Team DEC13-06 Design Documentseniord.ece.iastate.edu/projects/archive/dec1306/...Wen Ya Ting(Audrey) Ho Hsu (Lily) Li-yeh Yang (Leo) Shih-yao Yen (Lawrence) Tatung University Tatung

High Current Pulse Generator Team DEC13-06 Design Document

High Current Pulse Generator

Team DEC13-06 Page 1

Team Composition

Members:

Wen Ya Ting(Audrey) Ho Hsu (Lily) Li-yeh Yang (Leo) Shih-yao Yen (Lawrence)

Tatung University Tatung University Tatung University Tatung University

Stephen Chiev Greg Bulleit Matt Stegemann

Iowa State University Iowa State University Iowa State University

Advisors:

Robert Bouda

Mani Mina

John Pritchard

Client:

High-Speed Systems

Engineering Laboratory



Table of Contents

Executive Summary ................................................................................. 3

Requirements ............................................................................................ 3

Functional Decomposition ..................................................................... 3

Detailed Design ......................................................................................... 4

Simulation and Testing ........................................................................... 7



Executive Summary

Our goal of this project is to further research into high current pulse generators that

could be used as for Transcranial magnetic stimulation (TMS). The magnetic fields

used in TMS applications are pulsed at very short time intervals. A high current

pulse is sent through an electromagnetic coil to create these fields. The goal of this

Senior Design team is to create a device that can deliver such a pulse. This device will

have controllable parameters (such as pulse width and amplitude) and will be able to

manage inductive loads.

This document will cover the overall design of our circuit. We have broken down the

circuit into its basic parts; the power supply, power storage, switching device, and

switching device control. For each of these parts we have broken down our design

choices and considerations.

Requirements

Functional

1. Control of pulse width and amplitude

2. Initial device capable of 25A monophasic

3. 400 μs for maximum pulse width

4. Biphasic implementation

5. Higher current design or device

Non-Functional

1. Single device capable of monophasic and biphasic

2. The size and the weight of our machine would not be too big and heavy. It would

be easy to move and carry.

Functional Decomposition

The basis of our design comes from the idea of storing a large amount of energy in a

capacitor and being able to control its discharge through a load. Our device can be

broken down into four different parts; power conversion and storage, switching

device, load, and switching control. The first part power storage and conversion

covers both of our power supplies and our capacitors used to store the energy for the



pulse. The second part our switching device covers the large device we chose to

handle the circuits current and its protection diode. The third part load covers the

different loads we have used for the device. The last part switching control

encompasses the microcontroller and the different circuitry we are using to create

the switching devices gate voltage and pulse.

Figure 1: System level diagram.

Detailed Design

Input/Output

The device has four inputs and three outputs. The inputs are the wall outlet for

power, parameter control, a switch to select mono or bi-phasic operation, and the

button to initiate a pulse. The outputs are connections for the load device, a serial



connection over USB to read the circuits device parameters, and last a possible LCD

to display the current device parameters.

Inputs

120Vrms AC wall outlet

Button

Mono/Bi-phasic switch

Pulse length control

Pulse height control

Outputs

Load

Serial (USB)

Possible LCD

Power Conversion and Storage

Our device is power from a normal 120Vrma wall outlet. To easily store power we

need to convert the AC input voltage to a DC voltage. In our device we have used a

transformer to drop the AC voltage from 120Vrms to 40Vrms. We drop the voltage

because the capacitors become prohibitively expensive at high voltages. Once the AC

voltage is reduced we use a full wave rectifier and our capacitors to create a DC

voltage of 56V. Our secondary power supply is smaller and is used to power our

switching control. This design uses a transformer to create a 15Vrms signal that is

rectified to become a 21V DC voltage.

Switching device

In our design our switching device must be able to handle the full current flowing

through the load. The device we chose is an insulated-gate bipolar transistor (IGBT)

for its high speed and high voltage control. The device can handle up to 20V on its

gate and 600V from collector to emitter. The device can also handle 200A for short

pulses. In parallel with our switching device is a protection diode. This diode will

break down with voltages high than 70V. These voltages can occur when an inductive

load is used and its path to ground is suddenly cut off.

Switching control (Arduino)



An Arduino board was chosen to control the parameters of the pulse and to trigger

the pulse itself. This board is easy to use and allows for plenty of flexibility in the

design. The main purposes it will serve are:

Monophasic or Biphasic select

Control pulse amplitude

Control pulse width

Output pulse trigger

Serial display

Arduino Inputs

Two analog inputs will be used to control the width and amplitude parameters. The

voltage detected at each of the inputs will correspond to specific pulse and amplitude

ranges. A digital third input will be used to select either monophasic or biphasic. The

last digital input will be used to detect when to send to the pulse.

Arduino Outputs

A digital output will be used to send the initial pulse. This pulse will switch ‘off’ a BJT

that will allow current to flow to the IGBT switching circuit.

Figure 2: A system level diagram of the Arduino inputs and outputs.

Arduino

D1

D2

A1

A2

PWM

D3

TX

Power Amp

Filter/Amp

Inputs Outputs



A pulse-width-modulation (PWM) output will control the current flow to the gate of

the IGBT during the pulse, thus controlling the amplitude. The duty cycle of the

PWM will be controlled by one of the analog inputs. This PWM wave will then be

filtered and amplified to act as an analog voltage, depending on the duty cycle. This

voltage will be used as VDD in the circuit of Figure 2.

The last output will be a serial output to an LCD display. This will display

information such as the mode select (monophasic or biphasic) and the pulse width.

Simulation and Testing

Software: National Instruments (NI) Multisim

To simulate and test our design, we use National Instruments (NI) Multisim

software. Multisim is a very capable and widely used SPICE program. We have

access to Multisim on the campus lab computers and also through remote desktop.

The wide range of component selection and intuitive interface make it a very useful

tool in our design.

Pulse Circuit and Simulation Results

VDD

R

BJT

VA

VB

high

low

HIGH

LOW

VA

VB

Figure 3: Function of the digital output and the power amp circuit. VA

is connected to D3 from Figure 2 and VB goes to the IGBT.



Figure 4: Multisim schematic of a complete pulse circuit.

Figure 4 shows a complete pulse circuit. The following table lists the relevant

components:

Component Purpose V3 Simulates voltage from wall outlet T1 Transformer to step down the wall voltage D1 – D4 Full wave rectifier for conversion of AC to DC C1 and R2 Capacitor for energy storage with simulation of

built in series resistance L2 Inductive load R1 Parallel load resistor to minimize voltage

ringing Q1 IGBT for switching purposes V1 Substitute for Arduino power amplifier output D5 Protection diode

Table 1: A list of the components and their purposes for the circuit in Figure 4.

Simulating this circuit allows us to send a current pulse through the load. The

voltage source V1 controls what the output current waveform will look like. In

Multisim, we are able to adjust the source’s pulse width and amplitude to produce

different current outputs.



Figure 5: Load current for a pulsed amplitude of 9 volts and width of 375 microseconds. Total pulse time is close to 400 microseconds.

Figure 5 shows a sample output of the current through the load. The waveform

shows us the total pulse width will not be the same as the pulse width from the

source V1. There is additional time added due to the discharge of the inductor.

Figure 6: Output current pulse, with inclusion of the voltage spike at the end of the pulse.



Figure 6 shows the current output again (in red) and also the resulting voltage spike

(in green) from the discharging inductor. This voltage spike occurs at the collector of

the IGBT. Having the protection diode D5 greatly reduces the voltage spike and thus

prevents the IGBT from being damaged.

Arduino Power Amplifier and Filter Circuit

Figure 7: Multisim schematic for the power amplifier and filter circuits associated with the Arduino outputs.

The voltage source V1 in Figure 4 is a substitute for the above circuit in Figure 7. This

circuit lets us simulate the PWM output and the digital output from the Arduino.



Figure 8: Output from the filter circuit of Figure 7. This waveform shows that it takes about 100 milliseconds for our output to settle to the desired voltage.

Figure 8 is the output of the filter section from Figure 7. The waveform shows us

about how much time is needed until the output “settles” to the desired voltage.