CS3361_15 Datasheet, PDF (6/8 Pages) ON Semiconductor – Alternator Voltage Regulator FET Driver

CS3361
APPLICATIONS INFORMATION
The CS3361 is designed for use in an alternator charging
system.
In a standard alternator design (Figure 3), the rotor carries
the field winding. An alternator rotor usually has several N
and S poles. The magnetic field for the rotor is produced by
forcing current through a field or rotor winding. The Stator
windings are formed into a number of coils spaced around
a cylindrical core. The number of coils equals the number of
pairs of N and S poles on the rotor. The alternating current
in the Stator windings is rectified by the diodes and applied
to the regulator. By controlling the amount of field current,
the magnetic field strength is controlled and hence the
output voltage of the alternator.
Referring to Figure 7, a typical application diagram, the
oscillator frequency is set by an external capacitor
connected between OSC and ground. The sawtooth
waveform ramps between 1.0 V and 3.0 V and provides the
timing for the system. For the circuit shown the oscillator
frequency is approximately 140 Hz. The alternator voltage
is sensed at Terminal A via the resistor divider network
R1/R2 on the Sense pin of the IC. The voltage at the sense
pin determines the duty cycle for the regulator. The voltage
is adjusted by potentiometer R2. A relatively low voltage on
the sense pin causes a long duty cycle that increases the Field
current. A high voltage results in a short duty cycle.
The ignition Terminal (I) switches power to the IC
through the V_CC pin. The Stator pin monitors the voltage
from the stator and senses a stopped engine condition. It
drives the Lamp pin high after the stator timeout expires.
The Lamp pin also goes high when an overvoltage condition
is detected on the sense pin. This causes the darlington lamp
drive transistor to switch on and pull current through the
lamp. If the system voltage continues to increase, the field
and lamp output turn off as in an overvoltage or load dump
condition.
The SC or Short Circuit pin monitors the field voltage. If
the drive output and the SC voltage are simultaneously high
for a predetermined period, a short circuit condition is
assumed and the output is disabled. The regulator is forced
to a minimum short circuit duty cycle.
STATOR
Winding
FIELD
Winding
A
Regulator
S
FIELD
Lamp
I ^Indicator
IGNITION
SWITCH
GND
BATT
Figure 3. IAR System Block Diagram
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