دایره المعارف تاسیسات برق (اطلاعات عمومی برق)
The diacs, because of their symmetrical bidirectional switching characteristics, are widely used as triggering devices in triac phase control circuits employed for lamp dimmer, heat control, universal motor speed control etc.
Although a triac may be fired into the conducting state by a simple resistive triggering circuit, but triggering devices are typically placed in series with the gates of SCRs and triacs as they give reliable and fast triggering. Diac is the most popular triggering device for the triac. This is illustrated in the following applications.
The circuit for a triac controlled by an R-C phase-shift network and a diac is given in figure. This circuit is an example of a simple lamp dimmer. The triac conduction angle is adjusted by adjusting the potentiometer R. The longer the triac conducts, the brighter the lamp will be. The diac acts like an open-circuit until the voltage across the capacitor exceeds its breakover or switching voltage (and the triac’s required gate trigger voltage).
A typical diac-triac circuit used for smooth control of ac power to a heater is shown in figure. The capacitor C1 in series with choke L across the triac slows-up the voltage rise across the device during off-state. The resistor R4 across the diac ensures smooth control at all positions of potentiometer R2. The triac conduction angle is adjusted by adjusting the potentiometer R2. The longer the triac conducts, the larger the output will be from the heater. Thus a smooth control of the heat output from the heater is obtained.
Designer: Carlos Damian Lopez Herrero E-mail: Operating voltage: 220V AC 50 Hz Published at www.epanorama.net: 06/2008 Copyright: Pictures Carlos Damian Lopez Herrero, text www.epanorama.net
NOTE: This circuit design is not tested by www.epanorama.net staff. The circuit design as submitted by the designer is believed to be correct, but there is no guarantee of the correctness of the circuit design. The contents of the articles below might be totally inaccurate, inappropriate, or misguided. There is no guarantee as to the suitability of said circuits and information for any purpose.
Warning: This circuit operates at potentially lethal 220V AC mains voltage. The circuit should be built and used only by people who know hot to safely work with such dangerous voltages and how to built the circuit so that it is safe to use.
Solid-state light dimmers work by varying the "duty cycle" (on/off time) of the full AC voltage that is applied to the lights being controlled. For example, if the voltage is applied for only half of each AC cycle, the light bulb will appear to be much less bright than when it get the full AC voltage, because it get's less power to heat the filament. Solid-state dimmers use the brightness knob setting to determine at what point in each voltage cycle to switch the light on and off.
The exact time when the triac is triggered relative to the zero crossings of the AC power is used to determine the power level to the light bulb. When the the triac is triggered it keeps conducting until the current passing though it goes to zero (exactly at the next zero crossing if the load is purely resistive, like light bulb). By changing the phase at which you trigger the triac you change the duty cycle and therefore the brightness of the light.
The circuit contains a variable resistance that consists of R1 + PT1 in paralle with R2 + RV2. This variable resistance together with capacitors C1 and C2 form a delay from the mains zero crossing to the firing point of the diac. DIAC is a bidirectional trigger diode that conducts current only after its breakdown voltage (typically around 30V) has been exceeded momentarily. The larger the variable resistance feeding the capacitors, the longer it takes for the voltage across the capacitor to rise to the point where the DIAC fires turning on the triac TH1. The circuit is calibated in such way that first PT1 is turned to highest resistance values. The value of RV2 is turned in such position that the desired minumum brightness of the light bulb is reached. After this calibration the PT1 can be used to freely control the light bulb brightness at the desired control range form the maximum brightness to set minumum.
Capacitor C1 and inductor L1 make a simple radio frequency interference filter. Without it the circuit would generate quite much interference because firing of the triac in the middle of the AC phase causes fast rising current surges. The triac BT139 used in the circuit is rated for 16A continuous current when properly cooled with a large heat sink. The maximum current is less with less cooling. The components R4 and C4 for a RC nubber network that protects TRIAC from spurious triggering.
In this circuit of a dimmer the diac is replaced with a neon glow lamp, but it works exactly in the same way than a classic one: an RC network delays the trigger pulses on the gate of the triac. The glow lamp rises the trigger voltage from about 40 V to about 70 V. Some adjustments to R and C values may be required to match specific glow lamps and triacs.
The energy in the electrolytic capacitors can be lethal even when the circuit is switched off. Always discharge these capacitors before touching the circuit.
To use this monitor just set the trimmer to 0 V, power the circuit on (when no
field is present) and slowly turn the trimmer to rise the voltage until the glow lamp
lights. Turn now the trimmer in the other direction and stop as soon as the lamp
turns off: now the monitor is ready and a strong RF field will light the bulb.
For testing you can try a cellular phone or a transmitter (some Watts of power are
required) and the bulb will light in proximity of the antenna.
Connecting a small dipole to the lamps terminal dramatically increases its sensitivity.
Since this circuit is very simple is usually necessary to readjust often the trimmer to compensate the battery that is discharging itself.
Touch dimmer)ساخت دیمر با HT7700
اپتو ترایاك MOC 3041 داخل خودش Zero Crossing داره.
جذابیت های برق
در ستایش معماری
تکنیک های نورپردازی، مهندسی روشنایی
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تکنولوژی های روز دنیا
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