LED lighting - a detailed explanation of the low-cost DC-LED drive-CYT34065

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LED driver circuit control LED (light emitting diode) light in the power supply circuit of the power required. LED forward voltage drop (VF) with a manufacturing error and the ambient temperature changes, can not use a constant voltage drive. Thus, the general need to use the constant current driver to maintain a constant supply to the LED current. LED driver circuit structure and common switching regulator (DC-DC converter) is basically the same, not much difference. LED drivers have special requirements, there are basically two differences.

The first difference is that the feedback voltage is low (Figure). The feedback voltage detection output voltage feedback to the voltage of the switching regulator IC. LED driver IC with a constant current control, the feedback voltage as the output current is converted into voltage.

Typically, the feedback voltage set by the switching regulator IC is about 1.2V. But for the garden led lights driver IC, 1.2V is too large. Because the output current is converted into a voltage hundreds of mΩ resistor (current-sense resistor) in series with the LED. Used for li ghting fixtures and other high-brightness LED, flows through the large current of 1.5A and 2A. If the 500mΩ The current detection resistor 1.5A current alone will produce 0.75W of power loss. Therefore, LED driver IC to the feedback voltage set at a very low 0.2V. As a result, not only can use a smaller current sense resistor, and a large current through the power loss control at a lower level.

The second difference is the more accurate constant current control has been improved. Rely solely on the detected output current feedback, it is difficult to compensate for input voltage changes, the LED forward voltage drop changes the characteristics of inductors and capacitors change.

Improve the representativeness of the LED driver IC vendors in order to achieve a more accurate constant current control is the constant pulsating. After the above changes, the amplitude of the pulsation components of the overlap with the supply current to the LED will cha nge, resulting in LED brightness changes. In general, the amplitude of the fluctuating components of the input voltage, output voltage, inductance, switch control of the on-time decision. To this end, the constant pulse detection input voltage and output voltage to adjust the on-time, in accordance with the voltage. Is the precise control of switching frequency, the more accurate constant current control.