Isolated DC-DC Converter

Isolated DC-DC
Converter
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Abstract: This report presents a study of an isolated DC-DC Converter design. It
provides a software simulated design of a DC-DC Convertor done using mutism
software. pre-practical activities were performed prior actual design to prepare and
equip us with skills and information about Flyback converters. A number of analyses
under transient and parameter sweep analysis where a numerous different variables
values were used in order to study and analyse the behaviour of our design under
different conditions. Output simulated plots are also presented for better understanding
of our design.


1. INTRODUCTION/AIM needed output voltage. To store energy magnetic the
flyback transformer is used, it can operate at high
The purpose of this practical is to provide student with vital frequencies
exposure and skills that are necessary to comprehend the
fundamentals design of an isolated DC-DC flyback EQUATIONS
converter. Different variables are tested and their
behaviour and effect on the DC-DC flyback converter is Continuous Mode
analysed. We made use of mutism software to construct Increasing current 𝑡1 =
1
(𝑉𝑜𝑢𝑡 + 𝑉𝑓 ). (1)
our design, with the help of various analysis tools of the 𝑓𝑠𝑤
𝑛𝑝
software like transient and parameter sweep, schematic
and better understanding of DC-DC flyback converter 𝑉𝑖𝑛+(𝑉𝑜𝑢𝑡 +𝑉𝑓 )
1
design is performed. Decreasing current 𝑡2 = −1 (2)
𝑓𝑠𝑤

2. PREREQUISITES/THEORY Min primary current
𝑉𝑜𝑢𝑖𝑡 + 𝑉𝑓 𝐼𝑜𝑢𝑡 1
𝐼𝑝𝑟𝑖,𝑚𝑖𝑛 = − ∙ 𝐼𝑟𝑖𝑝𝑝𝑙𝑒 (3)
Flyback converter can be defined as power converters. 𝑉𝑖𝑛 ∙ 𝑓𝑠𝑤 2
when the current is flowing it retains energy then releases Max primary current
it when the power is not supplying power. mutually 𝐼𝑝𝑟𝑖,𝑚𝑖𝑛 = 𝐼𝑝𝑟𝑖,𝑚𝑖𝑛 +𝐼𝑝𝑟𝑖,𝑟𝑖𝑝𝑝𝑙𝑒 (4)
coupled inductors are used m, they perfume as isolated
switching converter, hence they can step down or up the Min secondary current
voltage. 𝑛𝑝
𝐼𝑠𝑒𝑐,𝑚𝑖𝑛 = 𝐼𝑝𝑟𝑖,𝑚𝑖𝑛 ∙ (5)
𝑛𝑠
With the range of input voltages, it regulates and controls
the output voltage. Compared to other witching mode Max secondary current
power, the components needed to construct a flyback 𝑛𝑝
𝐼𝑠𝑒𝑐,𝑚𝑎𝑥 = (𝐼𝑝𝑟𝑖,𝑚𝑖𝑛 +𝐼𝑝𝑟𝑖,𝑟𝑖𝑝𝑝𝑙𝑒 ) ∙ (6)
converter are few. The required components are 𝑛𝑠
transformer, switch, filter, rectifier, and the control
component to control the switch. The use of a switch is to Average input current
turn on and off the primary circuit. Due to turning on and 𝑉𝑜𝑢𝑖𝑡 + 𝑉𝑓 𝐼𝑜𝑢𝑡
off of the primary circuit magnetising and demagnetising 𝐼𝑖𝑛,𝑎𝑣𝑔 = (7)
𝑉𝑖𝑛 ∙
occurred. To control the switch the PWM is used, also
usually MOSFET transistor are used as switch. The
rectifiers are used to rectifier the voltage in the secondary
winding to obtain the pulsing dc output and separate the 3. <METHOD/RESULTS>
load from the secondary winding. the output voltage is
filtered by the capacitor filter and assist to increase the
1

, 3.1) Design specifications 3.2.2 Parameter sweep (Resistive Load) at
300KHz switching frequency
Vin (min) = 15V
Vin(max) = 30V
Vout = 20V
Vripple = 5% of Vout = 1 V or 1000mV
Power Output = 60 W
Efficiency = 90%
𝑉 20
𝑅= = = 6.67Ω
𝑃 60



Figure 4:Parameter sweep (Resistive Load) at 300kHz



Picked 5 different frequencies are 50Hz,
6kHz,12kHz,15kHz and 20kHz




Figure 1:Texas Instruments Output Values



3.2 Simulation of the open loop flyback

Figure 5:Parameter sweep (Resistive Load) at 50kHz




Figure 2:Open- loop flyback model



3.2.1 Transient analysis Figure 6:Parameter sweep (Resistive Load) at 6kHz




Figure 3:Transient analysis Figure 7:Parameter sweep (Resistive Load) at 12kHz

Yes, the output are expected, in the design
specification, the required output voltage must
be 20V, in this output plot we see that unstable
voltage from zero to about 5s, after 5s the
output volage stabilise to 20V.

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