Tektronix 1705A High VoltagePower Supply Diagram 8

Theory of Operation
1705A Spectrum Monitor 4-17
High VoltagePower Supply
Diagram 8
The High VoltagePower Supply generates the heater, cathode, control grid, focus
anode, and post accelerating potentials required to display the ou tputs of the
Verticaland Horizontal Output Amplifiers.
The High VoltagePower Supply is generated by a sine-wave oscillator and
step-up transformer. Q6 and T1 are the principal elements of an Armstrong
oscillator runningat about 22 kHz. Error AmplifierU2 regulates the +100 V
output and keeps theHigh Voltage Power Supply constant under varying load
conditions by controlling the base currentto Q6. The +100 V output is regulated
directly,while the High Voltage Power Supply is indirectly regulatedthrough a
current feedback circuit.
R48, C16, R60, and R64 form the High VoltagePower Supply current feedback
circuit. Asthe current from the High VoltagePower Supply is increased, the
voltage to the + side of the Error Amplifier(U2) increases, which increases the
base drive to Q6, the HV Osc. Thiscurrent feedback compromises the regula-
tion of the +100 V supply to keepthe high voltage constant with varying
intensities.
C66 and Q10 are astart delay circuit that holds the Error Amplifier output low,
through CR30, until C66 is charged. Delaying the startof the high voltage
oscillator allowsthe Low Voltage Power Supply to start, unencumbered by the
load from the high voltage oscillator.
HV Osc and Error Amp