1-3 Simulation of a Buck Converter!
Using LTspice
1. Installing LTspice and course simulation files
2. Simulation of a buck converter
3. Homework assignment: simulation of a boost
converter
Introduction to Power Electronics 1 1-3: Simulation of Power Converters
SPICE
Simulation Program with Integrated Circuit
Emphasis
Enter a circuit, then run a simulation that
plots voltage or current waveforms, and
computes other quantities of interest
In this course, we will use a version of
SPICE that is available for free from the
Linear Technology Corp., LTspice.
Versions of LTspice IV are available for both
Windows and Macintosh systems, along
with a getting started guide and examples.
Introduction to Power Electronics 2 1-3: Simulation of Power Converters
Getting Started
1. Download and install LTspice IVit can be downloaded from the
following site:
http://www.linear.com/designtools/software/
2. Download the buck converter zip file from Coursera, linked to
this lecture. Unzip this file and save in a folder on your disk
3. Double-click on buck.asc to open the file in LTspice. Then press
the run button to start the simulation.
4. To display a waveform, click on a node in the circuit diagram to
display its voltage (with respect to the circuit ground), or click on
an element to display its current (with respect to the direction
shown while clicking).
Introduction to Power Electronics 3 1-3: Simulation of Power Converters
Pulse-Width Modulator Block
The pulse-width modulator (PWM)
converts an analog input voltage vc into c(t)
a control switching waveform c whose
duty cycle d is dependent on vc .
Block functionality: vc(t)
D = (vc Voffset)/VM (duty cycle of c(t))
Frequency of c(t) is fs (switching frequency)
Dmin d Dmax (duty cycle limits)
In LTspice, the above parameters can
be entered in a window obtained by
right-clicking on the PWM block (or
command-click on Macintosh)
In the example at right, vc = 0.4 V. c(t)
has duty cycle d = 0.4 with switching
frequency of 100 kHz. Defaults:
Voffset = 0, Dmin = 0, Dmax = 0.9.
Introduction to Power Electronics 4 1-3: Simulation of Power Converters
Gate Driver Block
The gate driver converts an input control Driver
signal c(t) to a high-current output signal output
suitable for driving the gate of a power voltage
MOSFET transistor.
The input is a 0-5V logic signal relative to Driver input
the input reference terminal voltage c(t)
A power supply is required to operate the
driver output (12 V in example at left)
The output is connected to the MOSFET
gate, and the output reference is
connected to the MOSFET source. The Output signal
output high level is determined by the Output reference
power supply. The driver level-shifts the Driver power
signal, so that the input reference supply
(ground) need not be the same as the
Input signal
output reference (MOSFET source)
Input reference
Introduction to Power Electronics 5 1-3: Simulation of Power Converters
LTspice Simulation of Buck Converter
MOSFET M1 and diode D1 Switch node
operate as the switch voltage
The converter input power Inductor current
source is Vg = 24 V
The converter output voltage Output voltage
Vout is applied to a load
resistor Rload = 5 ohms.
The simulation models several
sources of loss:
Transistor and diode forward
voltage drops
Transistor and diode switching
losses
Inductor winding resistance RL
Gate driver power consumption
Introduction to Power Electronics 6 1-3: Simulation of Power Converters
Module 1 Homework Assignment
LTspice simulation of a Boost dc-dc converter
1. Download LTspice and boost simulation files onto your computer
2. Run simulation
3. Use LTspice to find steady-state output voltage, inductor current,
and system efficiency
Introduction to Power Electronics 7 1-3: Simulation of Power Converters
