Ve≈1V emitter voltage, which creates Ic≈Ve/Re≈1mA current

Middle:
Load is the collector resistor (NPN current sink)
Zener diode gives a reference voltage of Vbe=5.6V which gives Ve≈Vb-0.6V≈5V.
Ic≈Ve/Re≈0.5mA

Right:
Load is the emitter resistor (PNP current source)
Three diode drops creates Vb≈10-1.8≈8.2V
Vc≈Vb+0.6V≈8.8V (PNP)
Ie≈(10-Vc)/Rc=1.2/560≈2mA

published 9 years ago

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