Figure 3, 555 Timer Oscillator With Symmetry Flip Flop and Duty Cycle Control. In this diagram the battery is shown with its negative end grounded and its positive end going to one end of a switch. It is labeled on / off, S1. The other end of the switch goes to one end of a fuse which is labeled 3 A T/p. The other end of the fuse connects to the center tap of the primary of the transformer. The junction of the fuse and center tap is labeled plus twelve volts. This point goes to one end of a 100 ohm resistor. The other end is labeled V cc. This point goes to ground through the parallel combination of, C3 0.01 u f capacitor, and C4, 220 u f capacitor. V cc is also connected to the cathode of D1, a zener diode, 1N4747A. The anode of the zener is grounded. A 5 55 timer has pin 1 grounded. Pins 4 and 8 are tied together and connect to V cc. A 10 k ohm resistor goes from V cc to pin 7 of the timer. Pin 7 goes through a 100 k ohm resistor to pins 2 and 6 which are tied together. A 0.01 u f capacitor goes from pins 2 and 6 to ground. Another 0.01 uf capacitor connects from pin 5 of the timer to ground. Pin 3, output of the timer connects to pin 11 of U 2, CD4013, flip flop. Pin 14 connects to V cc and pins 7, 8, and 10, are all grounded. Pin 12 connects to pin 9. Pin 13 goes through a 10 k ohm resistor to the gate of Q1, IRF530. Pin 12 goes through another 10 k ohm resistor to the gate of Q2 another IRF530. The sources of both f e ts are grounded. The drain of Q1 goes to the top of the primary of the transformer. The drain of Q2 goes to the bottom of the transformer primary. Pin 13 of the flip flop goes to pin 2 input of nand gate A. Pin 12 of the flip flop goes to pin 1 of nand gate A. Pin 13 of the flip flop also goes to pin 6, input of nand gate C. Pin 12 of the flip flop goes to pin 5, input of nand gate C. The output of nand gate A coes to both inputs, pins 12 and 13 of nand gate B. It is being used as an inverter. Pin 11, output of nand gate B goes through a 4.7 k ohm resistor to the base of Q3. The output of nand gate C, pin 4, connects to both inputs of nand gate D, pins 8 and 9. The output of nand gate D, pin 10 goes through another 4.7 k ohm resistor to the base of Q4. The collector of Q3 connects to the gate of Q1. The collector of Q4 connects to the gate of Q2. If there is a circuit fault, Q3 and Q4 will shut down Q1 and Q2 preventing damage to them or the transformer. The high voltage secondary winding is not center tapped. Each side of the winding goes to the AC inputs, anode and cathode, of a bridge rectifier. The negative output of the bridge, two anodes, is grounded. The positive output, two cathodes, goes to the junction of a capacitor and resistor. The capacitor is C6, 10 u f with an appropriate voltage rating. The other end of the capacitor is grounded. The other end of the resistor goes to B plus point. The resistor is R8, 51 ohm 2 watt. The B plus point also goes to ground through another capacitor, C5, 150 u f. There is a resistor, R9, 100 k ohm, from the B plus point to ground. The B minus point is grounded. This completes the description of figure 3.
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