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The circuit shown here can be used to convert a digital input signal having any desired duty cycle into a output signal having a duty cycle that can be adjusted between 10% and 80% in steps of 10%. The circuit is built around a 74HC4017 decade Johnson counter IC. Individual pulses appear on the ten outputs (Q0–Q9) of this IC at well-defined times, depending on the number of input pulses (see the timing diagram). This characteristic is utilised in the circuit. The selected output is connected via a jumper to the Reset input (MR, pin 2) of a 74HC390 counter. A High level resets the output signals of the 74HC390 counter. Q9 of the 74HC4017 is permanently connected to the CP0 input of the counter to set the Q0 output of the 74HC390 (pin 3) High on its negative edge. As can be seen from the timing diagram, which shows the signals for a duty cycle of 30% as an example, this produces a signal with exactly the desired duty cycle. The circuit cannot be used to produce a duty cycle of 10% (which...

Capacitor duty switching contactor If contactors are used for switching of capacitor ,the capacitor must be completely discharged by means of resistance or discharging chokes. When capacitor are switch ON depending on the phase angle at the instant of switch ON sever current peaks may occur. Drawbacks: Welding of contactor Erosion of contacts Protective measures: The effective capacitor-load switching capabilities of a.c. contactors & their service life can be increased by following measure. • Choke coils: The transient condition which is caused when switching in on an existing capacitive load may be damped if an air cored inductance of at least 6 micro Henry connected in parallel connecting leads between the capacitors Fig. Choke •Pre-charge resistor: Connect precharge resistance in parallel with capacitors. fig.capacitor duty contactor