Operation Of Regulator (Lamar); Regulator Diagram (Lamar) - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
ENCAPSULATED
CONTROL ASSY.
R 12
GND
Figure 11-18. Regulator Diagram (Lamar)
direction, will also pass current in the reverse direction when a particular value of reverse voltage is applied.
This property makes it useful as a voltage reference device in the regulator.
d.
Capacitor: The capacitor (Symbol "C") is a device which will store electrical energy for short
periods of time. This property makes it useful as a filter element to smooth variations of voltage.
e.
Resistor: The resistor (Symbol "R") is a device which is used to limit current flow.
11-20. OPERATION OF REGULATOR (Lamar). (Refer to Figure 11-18.)
a.
When the alternator is turned on, battery voltage is applied to the "BUS" terminal of the
regulator and via Q4 through the "FIELD" terminal of the regulator to the alternator field terminal F2.
The amount of voltage applied to the field of the alternator is controlled automatically by action of the
regulator in response to alternator output as described below.
b.
Current flow through R6 and Z1 establishes a reference voltage across Z1.
c.
Resistors R1 and R2/R3 comprise a voltage divider which is adjustable by means of the variable
portion R3. Voltage at the junction of R1 and R2 and the reference voltage across Z1 are applied to
comparison transistor Q1. R3 is adjusted so that these voltages are balanced with the desired alternator
output voltage present on the "BUS" terminal of the regulator.
d.
Thereafter, whenever alternator output voltage (as applied to the "BUS" terminal) falls below the
desired regulation value, the comparison transistor Q1 will supply increased current to driver transistors
Q2/Q3, which in turn will drive power transistor Q4 to a higher value of field current. This will result in
alternator output voltage increasing to a value which will restore balance between the two voltages applied
to Q1.
e.
Conversely, if alternator output voltage (as applied to the "BUS" terminal) increases due to a
greater engine speed or reduced loading of the electrical system, the comparison transistor Q1 will act to
reduce current flow to the driver transistors Q2/Q3, and thus reduce the driver to power transistor Q4. This
will result in a reduction of alternator field current and automatically restore balance between the two
voltages applied to comparison transistor Q1.
f.
Capacitors Cl and C2 function, together with their related transistors, in a way to smooth
alternator output ripple and voltage spikes so that the alternator field current is controlled at a steady
value.
Reissued: 9/23/80
ELECTRICAL SYSTEM
3D4