Electronics II: Lab 4 Report Switching Voltage Regulators

1. 1
Katrina Little
Sean S.
Electronics II
Lab #4: Switching Voltage Regulators
Goals:
To introduce the concepts of using a switching regulator as a voltage regulator. The theory of a
switching regulator will be presented along with it’s a design. Data collected during this
laboratory experiment will be compared to the datasheet for the switching regulator used.
Equipment:
 Oscilloscope: DPO 4034B
 Triple Power supply
 Capacitors available in the laboratory
 Resistors available in the laboratory
 Multimeter
 Inductor (100 μH)
 Electrolytic Capacitors (470 μF at 15 volts)
 LM 2576-ADJ switching regulator
 Fast recovery diode MBR 1060
Pre-Laboratory:
Read this laboratory experiment carefully to become familiar with the background and the
procedural steps in this experiment. Carefully read each section and become familiar with the
equations for each circuit.
Using the simulation package of your choice in which you are the most familiar with: Mulitsim,
Workbench or LTSpice IV simulate the linear regulator of Figure 2.
A. Download the National Semiconductor LM 2576-ADJ Datasheet and become familiar
with this part.
B. Design a 5 volt DC output switching regulator with 10 volts DC of input.
C. Pick the ratio for R1 and R2 that sets the output to 5 volts DC (Figure 2 of datasheet).
The minimum values for R1 and R2 should be 1000 ohms.

2. 2
D. Compute E*T given on page 14 of datasheet.
For a maximum input voltage of Vin = 15V
E x T = (15 – 5) X (5/15) x (1000/ 52) = 64.1 [V x µs]
E. Assuming a maximum current of 1 to 1.5 amps find the optimum inductance L given in
Figure 7 of datasheet.

3. 3
F. Compute the minimum output capacitance (page 14 of datasheet).
[ ]
[µF]
[ ]
[µF] >>>>> Cout ≥ 266 [µF]
G. Assuming a 3 amp maximum load, calculate the efficiency of the switching regulator
(Performance Figures).

4. 4
Efficiency = Pout / Pin * 100%
Efficiency = Vout / Vin * 100%
H. Assuming a maximum load current of 3 amps, find the power dissipation of the output
and the regulator.
Output: P = 3A * 1.230V = 3.708W
Regulator: P = 3A * 5V = 15W
I. What is the expected dropout voltage at 3 amps (Vin - Vout)?
We can see in the figure above that the expected dropout voltage for 3A of current
and Tj= 25®C is approx. 1.85V.
J. What is the expected current limit for the LM2576 regulator?

5. 5
K. Approximately how much does the output voltage change if the input voltage goes from
10 volts to 15 volts (assume a junction temperature of 25 Degrees C)?
We can see from the figure above that Vo varies from [0 to 0.3V] as the input varies from
[10 – 15V]
Procedure:
General Setup:
1. Record the model and serial number of the scope, power supply, multimeter and function
generator used in laboratory experiment.
2. Download the datasheet LM 2576-ADJ switching regulator. This will be needed to obtain
the pin-out of the regulator. When comparing datasheet data values to experimental data
use the typical values in the datasheet if given.
3. When measuring any values make sure to measure all inputs as well as the output of the
circuit. Do not rely on the values indicated on the instruments. Always measure all signal
values.
4. Before turning any power on double check the wiring to make sure that it is correct.
5. Measure all resistors that are used in the amplifier circuits using the multimeter and
record these values.
6. Use all measured values to determine experimental results such as gain and current.
7. Comparing data means to calculate the percent difference between two values. For
example, theoretical values versus measured values.
8. Comparing data graphically means to plot the data on the same plot to see how the data
overlaps.
Switching regulator:
1. Have the lab assistant approve your design using a 100 μH inductor and two 470μF, 15
volts capacitors.

6. 6
2. Build your design making sure to correctly wire the LM2576, the polarity of the diode,
and the electrolytic capacitors.
3. Triple check you’re wiring before applying any power.
4. Select RL to be 500 ohms.
5. Vary the input voltage Vin between 0 and 15 volts and measure Vout, Iout and Iin.
6. Plot the output voltage Vout as a function of Vin.
7. What is the dropout voltage for this regulator?
8. Compare the dropout value in step 7 to the expected value from the datasheet.
9. Plot the output current Iout as a function of Vin.
0
1
2
3
4
5
6
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Volts
Vin (V)
Vout vs Vin
Vout (V)

7. 7
10. Plot the input current Iin as a function of Vin.
11. Calculate Pin and Pout from steps 6, 9, and 10.
0
0.002
0.004
0.006
0.008
0.01
0.012
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Amps
Vin (V)
Iout vs Vin
Iout (A)
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Amps
Vin (V)
Iin vs Vin
Iin (A)

8. 8
12. For step 11, plot the output efficiency Pout / Pin as a function of Vin once the output
voltage becomes constant. How does this value compare to the expected value.
13. Setting Vin to 10 volts and varying the RL between 100 and 10000 ohms measure Vout,
Iout, and Iin as a function of RL. Use at least 5 different resistor values. Do not forget to
measure the actual resistance of these resistors.
14. Plot Vout as a function of RL.
Vin (V) Vout (V) Iout (A) Iin (A) Pin Pout Output Efficiency
0 0 0 0 0 0 0
1 0.000027 5.4E-08 0.0001 0.0001 1.458E-12 0.000001458
2 0.0000272 5.4E-08 0.0021 0.0042 1.47968E-12 3.52305E-08
3 0.08864 0.00018 0.004 0.012 1.57141E-05 0.130950827
4 3.321 0.00664 0.028 0.112 0.022058082 19.69471607
5 4.291 0.00858 0.03 0.15 0.036825362 24.55024133
6 4.943 0.00989 0.024 0.144 0.048866498 33.93506806
7 4.985 0.00997 0.0187 0.1309 0.04970045 37.96825821
8 4.998 0.01 0.0162 0.1296 0.049960008 38.54938889
9 5.008 0.01002 0.0153 0.1377 0.050160128 36.42710821
10 5.0126 0.01003 0.0142 0.142 0.050252318 35.388956
11 5.0152 0.01003 0.0133 0.1463 0.050304462 34.38445802
12 5.01681 0.01003 0.0125 0.15 0.050336765 33.55784343
13 5.0179 0.01004 0.0121 0.1573 0.050358641 32.0143934
14 5.0234 0.01005 0.01141 0.15974 0.050469095 31.59452555
15 5.0248 0.01005 0.011 0.165 0.05049723 30.60438187
0
5
10
15
20
25
30
35
40
45
6 7 8 9 10 11 12 13 14 15
%Efficient
Vin (V)
Output Efficiency vs Vin
Output Efficiency

9. 9
15. Plot the output current Iout as a function of RL.
16. Plot the input current Iin as a function of RL.
4.96
4.97
4.98
4.99
5
5.01
5.02
5.03
RL Actual
(Ω)
100.91 998.9 2995 3496 3995 4993 5991 6993 7992 8989
Volts
RL Actual (Ω)
Vout vs RL Actual
Vout (V)
0
0.01
0.02
0.03
0.04
0.05
RL Actual
(Ω)
100.91 998.9 2995 3496 3995 4993 5991 6993 7992 8989
Amps
RL Actual (Ω)
Iout vs RL Actual
Iout (A)

10. 10
17. Calculate Pin and Pout from steps 14, 15, and 16.
Vin = 10V
18. For step 17, plot the output efficiency Pout / Pin as a function of RL.
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
RL Actual
(Ω)
100.91 998.9 2995 3496 3995 4993 5991 6993 7992 8989
Amps
RL Actual (Ω)
Iin vs RL Actual
Iin (A)
RL (Ω) RL Actual (Ω) Vout (V) Iout (A) Iin (A) Pin Pout Output Efficiency
100 100.91 4.987 0.04942 0.0381 0.381 0.246459 64.68737897
1000 998.9 5.0186 0.005024 0.0103 0.103 0.025214 24.47969073
3000 2995 5.0242 0.001678 0.0082 0.082 0.008428 10.27834425
3500 3496 5.0252 0.001437 0.0079 0.079 0.007223 9.143409843
4000 3995 5.0254 0.001258 0.0078 0.078 0.006322 8.104568262
5000 4993 5.0256 0.001007 0.0076 0.076 0.005058 6.655806382
6000 5991 5.0256 0.000839 0.0074 0.074 0.004216 5.696981364
7000 6993 5.0255 0.000719 0.0072 0.072 0.003612 5.016057774
8000 7992 5.0255 0.000629 0.0071 0.071 0.00316 4.450868166
9000 8989 5.0254 0.000559 0.007 0.07 0.00281 4.013579321
10000 9988 5.0254 0.000503 0.0069 0.069 0.002528 3.664490891

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19. For step 14 calculate the load regulation.
Vmin.load – Vmax.load
5.0254 – 4.987
Load Regulation = 0.0384 V
20. Measure with a scope the voltage on both sides of the inductor for Vin = 10v and RL =
500 ohms. Discuss your findings in the lab report.
0
10
20
30
40
50
60
70
RL
Actual
(Ω)
100.91 998.9 2995 3496 3995 4993 5991 6993 7992 8989
%Efficient
RL Actual (Ω)
Output Efficiency vs RL Actual
Output Efficiency