‰ NOW 30 WPM ‰ TEXT IS FROM SEPTEMBER 2018 QST PAGE 56 ‰ LOOP INCLUDES THE 3R3 K RESISTOR, Q2, Q1, AND THE MOSFET. THE POSITIVE LOOP FORCES THE MOSFET SWITCH TO BE EITHER FULL ON OR FULL OFF. TO UNDERSTAND THE CIRCUIT OPERATION, START WITH THE CAPACITOR VOLTAGE LESS THAN IS REQUIRED. Q1 SENSES THIS AND SATURATES, CLOSING THE MOSFET THE SWITCH WAVEFORM POINT A BY MAKING THE MOSFET GATE TO SOURCE VOLTAGE 7 V. WHEN A HALF SINE WAVE PULSE ARRIVES FROM THE RECTIFIER, THE CAPACITOR IS CHARGED THROUGH THE ALREADY CLOSED MOSFET SWITCH WAVEFORM POINT B. WHEN THE CAPACITOR CHARGE REACHES THE DESIRED VOLTAGE, Q1 DETECTS THIS AND OPENS THE MOSFET SWITCH BY ALLOWING THE MOSFETS GATE TO SOURCE VOLTAGE TO REACH 0. AS THE MOSFET SWITCH OPENS, LOAD ON THE TRANSFORMER IS REMOVED AND THE VOLTAGE INCREASES AT THE CONNECTION OF THE RECTIFIER OUTPUT, THE MOSFET SOURCE, AND THE 3R3 K RESISTOR THE END OF B. THIS VOLTAGE APPEARS ACROSS THE 3R3 K RESISTOR AND CAUSES CURRENT TO FLOW INTO THE EMITTER OF Q2. THAT CURRENT FLOWS OUT OF THE COLLECTOR OF Q2 AND RAISES THE EMITTER VOLTAGE OF Q1, CUTTING Q1 OFF. THIS ENSURES THAT THE MOSFET SWITCH REMAINS IN THE OPEN CONDITION UNTIL THE RECTIFIER VOLTAGE FALLS BACK BELOW THE OUTPUT ‰ END OF 30 WPM TEXT ‰ QST DE W1AW ƒ