22

ALQ07 DC-DC Converter Technical Reference Notes

DATE: Aug., 9, 2003

Input Reverse Voltage Protection

Under installation and cabling conditions where reverse polarity across the input

may occur, reverse polarity protection is recommended. Protection can easily be

provided as shown in Figure ‘Reverse Polarity Protection Circuit’. In both cases the

diode used is rated for 3A/100V. Placing the diode across the inputs rather than

in-line with the input offers an advantage in that the diode only conducts in a reverse

polarity condition, this increases circuit efficiency and thermal performance.

Reverse Polarity Protection Circuit

EMC

Input filters are included in the converters to help achieve standard system

emissions certifications. Some users however, may find that additional input filtering

is necessary. The ALQ07 series has an internal switching frequency of 360kHz so a

high frequency capacitor mounted close to the input terminals produces the best

results. To reduce reflected noise, a capacitor can be added across the input as

shown in Figure ‘Ripple Rejection Input Filter’, forming a 　 filter. A 47uF/100V

Ripple Rejection Input Filter

For conditions where EMI is a concern, a different input filter can be used. The

following figure ‘EMI Reduction Filter’ shows a filter designed to reduce EMI effects.

ALQ07 series can meet EN55022 CLASS A with the following figure.