Riverside: Isolated power supply with 3.3V input, 12V (15V) output


The Riversdie design (MAXREFDES8#) uses an H-bridge transformer driver (MAX256) and LDO (MAX1659) to convert a 3.3V input to a 12V (15V) isolated output supply (Figure 1). This versatile power solution can be used for isolated power applications in a variety of applications, but primarily for industrial sensors, industrial automation, process control, and medical electronics.

Figure 1. Block diagram of the Riverside subsystem design.

Figure 1. Block diagram of the Riverside subsystem design.


Isolated Power

12V/15V output voltage

Take up less PCB area

Compatible with Pmod (Note) Miniaturized Design


Industrial sensor

Process control system

automated industry

Medical electronics

Hardware circuit description

The Riverside reference design subsystem is powered by a 3.3V DC power supply. The MAX256 H-bridge transformer drive has a switching frequency of approximately 475KHz and can drive the primary side with a turns ratio of 1:2.6, such as the TGM-H281NF transformer from Halo Electronics. . The secondary side of the transformer is connected to a voltage doubler circuit to convert the AC voltage into a DC output. The MAX1659 linear regulator stabilizes the voltage at 12V, and Zener diode D3 protects the linear regulator from input voltages up to 16.1V.

Riverside (MAXREFDES8#)

Input power can be accessed from a J1 Pmod-compatible connector, or an external power supply can be connected to the EXT3.3V and DGND connectors. Simply change the feedback resistors R2 and R3 of the LDO to change the output voltage.

The output voltage of the MAX1659 is determined by the following formula:

Output voltage formula

For example, for applications that require a 15V output, change R2 to 187kΩ and R3 to 16.2kΩ. In some cases where the output voltage ripple is very high, a low-pass LC π filter can be added to the LDO front end.

The isolated transformer in the design provides 1500VRMS voltage isolation, meets UL60950 and EN60950 certification requirements, and “functionally” meets insulation rating requirements.

Quick assessment:

1. Equipment required:

Riverside (MAXREFDES8#) board

3.3V 1A power supply

Digital voltmeter

2. Evaluation steps

The Riverside board is a fully assembled and tested circuit board. Follow the steps below to confirm the operation.

(1) Place the bypasser at position 1–2 of JU1.

(2) The positive terminal of the power supply is connected to the EXT_+3.3V connector.

(3) Connect the negative terminal of the power supply to the DGND connector.

(4) The positive terminal of the voltmeter is connected to the +12V connector.

(5) Connect the negative terminal of the voltmeter to the GND connector.

(6) Turn on the power.

(7) Measure the output voltage with a voltmeter.

Laboratory measurement

The 12V and 15V output cases designed by Riverside are tested. Other output voltages can be obtained by adjusting the resistance of R2 and R3.

When set to 12V output, the circuit can provide a maximum load current of 165mA. When set to 15V, a load current of 60mA can be supplied.

In order to improve the load driving capability, the user can increase the voltage of the input power supply or appropriately increase the transformer turns ratio. For more information, please refer to the MAX256 data sheet. Power efficiency is noted in Figures 2 and 3.

Figure 2. Efficiency at 12V output voltage.

Figure 2. Efficiency at 12V output voltage.

Figure 3. Efficiency at 15V output voltage.

Figure 3. Efficiency at 15V output voltage.

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