CS3341 Datasheet, PDF (5/8 Pages) Cherry Semiconductor Corporation – Alternator Voltage Regulator Darlington Driver

CS3341, CS3351, CS387
APPLICATIONS INFORMATION
The CS3341 and CS3351 IC’s are designed for use in an
alternator charging system. The circuit is also available in
flip–chip form as the CS387.
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. In the CS3351 the Stator pin senses the
voltage from the stator. This will keep the device powered
while the voltage is high, and it also senses a stopped engine
condition and 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
S
FIELD
Regulator
Lamp
I ^Indicator
Ignition
Switch
GND
BATT
Figure 3. IAR System Block Diagram
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