Sinclair Microvision MTV1 Service Manual page 23

The EHT regulator comprises a constant current reference, a monostable triggered by the line
oscillator, and a push-pull type output driver for the converter transistor. The converter driver's
output is inhibited during the switch-on transient until the supply voltage Vcc has built up to greater
than 3.1V. This allows the line oscillator to start before the converter transistor switches on.
During flyback, T35 and T36 turn on, which makes TR1 and TR2 turn off. At this time a flyback
voltage on the EHT transformer produces a ±300V pulse. These pulses charge the 10pF capacitors
to their peak voltages. At the end of the flyback time the transistors TR35 and TR36 turn off and the
transistors TR1 and TR2 produce a voltage ramp at their collectors (and hence on the deflection
plates) due to their Miller capacitance of 10pF and the resultant constant current through the 12k
resistor and line amplitude pot. The maximum amplitude of scan voltage si when the transistors
TR1 and TR2 saturate.
This type of circuit has low output impedance due to the Miller capacitance, low power
consumption, and a single line amplitude control.
A careful choice of temperature coefficient of the 10pF capacitor makes the line scan amplitude
almost independent of temperature.
Page 23 of 39
Sinclair MTV1 service manual V2.1