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Name: ______________________________
ECET 242 – Electronic Circuits
Prelab 4
Regulated Power Supplies
Objective:
Students successfully completing this prelab exercise will accomplish the
following objectives:
1. Gain increased familiarity with using data sheets to determine device
parameters.
2. Gain increased understanding of how a zener diode can be used to regulate
a filtered power supply.
Lab Report:
A formal lab report will be required based on your combined results from labs 2,
3 and 4. Retain you results from this prelab exercise and combine them with
results from labs 2 and 3 and 4. The formal report will be due one week after lab
4 has been performed.
Equipment:
Zener diode data sheet.
Procedure:
1.
In Lab 4, you will be constructing a full wave rectifier with a zener diode regulator
(1N4734A) as given by the schematic of Figure 1. Using the data sheet on page 901 of the
course textbook for the zener diode, record each of the parameters specified in Table 1
below.
Table 1: Zener Diode Parameters
Quantity
Description
PD
Absolute maximum power dissipation
VZ
Typical zener voltage
IZK
Minimum zener (knee) current
IZT
Typical zener current
IZM
Maximum zener current
ZZ
Zener impedence
ZZK
Zener knee impedence
TA
Rated ambient temperature
Figure 1: Filtered, Regulated Power Supply
Value
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Examine the schematic for a full wave rectifier with a zener diode regulator shown in Figure 1.
Using the parameters for a zener diode obtained in the previous step, determine the quantities
which follow.
a. Peak secondary voltage, VS(P).
b. Peak capacitor voltage, VC(P).
c.
Series resistor current, IR.
d. Capacitor ripple voltage, VRPP.
e. Capacitor percent ripple, %VRPP = (VRPP / VC(P)) x 100%.
f.
DC output voltage, Vdc.
g. Load current, IL.
h. Zener current, IZ.
i.
Output ripple voltage, VRPP(Out).
j.
Output percent ripple, %VRPP(Out) = (VRPP(Out) / Vdc) x 100%.
2.
Remove the load resistance and determine the zener current, IZ. Will the zener diode be
safe with this current?
3.
If the load resistance is shorted out (RL = 0 Ω), determine each of the following quantities.
a. Total circuit current, IR.
b. Load current, IL.
c.
4.
Zener current, IZ.
A zener diode will regulate voltage as long as the zener current is greater than or equal to
the rated zener knee current, IZK. For the circuit of Figure 1, assume the zener current is
equal to IZK. With the 1 kΩ load resistor replaced, determine each of the following
quantities.
a. Total circuit current, IR.
b. Load current, IL.
c.
5.
Minimum allowable load resistance, RL(Min).
Calculate the output ripple and percent output ripple for RL = 470 Ω, and for the minimum
allowable load resistance. Record your results in Table 2 below. Does percent output
ripple increase, decrease or remain the same as resistance is decreased? Is the change
large or small?
Table 2: Output Ripple for Various Loads
Load
Resistance
(Ω)
RL(Min)
470 Ω
1 kΩ
Output Ripple
(mV)
Percent Output Ripple
(%)