Voltage Divider

TM 55-4920-430-13

b. Voltage Divider. The voltage dividers consists of ac voltage dividers R11 thru R41 and dc

voltage dividers R56 and R57.

c. DASH Drive Frequency Divider. The frequency divider consists of two voltage comparators, a

frequency divider, and a lamp drive circuit.

(1) The DASH drive signal cart be a steady 28-volt dc signal or a 7 pps 28-volt signal. This signal

is applied to the extend input at J1-1 or the retract input at J1-5.

(2) Comparator U2 senses the 28-volt dc extend input signal. Resistors R46 and R47 form a

voltage divider with a ratio of 50:1. With a 28-volt dc extend signal on J1-1 the voltage on pin 3 of

comparator U2 is +5.6-volt dc. The voltage on pin 2 of U2 is 1-volt dc; established by resistors R48 and

R49. With voltage on pin 3 greater than voltage on pin 2, output at pin 7 of U2 is close to positive

power supply voltage. When the input signal at J1-1 is ground or an open circuit, voltage at pin 3 of U2

is less than voltage at pin 2. The output at pin 7 is about 15 volt dc.

(3) Diode CR3 passes only the positive-half comparator output to transistor Q2 and Q3.

(4) Resistors R50, R51, diode CR4, and comparator U3 perform a similar function for the retract

signal at J1-5. Comparator U2 or U3 ouput is applied to the bases of Q2 and Q3.

(5) Transistor Q2 performs a voltage transformation to transistor transistor logic (TTL) logic

levels. The clock input at pin 2 of U4 is connected to a +5-volt dc thru pull-up resistor R53. When a

positive voltage is applied to the base of Q2, transistor Q2 conducts and connects pin 2 of U4 to ground

thru the collector emitter junction of Q2. The QC output of U4 performs a

8 function on the clock

input. For a clock input of 7 Hz (7 pps) the frequency at QC is 0.875 Hz.

(6) Inverter gate U6 is a buffer. If provides sufficient base current to the lamp drive transistor Q1,

which is a ground side switch for DASH DRIVE indicator DS16.

(7) The network formed by transistor Q3 thru Q5, capacitor C11, resistors R52 and U5 turn out

the DASH DRIVE lamp, when there is no DASH extend or retract signal. This is necessary since the

QC output from U4 could be left in either state. Its state would depend on its initial state and the

number of pulses applied to the clock input. The drive signal to the DASH drive lamp is turned off

when Darlington pair Q4 and Q5 conduct and ground the base of lamp drive transistor Q1. To ade-

quately form and bias transistors Q4 and Q5, the voltage at capacitor Cl1 must be 1.4 volt dc or

greater.

1-28