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Saturday, April 6, 2013

120 VAC Dimmer Lamp Circuit

It is a simple design full wave phase control. This circuit is supplied by AC line. In this circuit is there the four diodes provide a full wave rectified voltage to the anode of a SCR. This is the figure of this circuit;

This is a principle work of the circuit. Two small signal transistors are connected in a switch configuration so that when the voltage on the 2.2uF capacitor reaches about 8 volts, the transistors will switch on and discharge the capacitor through the SCR gate causing it to begin conducting. The time delay from the beginning of each half cycle to the point where the SCR switches on is controlled by the 50K resistor which adjusts the time required for the 2uF capacitor to charge to 8 volts. As the resistance is reduced, the time is reduced and the SCR will conduct earlier during each half cycle which applies a greater average voltage across the load. With the resistance set to minimum the SCR will trigger when the voltage rises to about 40 volts or 15 degrees into the cycle. To compensate for component tolerances, the 15K resistor can be adjusted slightly so that the output voltage is near zero when the 50K pot is set to maximum.
Note; Don’t touch this circuit when it is connected with Voltage AC and Current AC.

12V Speed Controller Dimmer

This handy circuit can be used as a speed controller for a 12V motor rated up to 5A (continuous) or as a dimmer for a 12V halogen or standard incandescent lamp rated up to 50W. It varies the power to the load (motor or lamp) using pulse width modulation (PWM) at a pulse frequency of around 220Hz. SILICON CHIP has produced a number of DC speed controllers over the years, the most recent being our high-power 24V 40A design featured in the March & April 2008 issues. Another very popular design is our 12V/24V 20A design featured in the June 1997 issue and we have also featured a number of reversible 12V designs.

Project Image :

12V Speed Controller/Dimmer Project Image

For many applications though, most of these designs are over-kill and a much simpler circuit will suffice. Which is why we are presenting this basic design which uses a 7555 timer IC, a Mosfet and not much else. Being a simple design, it does not monitor motor back-EMF to provide improved speed regulation and nor does it have any fancy overload protection apart from a fuse. However, it is a very efficient circuit and the kit cost is quite low.

Parts layout:

Connection diagram:

There are many applications for this circuit which will all be based on 12V motors, fans or lamps. You can use it in cars, boats, and recreational vehicles, in model boats and model railways and so on. Want to control a 12V fan in a car, caravan or computer? This circuit will do it for you. The circuit uses a 7555 timer (IC1) to generate variable width pulses at about 210Hz. This drives Mosfet Q3 (via transistors Q1 & Q2) to control the speed of a motor or to dim an incandescent lamp.

Circuit diagram :

12V Speed Controller/Dimmer Circuit Diagram

While the circuit can dim 12V halogen lamps, we should point out that dimming halogen lamps is very wasteful. In situations where you need dimmable 12V lamps, you will be much better off substituting 12V LED lamps which are now readily available in standard bayonet, miniature Edison screw (MES) and MR16 halogen bases. Not only are these LED replacement lamps much more efficient than halogen lamps, they do not get anywhere near as hot and will also last a great deal longer.

Source : Streampowers

Automatic Temperature Climate Controlled Mains Fan Regulator Dimmer Circuit

The following circuit of a temperature or climate controlled fan speed regulator circuit was requested by one of the followers of this blog Mr.Anil Kumar. Lets learn more about the request and the proposed design.

The Request

Hi Swagatam,

am doing project on automatic speed control of ceiling fan depending on temperature. am an engineering student. can help me abt circuit and all. please...

The Design

As can be seen in the given diagram, a very simple concept has been implemented in the proposed design of a climate controlled or temperature controlled fan regulator circuit.

A1, A2, and A3 are the 3 opamps from the IC LM324 which are configured as voltage comparators and amplifier.

The diode D1 which is a common "garden diode" has a very interesting "drawback", it changes its forward voltage drop by 2mV in response to every degree rise in the ambient temperature or the temperature surrounding it.

The above drawback of the device becomes our benefit here, because the feature here is exploited for sensing the ambient temperature of the premise.

The varying voltage across D1, in response to the varying surrounding temperature is effectively amplified at the output of A3.

The above amplified response is fed over an LED/LDR opto coupler, where the LED becomes the output load of A3.

Therefore the brightness of the LED varies proportionately in response to the temperature variations, it becomes brighter with increasing temperature and vice versa.

The above illumination falls over the built in LDR of the opto, which in turn varies its resistance according to the above information from D1.

Since the LDR is fixed as the gate control resistor of the dimmer circuit consisting of R11, C5, R13, DC1 and the TR1, the voltage across TR1 starts regulating the mains AC in accordance with the fed LED/LDR response.

When the LED is bright (at higher temperatures), the LDR resistance lowers. allowing the triac to pass more current. This increases the speed of the fan, and when the LED/LDR response decreases (at lower temperatures), the speed of the fan also decreases.

A compact power supply consisting of C3, C2, Z1 supplies the required filtered DC to the IC LM324 temperature sensor configuration for the intended operations.

Idealy P1 should be adjusted such that the LED just begins glowing at about 24 degree Celsius, initiating the rotation of the fan at the minimum level.

D1 must be kept exposed well outside the enclosure so that it is able to sense the fan breeze directly.

WARNING - THE CIRCUIT IS NOT ISOLATED FROM MAINS AC...... BE VERY MUCH CAUTIONED WHILE BUILDING AND TESTING THIS CIRCUIT.