Download Switch mode power supply - Mohammed Al Nasser e

Assessment Cover Sheet
Assessment Title:
Switch mode power supply
Programming Title:
Bachelor Engineering Technology
Course No.:
ENB6071
Course Title:
Electronics manufacturing and design
Student:
Mohammed AL Nasser
Tutor:
John Leek
Due Date: 23rd Nov 2014
201101137
Date submitted: 23rd Nov 2014
By submitting this assessment for marking, either electronically or as hard copy, I confirm the
following:




This assignment is my own work
Any information used has been properly referenced.
I understand that a copy of my work may be used for moderation.
I have kept a copy of this assignment
Assessor:
Grade/Mark:
Comments:
Date of Marking:
Abstract:
The purpose of this assignment was to build and test a small switch
mode power supply based on push-pull topology and to simulate particular
parts of the circuit. The circuit was supplied with 10 and 15 volts in order to
output (25v) without a conspicuous power loss. Several tests were
performed on the circuit by varying the load resistor -and hence varying the
power at the output- in order to measure the efficiency of the circuit.
Introduction:
In this document, an explanation of how the power supply works will
be presented. Some calculations of the wire size, number of turns and
losses of the transformer will be demonstrated. The components values of
the feedback resistor, compensation and soft start capacitors, snubber
circuit and oscillator frequency will be calculated discussed. At the end of
this paper, plots of the efficiency of the circuit will be included.
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Contents
Abstract: .......................................................................................................................................... 2
Introduction:.................................................................................................................................... 2
How the SMPS works: ..................................................................................................................... 6
Design specification ......................................................................................................................... 6
Skin effect: ................................................................................................................................... 7
Proximity effect transformer: ...................................................................................................... 7
Calculations for the transformer: .................................................................................................... 8
Wire size (with respect to current density (j)): ........................................................................... 8
Number of turns: ......................................................................................................................... 8
Explanation and reason: ........................................................................................................ 10
............................................................................................................................................... 10
Question1: why an inductor was used in the output circuit? ............................................... 11
Calculations of (primary and secondary) loss:- ......................................................................... 11
Wire losses: ........................................................................................................................... 11
Core losses: ............................................................................................................................ 12
Total losses of the transformer: ................................................................................................ 12
Transformer core size calculation: ............................................................................................ 13
Power in of the transformer: ................................................................................................. 13
Power out of the transformer: .............................................................................................. 14
Components values: ...................................................................................................................... 15
Calculation of feedback resistor value: ..................................................................................... 15
Calculation of compensation components:........................................................................... 15
Soft start circuit values: ............................................................................................................. 16
Correct oscillator frequency/ configuration: ............................................................................. 16
Output filters design .................................................................................................................. 18
Simulation results: ..................................................................................................................... 19
Snubber components values: .................................................................................................... 22
Output frequency after snubber circuit: ................................................................................... 24
Mosfet power loss calculation: ................................................................................................. 24
Power loss due to its resistance of the MOSFET: .................................................................. 24
Output switching losses: ....................................................................................................... 25
3|Page
Input switching losses: .......................................................................................................... 25
Diode loss calculation: ............................................................................................................... 26
The forward voltage drop times the forward current: .......................................................... 26
The losses caused by the forward & reverse recovery time of the diode: ........................... 26
Measurements of performance: ................................................................................................... 27
Plots of output voltage vs. output power: ................................................................................ 27
Measurements of efficiency: ..................................................................................................... 29
Plot of efficiency: ....................................................................................................................... 30
Automatic test (Labview results):.......................................................................................... 31
Appendix A: ................................................................................................................................... 32
MATLAB code of the Vout vs. Pout: .......................................................................................... 32
Appendix B: ................................................................................................................................... 33
MATLAB code of the load test efficiency plots: ........................................................................ 33
Appendix C:.................................................................................................................................... 35
MATLAB code of the Automatic efficiency test: ....................................................................... 35
Appendix D: ................................................................................................................................... 36
Core size calculations: ............................................................................................................... 36
4|Page
Table of figure:
Figure 1: skin effect. ........................................................................................................................ 7
Figure 2: proximity effect. ............................................................................................................... 7
Figure 3: Transformer core magnetic data N97. ........................................................................... 10
Figure 4: Error ± Amplifier connection .......................................................................................... 15
Figure 5: oscillator period graph. .................................................................................................. 16
Figure 6: Output LCR filter. ............................................................................................................ 18
Figure 7: Simulation of the Current and Vout. .............................................................................. 20
Figure 8: simulation of the resonate frequency. ........................................................................... 21
Figure 9: output before snubber circuit. ....................................................................................... 22
Figure 10: Output after snubber circuit. ....................................................................................... 24
Figure 11: output voltage vs. output power (10v). ....................................................................... 27
Figure 12: output voltage vs. output power (15v). ....................................................................... 28
Figure 13: plot of efficieny (load test)with the two supplies (10v,15v). ....................................... 30
Figure 14: Automatic efficiency test.............................................................................................. 31
Table of tables:
Table 1: How the circuit works technically...................................................................................... 6
Table 2: Design specification. .......................................................................................................... 6
Table 3: results of the simulation. ................................................................................................. 20
Table 4: A comparison between the simulated and experimental results. .................................. 21
Table 5: measurment of efficiency with supply 10v...................................................................... 29
Table 6: measurements of efficiency with 15v. ............................................................................ 29
5|Page
How the SMPS works:
Table 1: How the circuit works technically.
When the circuit supplied with (10v to 15v) at (100 KHz).
Part
PWM switching regulator
Mosfet driver
Mosfets
Transformer
Diode bridge
RLC filter
Function
Generates (5v) pulses in pins (16 and 13) at 100
KHz.
Increases the current to boost charging
capacitance of the MOSFETs and open the gate of
the each MOSFET faster.
When the MOSFET driver close the gate of the
MOSFET using high current it allows the current
flows through the primary windings to the ground.
The result of the two Mosfets operation will
generate a push-pull signal.
Produce magnetic flux from both primary windings
when the gate of the MOSFET is closed.
Rectify the secondary transformer output signal to
convert it to a DC signal.
Smooth the output rectified signal.
Snubber circuit
Reduces the ringing from the output of the bridge
to increases the efficiency of the circuit.
Feedback circuit
Maintain the output voltage to output a 25v.
Design specification
The calculation was carried to design a DC to DC push-pull converter with the following
specification:
Table 2: Design specification.
Specification
Operation frequency
Maximum output Power
Minimum input Voltage
Maximum input voltage
Output voltage with a load current of 250mA min
No load output voltage
Output voltage ripple
Soft start circuit
Efficiency
Value
100 KHz
30 Watts
10 Volts
15 Volts
25 Volts
As set voltage
0.01% V out
This is required
>78% @ Pout > 5Watts
6|Page
Skin effect:
Increasing the wire diameter will only increase the resistance of the wire, while the
effective area will be only on the skin of the wire (skin depth). This effect was occurred in the
secondary windings.
Figure 1: skin effect.
Proximity effect transformer:
Proximity effect is the uneven current distribution in the conductor. As it shown blow,
the current will flow only on one side of each wire. This effect was occurred in the two primary
windings.
Figure 2: proximity effect.
7|Page
Calculations for the transformer:
Wire size (with respect to current density (j)):
𝑃
30
=
= 1.2 𝐴
𝑣
25
𝑖𝑠𝑒𝑐 =
𝑗=
𝐴𝑚𝑝
𝐴𝑟𝑒𝑎
Where:
Current density (j) = 10
Amp = 1.2A
10 =
𝐴𝑟𝑒𝑎 =
1.2
𝐴𝑟𝑒𝑎
1.2
= 0.12 𝑚𝑚2
10
𝐴𝑟𝑒𝑎 = 𝜋𝑟 2
0.12 = 𝜋𝑟 2
𝑟 = 0.195 𝑚𝑚
𝑑 = 0.390 𝑚𝑚
Number of turns:
Primary turns:
𝑁𝑝𝑟𝑖𝑚𝑎𝑟𝑦 =
𝑉𝑚𝑎𝑥
𝑓∗𝛽∗𝐴
Where:
Switching frequency (f) = 100 kHz.
Flux density (B) = 0.35 Tesla.
Area (A) = 31 mm2.
Vmax = 15v.
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𝑁𝑝 =
15
= 13.8 ≈ 14 𝑡𝑢𝑟𝑛𝑠
350
31
(100 ∗ 103 ) ∗ (
)
∗
(
)
1000
1000000
𝑉𝑜𝑢𝑡 = 25 + (2 ∗ 𝑑𝑖𝑜𝑑𝑒𝑉𝑓 )
Diode forward voltage drop = 0.7v
𝑑𝑖𝑑𝑜𝑒𝑉𝑓 = 0.7 ≈ 1𝑣
𝑽𝒐𝒖𝒕 = 25 + (2 ∗ 1) = 27𝑣
Secondary turns:
𝑁𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 =
𝑁𝑝 ∗ 𝑉𝑜𝑢𝑡
𝑉𝑖𝑛(minimum) ∗ 2 ∗ 𝐷𝑢𝑡𝑦 𝑐𝑦𝑐𝑙𝑒
Where:
N primary = 13.8
Vout = 27
Vin= 10v
Duty cycle = 0.45
𝑁𝑠 =
13.8 ∗ 27
= 41.4 ≈ 42 𝑡𝑢𝑟𝑛𝑠
10 ∗ 2 ∗ 0.45
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Explanation and reason:
Saturation is when the magnetic field (H) stops increasing the magnetization of the
material, so the total magnetic flux density (B) will level off.
When the magnetic core saturates, the inductance of the transformer will change with
the change of the driving current, so this considered as unwanted departure from the ideal
behavior. As a result, when the core saturates the current will keep flowing until the
temperature of the transformer raises.
Figure 3: Transformer core magnetic data N97.
As it is described in the BH curves, the maximum flux density for N97 is (550 mT). As
results, the core will start to saturate when the flux density exceed (550 mT).
10 | P a g e
Question1: why an inductor was used in the output circuit?
To produce DC current and to keep the current flowing during the (off) periods. In
𝐷𝑣
another word, to reduce ( 𝐷𝑡 ), which is (ration of voltage with respect to time).
Calculations of (primary and secondary) loss:Wire losses:
𝑃𝑤𝑖𝑟𝑒 = 𝐼 2 ∗ 𝑅
𝑅 = 𝑡𝑢𝑟𝑛𝑠 ∗ 𝐼𝑛 ∗ 𝑐𝑜𝑛𝑑𝑎𝑐𝑡𝑜𝑟 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
Where:
In: length per turn = 0.04 m (measured using a ruler).
Conductance = 0.1382 Ω/m (from core wire tables, Appendix E - Work book).
Primary power loss:
𝑅𝑝𝑟𝑖𝑚𝑎𝑟𝑦 = 14 ∗ 0.04 ∗ 0.1382 = 0.07Ω
𝑃𝑤𝑖𝑟𝑒 = (1.5)2 ∗ 0.07 = 0.1575 𝑤
Secondary power loss:
𝑅𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 = 42 ∗ 0.04 ∗ 0.1382 = 0.23Ω
𝑃𝑤𝑖𝑟𝑒 = (1.2)2 ∗ 0.23 = 0.3312 𝑤
Comments:
The procedure was preceded, due to the similarity in results:

Calculated current = 𝑱 ∗ 𝑨𝒓𝒆𝒂 = 𝟏𝟎 ∗ 𝟎. 𝟏𝟑𝟕 = 𝟏. 𝟑𝟕 𝑨.

Secondary current =
𝑷𝒐𝒖𝒕
𝑽𝒐𝒖𝒕
=
𝟑𝟎
𝟐𝟓
= 𝟏. 𝟐 𝑨.
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Core losses:
Core material number: N97
By knowing the frequency required (100 KHZ):
𝑐𝑜𝑟𝑒 𝑙𝑜𝑠𝑠 = 𝐸𝑒𝑣 ∗ 𝑉𝑒
Where:
Core volume (Ve) = 1460 mm2. (From Appendix D – work book).
Spectral irradiance = (Eev) = 300 Kw per m3. (From Appendix B(transformer core magnetic) –
work book
𝑐𝑜𝑟𝑒 𝑙𝑜𝑠𝑠 = 300
𝐾𝑤
∗ 1460 𝑚𝑚3
𝑚3
𝑐𝑜𝑟𝑒 𝑙𝑜𝑠𝑠 = 0.438 𝑤
Total losses of the transformer:
𝑇 = (2 ∗ 𝑝𝑟𝑖𝑚𝑎𝑟𝑦 𝑝𝑜𝑤𝑒𝑟 𝑙𝑜𝑠𝑠) + 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 𝑝𝑜𝑤𝑒𝑟 𝑙𝑜𝑠𝑠 + 𝑐𝑜𝑟𝑒 𝑙𝑜𝑠𝑠
And by substituting in the total losses of the transformer equation:
𝑇 = (2 ∗ 0.1575) + 0.3321 + 0.438 = 1.0851 𝑤
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Transformer core size calculation:
Power in of the transformer:
𝐴𝑝 = 𝐴𝑐 ∗ 𝐴𝑤 = [
11.1 ∗ 𝑃𝑖𝑛 1.143
∗ 104 (𝑚𝑚4 )
]
𝐾𝑡 ∗ ∆𝐵 ∗ 𝑓𝑠
Where:
Pin = power in (watts).
Kt = constant of topology = 0.141
∆𝑩 = Magnetic flux density wing (typically 0.2 to 0.3 T).
Fs = switching frequency (Hz).
Ap = Area product (mm4).
Ae = core area (mm2) = 31 mm2.
Aw = winding area (mm2) = 28.1 mm2.
The maximum power in of the transformer (the value of (power in) was obtained from the
MATLAB code):
𝑃𝑖𝑛 = 45.0378 𝑤𝑎𝑡𝑡𝑠
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Power out of the transformer:
𝑃𝑜𝑢𝑡 =
0.001 ∗ 𝐵𝑚𝑎𝑥 ∗ 𝑓𝑠 ∗ 𝐴𝑒 ∗ 𝐴𝑐
𝐷𝑐𝑚𝑎
Where:
Bmax = magnetic flux density = 350mT
Ae = core area = 31 mm2.
Dcma = 500 circular mil per RMS current
Fs = switching frequency = 100 kHz.
Ac = winding area square = 28.1 mm2.
𝑃𝑜𝑢𝑡 =
0.001 ∗ 3500 ∗ 100000 ∗ 0.31 ∗ 0.281
500
𝑃𝑜𝑢𝑡 = 60.977 𝑤𝑎𝑡𝑡𝑠
14 | P a g e
Components values:
Calculation of feedback resistor value:
Figure 4: Error ± Amplifier connection
Voltage divider rule was used to calculate the values of the two resistors used in the
feedback and by assuming R1=1KΩ:
𝑽𝒐𝒖𝒕
𝑹𝟏
=
𝑽𝒊𝒏
𝑹𝟐 + 𝑹𝟏
By using the voltage divider formula, the input voltage value is 25v and it was required
to reduce the input (25v) to (2.5v) output.
2.5
1000
=
25 𝑅2 + 1000
0.1 =
𝑅2 =
1000
𝑅2 + 1000
1000
− 1000
0.1
𝑅2 = 9000 = 9𝑘Ω
The feedback resistors:
R1= 1kΩ.
R2= 9kΩ.
Calculation of compensation components:
The output signal at (pin3) of the switching regulator was oscillating when the voltage
increased. A compensation capacitor was connected at pin 3 to stabilize the signal and stop the
oscillating.
C compensation = 100nF
15 | P a g e
Soft start circuit values:
In the soft start circuit in the switching regulator (pin4), an equation was used to calculate the
values:
𝐶∗𝑉 =𝑖∗𝑡
By performing a variety of capacitor to obtain an acceptable time, the capacitor value was used
in the circuit = 10uF, and by substituting in the formula above:
𝑡=
𝐶∗𝑉
10 ∗ 10−6 ∗ 2.5
=
= 0.25𝑠 = 250 𝑚𝑠
𝑖
100 ∗ 10−6
The function of the soft start capacitor is to protect the transistors and diodes inside the
switching regulator from high current when the power supply is turned on.
Correct oscillator frequency/ configuration:
Figure 5: oscillator period graph.
As it shown in figure 5, the frequency at each driver output is half the oscillator frequency. The
switching frequency is (100 KHz):
16 | P a g e
The oscillator frequency (200 KHz), and the period (5us), and the capacitor is 1nF. From the
graph the value of the resistor used almost (8KΩ).
The values used in the circuit:
Switching frequency: 100 KHz.
Oscillator frequency: 200 KHz.
Oscillator period: 5us.
RT: 6.8 KΩ.
CT: 1nF.
17 | P a g e
Output filters design
Figure 6: Output LCR filter.
18 | P a g e
A 2nd order low pass filter circuit was designed on Altium software to determine the frequency
response:
Calculating value of the inductor:
𝐿=
(𝑉𝑝𝑒𝑎𝑘 − 𝑉𝑜𝑢𝑡) ∗ ∆𝑡
∆𝑖
Where:
Vpeak = 30v.
Vout = 25v.
∆𝒕 = 𝟓 ∗ 𝟏𝟎−𝟔 𝒔.
∆𝒊 = 0.12 A.
(30 − 25) ∗ 5 ∗ 10−6
𝐿=
= 208.33 ∗ 10−6 𝐻
0.12
The value of the inductor used in the circuit (L=227 uH).
Output capacitor calculations:
𝐶𝑚𝑖𝑛 ≥
1 ∆𝑖 ∗ 𝑡
∗
8 ∆𝑉𝑜𝑢𝑡
Where: (from Equation 20. in AN2794 application note).
∆𝑽𝒐𝒖𝒕 = 𝟐. 𝟓 𝒎𝑽
∆𝒊 = 𝟎. 𝟏𝟐 𝑨
𝒕 = 𝟒. 𝟓 ∗ 𝟏𝟎−𝟔s
𝐶𝑚𝑖𝑛 ≥
1 𝟎. 𝟏𝟐 ∗ 𝟒. 𝟓 ∗ 𝟏𝟎−𝟔
∗
= 27𝑢𝐹
8
𝟐. 𝟓 ∗ 𝟏𝟎−𝟑
The values of the output filter components:
C= 27uF.
L=227uH.
19 | P a g e
Simulation results:
Table 3: results of the simulation.
Load
resistors (Ω)
Load current
(A)
100
80
50
22
0.25
0.34
0.5
1.14
Delta current
∆IL (inductor)
(mA)
38
38
38
38
Resonate
frequency
(Hz)
2.39
2.39
2.39
2.39
Output
voltage (V)
Time one (us)
25.1
25.1
25.1
25.1
4.65
4.65
4.65
4.65
Figure 7: Simulation of the Current and Vout.
20 | P a g e
Figure 8: simulation of the resonate frequency.
From the simulation figures, the results of the (RLC) simulation were obtained.
Different load resistors were used in the simulation.
Table 4: A comparison between the simulated and experimental results.
Method
Simulation
Experimental 10v
Experimental 15v
Load resistors (Ω)
100
100
100
Load current (A)
0.25
0.249
0.25
Output voltage (V)
25.1
24.9
25
21 | P a g e
Snubber components values:
Frequency of the ringing before adding Cadded :
Figure 9: output before snubber circuit.
1
From figure 9, the frequency of the ringing before snubber circuit equals (𝑓1 = 180∗10^−9 =
5.56 ∗ 106 𝐻𝑧).
22 | P a g e
Frequency of the ringing after adding Cadded :
𝑐𝑎𝑑𝑑𝑒𝑑 = 0.47 ∗ 10−9 𝐹 (The value of the added capacitor was assumed).
𝑓2 =
1
= 2.778 ∗ 106 𝐻𝑧
360 ∗ 10−9
Calculating Cstray:
𝑓1 2
𝐶𝑎𝑑𝑑𝑒𝑑
( ) =1+
𝑓2
𝐶𝑠𝑡𝑟𝑎𝑦
2
5.6 ∗ 106
0.47 ∗ 10−9
=
1
+
(
)
2.778 ∗ 106
𝐶𝑠𝑡𝑟𝑎𝑦
𝐶𝑠𝑡𝑟𝑎𝑦 = 0.15 ∗ 10−9 𝑓
Snubber components value used in the SMPS:
The value of the capacitor used in the snubber circuit must 10 times the value of Cstray :
C = 0.15*10-9 * 10
C1= 1.5*10-9 F
The value of the resistor used:
R1 = 6.2 KΩ (the value of the resistor was assumed)
The diode used in snubber circuit:
D1 = STTH1R02QRL
23 | P a g e
Output frequency after snubber circuit:
Figure 10: Output after snubber circuit.
After adding the snubber circuit in the SMPS, the ringing in the output signal was reduced. The
frequency of the ringing (𝑓 =
1
130∗10−9
= 7.7 ∗ 106 𝐻𝑧).
Mosfet power loss calculation:
Power loss due to its resistance of the MOSFET:
𝑃𝑟𝑑𝑠(𝑜𝑛) = 𝑅𝑑𝑠(𝑜𝑛) ∗ 𝐼 2 𝑑𝑐
Where: (from the datasheet)
Rds (on) = 6mΩ.
I2dc = 1.5A (for each MOSFET).
𝑃𝑟𝑑𝑠(𝑜𝑛) = (6 ∗ 10−3 ) ∗ (1.5)2 = 9 ∗ 10−3 𝑤.
24 | P a g e
Output switching losses:
𝑃𝑠𝑤(𝑚𝑜𝑠𝑓𝑒𝑡) =
𝑉𝑑𝑠 ∗ 𝐼𝑑𝑠 ∗ (𝑡𝑟 + 𝑡𝑓) ∗ 𝑓𝑠𝑤𝑖𝑡𝑐ℎ𝑖𝑛𝑔
2
Where: (from the datasheet)
Vds = 9mv.
Tr = 60*10-9 s.
Tf = 57*10-9 s.
Fswitching = 100 KHz.
(9 ∗ 10−3 ) ∗ (1.5) ∗ ((60 ∗ 10−9 ) + (57 ∗ 10−9 )) ∗ 100 ∗ 103
2
= 52.65 ∗ 10−6 𝑤.
𝑃𝑠𝑤(𝑚𝑜𝑠𝑓𝑒𝑡) =
Input switching losses:
𝑃𝑖𝑛(𝑙𝑜𝑠𝑠) =
𝐶𝑖𝑛 ∗ 𝑉 2 𝑔𝑠
2
Where: (from the data sheet)
Cin = 6860pF.
Vgs= ±20v.
(6860 ∗ 10−12 ) ∗ (20)2
𝑃𝑖𝑛(𝑙𝑜𝑠𝑠) =
= 0.1372 𝑤.
2
25 | P a g e
Diode loss calculation:
The forward voltage drop times the forward current:
𝑃𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑙𝑜𝑠𝑠 = 𝑉𝑑 ∗ 𝐼𝑓
Where:
Vd = 0.7v ≈ 1𝑣 (the drop voltage o the diode was considered as 1v for each diode).
If = 1.5A.
𝑃𝑐𝑜𝑛𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑙𝑜𝑠𝑠 = 2 ∗ (1) ∗ (1.5) = 3 𝑤.
The losses caused by the forward & reverse recovery time of the diode:
𝑃𝑠𝑤𝑖𝑡𝑐ℎ𝑖𝑛𝑔(𝐷𝑖𝑜𝑑𝑒) =
𝑉𝑠𝑒𝑐 ∗ 𝐼𝑜𝑢𝑡 ∗ (𝑡𝑓𝑟 + 𝑡𝑟𝑟) ∗ 𝑓𝑠𝑤𝑖𝑡𝑐ℎ𝑖𝑛𝑔
2
Where: (from the datasheet)
Vsec = 30v.
Iout = 1.2 A.
Tfr = 50ns.
Trr = 15ns.
Fswitching = 100 KHz.
𝑃𝑠𝑤𝑖𝑡𝑐ℎ𝑖𝑛𝑔(𝐷𝑖𝑜𝑑𝑒) =
(30) ∗ (1.2) ∗ ((50 ∗ 10−9 ) + (15 ∗ 10−9 )) ∗ 100 ∗ 103
= 0.117 𝑤
2
Due to there are two switching diodes (Pswitching = 0.117 * 2 = 0.234 watts).
26 | P a g e
Measurements of performance:
Plots of output voltage vs. output power:
With supply = 10v:
Figure 11: output voltage vs. output power (10v).
27 | P a g e
With supply = 15v:
Figure 12: output voltage vs. output power (15v).
From both figures above, while increasing the output power, a small drop in voltage
will be occurred in the output.
28 | P a g e
Measurements of efficiency:
Table 5: measurment of efficiency with supply 10v.
Load Ω
100
68
47
33
22
Input measurements
Current in Voltage
Power in
A
in
Watt
V
0.68
10
6.8
1.01
10
10.1
1.48
10
14.8
1.97
10
19.7
2.89
10
28.9
Output measurements
Current
Voltage
Power
out A
out V
out Watt
0.249
0.365
0.53
0.73
1.07
24.9
24.9
24.8
24.5
23.5
6.2
9.1
13.1
18
25.1
Efficiency
Pout/Pin
%
91.2
90.1
88.5
91.37
86.85
Table 6: measurements of efficiency with 15v.
Load Ω
100
68
47
33
22
15
Input measurements
Current in Voltage
Power in
A
in
Watt
V
0.49
15
7.35
0.71
15
10.65
1
15
15
1.39
15
20.85
2.13
15
31.95
3.27
15
49.05
Output measurements
Current
Voltage
Power
out A
out V
out Watt
0.25
0.37
0.53
0.7
1.12
24
25
25
24.7
24.7
24.7
24
6.25
9.19
12.98
18.48
27.7
38.4
Efficiency
Pout/Pin
%
85.03
86.29
86.5
88.6
86.69
78.28
29 | P a g e
Plot of efficiency:
Figure 13: plot of efficieny (load test)with the two supplies (10v,15v).
The previous figure demonstrates the efficiency of the 30w push-pull DC to DC
converter circuit using the load test. The efficiency at both supplies (10v, 15v), was more than
80%. From the assignment sheet in the design specification section, the acceptable efficiency
should be more than 78%.
30 | P a g e
Automatic test (Labview results):
Figure 14: Automatic efficiency test.
In the design specification table, the required efficiency should be more that 78%. The
automatic and load test efficiency plot demonstrated the efficiency of the SMPS circuit, which is
(>80%).
31 | P a g e
Appendix A:
MATLAB code of the Vout vs. Pout:
%10v:
vout= [24.9,24.9,24.8,24.5,23.5];
pout= [6.2,9.1,13.1,18,25.1];
plot(pout,vout);grid;
xlabel('output power');
ylabel('output voltage');
title('Output voltage Vs output power (10v)');
figure;
%15v:
vout1= [25,25,24.7,24.7,24.7];
pout1= [6.25,9.19,12.98,18.48,27.7];
plot(pout1,vout1);grid;
xlabel('output power');
ylabel('output voltage');
title('Output voltage Vs output power (15v)');
32 | P a g e
Appendix B:
MATLAB code of the load test efficiency plots:
%load test plots
%10v
pout1 = [6.2,9.1,13.1,18,25.1];
eff1 = [91.2,90.1,88.5,91.37,86.85];
plot(pout1,eff1);
xlabel('Output power(watt)');
ylabel('Efficiency %');
title('Efficiency with 10v supply');
ylim([0 100]);
grid;
figure;
%15v
pout2 = [6.25,9.19,12.98,18.48,27.7,38.4];
eff2 = [85,86.29,86.5,88.6,86.69,78.29];
plot(pout2,eff2);
xlabel('Output power(watt)');
ylabel('Efficiency %');
title('Efficiency with 15v supply');
ylim([0 100]);
grid;
figure;
33 | P a g e
%both
plot(pout1,eff1,pout2,eff2);
xlabel('Output power(watt)');
ylabel('Efficiency %');
title('Efficiency Of the SMPS');
legend ('supply = 10v','supply = 15v');
xlim([5 30]);
ylim([0 100]);
grid;
34 | P a g e
Appendix C:
MATLAB code of the Automatic efficiency test:
%10v
f = dlmread('10v.txt');
vo = f(:,1);
io = f(:,2);
vin = f(:,3);
iin = f(:,4);
pout = vo.*io;
pin = vin.*iin;
eff= (pout./pin)*100;
%15v
f2 = dlmread('15v.txt');
vo2 = f2(:,1);
io2 = f2(:,2);
vin2 = f2(:,3);
iin2 = f2(:,4);
pout2 = vo2.*io2;
pin2 = vin2.*iin2;
eff2= (pout2./pin2)*100;
plot(pout,eff,pout2,eff2); grid;
xlabel('Output power (watts)');
ylabel('Efficiency (%)')
title('plot of efficiency of SMPS')
legend('supply = 10v',' supply = 15v');
35 | P a g e
Appendix D:
Core size calculations:
%Matlab code to calculate the maximum power in the trasformer.
Kt = 0.141; %constant topology.
deltaB = 0.3; % magneic flux.
fs = 100000; %swtiching fequency Hz.
Aw = 28.1*10^-6; %winding area.
Ae = 31*10^-6; % core area.
Ap = Aw*Ae*(10^8); %product area.
pin = (Ap^(7/8))*((Kt*deltaB*fs)/(11.1)); % power in(watts).
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