COSEL CO.,LTD. : Caution For Safety And Products

Frequently Asked Questions

Q. What is harmful effect of input line impedance?

1. Summary

If the input line impedance for the DC/DC converter is high, the input voltage might get fluctuation, then it causes the output voltage unstable.

2. Input voltage fluctuation

If the inductance value is too much (see Fig. 2.1), the resonance circuit is composed by inductor L and capacitor C, and then it makes the input voltage change.

Fig. 2.1 The input line circuit

Please refer to the following for the change level of the input voltage.
In the circuit as shown in Fig. 2.1, the energy of inductor and capacitor is shown as the following.

Energy of inductor El : 1 / 2 x L x rI²
Energy of capacitor Ec : 1 / 2 x C x rV²

In the resonance circuit, energy of inductor and energy of capacitor are same. Therefore, the input voltage fluctuation (rV) is shown as the following.

rV = √(L x rI ² / C) -------(1)

3. Proposed measures for the input voltage fluctuation

Please refer to Table 3.1 for the measures to inhibit the input voltage fluctuation derived by the formula (1).

Table 3.1 Proposed measures for the input voltage fluctuation

No.	Measure	Concrete measures
1	Decrease L	Make input line short and use thick cable
2	Increase C	Add capacitor to DC/DC converter input
3	Reduce I	Reduce the output current

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♦ Technical Data

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Cosel is one of the world's leading power supply manufacturers offeringhigh-quality, ultra small size AC-DC power supplies,DC-DC converters of the state-of-the-art technologies, and effective andeasy-to-use noise filters.

Cosel is one of the world's leading power supply manufacturers offering
high-quality, ultra small size AC-DC power supplies,
DC-DC converters of the state-of-the-art technologies, and effective and
easy-to-use noise filters.