Low power LED drive power technology topology

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Overview:
As countries around the world pay more and more attention to the requirements of energy saving and emission reduction, LED is widely used as a new light source for its high efficiency and energy saving. The following is an introduction to the non-isolation technology for LED driver applications between 1-30W in the small power section.

A resistance to buck:
1. Principle and application of resistance to voltage reduction:
Capacitor bucking is actually using capacitive reactance current limiting, and the capacitor actually acts as a limiting current and dynamically distributing the voltage across the capacitor and the load.

2. Pay attention to the following points when using capacitor step-down:
According to the current of the load and the operating frequency of the AC, select the appropriate capacitor instead of the voltage and power of the load. The current-limiting capacitor must use a non-polar capacitor and cannot use an electrolytic capacitor. Moreover, the withstand voltage of the capacitor must be above 400V, and the most ideal capacitor is a polypropylene metal film capacitor. Capacitor buck can not be used for high power conditions. It is generally used for low power applications below 5W. Capacitor buck is not suitable for dynamic load conditions. Capacitor buck is not suitable for capacitive and inductive loads. It is suitable for driving in LED power supply. Voltage application.

3. The basic circuit of the RC capacitor is as shown in (Figure 1).

figure 1.
C1 is a step-down capacitor, D1, 2, 3, 4 are bridge rectifier diodes, ZD1 is a Zener diode, and R1 is the charge bleeder of C1 after the power is turned off.

4. When designing the device selection circuit, first determine the exact value of the load current, then refer to the example to select the capacity of the step-down capacitor. Since the current Io supplied to the load through the step-down capacitor C1 is actually the larger the capacity of the charge and discharge current Ic.C1 flowing through C1, the smaller the capacitive reactance Xc is, the larger the charge and discharge current flowing through C1 is. When the load current Io is less than the charge and discharge current of C1, the excess current will flow through the Zener diode. If the maximum allowable current Idmax of the Zener diode is less than Ic-Io, the regulator tube will burn out. In order to ensure reliable operation of C1, the withstand voltage selection should be greater than twice the supply voltage. The bleeder resistor R1 must be selected to vent the charge on C1 for a specified period of time.

5. Actual parameter calculation method:
It is known that C1 is 0.33μF and the AC input is 220V/50Hz. Find the maximum current that the circuit can supply to the load.
The capacitive reactance Xc of C1 in the circuit is:
Xc=1 /(2 πf C)= 1/(2*3.14*50*0.33*10-6)= 9.65K
The charging current (Ic) flowing through capacitor C1 is:
Ic = U / Xc = 220 / 9.65 = 22mA.
(Please read the PDF for details)