Introduction to the core problem of LED lighting power supply design
There are in the LED lighting power supply design, some design problems electrolytic capacitor life and the LED does not match, a common cause of LED lights flashing and treatment method, PWM
move light have any effect on the service life of the LED, the use of TRIAC dimming control LED brightness of potential problems. Aimed at the causes of these problems and solutions.
life of electrolytic capacitors and LED does not match the
LED lighting is an important consideration, is the LED driver circuit and the working life of the LED itself should be able to compare. Although there are many factors that can affect the reliability of the drive circuit, but the electrolytic capacitor has a crucial effect on the overall reliability. In order to prolong the working life of the system, need a targeted analysis of the application of capacitance, and select the appropriate electrolytic capacitor.
in fact, the effective work of aluminum electrolytic capacitor life to a great extent affected by the environment temperature and the effect on the internal impedance of the ripple current caused by internal temperature rise effect. Electrolytic capacitor manufacturers provide electrolytic capacitor rated life is according to the exposure to the highest rated temperature environment and exert maximum rated ripple current conditions. Typical capacitance at 105 ° C rated life could be 5000 hours, rated capacitance than actually suffered from job stress level is lower, the effective working life is longer. Therefore, on the one hand, choose the rated working life is long and able to work under high rated temperature of the electrolytic capacitor, of course, can prolong the working life. On the other hand, according to the actual stress and working temperature, still can choose low rated working temperature and rated life capacitance, providing lower cost solution; Said another way, keep the appropriate stress is taken into account in design and the working temperature, can effectively prolong the working life of the electrolytic capacitor, make it can match the LED life more.
, for example, various semiconductor solid-state lighting energy star standards from the linear LED drive GreenPoint ® chose panasonic ECA - reference design 1 em102 aluminum electrolytic capacitor, the rating of 1000 (including F,
25 V, 850 ma, 2000 hours and 85 ° C. On the assumption that 50 ° C temperature conditions, the capacitance of the usable life of more than 120000 hours. Therefore, do our best to make the LED driver circuit work in appropriate conditions of temperature and properly handle the heat dissipation problem, can achieve the LED driver circuit and the matching problem of the LED working life.
in general, if the LED driver circuit must be used in electrolytic capacitor, it must strive to control capacitance and working temperature in the application of force, so as to prolong the working life of the capacitor to the greatest extent, in order to match its LED life; Designers, on the other hand, also should as far as possible to avoid the use of electrolytic capacitors.
a common cause of LED lights flashing and treatment method of
the human eye can generally perceived frequency of 70 hz light flashing, higher than the frequency does not perceive. So in LED lighting applications, if the pulse signal frequency is lower than 70 hz low frequency component, the human eye will feel the shine. In the specific application, of course, there are many factors may lead to LED lights flashing. For example, in an off-line low power LED lighting applications, a common power supply topology structure type is to isolate the flyback topology. With various semiconductor solid-state lighting energy star standards from line 8 w LED drive GreenPoint ® reference design as an example, because of the flyback voltage stabilizer sine square wave power conversion did not provide primary offset constant energy, dynamic self-supply ( DSS) Circuit may activate and trigger light flashing. To avoid this problem, must enable primary bias to partial discharge in each half cycle, accordingly, need to choose appropriate constitute the bias circuit of capacitance and resistance value.
in addition, even if in use to provide excellent support power factor correction, TRIAC dimming LED drive applications, also calls for electromagnetic interference ( EMI) Filter. By a TRIAC step ( 步骤) Caused by the transient current inspire EMI filter inductance and capacitance in the natural resonance. If the resonant characteristics lead to fall below TRIAC maintain current input current, TRIAC will be closed. After a brief delay, TRIAC usually will conduction, inspire the same resonance. In the input voltage waveform of one and a half cycle, this series of events may be repeated many times, to form a visible LED flashing. In order to deal with this problem, a key demand of TRIAC dimmer is EMI filter input capacitance is extremely low, and the capacity to be able to through the TRIAC and winding impedance decoupling. According to the formula, adjustable capacitance decrease in optical module, can increase the resistance of the resonant circuit, the principle on inhibiting oscillation, restore to the circuit work.
to have any effect on the lifespan of the LED PWM dimming
the LED itself is very long, the life of a PWM dimming LED life expectancy will not hurt, Even the PWM dimming help reduce LED calorific value, can actually help extend lifespan of LED. In system design, of course, need to effectively LED temperature detection and control, ensure the LED work, reflect the advantage of its long life and low maintenance cost.
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