Relay Driver

TM 11-5820-695-35

CR3 and through C2 to ground. As soon as C2 is

discharged Q7 turns off. C2 continues to charge with

(1) Lamp drivers Q1, Q3 and Q9 have a

negative polarity on the side connected to the base of

resistor in series with the transistor base. The resistor

Q7. When the input goes high, this reverse voltage on

serves to limit the base current of the transistor and

C2 must be discharged before it can be recharged with

reduce the loading on the logic circuit that controls the

positive polarity. Thus, turning on Q7, which occurs

transistor.

after a failure has been corrected, is slow, and turn-off,

which occurs when the failure is detected, is also

(2) Lamp drivers Q2, Q4, Q8 and Q11

delayed. This allows Q2 to maintain an on or off

have +5v connected to the base through a resistor, in

condition with interruptions in either state.

addition to the logic signal connection. This is called a

base pull-up resistor.

It is required because the

Integrator Driver. The integrator driver Q5,

inverters that supply the logic signal to the base do not

Q6 consists of the following components: R10 R15,

have the capability to supply enough base drive current

CR5, Rll, R12, C1, R13, R14. The input network (R10,

in the logic one state. When the output of A3A is low,

Rll, R12, R15, and C1) is comprised of a level converter

the +5v is dropped across R3 and Q2 is off. When the

and integrator for the driver circuit. The output of the

output of A3A is high (+5v), R3 supplies additional drive

integrator the base of Q5 which, in turn, controls

current to the base of Q2 to assure turn-on. Operation

transistor Q6. Resistor R14 provides current limiting to

of lamp drivers Q4, Q8 and Q11 is the same.

transistor Q6. There is no inversion of an input signal

and a logic one input will become +28 volts at the

(3) Inverter A3E drives A2A, A3F, and

output; a logic zero input will become zero volts. The

A4C in addition to Q10, so a base pull-up circuit is

output major alarm summary signal (OMARY) is

required at Q10 for either logic state of A3E. When the

integrated to prevent a false input from triggering this

output of A3E is low, CR6 is forward biased and current

major alarm output. When the input signal (from A3D)

flow through R24 and CR6 drops the voltage at the

is high, electron flow from -6 volts through Rll, CR5 and

junction point of CR6, CR7 and R24 to +0.7v. Current

R15 and R10 produces a positive voltage at the junction

flow through R25, CR8 and CR7 drops the voltage at the

of CR5 and Rll because most of the voltage is dropped

base to -1.4v and Q10 is off. When the output of A3E is

across Rll. C1 charges to this positive voltage and turns

high (+5v), CR6 is reverse biased. Current flow through

on Q5. Resistor R14 is a current limiter. With Q5 at

R25, CR7, CR8 and R24 drops the voltage at the base

saturation, Q6 has zero volts at the base and is off.

to approximately +2v and Q10 turns on.

When the input changes to low (ground), the positive

charging voltage is removed from C2 and it discharges.

Relay Driver.

Relay driver Q7, which

When the voltage at the cathode side of CR5 goes

generates the bypass orderwire 1BPOW signal, has the

negative (as C1 discharges), Q5 is reverse biased and

cathode of CR4 connected to its output, with the anode

turns off. The positive voltage through R13 then turns

returned to ground. Diode CR4 is a 27-volt zener diode

on Q6 and the output signal major alarm summary

which provides protection against normal transient

(OMARY) is logic zero.

voltages generated by the relay. The components

associated with the circuit are: CR2, R16, CR3, R17,

Cable Traffic Detector, Synchronoue Mode

C2, Q7, CR4 and R18. The components (R16, R17,

(650545).

CR2 and CR3) are used to convert the logic input signal

into a base turn-on, turn-off signal. Capacitor C2

(1) The cable traffic detector consists of

prevents the relay from following a transient (false)

four sections: cable traffic amplifier AS, 2304 KHz

alarm input. Resistor R18 is a current limiting resistor.

crystal with slicer bias and dc tracking network Q13A

When the input signal to Q7 is logic one (high), CR2 is

and Q13B, slicer comparator A6, and transistor

reverse biased. Electron flow from ground through C2,

integrator Q12. The cable traffic input signal XCPCM to

CR3 and R16 to +5 volts charges C2 and turns on Q7.

the traffic detector is ac coupled to the input of high gain

When the input signal changes to logic zero (low), CR2

amplifier AS. Amplifier AS drives crystal Y1 which

is forward biased. Electron flow is then from the

resonates at 2304 KHz (nominal pcm cable component);

cathode side of CR2 to the positive voltage and also

the two transistors, Q13A and Q13B, provide bias

from negative voltage and through R17 to C2, and from

(Q13B) and dc tracking with temperature (Q13A). The

ground through Q7 emitter and base to CR3. This

components used in the bias network are: R37, C13,

delays the turn-off of C2. With C2 discharged, the

Q13B, R39, C14 and R.38. The

negative voltage through R17 has two paths, through

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