AXBM2001 datasheet(9/14 Pages) ZETEX

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Another hazard with the excessive voltages

from the blocking diodes is that it can cause

this energy to be dissipated within the Zener

clamping arrangement. As this energy would

normally have been returned to the supply for

reuse it seems appropriate to attempt to save

the energy for reuse within the fan itself. This

is achieved with the Capacitor C5 in Figure 17.

Care needs to be taken with the selection of

the capacitor type and value for each

application. For multilayer chip capacitors it

will be a cost verses value issue and for

electrolytic capacitors a size verses value

issue. In both cases the voltage tolerance of

the chosen part needs careful consideration

as the capacitor needs to reliably withstand

the peak voltages.

When used, the capacitor gives considerable

efficiency improvements with noted

reductions in supply current and driver

device temperature. Figure 11 shows the

winding supply at the winding common point

and shows the voltage being clamped by the

driver active clamping. Figure 12 shows the

effects of adding a 4.7 F multilayer ceramic

capacitor (C5 in Figure 17).

APPLICATION CIRCUIT EXAMPLES

In this section are shown complete circuit

examples developed using the ZXBM2001

together with the type of fan it was developed

for. Examples are given for a variety of

applications with the intention that these

circuits will form the starting point for a users

future development in conjunction with the

guidelines given in the previous section.

AN 36 - 9

Applications Note AN36

Issue1 - JULY 2002

Figure 11

Winding Supply

Figure 12

Winding Supply with 4.7 F Capacitor

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