Introduction to the principle of voltage stabilization circuit

Figure 11-4 RC (π) filter circuit
3. Voltage stabilization circuit
Although the ripple factor is greatly reduced after filtering, the output voltage is still not stable enough, mainly when the load current or power grid fluctuates,
the output voltage will change accordingly. For this reason, voltage stabilization measures are also needed.

The integrated voltage regulator contains four basic components, including sampling, comparison and amplification, reference voltage, and adjustment, which are composed of discrete components
, as well as overcurrent, overheating, and safety zone protection.
The DC voltage regulator composed of a three-terminal voltage regulator, bridge distillation, and capacitor filtering is shown in Figure 11-6.

Figure 11-6 DC regulated power supply
4 Main technical indicators of voltage stabilization circuit
(1) Voltage stabilization coefficient Sr

The internal resistance of the voltage stabilizing circuit reflects the load characteristics of the voltage stabilizing circuit. As long as the UI is fixed, the
output voltage UOL can be measured when the load current is rated (RL=∞) and the U0 when no load is measured .

Calculate R0
(3) Ripple factor γ
The ripple factor of the voltage regulator circuit refers to the ratio of the ripple voltage U0 output by the voltage regulator circuit to the output DC voltage U0, that is,

IV. Experimental instruments
1. An oscilloscope
2. An AC millivoltmeter
3. A voltage regulator
4. A multimeter
5. A digital multimeter
6. A power transformer
V. Experimental content:
(I) Observation of the rectifier circuit:
(1) Connect the half-wave rectifier bridge rectifier circuit according to Figures 11-1 (a) and 11-2 (a), respectively. After checking that everything is correct, adjust the voltage regulator to zero and then
turn on the power supply.
(2) Adjust the voltage regulator so that the transformer secondary voltage U2 = 15V, use the DC voltage range of the digital multimeter to measure the output voltage average value U0 (AV), and
use the millivoltmeter to measure the ripple voltage 2
~ U at the output end. Calculate the ripple factor γ.
(3) Use an oscilloscope to observe the output waveform after rectification. Fill in the results in Table 11-1.

2. Observation of C-type and RC-type filter circuits
(1) Disconnect the power supply, and connect the C-type and RC-type filter circuits as shown in Figures 11-3 (a) and 11-4, respectively. After checking that everything is correct, connect the power supply.
(2) Measure the output DC voltage Uo (AV) and ripple voltage 2 ~ U of the C-type and RC-type filter circuit,
and calculate the ripple factor γ.
(3) Use an oscilloscope to observe the output waveform at the output end.

(4) Change C=220mf in Figure 11-3 (a) to C1'=1000mf, and
change CA, C2 in Figure 11-4 from the original 220mf to C1'=C2'=1000mf, and repeat the above (2) and (3).
Fill in the results in Table 11-2.
Table 11-2

3. Measurement of the main indicators of the voltage stabilization circuit
(1) Connect the DC voltage stabilization power supply according to Figure 11-6, and turn on the power supply after checking.
(2) Adjust the voltage regulator. Use a multimeter to measure the output AC voltage U1 = 220V of the voltage regulator. Use a digital multimeter to measure
the input voltage UI and output voltage Uo of the voltage stabilization circuit. Fill in the results in Table 11-3.
(3) Measure the voltage stabilization coefficient Sr.
Adjust the voltage regulator to simulate the grid voltage fluctuation. The output voltage U1 of the voltage regulator is 198V and 242V respectively. Use a digital meter to measure the corresponding
input voltage UI and output voltage Uo of the voltage stabilization circuit. Calculate Sr according to formula (11-6). Fill in the results
in 11-3

(4) Measure the internal resistance Ro of the voltage stabilizing circuit.
Adjust the voltage regulator to make U2=15V, and measure the output Uo of the voltage stabilizing circuit when it is unloaded (RL=∞) and
the output . Calculate Ro according to formula (11-8).
(5) Measurement of ripple voltage
. Under normal conditions of U2=15V, RL=220Ω, use a millivoltmeter to measure the ripple voltage 2
~U of the voltage stabilizing circuit output, and calculate the ripple factor γ according to formula (11-9)
.
VI. Precautions
1. When rewiring the experimental circuit, be sure to cut off the grid voltage first.
2. Do not use a dual-trace oscilloscope to simultaneously observe the waveforms of the transformer secondary voltage U2 and the output voltage Uo after rectification and filtering.
3. The polarity of the electrolytic capacitor cannot be connected incorrectly.
VII. Experimental report
1. Arrange the experimental data and fill in each table.
2. Summarize the characteristics of various rectifier circuits, filter circuits and voltage stabilizing circuits.