1769205x2, 176881212, 176861512

FISM

– Fixed Isolated SMT Module

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Würth Elektronik eiSos GmbH & Co. KG

– Data Sheet Rev. 1.0

©July 2018

26/37

Generating Complementary Output Voltages

Another common requirement in industrial applications is to provide a complementary voltage (e.g. ±5V). The circuit below

shows how this target can be achieved simply combining a 176xxxxx2 used in a standard configuration (delivering a positive

output voltage) with a 176xxxxx2 in a reverse configuration. It is a common practice to connect an additional capacitor

across each output voltage.

+VIN

-VIN

-VOUT

+VOUT

Module 2

2

1

4

5

L2

C2

Decoupl ing fi lter

+VIN

-VIN

-VOUT

+VOUT

Module 1

2

1

4

5

L1

C1

Decoupl ing fi lter

Capacitor

Capacitor

DC

BUS

+

-

+

-

-

+

When using multiple modules connected to a single dc bus voltage the individual module inputs have to be decoupled by LC

filters. The LC filter reduces the likelihood of oscillations due to parasitics of a layout/routing. Therefore, it is not

recommended to connect power modules in parallel on the primary side without an LC filter. See also Primary side parallel

connection on page 25.

Note: The decoupling filters are present to avoid oscillations between the two power modules. These filters don´t replace the

EMI input filter.

Reverse Polarity Protection

A simple way of creating an input reverse polarity protection is to place a diode in series with the plus input line. The diode

blocks all negative voltages that might be applied at the plus input because of operating reverse biased. Due to the forward

voltage drop of the diode the application efficiency drops.

+VIN

-VIN

-VOUT

+VOUT

Module

2

1

4

5

Reverse polarity

blocking diode

DC

BUS

+

-