Learning Event 2:
DESCRIBE FUNCTION OF DC POWER CIRCUITRY
1. General. All DC power required by the camera head is supplied from the power
supply frame. The output of the DC power supply is connected to the camera cable
and inputted to the camera head.
2. The DC converter module works in combination with the DC converter control
module, at the camera head, to act as a DC transformer. The transformer changes a
high DC voltage, low current supply, to low DC voltage, high current supply. The
low voltage obtained is used by the camera head modules.
3. The common voltages needed to operate a studio camera are high voltage, G2
voltage, focus current, heater supply voltage, and various regulated and
unregulated voltages.
a. High Voltage (fig 25 foldout located at end of Lesson 3). High voltage
AC from transformer T101 in the power supply is full wave rectified by a diode
network and filtered capacitively. A shunt regulator provides additional filtering
and regulation.
(1) The next circuitry involved is a resistive network. This resistive
network divides the high voltage down to a nominal working voltage. This working
voltage is compared to a reference voltage.
(2) Reference voltage is compared to the divider voltage and the
amplified error signal is applied to the shunt regulator so that it draws more
current if the compared voltage increases, and less current if the voltage
decreases.
(3) The result is that a constant DC voltage output is maintained.
(4) The voltage supply for the control amplifier is obtained from the
unregulated 150 volt positive supply through R15. Zener diodes CR20 and CR21
provide regulated voltage sources.
b. G2 voltage (positive 285 volts). Diodes CR13 through CR16 and capacitor
C1 fullwave rectify and filter the AC from power transformer T101. The filtered DC
is fed through an overload protection circuit to a series regulator.
(1) The base voltage of the driver transistor Q4 is obtained from a
resistive voltage divider and connected across the +930 volt supply, which
establishes the +285 volt output.
(2) The +285 volt output feeds through the power supply cable to the
camera cable and is passed to the deflection module, located in the camera head
(fig 12 foldout located at the end of Lesson 3).
c. Focus Current. (129 ma). This is a stable current and compensates for
input voltage and load resistance changes.
(1) This circuit is basically a comparatortype circuit. The amplified
error signal is sent to the series regulator which maintains a constant current of
129 ma.
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