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Power LEDs have changed the world of illumination. The number of experimentation on the ouput of power LEDs is the highest in the electronic hobby world. Before going through the intricacies of the luminance of power LEDs we must first know the characteristics of LEDs. A white LED is generally biased at a voltage range of 2.5 to 3.5V DC. Depending on the wattage of LED, the input current is determined. White LEDs are used for illumination purposes and are available right from 0.1Watt to 3Watts in general, with the same voltage characteristic but different current rating. Though very simplistic, it is interesting to use the following serially connected white LEDs in a chain. Here in this circuit 25 LEDs in a series have been considered a safe zone operation. We decide the bias voltage to be 3V DC in each of this rung. The total potential required to bias the LEDs is 25x3= 75V DC. A bridge rectifier is employed to rectify 120V AC line without any filter circuit being employe...

Because of energy crisis Load shedding may be a common problem in several countries.. Sudden power fluctuations, surge and high voltage may spoil sophisticated household appliances like TV, VCR, VCP and music system. This circuit provides protection against these problems and automatically changes the power supply from Generator output to mains supply and also switches off the generator. Circuit descriptions This circuit is self explanatory. When lines supply voltage crosses the preset level, Zener diode ZD4 break down and thus transistor T2 conducts, T3 does not conduct, causing the relay to de-energise. Voltage surge at the time of power resumption is protected by the delay circuit around transistor T1. All the portable petrol and kerosene generators have a connection from CDI. To stop the engine of the generator-set, this connection is to be grounded momentarily (through the switch). This lead is to be connected with the ground through the N/C point of the relay. Auto Changeover ...

This Digital Mains Voltage Indicator Circuit diagram project designed by  Pratap Chandra Sahu . Continuous monitoring of the mains voltage is required in many ap-plications such as manual volt-age stabilisers and motor pumps. An ana-logue voltmeter, though cheap, has many disadvantages as it has moving parts and is sensitive to vibrations. The solidstate voltmeter circuit described here indicates the mains voltage with a resolution that is comparable to that of a general-pur-pose analogue voltmeter. The status of the mains voltage is available in the form of an LED bar graph. Presets VR1 through VR16 are used to set the DC voltages corresponding to the 16 voltage levels over the 50-250V range as marked on LED1 through LED16, respectively, in the figure. The LED bar graph is multiplexed from the bottom to the top with the help of ICs CD4067B (16-channel multiplexer) and CD4029B (counter). The counter clocked by NE555 timer-based astable multivibrator generates 4-bit binary ad-dress...

Are you having problems with your input Mains supply? That’s common problem associated with our input mains AC line, where a high and a low voltage conditions are quite frequently encountered by us. The simple circuit shown here can be built and installed in you house electrical board for getting a 24/7 safety from the possible dangerous AC voltage conditions. The circuit keeps the relay and the wired appliances as long as the mains input stays within a safe tolerable level and switches the load OFF the moment a dangerous or unfavorable voltage condition is sensed by the circuit. Parts List R1, R2 = 1K, P1, P2 = 10K Preset, T1, T2 = BC547B, C1 = 100uF/25V, D1 = 1N4007 RL1 = 12V, SPDT, TR1 = 0-12V, 500mA

Although you may well be the proud owner of the very latest NiCd battery charger, you may still come across the odd 'incompatible' battery, for example, one having a rare voltage or requiring a much higher charging current than can be supplied by your off-the-shelf charger. In these cases, many of you will resort to an adjustable mains adaptor (say, a 500-mA type) because that is probably the cheapest way of providing the direct voltage required to charge the battery. Not fast and not very efficient, this 'rustic' charging system works, although subject to the following restrictions: Circuit diagram: Battery-Charging Indicator Circuit Diagram You should have some idea of the charging current. In case you use an adaptor which is adjustable but of the unregulated, low output current type, you can adjust the current by adjusting the output voltage. You have to know if the current actually flows through the battery. A current-detecting indicator is therefore much to be pref...

It will be easier to understand the operation of the circuit if we separate the under and over-voltage protection circuitry comprising transistors T1, T2 and associated components from the rest of the regulator circuit. Diode Dl arid. capacitor C2 provide 24V DC supply required to operate the relays.  Diode D2 and capacitor Cl provide the sample DC voltage for generating reference voltages for the cutout. For initial setting of cutout, collector of Tl is not connected to the base of T2. Also the time delay capacitor C4 is only connected after both under- and over- voltage points have been preset independently. Initially, due to the potential divider action of resistors R4, R6 and preset VR2, a voltage would appear at the base of T2. · lf this voltage is 0.6 ·V or more above the zener diode voltage of D4, transistor T2 would conduct, energising the relay and connecting the hot tap of the auto-transformer to the universal socket’s hot terminal through N/O contacts of the relay RLl....

While repairing or installing electrical machines in a building, the AC mains power supply is switched off from the mains electrical switchboard installed outside the building. There is a chance that someone who is not aware of the same may switch on the mains from outside. This poses a great danger for the technician working inside. Hence, an indicator like the one described here, which can be plugged into a nearby mains wall socket, might prove very useful for the technician. This circuit can also be useful for people who are living in a place where there is frequent mains power cut. Circuit and working The circuit diagram of the light and sound indicator for the mains power supply is shown Fig. 1. The circuit is built around capacitors C1 and C2, resistors R1 and R2, diode D1, zener diode ZD1, LED1 and a piezo buzzer (PZ1). Resistor R1 and capacitor C1 are used for reducing the voltage and limiting the current. Diode D1 is a rectifier. C2 is used as a filtering capacitor. Zener diod...