Maxim > Design Support > Technical Documents > Reference Designs > Medical > APP 5512 Maxim > Design Support > Technical Documents > Reference Designs > Power-Supply Circuits > APP 5512 Maxim > Design Support > Technical Documents > Reference Designs > Protection and Isolation > APP 5512 Keywords: power, 15V, 12V, pmod, industrial sensors, process control, industrial automation, medical, industrial power, halo, transformer, riverside, maxrefdes8, industrial, power REFERENCE DESIGN 5512 INCLUDES: Tested Circuit Schematic BOM Description Test Data Layout Riverside (MAXREFDES8 ): 3.3V Input, 12V (15V) Output Isolated Power Supply Nov 06, 2012 Abstract: This document details the Riverside (MAXREFDES8 ) subsystem reference design, a 3.3V input, 12V (15V) output isolated power supply. The Riverside reference design includes a 3W primary-side transformer H- bridge driver for isolated supplies, and one wide input range and adjustable output low dropout (LDO) linear regulator. Test results and hardware files are included. Introduction The Riverside design (MAXREFDES8 ) uses an H-bridge transformer driver (MAX256) and a low dropout (LDO) linear regulator (MAX1659) 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 (JPG) Figure 1. The Riverside subsystem design block diagram. Features Applications Isolated power Industrial sensors 12V (15V) output Process control Small printed circuit board (PCB) area Industrial automation Pmod-compatible form factor Medical Detailed Description of Hardware The Riverside subsystem reference design operates from a 3.3V DC power source. The MAX256 H-bridge Page 1 of 5transformer driver switches at approximately 475kHz and drives the primary side of the 1:2.6 turns ratio, with the use of a TGM-H281NF transformer from Halo Electronics. The transformer secondary side is connected to a voltage doubler that rectifies the AC output into DC output. The MAX1659 LDO regulates the voltage to 12V. The Zener diode D3 protects the LDO by keeping its input voltage 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 voltage of this reference design, simply change the feedback resistors (R2, R3) of the LDO. The output voltage of the MAX1659 LDO is set by the following equation: V = V (1 + R2/R3) OUT SET Where V = 1.21V. SET For example, for the 15V output application, change R2 to 187k and change R3 to 16.2k. 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 . It is recognized by UL 60950 and EN RMS 60950 and falls into thefunctiona insulation class. Quick Start Required equipment: Riverside (MAXREFDES8 ) board 3.3V 1A power supply One digital voltmeter Procedure The Riverside board is fully assembled and tested. Follow the steps below to verify board operation. 1. Place the shunt on jumper JU1 to the 12 position. 2. Connect the positive terminal of the power supply to the EXT +3.3V connector. 3. Connect the negative terminal of the power supply to the DGND connector. 4. Connect the positive terminal of the voltmeter to the +12V connector. 5. Connect the negative terminal of the voltmeter to the GND connector. 6. Turn on the power supply. 7. Use the voltmeter to measure the output voltage. Lab Measurements The Riverside design was tested for two output voltage rails: 12V and 15V. Other voltage rails can be achieved by modifying the resistor values of R2 and R3. When set for 12V output, the circuit can deliver a maximum load current of approximately 165mA. When set for 15V output, the circuit can deliver a maximum load current of approximately 60mA. 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. Page 2 of 5