‰  NOW 25 WPM  ‰  TEXT IS FROM SEPTEMBER 2018  QST  PAGE 56 ‰

CAPACITOR VOLTAGE END OF WAVEFORM POINT C AND BEGINNING OF A.  AT THIS
POINT, THE VOLTAGE ACROSS THE 3R3 K RESISTOR HAS FALLEN TO 0 V.  THERE IS
NO LONGER ANY CURRENT TO THE EMITTER OF Q2 TO HOLD Q1 OFF.  Q1 THEN DETECTS
THAT THE VOLTAGE ON THE OUTPUT CAPACITOR IS LOWER THAN REQUIRED AGAIN.  Q1
CLOSES THE MOSFET SWITCH TO WAIT FOR THE NEXT HALF SINE WAVE PULSE
BEGINNING THE CYCLE OF OPERATION AGAIN.  IN THIS CIRCUIT, THE MOSFET SWITCH
IS TURNED ON BEFORE ANY POWER IS CONDUCTED.  THIS IS TRUE ZERO POWER
SWITCHING.  WHEN THE MOSFET TURNS OFF, THE TRANSFORMER INDUCTANCE TRIES TO
CONTINUE THE FLOW OF CURRENT, CAUSING SOME SMALL POWER LOSS IN THE MOSFET
AS IT IS TURNING OFF.  THE TEMPERATURE OF THE MOSFET CASE SHOULD BE LESS
THAN 20 C ABOVE AMBIENT ABOUT 0R75 W WITH 1 X 1 INCH AREA OF CIRCUIT BOARD
FOR A HEATSINK SEE FIGURE 2 AND A REGULATED OUTPUT OF 1 1R2 A AT 12 V.  IF
A DIRECT SHORT IS APPLIED, THE REGULATOR WILL SHUT COMPLETELY OFF.  WHEN
‰  END OF 25 WPM TEXT  ‰  QST DE W1AW  ƒ