Sierra Video 10 Series - Manual (Page 18)

SIERRA VIDEO
12
501022 Pulse DA
The 501022 is a plug-in module specifically designed to drive 10 loads with 4V p-p
composite sync and similar drive pulses.
Circuit Description
The 501022 is a plug-in module. Refer to the 501022 schematic diagrams in the
schematic section of this manual.
The 501022 is powered by low voltage AC which comes into the module through the
edge connector. When dual power supplies are ordered, the two supplies enter the
501022 separately and are paralleled after the AC to DC rectification. This provides total
in frame isolation between the two supplies. The rectified DC is filtered by C8 and C9. U2
provides regulated +8VDC. U3 is an LM337, adjustable negative voltage regulator. The
adjustment input of U3 is connected to a well filtered sample of the raw input voltage. In
this way U3 provides filtering and current limit protection, but does not regulate to a
specific voltage. This results in a negative supply voltage that slowly follows changes in
the raw low voltage AC input. The result is about -19 to -14 volts at the output of U3. On
the front edge of the 501022 separate LEDs indicate the presence of the + and – VDC
levels.
Input video enters the 501022 on the edge connector pin 2. The incoming signal’s shield
enters the 501022 on pin 1 and is then connected directly to the circuit ground.
Q3 and Q4 clip signal levels over 6 volts peak to peak. This occurs only if the input
connection is accidentally unterminated. The basic element of the 501022 is a 120MHz
amplifier, U1, followed by a current boosting stage.
Q1 and Q2 are inside the gain determining feedback loop of U1. D1 and D2 provide class
AB operating bias for Q1 and Q2. Q1 and Q2 are 200MHz 500ma devices. They provide
a very low output impedance (about 0.1 ohm). R1 through R10 are each precision 75
ohm resistors. Each drives a separate output line.
The gain of the 501022 is set by U1’s feedback network. R19 is a 15 turn potentiometer
gain adjustment located on the front of the 501022.