Soft-start enhances LED driver

  作者：dolphin 时间：2012-08-02
To emulate the natural soft start of an incandescent bulb, this circuit makes use of the thermal-foldback protection built into an LED-driver IC (MAX16832). It thereby avoids the annoying and almost instantaneous startup otherwise exhibited by LEDs. Fortunately, you can use the thermal-foldback protection built into an LED-driver IC (MAX16832) to emulate the natural soft start of an incandescent bulb. Figure 1 shows the typical application circuit for this IC.Figure 1. This application circuit is typical for the MAX16832.Figure 2. A simplified diagram (left) shows internal operation of the IC in Figure 1. The graph of LED output current versus VTEMP_I (right) assumes RSENSE = 300mΩ.Figure 3. In Figure 1, a graph of LED current vs. startup time with C2 = 10nF shows a soft-start interval of less than two milliseconds.Figure 4. In Figure 1, a graph of LED current vs. startup time with C2 = 1µF shows a soft-start interval of ~200ms.
Using the thermal-foldback circuitry to implement a soft-start for LEDs does not interfere with its protection function. The big capacitor slows that function, but its operation remains satisfactory because thermal effects are inherently slow. Nor is the PWM dimming feature affected. Only the reference voltage is influenced; the rest of the driver behaves normally.

关键词： 电子电路图，LED driver

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