Thangamani is electronics reverse engineer with 38 years of service in the electronics industry. The power-on delay timer is now ready for use.Ī suitable heat-sink is recommended for triac BT139. Now, remove the LED and insert the optotriac MOC3041, triac BT139 and associated components. If LED glows after a time delay, your circuit is working well. It gives you the time it takes for the voltage to rise from zero to approximately 63.2 of the voltage you apply. If voltage pulses are available at pin 3 of IC NE555, check 4017B and its associated components. You can calculate the delay time of your RC delay element with a simple formula: That’s the RC time constant, also called tau, which is written like. If LED does not glow, check voltage at pin 3 of NE555 with multimeter. 5: Components layout of the PCB Download PCB and Component Layout PDFs: click hereįor initial testing, remove IC3 from the circuit and connect an LED across pins 1 and 2 of MOC3041. 4: PCB layout for the power-on delay timer Fig. After assembling the circuit, connect the 230V, 50Hz AC supply across CON1. Construction and testingĪ PCB layout for the power-on delay timer is shown in Fig. To improve the life of triac, the spike arrester circuit built around resistor R9, metal oxide varistor MOV1 and capacitor C7 is used. This triggers the main triac BT139 and the AC supply for the load becomes available across connector CON2. High state at Q9 makes MOC3041 to conduct. The current high output states of 4017B remain high till the power is off. This stops the counting process in 4017B. When Q9 goes high with tenth pulse, CLK EN also goes high. Each output of 4017B goes high one by one after each clock pulse. You can change the delay time (0.1 to 1-sec) of this circuit by varying VR1.ĭuring power-on, clock enable pin 13 (CLK EN) and pin 11 (Q9) of 4017B are in low states. Resistor R2, capacitor C5 and preset VR1 are timing components for NE555 IC. Optotriac has the advantage of triggering 230V AC power by itself and providing circuit isolation.ĭC power for this circuit is derived from step-down transformer X1, bridge rectifier BR1 and capacitors C3 and C4. The triac is triggered by optotriac MOC3041 (IC3). The optimum load will be 220V×9.6A=2112 watts. The maximum 16-ampere current means we can have 60 per cent as optimum current, that is, up to 9.6 amperes (or 16×0.6=9.6 amperes). The output is built around triac BT139, which can switch up to 16-ampere AC load. Output pin 11 (Q9) of 4017B goes high at 10th pulse received from NE555. As a result, 4017B gets breezed and its ten outputs (Q0 through Q9) become high sequentially. The output pulses from NE555 are fed to clock input pin 14 of 4017B. When the main power is switched on, 4017B starts counting the pulses received from NE555. VR1 preset is used to vary the timings from 0.1-sec to 1-sec pulse in NE555 IC. NE555 IC is used as a bistable oscillator. The time delay period can be accomplished by appropriately selecting the values of the 330K resistor, the 1000uF capacitor and the 3V zener diode, as per the user's preference.Timing accuracy is achieved by using decade counter 4017B. The 1000uF capacitor stays charged as long as power is available to the circuit, and during power failures the capacitor discharges through the parallel 100k resistor so that it can get into the standby mode for the next delay ON cycle operation. The triac now begins acquiring the required gate voltage and within moments switches ON the fridge. However, the 1000uF now gradually begins charging via the 330K resistor and when the potential difference across it reaches the approximate total of transistor's biasing limit plus the emitter zener value (0.6 + 3 = 3.6V), the transistor begins switching ON which prompts the BC557 also to switch ON. The load is therefore unable to receive power and stays switched OFF too. Whenever power is switched ON, may it be during the first initialization, or during a power failure situation, the associated 1000uF capacitor prevents the BC547 from switching ON at the onset, which in turn keeps the BC557 and the triac switched OFF. Which is appropriately stabilized at 12V and fed to the delay circuit. The power supply to the circuit is derived from the mains via a transformerless power supply circuit Referring to the above shown refrigerator protection circuit, we are able to witness a two transistor circuit which forms a very basic yet effective delay ON timer circuit, meaning this circuit switches ON its output after some delay, after power is applied to it.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |