Service manual

PT300, Service Manual
Rev B, October, 2000
11
Low Voltage Sensor:
R9, D7, and Q2 work much the same as R6, D6 and Q5 in the power switch
section. The addition of D8 causes Q2 to switch 0.3 volts before Q5. In
practical terms, Q2 will be biased on until the switched voltage drops to 7.2 volts.
Below this voltage the low voltage sense line goes high. R10 provides a path for
any leakage current through D7 and D8.
Regulator:
Q3 a standard 3 terminal regulator in a TO-92 package. U19 is a voltage
inverter chip that uses a charge pump to convert 5.0 volts to -5.0 volts. C1, C2,
and C3 are used to stabilize Q3, C5 and C6 are necessary to the operation of
U19.