Mains Powered White LEDs using Resistor only

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 employed. The peak of the rectifier voltage would be 120x 1.414= 169.68 V DC.

To play with the value of R in the first circuit is very simple as R has to create a potential drop of 95V DC with a justified calculation of the current going through it of wattage is very simple to decide.

Now let us consider the second circuit with half watt rectification with single diode only. This circuit is cheaper and at the same time the heat dissipated in the current limiting resistance is much less. This happens as the circuit employs a half wave rectifier and using an anti parallel diode across a LED chain.

The reminiscent energy is flown back, considering the LED series current to be 20mA. Resistance of value 1200 K is adequate to control the current through the LED chain.

This circuit obviously pushes a larger peak current to the LEDs but this will not be harmful to the circuit operation because it lasts only half the cycle.

In this particular case each LED is biased in such a way that it delivers 0.06 watt of power, in total the entire chain is a 1.5 watt power source which probably is sufficient for reading purpose and worth its cost and life.

As the circuit is designed around live mains, user must be cautious of electrical seepage or short circuits and for this an insulated cover properly designed is a strong recommendation.

Comments

Digital Fan Regulator Circuit Diagram

This is the project of Digital Fan Regulator Circuit diagram. The circuit presented here can be used to control the speed of fans using induction motor. The speed control is nonlinear, i.e. in steps. The current step number is displayed on a 7-segment display. Speed can be varied over a wide range because the circuit can alter the voltage applied to the fan motor from 130V to 230V RMS in a maximum of seven steps. The triac used in the final stage is fired at different angles to get different voltage outputs by applying short-dura-tion current pulses at its gate. For this pur-pose a UJT relax-ation oscillator is used that outputs sawtooth waveform. This waveform is coupled to the gate of the triac through an optocoupler (MOC3011) that has a triac driver output stage. Pedestal voltage control is used for varying the firing angle of the triac. The power supply for the relaxation oscillator is derived from the rectified mains via 10-kilo-ohm, 10W series dropping/limit-ing...

Using the SG3525 PWM Controller Explanation and Example Circuit Diagram Schematic of Push Pull Converter

PWM is used in all sorts of power control and converter circuits. Some common examples include motor control, DC-DC converters, DC-AC inverters and lamp dimmers. There are numerous PWM controllers available that make the use and application of PWM quite easy. One of the most popular of such controllers is the versatile and ubiquitous SG3525 produced by multiple manufacturers – ST Microelectronics, Fairchild Semiconductors, On Semiconductors, to name a few. SG3525 is used extensively in DC-DC converters, DC-AC inverters, home UPS systems, solar inverters, power supplies, battery chargers and numerous other applications. With proper understanding, you can soon start using SG3525 yourself in such applications or any other application really that demands PWM control. Before going on to the description and application, let’s first take a look at the block diagram and the pin layout. Pins 1 (Inverting Input) and 2 (Non Inverting Input) are the inputs to the on-board error amplifier. If you a...

Automatic Intruder Alarm Circuit Diagram

Description: This is a simple single-zone burglar alarm circuit. Its features include automatic Exit and Entry delays and a timed Bell/Siren Cut-Off. It's designed to be used with the usual types of normally-closed input devices such as - magnetic reed contacts - micro switches - foil tape - and PIRs. But it can be Easily Modified to accept normally-open triggering devices - such as pressure mats. Circuit Diagram Notes: It's easy to use. First check that the building is secure and that the green LED is lit. Then move SW1 to the "set" position. The red LED will light. You now have about 30 seconds to leave the building. When you return and open the door - the Buzzer will sound. You then have about 30 seconds to move SW1 to the "off" position. If you fail to do so - the relay will energize and the Siren will sound. While at least one of the switches in the normally-closed loop remains open - the Siren will continue to sound. However, about 15-minutes aft...

ffd

Search This Blog