Based on dimming LED lighting drive program

1) the existing dimmers are designed for incandescent, and incandescent lamp is pure resistivity; LED as a solid-state semiconductor lighting devices, the need for constant DC current drive, so LED lighting generally need to drive from the exchange 110V / 220V to convert to the required DC current.

2) a wide range of dimmers, and the working principle varies, including the former cut, after cutting and intelligent and so on;

3) There are many types of LED lighting fixtures. In this way, for different LED lighting to match different types of dimmers; LED drivers face great challenges; where reliability and security are particularly important. Lighting is a consumer electronics products, direct contact with thousands of households of consumers, not only the price should be appropriate, more important is to be safe and reliable; even if any component failure or dimmer and LED does not match, can not cause leakage, Overcurrent and any other safety.

For the development of LED lighting market, a number of IC manufacturers introduced the application of dimming LED lamps in the drive program. This article describes the iW3610 is compatible with traditional front and rear cut-type dimmer digital controller, can automatically identify the cut-off dimmer, with different modes of operation, so that the entire system is always working in the optimized state.

LED lighting driver design points

LED is a one-way current-type solid-state semiconductor light-emitting devices, it is a branch of the traditional diode; LED also has the characteristics of the diode: 1) the working junction temperature must be within the specified range to ensure its normal working life; Only when it receives the voltage exceeds the forward voltage, the LED began to have the current through, and light; as a light emitting device, LED lighting also has other features:

1) lighting requirements: a. Current adjustment accuracy is high; b. No flicker and glare; c. Current ripple to be stable.

2) thermal design points: a. Non-isolated drive to facilitate the design and cost control of the radiator; b. Efficient drive to reduce power dissipation; c. Overheating adjustment, adjust the output luminous flux when the temperature exceeds the safe junction temperature.

3) safety and reliability points: a. Any device failure (short circuit, open circuit, floating) should lead to LED lighting off protection; b reliable overheating overcurrent protection; c.LED open and short circuit protection.

Of course, to popularize LED lighting to millions of households, the cost is the most important considerations, LED products are both reliable but also small size, and efficient, low cost.

 

LED dimming lighting applications in the difficult

Compared to the traditional incandescent, LED lighting with environmental protection, high luminous efficiency and long life advantages. But in completely replace the incandescent lamp with a wall-mounted dimmer, LED lighting is still poor compatibility of the shortcomings. The traditional dimmer is used to drive the pure resistive load, and the dimmer has a wide range, including cutting edge dimmer, cutting edge dimmer, intelligent dimming, etc., and the power is relatively large (200W ~ 600W) Need to provide a resistive or resistive load in order to stabilize the dimmer work; when connecting capacitive load, the dimmer may not work properly.

 

For thyristor cut-out dimmers, with a simple bleeder circuit (BLEEDER) to match the specifications of the SCR dimmer work, it is difficult to satisfactory. The traditional dimmer power is relatively large (200W ~ 600W), SCR need to maintain a certain current to maintain its conduction, and in low-power LED driver applications, generally can not guarantee a large enough input current to maintain controllable Silicon stable work. So that there may be a number of conduction, and thus supply the LED drive voltage and cut-off signal is not stable, if the dimming signal processing will cause the LED flashing.

In addition, in Europe and the United States market, along the cutting-type dimmers and halogen lamps are also widely used. Halogen lamps need constant voltage control and soft start to improve reliability, but the halogen light efficiency is far less than LED lights, so many users also want to use adjustable LED to replace the halogen and electronic transformers.

 

Since the rear-trimmer dimmer needs to match the capacitive electronic transformer, its design and process are more complex than the conventional thyristor dimmer, with precise time-constant circuitry to control the field-effect transistor And the need for a stable voltage for these circuits to work; because the dimmer used in the switching device is a field effect transistor, generally in parallel with a larger value of the X capacitor to protect the field effect Tube, thus increasing the sine wave in the cutting edge of the cutting when the difficulty of detection. Therefore, the LED driver for the trailing edge dimmer design, it is necessary to be able to in any cutting position to ensure that the dimmer internal circuit work, but also to provide a very low impedance to accurately detect the cutting position, and can not affect the LED Driven conversion efficiency.

Intelligent digital dimming controller iW3610

iWatt's digital dimming control chip uses high-precision primary constant current control, no need for couplers and components of the many secondary feedback control components; power conversion operation frequency up to 200kHz, conducive to small size high power density design; The chopper dimmer detection technology, but also improve the power factor and harmonic current; output ripple current is small, optimize the LED luminous efficiency; built-in multiple protection, external NTC program over-temperature protection.

 

IW3610 chopper circuit is designed for the characteristics of thyristors and FET dimmers. As shown in Figure 4, RcLcQcD1D2 circuit can make the dimmer work, but also through the Boost circuit to improve the power factor, IC internal digital circuit by detecting the rate of change in voltage to determine the type of cut signal, so intelligent decision It is equipped with a dimmer.

 

When the iW3610 detects the thyristor's dimming signal, it will work in the cutting edge mode. As shown in Figure 5, when the thyristor is turned off, the Output_TR of the IC is high and the MOSFET is turned on, which is equivalent to connecting the BLEEDER resistor to the output of the dimmer because the impedance of the BLEEDER is the same as that of the conventional tungsten When the thyristor is on, Ouput_TR will output a set of high-frequency control signals. The chopper circuit operates in the high-frequency switching state. The chopper circuit draws more current from the input to maintain thyristor operation ; Most of the energy absorbed is passed through the Boost circuit to the primary capacitor. IC for different input tangential signal adjustment chopper circuit working time, to avoid the multi-turn of the thyristor.

 

When the iW3610 detects the field effect transistor dimmer it will work in the trailing edge of the cut mode. As shown in Figure 6, when the field effect transistor inside the dimmer turns on, the output_TR of the IC gives a set of high frequency control pulse signals. The chopper circuit operates in the Boost state. When the IC detects the dimmer Of the field effect transistor cut-off, Output_TR will jump into a high level signal, chopper circuit Qc conduction, LED driver was low input impedance to restore the AC input tangential waveform.

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