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Triac dimming power supply application
2021-07-29 17:20:19
Triac dimming power supply is the mainstream equipment in stage lighting and environment lighting field. All kinds of dimmers used in the triac dimming power supply lighting system are essentially AC voltage regulators. The old transformers and rheostat dimmer by adjusting the amplitude of voltage or current. U1 is the WAVEFORM of 220V AC without voltage regulation, and the voltage waveform after voltage regulation is U2. Because its amplitude is less than U1, the lights are dimmed. In this dimming mode, although the amplitude of the sinusoidal alternating current is changed, the essence of the sine wave does not change.
Compared with transformer and resistor, triac dimmer has a completely different dimming mechanism. The triac dimming power supply adopts the method of phase control to realize voltage regulation or dimming. For the common reverse blocking triac, the characteristics of the triac are as follows: when the triac is applied a positive anode voltage and an appropriate positive control voltage, the triac is on; This conduction is maintained even after the gate control voltage has been removed and is not turned off until a reverse anode voltage is applied or the anode current is less than the holding current of the triac itself. The common SCR dimming power uses this characteristic of the triac to realize the leading-edge trigger phased voltage regulation. triac dimming power at a certain time T1 (or a certain phase Angle WT1) after sinusoidal ac crossing zero, the trigger pulse is applied to the control electrode of the triac to conduction the triac. According to the switching characteristics of the triac dimming power supply above, this conduction will remain until the end of the positive half cycle of the sine wave. Therefore, in the positive half cycle of the sine wave (i.e., the interval of 0~ P), the triac in the range of 0~ WT1 does not conduct, and this range is called the control Angle, which is usually expressed as A; The triac conducts between WT1-P and P. This range is called the conduction Angle and is usually denoted by J. Similarly, in the negative half cycle of a sine wave ac, a trigger pulse at time T2 (i.e., phase Angle WT2) is applied to another triac connected inversely (in the case of two unidirectional triacs in an inversely parallel or bidirectional triac) to cause it to conduction. In this way, the conduction of the sine wave is controlled every half cycle to obtain the same conduction Angle. If the application time (or phase) of the trigger pulse changes, the size of the conduction Angle J (or control Angle A) will also change. The larger the conduction Angle, the higher the output voltage of the dimmer, the brighter the lamp. According to the above triac dimming principle, the voltage waveform output by the dimmer is no longer sine wave unless the dimmer is in full conduction state, that is, the conduction Angle is 180°(or P). It is because the sine wave is cut, the waveform is destroyed, it will bring interference to the power grid...
Good dimming equipment should take necessary measures to reduce the interference caused by using triac technology.
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