Applications Note AN36
Issue1 - JULY 2002
12V Supply with Reverse Supply
Protection
The higher voltage, 100V,
Zetex
ZXMN10N11G MOSFETs are used with 75V
Zener active clamping.
This following circuit in Figure 17 is similar to
that in Figure 15 except that it has the reverse
polarity protection feature added. This is
achieved with D3 providing protection to the
ZXBM2001 and D4 providing protection to
the motor windings. C5 is also added to
smooth out the excessive supply disturbance
as discussed in previous sections.
The circuit in Figure 18 has also been used for
a motor design with an input supply of 48V. In
this case higher voltage rating components
were selected to withstand the higher
winding avalanche voltages.
Figure 18
Figure 17
24V motor with Reverse Polarity Protection.
12V Supply with Reverse Supply Protection.
Another point of note with this circuit is that
the PWM frequency was set to run at 34kHz by
making C1 the more readily available 100pF
value. Running at this higher frequency has
not been seen to be a problem with MOSFETs
where the on and off switching is clean and
thus gives minimal switching losses.
USEFUL APPLICATION IDEAS
Failsafe dual fan systems
In high reliability systems there is a need to
ensure the cooling scheme is also reliable.
This is often achieved by the use of 2 fans that
will ensure there is still a degree of cooling
should one fan fail. An improvement to this is
to run each of the two fans at half speed and in
the event of a failure of one fan to speed up
the remaining fan to full speed. Figure 19
illustrates such a system where two fans
using the ZXBM2001 are connected together.
24V Supply with Reverse Supply
Protection
The final circuit example in Figure 18 is used
to illustrate the supply provision for a 24 V
application. Again MOSFETs are used with
reverse supply protection incorporated. The
ZXBM2001 takes its supply from the same
protection diode as the windings, however,
because C4 is large and the supply to the
ZXBM2001 regulated by ZD3 and C3 the
supply commutation ripple is not a problem.
AN 36 - 11
ZETEX [ ZETEX SEMICONDUCTORS ]
