Thyristor Dimming--In-depth Analysis and Application
Introduction to Thyristor Dimming
Thyristor, short for thyristor rectifier element, is a high-power semiconductor device with a four-layer structure and three PN junctions. It is usually composed of two thyristors connected in reverse anti-parallel. With versatile functions, it can not only be used for rectification but also act as a contactless switch for fast switching on and off. It can even convert direct current into alternating current, or alternating current of one frequency into alternating current of another frequency. The invention of the thyristor marked the leap of semiconductor technology from the low-voltage field to the high-power field, and it has been widely used in industry, agriculture, transportation, military scientific research, as well as commercial and civil electrical appliances. At present, thyristors play an important role in automatic control, electromechanical applications, industrial electrical appliances and household appliances.
Thyristor Dimming Circuit
The components of a thyristor dimming circuit include a power supply, wires, switches and lamps. Currently, many LED lamps adopt constant-current thyristor driving technology. This technology eliminates the need for series current-limiting resistors in the output circuit, and ensures that the current flowing through the LED is immune to fluctuations in the external power supply voltage, thus achieving stable current and fully demonstrating the excellent performance of LEDs.
Principle and Advantages of Thyristor Dimming
Dimming Principle
What is the dimming principle of thyristors? When a lamp needs to be dimmed via a thyristor signal, the input voltage waveform in the circuit deviates with the change of the thyristor’s conduction angle, resulting in a variation of the effective input voltage value, thereby realizing the dimming function. This process can be understood more intuitively through diagrams.
However, the real key to achieving thyristor dimming lies in the switch inside the thyristor potentiometer. During the conduction of the thyristor, this switch adjusts the voltage division ratio of the internal resistance, which in turn changes the conduction angle of the thyristor. This change directly adjusts the effective value of the output voltage, thus achieving dimming. This principle can be visually displayed through diagrams and other methods.
Conventional incandescent and halogen lamps are often dimmed by thyristors. This is because incandescent and halogen lamps are purely resistive devices, whose current waveforms are consistent with voltage waveforms and unaffected by the input voltage waveform. Therefore, dimming these two types of lamps can be realized by changing the effective value of the input voltage. Thyristors achieve this by chopping the sine wave of alternating current to alter its effective value, enabling flexible light regulation.
Advantages and Disadvantages of Thyristor Dimming Technology
Nevertheless, every technology has two sides, and thyristor dimming is no exception. Below we discuss its advantages and disadvantages.
Advantages
1.After long-term development, thyristor dimming technology is quite mature and stable. Its perfect compatibility with incandescent and halogen lamps has secured it a prominent position in the dimming market.
2.Thyristor dimming is rather simple to install and use. Existing LED lamps can be directly replaced to be compatible with the current wiring, without cumbersome rewiring.
3.Thyristor dimmers are widely used in traditional lighting markets such as incandescent lamps, which conforms to people’s long-term usage habits. Meanwhile, the cost of thyristor dimming is relatively low.
Disadvantages
However, thyristor dimming also has drawbacks. It distorts the sine wave during dimming, which reduces the power factor. Such non-sinusoidal waveforms also increase the harmonic coefficient and may cause serious electromagnetic interference (EMI). Its stability is easily affected especially under low-load conditions, so an additional bleeder resistor is required to ensure stable operation. Furthermore, other potential problems may occur during use:
*The color spectrum of LEDs is closely related to current. Therefore, current fluctuations will cause color shift in LEDs, thus affecting the luminous quality of white LEDs.
*Long-term operation of LED lamps under non-rated voltage and current will negatively impact their designed service life. Analog dimming has problems such as narrow dimming range, poor consistency and linearity.
*During analog dimming, the LED driver remains operational, and its conversion efficiency drops significantly as the output current decreases, resulting in increased power loss of the power supply system. To optimize the dimming effect, it is crucial to select high-quality dimming equipment with corresponding measures to effectively reduce electromagnetic interference generated during the application of thyristor technology.