Frequency Counter-Display-CONT.

TM 11-6625-922-15

current-sensing resistor. If the voltage drop across R6.

-12-volt circuit is similar to that of the + 12-volt circuit.

exceeds a level as determined by R15 and R16, Q2 will

o. +5-volt Regulator A5 (fig. 9-32). The operation

turn off and Q4 will turn on. Transistor Q8 will also turn

of the + 5-volt circuit is similar to that of the + 12-volt

on, thereby taking all the current from Q7 which had

regulator circuit. The 1-ohm, 2.5-watt resistor is the

been supplying the base current for pass transistor Q13.

current-sensing component. Zener diodes CR3 and

With no more base current, the pass transistors cannot

CR4 derive +18 volts at pin C from the higher voltage

supply any more output current. The operation of the

input at pin A.

5-15