EE 525 – Electronic Circuits II Laboratory
3 Voltage Regulator Circuits
3.1 Objective
• Understanding the principle of voltage regulator circuits.
3.2 Description
Series Voltage Regulator
The basic connection of a series regulator circuits is shown in the block diagram of Figure 1.
The series element controls the amount of the input voltage that gets to the output.
Figure 1- Series regulator block diagram
The output voltage is sampled by a circuit that provides a feedback voltage to be compared to a
reference voltage.
1. If output voltage increases, the comparator circuit provides a control signal to cause the
series control element to decrease the output voltage-thereby maintaining the output
voltage.
2. If the output voltage decreases, the comparator circuit provides a control signal to cause the
series control element to increase the amount of the output voltage.
Series Regulator Circuit : A simple series regulator circuits is shown in Fig. 2. Transistor
the series control element and Zener diode
operation can be described as follows:
is
provides the reference voltage. The regulating
EE 525 – Electronic Circuits II Laboratory
Figure 2 - Series regulator circuit
1. If the output voltage decreases, the increased base-emitter voltage causes transistor
to
conduct more, thereby raising the output voltage-maintaining the output constant.
2. If the output voltage increases, the decreased base emitter voltage causes transistor
conduct less, thereby reducing the output voltage-maintaining the output constant
Example
Calculate the output voltage and the zener current in the regulator circuit of Fig 3 for
Figure 3 – Example
Solution :
V0 = VZ − VBE = 12 − 0.7 = 11.3 V
VCE = Vi − V0 = 20 − 11.3 = 8.7 V
IR =
For
20 − 12
8
=
= 36.4mA
220
220
=1 kΩ,
IR =
V0 11.3
=
= 11.3 mA
RL
1k
=1 kΩ.
to
EE 525 – Electronic Circuits II Laboratory
3.3 Procedure
Step 1 - Input Voltage vs Output Voltage at a fixed load resistance
Figure 4
1. Build the series voltage regulator circuit in figure above.
2. Use analog voltmeter on KL-21001 for collector current measurements.
3. Use digital multimeter for VINPUT, VO and VZ measurements.
4. Using the variable voltage supply, apply a range of input voltages and measure
the values that are shown in Table 1.
5. Also calculate approx. IZ at regulation states.(β=150)
VINPUT
VOUT
IC
VZ
IZ
(Calculated)
3V
6V
9V
12V
15V
18V