In the LED driver power market, non-isolated solutions have become application hotspots due to their smaller magnetic components, higher energy efficiency, fewer component counts, lower total bill of materials costs, and the ability to meet safety regulations with mechanical design. This article introduces a 10W LED driver power supply designed with the TI control chip TPS92210. Using the TPS92210's unique critical mode fixed peak current control function, the design does not require feedback, so the whole design is simple, the device is small, the cost is low, and the efficiency is high.
1. Introduction to power supply scheme
This scheme adopts the critical Buck circuit controlled by TPS92210, and sets the TPS92210 to work on the fixed peak current, so that the peak value of the inductor current is fixed. Because the circuit works in the critical mode, the average value of the inductor current is equal to half of the peak current, thus achieving the output constant current. the goal of.
At the same time, this solution does not require additional circuitry, and the TPS92210 itself can provide protection against overcurrent, short circuit, and open circuit. Therefore, the entire program has fewer components and lower costs.
The input uses a valley filling circuit, so that the PF value of the whole machine is always above 0.7.
C8, L2, and C5 form a pi-type filter. The whole machine passed the conduction test.
Figure 1: 10W LED Power Solution
Figure 2: 10W LED power supply physical map
1.1 TPS92210 critical mode setting
The TPS92210 needs to meet three conditions to start a new cycle:
1) The time from the last turn-on needs to be greater than the time controlled by the Ifb current.
2) The time from the last turn-on needs to be 7.5us longer than the maximum frequency of the chip.
3) The Tze foot must have a high to low zero crossing.
Because the above three conditions need to be met, the FB pin is connected to Vdd through the resistor to set a fixed DC offset, so that the turn-on of the TPS92210 is completely determined by the voltage zero crossing of the Tze pin, which ensures that the converter always works. Critical current mode.
1.2 Inductor design
Calculate the inductance according to the input and output requirements. In this scheme, input 176V~264Vac, output 40V, 0.25A. Since the input uses a valley fill circuit, the input voltage range can be calculated as follows:
Based on the minimum and maximum input voltages calculated above, the minimum and maximum duty cycles can be calculated:
The inductor needs about 67 åŒ. The AWG 30 is selected to wind the inductor based on the previously calculated current RMS value and the set current density j. One strand of AWG30 was selected as the winding.
2, test results
Based on the above analysis and design, the prototype was fabricated and its performance was verified. The experimental results are as follows.
Short circuit protection
Open circuit protection
3. Conclusion
This paper analyzes and designs a critical mode buck converter controlled by TPS92210. The feasibility and setting of the TPS92210 critical mode are analyzed. The calculation and design method of the inductor is described in detail. Finally, the prototype was produced to verify the correctness of the analysis and calculation. The feasibility of the TPS92210 for non-isolated constant current LED drive power is guaranteed.
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