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Cover Story — Design Cover Story — Design
cycle is fixed at 50% and is independent of the load. The output voltage is unregulated and is The resolution that an ADC can provide, i.e., how many bits it effectively makes available, depends,
determined by the transformer turns ratio. The output power of 1 W can be provided up to an among other things, on the noise component of the supply voltage.
ambient temperature of T = 100˚C without any output current derating. The parasitic coupling
A
capacitance between the primary and secondary side has a typical value of 8 pF due to the design. The red circuit board in the application in Figure 2 generates a galvanically isolated dual voltage of
With an efficiency of 91%, it is the “best in class” in Würth Elektronik’s complete isolated power ±5 V from an input voltage of 5 V.
module portfolio.
Special features of the circuit are:
Galvanically isolated DC/DC converters are specifically designed to implement voltage isolation ▶ Very low residual ripple at the output
within distributed power supply systems. The FIMM module is particularly suitable for applications ▶ Broadband decoupling between input and output
sensitive to supply interference, such as analog low-frequency circuits and relay-controlled circuits.
The low parasitic capacitance between the primary and secondary sides of the circuitry ensure The dual-voltage supply consists broadly of four functional blocks (Figure 3):
a high degree of decoupling from high-frequency interference. Furthermore, this low parasitic ▶ Input protection circuit: The protection circuit integrates reverse-polarity protection and
capacitance mitigates the potential for common-mode interference to propagate from the primary voltage-transient protection.
switching side to the secondary side of the converter. ▶ Input filter: The first filter stage serves to attenuate conducted interference levels.
Harmonics generated by the switching operations of the DC/DC converter, in the direction
SUPPLYING SENSITIVE SENSORS of the supplying source, are reduced in their amplitude. On the other hand, interference
Applications such as measurement and data acquisition are often built with ADCs, which convert can reach the power module via the power supply and is attenuated by the filter.
the analog measured values, such as a temperature value or a current, into a digital quantity. ▶ The power supply (2 FIMM modules): The power modules convert the voltage and provide
For the acquisition of positive and negative measurement signals, a dual-voltage supply is required. galvanic isolation between the input and output.
Usually, a supply of ±5 V is used in such applications. ▶ Output filter: The current supplied by the power module is a superposition of a DC
current with an AC component. The AC component is the part that is reduced in
amplitude by the filter to provide a “clean” DC voltage for the application to be supplied,
such as an ADC.
Figure 3: The decoupled dual-voltage supply (red board in Figure 2) includes a protection circuit on the input side, a
Figure 2: Example of a sensor application using a decoupled dual-voltage supply (red board) filter on the input side, a power supply (2 FIMM modules),, and a filter on the output side.
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