[Source: Gaogong LED's "LED Good Products" magazine February issue] Looking at the current LED lamp industrialization competition, "primary feedback (PSR)" without optocoupler and without TL431 attracts the attention of the industry. In order to meet the needs of the development of China's LED lamp industry, Shaanxi Xicheng Electronics Co., Ltd. quickly introduced the RM3261S/D with built-in MOS power tube. The schematic diagram of its application circuit is shown in Figure 1.
(Fig. 1) The working principle is as follows: input AC power supply 85Vac-264Vac, converted to DC power by full-wave bridge rectification; filtered by C1, after smoothing 100Hz ripple, for DC bus power supply, one way through starting resistor R1 string R2 step-down is used to connect Vcc to the first leg, and the other is connected to the same name of the transformer primary winding N1. The N1 winding is not connected to the D pole of the built-in MOS power (the fifth leg is connected in parallel with the sixth pin). When the built-in MOS power tube is controlled to be OFF (OFF), the magnetic energy of N1 is induced to the isolated secondary winding N2. After D7 half-wave rectification, the low-voltage large-capacity electrolytic capacitor C6 smoothes the ripple, and the J3-J4 output terminal , power supply to the load LED (7W-9W). The primary winding TF1B is tightly coupled to the secondary N2, and the primary winding TF1B reflects the operation of the secondary N2 to achieve "primary feedback (PSR)". Without the optocoupler feedback, the fourth pin (R7 parallel R7A) resistor is sampled. , control the LED to get constant current accuracy within ± 5%. The voltage of the primary winding TF1B is controlled by the R5 and R6 voltage division to the third leg, and the RM3261S/D is stable in the range of the wide power supply 85Vac-264Vac. The 7th and 8th feet are connected in parallel to each other for heat dissipation. It should be noted that (Fig. 1) is a low-cost topology with electrolytic capacitors, and it is necessary to improve the reliability. In addition, (Fig. 1) is a flyback topology, and the transformer core is limited to the first quadrant of the magnetic characteristics. It is where there is potential for improvement.
The existence of electrolytic capacitors is not conducive to matching LED long life
As we all know, LED working life of 100,000 hours or longer can be achieved, but in the design of power supply structure for LED services, there is a shorter life of electrolytic capacitors, which seriously limits the overall reliability of LED lights.
The electrolyte inside the electrolytic capacitor may be vaporized and explode at high temperature. Therefore, the electrolytic capacitor manufacturer has a cross-shaped mark or a K-shaped mark on the outer casing of the electrolytic capacitor, allowing the cross from being able to escape from the internal oxygen pressure. Bleed at the mark or K mark.
The external capacitance of the capacitor indicates that the capacitor allows the maximum temperature limit: 8 5 ° C (civil goods), 1 0 5 ° C (industrial products), high-priced special-grade (125 ° C), high-priced special military products (180 ° C).
At low temperatures, if the inside is frozen, bulk expansion will occur, and low temperature will freeze, which will reduce the capacitance much less than the nominal value. This is one of the reasons why the outdoor LED lights flash or turn off in winter. After years of practice, more and more people in the LED industry have the same consensus - the existence of electrolytic capacitors is not conducive to matching LED long life.
Therefore, LED lamps without electrolytic capacitors are considered by the industry to be high-quality, high-end products with high price positioning.
Magnetic characteristics I-III quadrant, worthy of attention
People who do LEDs don't necessarily understand "light", let alone higher-level "light art" or "art light"; but LEDs must rely on light art to make profits, so more and more people in the LED industry begin to pay attention to " Light art." People who are engaged in LED power supply pay attention to "electricity", but do not necessarily pay attention to "magnetic", but magnetic characteristics are one of the core technologies of LED power supply. See (Figure 2) H = f (B) magnetic characteristics. (Fig. 2) The first quadrant is the positive excitation quadrant.
In the flyback type (Fig. 1), the electronic transformer N1 operates in the first quadrant of (Fig. 2), so the magnetic energy stored in the N1 excitation is cut off in the RM3261S/D built-in MOS power tube, that is, the N1 excitation suddenly loses power, and the N1 stores magnetic energy. Released, converted into the unidirectional pulse current io of the same name end of the secondary N2 winding, converted into Co storage DC power Vco by Do.
Obviously, the TR of (Fig. 1) only works in the first quadrant of (Fig. 2).
Figure (3) LED power, by DC-free N11-N12 as a high-frequency AC inductor, power supply to the load BUCK, while the secondary current N2 of TR1 and Co1 and Co2 series resonance, the DC current source, and Co Parallel connection suppresses the current ripple of the output to the LED lamp by less than 10% without the need for a short-life and large-capacity electrolytic capacitor, so that the electrolytic capacitor is not used but does not cause deterioration of the LED current ripple.
Unfinished: For more information, please refer to the February issue of Gaogong LED's "LED Good Products" magazine.
(Fig. 1) The working principle is as follows: input AC power supply 85Vac-264Vac, converted to DC power by full-wave bridge rectification; filtered by C1, after smoothing 100Hz ripple, for DC bus power supply, one way through starting resistor R1 string R2 step-down is used to connect Vcc to the first leg, and the other is connected to the same name of the transformer primary winding N1. The N1 winding is not connected to the D pole of the built-in MOS power (the fifth leg is connected in parallel with the sixth pin). When the built-in MOS power tube is controlled to be OFF (OFF), the magnetic energy of N1 is induced to the isolated secondary winding N2. After D7 half-wave rectification, the low-voltage large-capacity electrolytic capacitor C6 smoothes the ripple, and the J3-J4 output terminal , power supply to the load LED (7W-9W). The primary winding TF1B is tightly coupled to the secondary N2, and the primary winding TF1B reflects the operation of the secondary N2 to achieve "primary feedback (PSR)". Without the optocoupler feedback, the fourth pin (R7 parallel R7A) resistor is sampled. , control the LED to get constant current accuracy within ± 5%. The voltage of the primary winding TF1B is controlled by the R5 and R6 voltage division to the third leg, and the RM3261S/D is stable in the range of the wide power supply 85Vac-264Vac. The 7th and 8th feet are connected in parallel to each other for heat dissipation. It should be noted that (Fig. 1) is a low-cost topology with electrolytic capacitors, and it is necessary to improve the reliability. In addition, (Fig. 1) is a flyback topology, and the transformer core is limited to the first quadrant of the magnetic characteristics. It is where there is potential for improvement.
The existence of electrolytic capacitors is not conducive to matching LED long life
As we all know, LED working life of 100,000 hours or longer can be achieved, but in the design of power supply structure for LED services, there is a shorter life of electrolytic capacitors, which seriously limits the overall reliability of LED lights.
The electrolyte inside the electrolytic capacitor may be vaporized and explode at high temperature. Therefore, the electrolytic capacitor manufacturer has a cross-shaped mark or a K-shaped mark on the outer casing of the electrolytic capacitor, allowing the cross from being able to escape from the internal oxygen pressure. Bleed at the mark or K mark.
The external capacitance of the capacitor indicates that the capacitor allows the maximum temperature limit: 8 5 ° C (civil goods), 1 0 5 ° C (industrial products), high-priced special-grade (125 ° C), high-priced special military products (180 ° C).
At low temperatures, if the inside is frozen, bulk expansion will occur, and low temperature will freeze, which will reduce the capacitance much less than the nominal value. This is one of the reasons why the outdoor LED lights flash or turn off in winter. After years of practice, more and more people in the LED industry have the same consensus - the existence of electrolytic capacitors is not conducive to matching LED long life.
Therefore, LED lamps without electrolytic capacitors are considered by the industry to be high-quality, high-end products with high price positioning.
Magnetic characteristics I-III quadrant, worthy of attention
People who do LEDs don't necessarily understand "light", let alone higher-level "light art" or "art light"; but LEDs must rely on light art to make profits, so more and more people in the LED industry begin to pay attention to " Light art." People who are engaged in LED power supply pay attention to "electricity", but do not necessarily pay attention to "magnetic", but magnetic characteristics are one of the core technologies of LED power supply. See (Figure 2) H = f (B) magnetic characteristics. (Fig. 2) The first quadrant is the positive excitation quadrant.
In the flyback type (Fig. 1), the electronic transformer N1 operates in the first quadrant of (Fig. 2), so the magnetic energy stored in the N1 excitation is cut off in the RM3261S/D built-in MOS power tube, that is, the N1 excitation suddenly loses power, and the N1 stores magnetic energy. Released, converted into the unidirectional pulse current io of the same name end of the secondary N2 winding, converted into Co storage DC power Vco by Do.
Obviously, the TR of (Fig. 1) only works in the first quadrant of (Fig. 2).
Figure (3) LED power, by DC-free N11-N12 as a high-frequency AC inductor, power supply to the load BUCK, while the secondary current N2 of TR1 and Co1 and Co2 series resonance, the DC current source, and Co Parallel connection suppresses the current ripple of the output to the LED lamp by less than 10% without the need for a short-life and large-capacity electrolytic capacitor, so that the electrolytic capacitor is not used but does not cause deterioration of the LED current ripple.
Unfinished: For more information, please refer to the February issue of Gaogong LED's "LED Good Products" magazine.
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