General Description
The MAX5003 50W forward converter evaluation kit (EV
kit) provides a regulated +5V output voltage at currents
up to 10A, when operated from a +36V to +72V input
voltage range.
This EV kit is fully assembled and tested. The output
voltage is preset to +5V. A single-transistor forward-
converter topology with a reset winding is used for high
output power and high efficiency. The use of an opto-
coupler in the feedback circuit provides full 1500V pri-
mary to secondary galvanic isolation. A bottom-mount-
ed heatsink plate safely dissipates the heat generated
by the power MOSFET and the output diode. The power
supply is designed to fit into a small footprint.
WARNING: Dangerous voltages are present on this
EV kit and on equipment connected to it. Users who
power-up this EV kit or power the sources connect-
ed to it must be careful to follow safety procedures
appropriate to working with high-voltage electrical
equipment.
Under severe fault or failure conditions, this EV kit
may dissipate large amounts of power, which could
result in the mechanical ejection of a component or
of component debris at high velocity. Operate this
EV kit with care to avoid possible personal injury.
Features
♦+5V at 10A Output
♦±36V to ±72V Input Voltage Range
♦250kHz Switching Frequency
♦Fully Isolated Design with 1500V Isolation Built
into the Transformer
♦Fully Assembled and Tested Board with Minimum
PC Board Footprint
♦0.3% typical Line and Load Regulation
♦85% typical Efficiency at 25W
Evaluates: MAX5003
MAX5003-50W Evaluation Kit
________________________________________________________________ Maxim Integrated Products 1
19-1914; Rev 0; 3/01
Component List
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Ordering Information
DESIGNATOR QTY DESCRIPTION
C 1, C 3, C 10, C 15 4 0.1µF ceramic caps (0805)
C2 1 470pF ceramic cap (0805)
C4, C5, C6 3 0.47µF, 100V ceramic caps
(2220)
C7, C13, C14 3
560µF, 6.3V electrolytic
capacitors
Nichicon UPW0J561MPH
C8, C9 2 47nF ceramic capacitors (0805)
C11 1 22nF ceramic capacitor (0805)
C12 1 1nF, 100V ceramic capacitor
(0805)
C16 1 4.7nF, 1500V ceramic capacitor
D3 1 200mA, 100V diode
Panasonic MA111CT
D4 1
20A, 40V low forward voltage
Schottky diode
General Semi SBL2040CT
D5 1 200mA, 200V, diode
Panasonic MA115CT
Q1 1 200V MOSFET, Rds = 0.18Ω
International Rectifier IRF640N
Q2 1 NPN transistor, FMMT3904
DESIGNATOR QTY DESCRIPTION
R1 1 1MΩ ±1% resistor (0805)
R2 1 39.2kΩ ±1% resistor (0805)
R3 1 80.6kΩ ±1% resistor (0805)
R4 1 1.24kΩ ±1% resistor (0805)
R5 1 56kΩ ±1% resistor (0805)
R6 1
0.02Ω resistor
Dale-Vishay WSL1206 0.02Ω
±1.0% R86
R8 1 100Ω ±5% resistor (0805)
R9 1 470Ω ±5% resistor (0805)
R11, R12 2 10kΩ ±1% resistors (0805)
R13 1 20Ω ±5% resistor (1206)
R14 1 10kΩ ±5% resistor (0805)
R15 1 240kΩ ±5% resistor (0805)
R16 1 1Ω ±5% resistor (0805)
L1 1 4.7µH inductor
Coiltronics HC2-4R7
T1 1 Transformer
Coiltronics CTX03-14856
PART TEMP. RANGE IC PACKAGE
MAX5003EVKIT50W 0°C to +50°C* 16 SOIC
*With air flow.
Evaluates: MAX5003
MAX5003-50W Evaluation Kit
2 _______________________________________________________________________________________
Quick Start
The MAX5003 50W EV kit is fully assembled and tested.
The power supply has full isolation between the primary
and secondary circuit. A heatsink is included at the non-
component side for heatsinking the power MOSFET and
the output dual diode D4. During normal operation at full
output current, this heatsink becomes hot. A small fan
with direct airflow towards this heatsink is recommended
to keep the temperature rise to acceptable levels.
This power supply is not fused at the input. For
added protection, a 3A to 5A fuse should be used at
the input.
Appropriately sized heavy-gauge wires should be used
to connect the power supply to the EV kit and load.
Follow these steps to verify board operation. Do not
turn on the power supply until all connections are
made.
1) Connect a 220µF bulk storage capacitor at the input
terminals of the EV kit. This capacitor should be
rated for 100V and be able to handle 1.5A of ripple
current.
2) Connect a +36V to +72V power supply to the pads
labeled VIN. The positive power-supply terminal
should connect to VIN(+) and the negative power-
supply terminal should connect to VIN(-). The power
supply must be rated to at least 3A. The input volt-
age to the MAX5003 EV kit should not exceed 80V
at any time.
3) Connect a variable load capable of sinking at least
10A at 5V and a voltmeter to the pads labeled +VO
and -VO.
4) Set the load current to approximately 5A.
5) Turn on the input power and verify that the output
voltage is +5V.
6) To evaluate the load regulation of the EV kit, vary
the load from 0 to 10A and record the output volt-
age variation as needed. For best measurement
accuracy, the voltmeter must be connected right to
the output pads of the EV kit.
7) To evaluate the line regulation of the EV kit, vary the
input voltage from +36V to +72V and record the
output voltage.
Note: The MAX5003 EV kit undervoltage lockout circuit-
ry has been designed to shut down when the input sup-
ply voltage is under 32V.
Power Supply Typical
Specifications
Table 1 summarizes the typical performance of the 50W
power supply.
Table 1. Typical Specifications
SUPPLIER PHONE FAX
Coiltronics 561-241-7876 561-241-9339
Dale-Vishay 402-564-3131 402-563-6418
General Semiconductor 631-847-3000 631-847-3236
International Rectifier 310-322-3331 310-322-3332
Nichicon 847-843-7500 847-843-2798
Panasonic 201-392-7522 201-392-4441
QT Optoelectronics 408-720-1440 408-720-0848
DESIGNATOR QTY DESCRIPTION
U2 1 Optocoupler
QT Optoelectronics MOC217
U3 1 Shunt regulator TL431AID
U1 1 MAX5003ESE, 16-pin narrow SO
Z1 1 15V Zener diode
Panasonic MA8150
Component List (continued)
Component Suppliers
Output Power 50W
Input Voltage (VIN) ±36V to ±72V
Output Voltage (VOUT) +5V
Output Current (IOUT) 10A
Initial Output Accuracy ±3%*
Output Voltage Regulation 0.3%, over line and load
Efficiency 85% at 48V and 25W
Input Output Isolation 1500V for 1s
Switching Topology Feedforward Compensated
Forward Converter
Dimensions 4.05in x 1.3in
*Initial setpoint accuracy can be improved by using tighter tol-
erance resistor divider (R11 and R12).
Power Supply Performance
Key performance characteristics of the power supply
include efficiency and output voltage regulation. Figure 1
shows the efficiency vs. output power. The efficiency
reaches 85% at about 25W of output power and stays
relatively flat up to 50W. Even though the efficiency is
very high, heatsinking is required for the power MOSFET
and output diode. The diode will dissipate about 6W with
a 10A output current and the MOSFET can be expected
to dissipate about 3W to 4W at full 50W load. Sufficient
airflow over the power supply is recommended to cool
down the power transformer and output inductor.
Figure 2 shows the output voltage regulation of the
power supply from 0 to 10A of output current. Voltage
measurement was done across the output voltage
sense points +VOand -VO.
Another interesting performance waveform for power
supplies is the output voltage transient response to a
step change in output current. Figure 3 shows load
transient response when the load is stepped from 10A
to 0.8A.
As can be seen from Figure 3, the initial transient
response time is less than 30µs. This is a side benefit of
using an optocoupler in conjunction with a TL431 shunt
regulator for isolation.
Figure 4 shows the well-behaved startup characteristics
of this power supply, which are characterized by the
monotonic rise of the output voltage as well as the
absence of any overshoots at the end of the rise period.
Evaluates: MAX5003
MAX5003-50W Evaluation Kit
_______________________________________________________________________________________ 3
0
20
10
50
40
30
60
70
80
90
0 1020304050
MAX5003EV fig01
OUTPUT POWER (W)
EFFICIENCY (%)
Figure 1. Efficiency vs. Output Power
-0.15
0
-0.05
-0.10
0.05
0.10
0.20
0.15
0.25
MAX5003EV fig03
10µs/div
VOLTS
Figure 3. Output Transient Response (IOUT: 10A to 0.8A)
4.5
4.8
4.7
4.6
4.9
5.0
5.1
5.2
5.3
5.4
5.5
0426810
MAX5003EV fig02
IOUT (A)
VOUT (V)
Figure 2. Output Voltage Regulation vs. Output Current
MAX5003 fig04
1V/div
VOUT (V)
2ms/div
Figure 4. Output Voltage Transient At Power-Up
(VIN = 48V, IOUT = 5A)
Evaluates: MAX5003
The Power Circuit Topology
Among the several power topologies available, the sin-
gle-transistor forward topology offers a simple and low-
cost solution and provides very good efficiency
throughout the operating power range. However, this
topology requires a transformer reset winding connect-
ed to pins T1–3 and T1–4 (Figure 7). The forward con-
verter was chosen because it offers higher power den-
sity and higher efficiency than a flyback converter at
these power levels. Transformer T1 provides 1500V iso-
lation between primary and secondary. Efficiency is fur-
ther improved by powering the control circuit from a
primary bias winding (T1–5, T1–6, Figure 7) after initial
startup. A 250kHz switching frequency was selected to
allow small form-factor transformer, inductor, and out-
put capacitors.
Key Operating Waveforms
Key operating waveforms are always useful in under-
standing the operation of switching power supplies. A
10×oscilloscope probe is necessary for effective prob-
ing. A digital scope is very useful in capturing startup
sequences. However, extreme caution should be exer-
cised when probing live power supplies. For example,
shorting the drain-source terminals of Q1 while power is
applied is sure to produce a big spark and may dam-
age the EV kit.
Figure 5 shows the drain-to-source waveform of Q1.
Notice the leading-edge voltage spike. This is a result
of the energy stored in transformer T1’s leakage induc-
tance.
Figure 6 shows the voltage at the output of the sec-
ondary rectifier (cathode of D4).
PC Board Layout and
Component Placement
As with any other switching power supply, component
placement is very important. Because of the primary-to-
secondary isolation, the primary and secondary
grounds are separated. Figure 10 clearly shows the
separation on both sides of the PC board. The layout of
the board can be changed to accommodate different
footprints. Also, the power MOSFET and output rectifier
should be mounted on a heatsink for best thermal man-
agement. In this implementation, both of these compo-
nents are on the noncomponent side of the board, with
their tabs mounted to the heatsink plate.
The critical layout considerations are as follows:
•Distance from the secondary transformer leads to
diode D4 should be kept to a minimum. This will
improve EMI as well as the effective available
power transfer.
•Bypass capacitors C4, C5, and C6 should be as
close as possible to T1–1.
•The PC board trace connecting T1–2 to the drain of
Q1 should be as short as possible.
•The current-sense resistor R6 should be as close as
possible to the source of Q1 and should return with a
very short trace either to the ground plane or to the
negative lead of bypass capacitors C4, C5, and C6.
•The gate-drive loop, consisting of pin 14 of
MAX5003, R16, Q1, R6, and pin 13 of the
MAX5003, must be kept as short as possible and
preferably routed over a ground plane.
•Relevant trace spacing (relating to trace creepage)
must be observed according to applicable safety
agency guidelines.
MAX5003-50W Evaluation Kit
4 _______________________________________________________________________________________
MAX5003 fig05
50V/div
VDS(V)
400ns/div
Figure 5. Drain-Source Voltage Waveform
MAX5003 fig06
200ns/div
5V/div
Figure 6. Waveform at Cathode of D4
Evaluates: MAX5003
MAX5003-50W Evaluation Kit
Figure 7. MAX5003 50W EV Kit Schematic
1
SGND: DENOTES SECONDARY GROUND
SGND
SGND
SGND
U3
U2
U1
C
A
A
NC
R
A
A
NC
SGND
D4
Q1 GND
GND
VDD C11
22nF
C8
47nF
C9
47nF
C10
0.1µF
C3
0.1µF
C1
0.1µF
C2
470pF
16
3
16
11
9
8
12
12T
4T
14T
4
6
5
2
15
14
13
12
11
10
9
16
15
14
13
12
11
10
9
VDD
VCC
NDRV
PGND
CS
AGND
MAXTON
FB
V+
INDIV
ES
FREQ
SS
REF
CON
COMP
1
1
2
3
4
2
8
7
7
6
5
6
5
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
VDD
Q2
Z1
D3
MA111CT
D5
MA115
GNDGND
C15
0.1µF
C12
1nF
100V
C6
0.47µF
100V
C5
0.47µF
100V
C4
0.47µF
100V
C16
4.7nF
1500V
R6
0.02Ω
1%
R13
20Ω
R16
1Ω
R8
100Ω
R14
10kΩ
R15
240kΩR9
470Ω
R5
56kΩ
1%
R11
10kΩ
1%
R4
1.24kΩ
1%
R3
80.6kΩ
1%
R2
39.2kΩ
1%
R1
1MΩ
1%
R12
10kΩ
1%
L1
4.7µH
C14
560µF
6.3V
C13
560µF
6.3V
C7
560µF
6.3V
++
+
-VIN
U1
MAX5003
GND
T1
+VO
-VO
SGND
_______________________________________________________________________________________ 5
Evaluates: MAX5003
MAX5003-50W Evaluation Kit
Figure 8. MAX5003-50W EV Kit PC Board Layout—Component Side
Figure 10. MAX5003-50W EV Kit PC Board Layout—Solder Side
Figure 9. MAX5003-50W EV Kit Component Placement Guide—Component Side.
Note: Q1 and D4 are placed on the bottom side where their metal tabs are exposed to heatsink plate.
1.0"
1.0"
1.0"
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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