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What is the LED SCR dimming power supply
Release time:
2024-02-21
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What is the LED SCR dimming power supply
What is the LED SCR dimming power supply
Want to know what is LED thyristor dimming power supply, we must first know the mission principle of thyristor and thyristor. Silicon controlled rectifier is the abbreviation of silicon controlled rectifier, is a kind of four layer structure with three PN junction of high-power semiconductor devices, common by two thyristor reverse connection. Its function is not only rectification, but also can be used as a non-contact switch to quickly turn on or block the circuit, the end of the direct current into alternating current inverter, the frequency of alternating current into another frequency of alternating current and so on. SCR and other semiconductor devices are the same, its small size, high efficiency, good stability, reliable mission and other benefits. Its emergence, semiconductor technology from the field of weak electricity into the field of strong electricity, industry, agriculture, transportation, military research resulting in commercial, civilian electrical appliances and other aspects of the choice of components.
A key use of SCR is as a non-contact switch. In automation equipment, non-contact switches have been used to replace general-purpose relays. Its distinctive features are no noise and long life. It is precisely because of these characteristics of the thyristor, so the thyristor used in the field of dimming, has a huge pole role. LED drive power lighting as a green lighting approach, previously known to all mankind, so LED SCR dimming was born.
Silicon controlled dimming was the main stream equipment in the field of stage lighting and ambient lighting at that time.
The various dimmers used in lighting systems are essentially an AC voltage regulator. The old-fashioned transformer and rheostat dimming are completed by using the rugged scheduling voltage or current, as shown in the following figure. U1 is the waveform of 220V AC without voltage regulation. The voltage waveform after voltage regulation is u2. Because its ruggedness is less than u1, the light is dimmed. In this dimming mode, of course, the amplitude of the sinusoidal alternating current is changed, but the nature of its sinusoidal waveform is not changed.
Compared with the transformer, resistor, SCR dimmer has a completely abnormal dimming mechanism, it is the choice of phase control method to complete voltage regulation or dimming. As for the common reverse blocking thyristor, its thyristor current characteristics are shown as turning on when the thyristor is added with a forward anode voltage and an appropriate forward control voltage. This conduction will persist even after the gate control voltage is removed, and will not be turned off until the reverse anode voltage or anode current is less than the persistent current of the thyristor itself. Ordinary SCR dimming power supply is the use of this feature of the SCR to trigger the phase-controlled voltage regulation. At a certain hour t1 (or a certain phase angle wt1) after the sine wave alternating current crosses zero, a trigger pulse is added to the thyristor control pole to make the thyristor turn on. According to the thyristor switching characteristics previously seen, this turn-on will persist 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 0 ~ p interval), 0 ~ wt1 plans the SCR to be non-conductive. This plan is called the control angle and is usually indicated by A. However, the SCR conducts between wt1 and p. This plan is called the conduction angle and is usually indicated by J. Similarly, in the negative half cycle of sine wave alternating current, a trigger pulse is applied to the other SCR in reverse connection (for two unidirectional SCR anti-parallel or bidirectional SCR) at t2 (I. e. phase angle wt2) to make it conductive. This cycle, the sine wave every half cycle control its conduction, to obtain the same conduction angle. If the application time (or phase) of the trigger pulse is changed, the magnitude of the conduction angle j (or the control angle a) is changed. The larger the conduction angle, the higher the voltage output by the dimmer, the brighter the lamp will be.
It can be seen from the principle of SCR dimming power supply described above that the voltage waveform output by the dimmer is no longer a sine wave unless the dimmer is in full conduction, I .e. the conduction angle is 180 ° (or p). It is because the sine wave is cut, waveform damage, will bring trouble to the power grid.
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