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Protection and Isolation
> APP 5510
Keywords:
power, pmod, industrial sensors, process control, industrial automation, medical, industrial power, halo
electronics, transformer, lakewood, maxrefdes7, industrial, dual supplies, power
REFERENCE DESIGN 5510 INCLUDES:
Tested Circuit
Schematic
BOM
Description
Test Data
Layout
Lakewood (MAXREFDES7#): 3.3V Input, ±12V (±15V)
Output Isolated Power Supply
Nov 06, 2012
Abstract: This document details the Lakewood (MAXREFDES7#) subsystem reference design, a 3.3V input, ±12V
(±15V) output, isolated power supply. The Lakewood reference design includes a 3W primary-side transformer H-
bridge driver for isolated supplies, and two wide input range and adjustable output low dropout (LDO) linear
regulators. Test results and hardware files are included.
Introduction
The Lakewood design (MAXREFDES7#) uses an H-bridge
transformer driver (MAX256) and a pair of low dropout (LDO)
linear regulators (MAX1659 x2) to create a ±12V (±15V)
output isolated power supply from a 3.3V voltage input
(Figure
1).
This general-purpose power solution can be used
in many different types of isolated power applications, but is
mainly targeted for industrial sensors, industrial automation,
process control, and medical applications.
More detailed image
(PDF, 1.9MB)
Figure 1. The Lakewood subsystem design block diagram.
Features
Isolated power
±12V (±15V) outputs
Small printed circuit board (PCB) area
Pmod™-compatible form factor
Applications
Industrial sensors
Process control
Industrial automation
Medical
Detailed Description of Hardware
The Lakewood subsystem reference design operates from a 3.3V DC power source. The MAX256 H-bridge
transformer driver switches at approximately 475kHz and drives the primary side of the 1:2.6 turns ratio, with the
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use of a TGM-H281NF transformer from Halo
®
Electronics. The transformer secondary side is connected to voltage
doublers that rectify the AC outputs into DC outputs. Two MAX1659 LDOs regulate the voltages to +12V and -12V,
respectively. The Zener diodes (D3 and D6) protect the LDOs by keeping their input voltages below 16.1V.
The input power can be from the J1 Pmod-compatible connector or from an external power supply connected to the
EXT_+3.3V and DGND connectors. To change the output voltages of this reference design, simply change the
feedback resistors (R2–R5) of the LDOs (U2 and U3).
The output voltage of the MAX1659 LDOs is set by the following equations:
V
OUT
= V
SET
× (1 + R2/R3) for U2
V
OUT
= V
SET
× (1 + R4/R5) for U3
Where V
SET
= 1.21V.
For example, for the ±15V outputs application, change R2 and R4 to 187kΩ, and change R3 and R5 to 16.2kΩ.
This circuit can also be configured for asymmetrical applications.
In applications sensitive to output voltage ripple, a lowpass LC pi filter can be added in front of the LDO input.
The isolation transformer in this design has an isolation voltage of 1500V
RMS
. It is recognized by UL 60950 and EN
60950 and falls into the "functional" insulation class.
Quick Start
Required equipment:
Lakewood (MAXREFDES7#) board
3.3V 1A power supply
Two digital voltmeters
Procedure
The Lakewood board is fully assembled and tested. Follow the steps below to verify board operation.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Place the shunt on jumper JU1 to the 1–2 position.
Connect the positive terminal of the power supply to the EXT_+3.3V connector.
Connect the negative terminal of the power supply to the DGND connector.
Connect the positive terminal of the first voltmeter to the +12V connector.
Connect the negative terminal of the first voltmeter to the GND1 connector.
Connect the positive terminal of the second voltmeter to the -12V connector.
Connect the negative terminal of the second voltmeter to the GND2 connector.
Turn on the power supply.
Use the respective voltmeters to measure the corresponding positive and negative output voltages.
Lab Measurements
The Lakewood design was tested for two pairs of output voltage rails: ±12V and ±15V. Other voltage rails can be
achieved by modifying the resistor values of R2, R3, R4, and R5. When set for ±12V outputs, the circuit can deliver
a maximum load current of approximately 90mA for each of the two rails simultaneously. When set for ±15V
outputs, the circuit can deliver a maximum load current of approximately 40mA for each of the two rails
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simultaneously.
To achieve a larger maximum load, the user can either increase the input power supply voltage or increase the
transformer turns ratio properly. Refer to the
MAX256 data sheet
for details. The power efficiencies are illustrated in
Figure 2
and
Figure 3.
For asymmetrical voltage level applications, the maximum load can be larger for one rail and less for the other rail.
Figure 2. Power efficiency vs. current load for ±12V
outputs.
Figure 3. Power efficiency vs. current load for ±15V
outputs.
The output noise is well below 0.5% of the output voltages. The noise is mainly due to the switching pulses of the
MAX256.
Figure 4
and
Figure 5
display the noise at no load for 12V and 15V outputs, respectively.
Figure 6
and
Figure 7
display the noise at the maximum loads for 12V and 15V outputs, respectively.
The noise on the negative rails is identical to the positive rails for symmetrical load applications.
Figure 4. Noise at VOUT = 12V, IOUT = 0mA.
Figure 5. Noise at VOUT = 15V, IOUT = 0mA.
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Figure 6. Noise at VOUT = 12V, IOUT = 90mA.
Figure 7. Noise at VOUT = 15V, IOUT = 40mA.
All Design Files
Hardware Files
Schematic
Bill of materials (BOM)
PCB layout
PCB Gerber
PCB CAD (PADS 9.0)
Buy Reference Design
Lakewood (MAXREFDES7#)
Halo is a registered trademark of Halo Electronics, Inc.
Pmod is a trademark of Digilent Inc.
Related Parts
MAX1659
MAX256
MAXREFDES7
350mA, 16.5V Input, Low-Dropout Linear Regulators
3W Primary-Side Transformer H-Bridge Driver for Isolated
Supplies
Lakewood (MAXREFDES7#): 3.3V Input, ±12V (±15V) Output
Isolated Power Supply
Free Samples
Free Samples
More Information
For Technical Support:
http://www.maximintegrated.com/support
For Samples:
http://www.maximintegrated.com/samples
Other Questions and Comments:
http://www.maximintegrated.com/contact
Application Note 5510:
http://www.maximintegrated.com/an5510
REFERENCE DESIGN 5510, AN5510, AN 5510, APP5510, Appnote5510, Appnote 5510
© 2013 Maxim Integrated Products, Inc.
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