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DN6-1DN5-1
Design Note 5
Issue 2 June 1995
Remote Control Servo Amplifier using Protection
Free 1A DC Rated SOT23 Devices
FMMT489
FMMT589
FEEDBACK
+4.8V
+2.4V
Control Logic
Signal Input
0V
0.75 to 2ms
The Zetex high performance SOT23
package, permitting power dissipation
to 500mW (now up to 625mW with the
FMMT618 and FMMT718 “SuperSOT”
series), and the high efficiency of the
’MATRIX’ geometry design, produces a
performance previously only available
in TO92, SOT89 or larger package styles.
This advantage can be demonstrated by
the servo amplifier driver shown above.
This circuit uses the high gain 30V BV
CEO
rated FMMT489 and FMMT589, that
possess typical gains of 200 at 1A and
0.5A respectively, low V
CE(sat)
(0.3V and
0.35V at 1A), and capable of handling
peak currents of up to 2A, and 1A
continuous. These features allow
surface mount designs to be realised at
low cost, to exhibit better switching
performance, and using a minimum of
board area. Higher voltage variants are
available as the FMMT491 and
FMMT591, which are rated at 60V.
Design Note 6
Issue 2 June 1995
6V Battery Operated Fluorescent
Lamp
ZTX651
NICAD
5 x 1.2V
+6V
To handle tube striking and normal
operating characteristics, the converter
transistor used in this simple fluorescent
lamp ballast requires a high current
capability and a high breakdown
voltage. The ZTX651, possessing a B
VCBO
rating of 80V, and a current rating of 2A
continuous and 6A peak, performs more
efficiently than the expensive TO220
transistor normally used. Due to the
lower on-state losses of the Zetex
transistor, the circuit is capable of 75%
efficiency, with a resulting 12% increase
in battery life. With a saturation voltage
of only 0.2V at 2A, power dissipation in
the E-Line (TO92 style) transistor is kept
well within its 1W rating. The small size
of the ZTX651 and the converter’s 25kHz
oscillation frequency allows the circuit
to be constructed in a compact form,
small enough to fit in a torch handle, etc.
Higher gain variants (Super-β devices
such as the ZTX688B and ZTX788B
series) are now available to help reduce
base drive requirements and thereby
improve efficiency still further.
