Download Progress Report #2

Progress Report #2 - Group #6
To:
Cc:
Dr. A. K. S. Bhat
Dr. A. Zielinski, Mr. Kiran Swaroop
Date:
March 7, 2005
Group:
Jen Magdalenich
Stephen Spratt
Lauren Woolstencroft
The implementation of a Zero Voltage Transition (ZVT) Pulse Width Modulated (PWM) DC/DC
Boost Converter is making progress with much of the design phase completed, and aspects of
the testing and implementation in progress. This progress report divides the project into 4 main
sections, and comments on the work completed, and any remaining tasks. The 4 sections are;
the boost converter, the snubber cell, the control circuit, and a miscellaneous section including
website design etc.
1. The Boost Converter
Prior to implementing the snubber cell, a boost converter was designed with the following
specifications:
Vin = 18V – 30V DC
Vout = 48V DC
fs = 200kHz
P=250W
The following design calculations were completed by Lauren.
Figure 1: Boost Converter
Given the input voltage range of 18 – 30 V, the duty cycle D can be calculated as follows:
Vin
Vout
18V
30V
D  1
 0.625 , and D  1 
 0.375
48V
48V
D  1
The design problem specifies a switching frequency of 200kHz, however initial calculations are
done using 100kHz. This leads to a period T=1/fs=1e-5. The design problem also specifies a
max output power of 250W.
P
V2
RL
RL 
V 2 (48V )2

 9.216
P
250W
The inductor Lb can be calculated using the following inequality: (please note that
Lb  Lcrit in
order for the circuit to always operate in continuous conduction mode (CCM)).
RT
(1  D) 2 D
2
(9.216)(105 s)
for D=0.625 Lcrit 
(1  0.625)2 (0.625)  4.05 H
2
(9.216)(105 s)
for D=0.375 Lcrit 
(1  0.375)2 (0.375)  6.75 H
2
 Lb  6.75 H
Lb  Lcrit 
Let
LB  33.75 H which is 5 times the initial value of Lcrit.
An inductance of L=33.75uH can be realized given:
N2
l
L
0  r A
Where N represents the number of turns around the core. Using a core of material TDK PQ5050
PC44, and the fact that with 13 turns the inductance is measured in the laboratory to be 75.3uH,
N can be calculated using the ratio:
L1 N12
75.3uH 132
 N2  9

 2 
33.75uH N 22
L2 N 2
Using an inductance value of LB
 33.75 H , the maximum load can be calculated as follows:
RT
(1  D ) 2 D
2
R (105 s )
33.75 H 
(1  0.375) 2 (0.375)
2
R  46.08
Lcrit 
In theory, the load should be no higher then R  46.08 to ensure the circuit remains in CCM,
however in reality load should be kept at a lower value due to the potential of parasitic
resistances present in the circuit.
All of the components required for the implementation of the boost converter have been obtained
with the help of Dr. Bhat and the lab technicians. Jen, Stephen, and Lauren have all been
involved in the acquisition of all of the components. Component information is as follows:

Power Mosfet: IRF640 (International Rectifier)




Schottkey Diode Db: BR10100
Zener Diode
Caps/Resistors – values as shown on circuit diagram
Inductor – Wound with 9 turns using a core of material TDK PQ5050 PC44.
The majority of the components have been soldered to the PCB provided by Dr. Bhat by Jen and
Stephen and full testing of the circuit is yet to be completed by Jen, Stephen and Lauren.
2. The Snubber Cell
The snubber cell is used to decreases switching losses. The following design calculations were
completed by Lauren and Stephen.
Figure 2: ZVT Boost Converter
The value of Lr can be calculated using the following equation:
Vo
3trr  I in ,max Where trr represents the reverse recovery time of the main diode Db. Db is a
Lr
schottkey diode with a very fast recovery time of 5ns.
Vo
3trr  I in ,max
Lr
Vo
P
3trr 
Lr
Vin ,min
48V
250W
3(5ns) 
Lr
18V
Lr  51.8nH
Let
Lr  75nH
The value of Cb can be calculated using the following equation:

2
Lr CB  t f 2 Where t f 2 represents the fall time of the auxiliary mosfet M2.

(75nH )CB  36ns
2
CB  7nF
Let
CB  7nF
The value of Cr can be calculated using the following equation:
Cr  CB
Vo  t f 1 Where t f 1 represents the fall time of the main mosfet M1.
I in,max
Cr  7nF
(48V )  36ns
13.89 A
Cr  3.418nF
These values of Cr, Cb, and Lr also satisfy the following equation:
1
1
1
Lr ( I in,max  I rr ,max ) 2  CrVo2  CBVo2
2
2
2
In order to get a reference feedback voltage of 2.5V, R12 and R14 can be calculated as follows:
R14
Vo  Vref
R14  R12
R14
(48V )  2.5V
R14  R12
Let
R14  1k  and R12  18.2k  .
The components for the snubber cell are still in the process of being obtained by Jen, Stephen
and Lauren. The following is a list of the components required for the snubber cell that have
already been obtained.
 Power Mosfet IRF640
 Schottkey Diode: BR10100
 Cr=4nF & Cb=7nF
 Resistors (values as per above)
The above components have been soldered to the auxiliary PCB by Jen and Stephen.
The following is a list of components yet to be obtained:
 Inductor L=75nH
As soon as the above component is realized, testing of the snubber cell will be completed by Jen,
Stephen and Lauren.
3. The Control Circuit
The control circuit uses an ATMEGA8 microprocessor to send pulse trains to both the main and
auxiliary mosfets, and to adjust the duty cycle of the pulse train depending on the input voltage.
Please see appendix 1 of this report for a schematic of the Control Circuit.
The pulse trains to both the main and aux. mosfets have been programmed and tested with the
use of the optoisolator and the fet driver. An external Crystal of 16MHz is used to ensure a fast
switching frequency. This task was completed by Jen and Lauren.
The use of the ATMEGA8 A/D is required to read a reference voltage at the output and determine
the change of pulse width required or a constant 48V output. A voltage divider as shown in figure
2 is used to provide a reference voltage of 2.5V when the output is indeed 48V. This aspect of
the control circuit is still in progress and is being completed by Jen.
All of the components required for the control circuit have been obtained by Jen, Stephen and
Lauren. Below is a list of the components used in the control circuit:
 Atmel ATMEGA8 microprocessor and development kit.
 Optoisolator HCPL 2601
 FET Driver UC2710
 5V Voltage Regulator LM7805C
 Resistors/capacitors – values as shown on schematic
All of the above components have been soldered to both the main and aux PCB’s by Jen and
Stephen.
4. Miscellaneous
Website – Task in progress and being completed by Lauren
Poster – to be completed by Jen
Presentation – April 1, 2005 – to be organized by Jen, Stephen and Lauren
Progress Reports – Completed by Stephen, with contributions from Jen and Lauren
Final Report – to be sectionalized by Jen, Stephen and Lauren
Regards,
Direct Current Innovations (499 Group 6)
Jen Magdalenich
Stephen Spratt
Lauren Woolstencroft
Appendix 1 – Control Circuit Schematic