AN6

Application Note 6
Issue 2 November 1995
The Use of Zetex E-Line Transistors
in Motor and Solenoid Functions within Printers
Effective Logic to High Current Load Interfacing
Neil Chadderton
Introduction
The majority of modern printers use
stepper motors and solenoids for driving
the various transport and print
mechanisms. These applications usually
involve using drive signals directly from
the control logic; and handling
high-pulsed currents and voltages. In the
past this has led to TO220 and similar
devices being used, but an alternative is
now available. Devices from the Super
E-Line range of transistors are direct
replacements for the aforementioned
devices in medium power situations.
This Application Note outlines a few
examples that are applicable and is by
no means comprehensive.
Motor Drivers
Stepper motors are used for many
printer functions, such as platten roller
and print head position drivers, and
daisy wheel drivers.
A typical circuit used in many printers is
shown conceptually in Figure 1. The
driver transistors Q1-Q4 are switched in
an ordered sequence to energise the
motor’s coils to produce the desired
action. As the transistor load is
ind uc tive, the v oltage present on
switching off easily exceeds the supply
voltage, while the current flowing in the
on-state follows a ramp-like appearance.
V logic
Control
Logic
Q1
Q
Q2
Q4
Figure 1
Typical Stepper Motor Drive Circuit
(diagramatic).
These conditions are illustrated in Figure
2, which shows the voltage and current
experienced by the transistor in a typical
cycle. (In this case, a centre drain
MOSFET, the ZVN4206C has been
employed).
AN 6 - 1
Application Note 6
Issue 2 November 1995
The negative current pulses due to the
driving configuration, and the high
current involved (greater than 3A), make
th is a n id eal situation fo r a high
performance E-Line Darlington
transistor. Used with an inexpensive
externally-wired diode, this offers up to
a four-times cost-saving on the
expensive TO220 alternative.
Figure 2
Typical Waveforms on a 4-Phase Stepper
Motor Driver Transistor (ZVN4206C).
Upper Trace: Collector Current - 0.5A/div.
Lower Trace: Collector Voltage - 20V/div.
(26V supply)
For circuit simplicity and ease of driving,
Darlington devices are a favourite in this
application, but a consequence of
driving inductive loads such as these is
the need to protect the device from
negative current pulses. In many of the
e x p e n s i v e l y p a c k a g e d D a r li n g to n
transistors, this is effected by an integral
collector-emitter diode.
A n al ter n a tiv e is t o u s e M O S F ET
transistors, which exhibit all the
electrical requirements in a smaller
package and at much reduced cost, and
possess the necessary protection diode
due to the inherent nature of MOSFET
technology.
Even in very demanding driving
applications for Iarger printer motors
such as illustrated in Figure 3, E-Line
transistors can be used to obtain a large
cost advantage.
Figure 3
Waveforms on Stepper Motor Driver
Transistor for a Large Printer (FXT605).
Upper Trace: Collector Current - 1A/div.
Lower Trace: 20V/div.
Dot Matrix Head Drivers
For the dot matrix form of printer,
solenoids are usually used to force a pin
to strike the ribbon and thereby produce a
dot on the paper. A column of these pins
is driven as required to match the matrix
representation of printable characters.
As in the motor driver example, the
solenoid also presents an inductive load
and Figure 4 typifies the circuit used to
drive it. A control pulse from the logic
turns the transistor on to energise the
solenoid coil.
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Application Note 6
Issue 2 November 1995
V supply
V logic
Print
Head
Solenoid
Control
Logic
FXT605
Figure 4
Typical Circuit of a Dot Matrix Head Driver.
The waveforms shown in Figure 5 were
obtained for a dot matrix head driver.
The back-emf and the high current peaks
demand a device of superior performance
easily met by the Zetex range of E-Line
devices.
Centre Collector E-line Transistors
Zetex Semiconductors offer a
comprehensive range of centre collector
E-Line transistors that can directly
replace TO220 and similar devices in
many applications. These devices match
all the electrical requirements, and also
show a large saving in size and cost.
Figure 5
Waveforms on a Dot Matrix Head Driver
Transistor (FXT605).
Upper trace: 1A/div. Lower trace: 50V/div.
Summary
Zetex transistors can be used with
confidence in many motor and solenoid
driver applications of which the above
are examples.The state of the art
transistor technology coupled with the
excellent thermal characteristics of the
E-Line package, and the convenience of
the centre collector option, produce an
attractive solution to an otherwise costly
situation.
Appendix A
FXT605 Centre Collector NPN Power Darlington Transistor
SYMBOL
MIN.
IC
ICM
V(BR)CEO
MAX.
UNIT
CONDITIONS.
1
4
A
A
Continuous
Pulsed
V
IC=10mA, IB=0
1.0
1.5
V
V
IC=0.25A, IB=0.25mA
IC=1A, IB=1mA
120
VCE(sat)
hFE
2000
500
fT
150
IC=50mA, V CE=5V
IC=2A, V CE=5V
MHz
AN 6 - 3
IC=100mA, V CE=10V f=20MHz
Application Note 6
Issue 2 November 1995
Appendix B
ZVN4206C N-Channel Enhancement Mode Vertical DMOS FET
ABSOLUTE MAXIMUM RATINGS
PARAMETER
SYMBOL
VALUE
UNIT
Drain-Source Voltage
V DS
60
V
Continuous Drain Current at Tamb =25°C
ID
600
mA
Pulsed Drain Current
IDM
8
A
Gate-Source Voltage
VGS
± 20
V
Power Dissipation at T amb =25°C
Ptot
Operating and Storage Temperature Range
Tj:Tstg
0.7
W
-55 to +150
°C
ELECTRICAL CHARACTERISTICS (at Tamb = 25°C unless otherwise
stated).
PARAMETER
SYMBOL MIN.
Drain-Source Breakdown
Voltage
BV DSS
60
1.3
MAX. UNIT CONDITIONS.
V
ID=1mA, V GS=0V
Gate-Source Threshold Voltage
VGS(th)
3
V
ID =1mA, V DS= V GS
Gate-Body Leakage
IGSS
100
nA
Zero Gate Voltage Drain Current
IDSS
10
100
µA
µA
V GS=± 20V, V DS=0V
V DS=60V, VGS=0V
V DS=48V, VGS=0V, T=125°C(2)
On-State Drain Current(1)
ID(on)
Static Drain-Source On-State
Resistance (1)
RDS(on)
Forward Transconductance(1)(2)
gfs
3
A
1
1.5
300
Ω
Ω
V DS=25V, VGS=10V
V GS=10V,ID=1.5A
V GS=5V,ID=500mA
mS
V DS=25V,ID=1.5A
Input Capacitance (2)
Ciss
100
pF
Common Source Output
Capacitance (2)
Coss
60
pF
Reverse Transfer Capacitance (2) Crss
20
pF
V DS=25V, VGS=0V, f=1MHz
Both Appendix A and B are extracts from the Discrete Through Hole Components Data
Book which detail full characterisation of the products quoted.
AN 6 - 4
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