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CHAPTER 5. DISCRETE SEMICONDUCTOR CIRCUITS
INSTRUCTIONS
Build this simple circuit, being sure to connect the diode in "reverse-bias" fashion (cathode
positive and anode negative), and measure the voltage across the diode with one battery as a power
source. Record this voltage drop for future reference. Also, measure and record the voltage drop
across the 10 k resistor.
Modify the circuit by connecting two 6-volt batteries in series, for 12 volts total power source
voltage. Re-measure the diode's voltage drop, as well as the resistor's voltage drop, with a voltmeter:
+
-
+
-
COM
A
V
V
A
A
OFF
Connect three, then four 6-volt batteries together in series, forming an 18 volt and 24 volt power
source, respectively. Measure and record the diode's and resistor's voltage drops for each new power
supply voltage. What do you notice about the diode's voltage drop for these four different source
voltages? Do you see how the diode voltage never exceeds a level of 12 volts? What do you notice
about the resistor's voltage drop for these four different source voltage levels?
Zener diodes are frequently used as voltage regulating devices, because they act to clamp the
voltage drop across themselves at a predetermined level. Whatever excess voltage is supplied by the
power source becomes dropped across the series resistor. However, it is important to note that a
zener diode cannot make up for a deficiency in source voltage. For instance, this 12-volt zener diode
does not drop 12 volts when the power source is only 6 volts strong. It is helpful to think of a zener
diode as a voltage limiter : establishing a maximum voltage drop, but not a minimum voltage drop.
COMPUTER SIMULATION
Summary :
Re-measure the diode's voltage drop, as well as the resistor's voltage drop, with a voltmeter: + - + - COM A V V A A OFF Connect three, then four 6-volt batteries together in series, forming an 18 volt and 24 volt power source, respectively. It is helpful to think of a zener diode as a voltage limiter : establishing a maximum voltage drop, but not a minimum voltage drop.
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source,diode,power,olts,diodes,zener,across,measure,series,resistors,record,four,resistor