Applications Note AN36
Issue1 - JULY 2002
6V supply with ‘naked’ hall and
bipolar drive
12V Supply with buffered Hall and
MOSFET drivers
The first example in Figure 13 is for a 6V axial
fan driver. The design uses an unbuffered
Hall sensor and bipolar drive transistors. The
Zetex FMMT619 transistor will furnish output
powers up to 2W with the SOT23 package,
however, in excess of this the SOT89 package
(FCX619) might be more suitable if driver
temperature is excessive. Measurements of
the fan speed verses the thermistor
temperature is shown in the accompanying
graph in Figure 14.
This second example in Figure 15 shows a
complete circuit using MOSFET drivers and a
12V supply. It also makes use of the more
common buffered Hall sensor. The output
devices are the Zetex ZXMN6A11G MOSFETs
which are rated at 60V so the clamping is
achieved with 56V Zeners. Avalanche
problems are averted by not attempting to
turn the MOSFETs off too quickly and 1k⍀ for
R3 and R4 meets those aims. It should be
suitable for powers up to 20W. The speed
response is shown in Figure 16.
Figure 15
12V motor with MOSFET drive.
Figure 13
6V Axial Fan using bipolar drive.
Figure 14.
Figure 16.
AN 36 - 10
ZETEX [ ZETEX SEMICONDUCTORS ]
