of there are differences with the target value, the conol will automatically adjust the temperature the temperature of the base to make the led's forward voltage vf achieve the target junction temperature value corresponding to the junction voltage. in the rapid determination of vf, the device will automatically reply to the led current through the work of the state. when the measured operating current through the led in the case, the junction temperature reaches the target value (that is, the junction temperature reaches the value of the corresponding target value vf) and heat balance, the system will automatically start specometer measurement of light and color parameters simultaneously read its elecical parameters .
vinyl signs figure 2.1 diagram of constant power conol can be seen from the diagram of switching power supply flyback general than constant power program more than a dimmer signal conol circuit for detecting the input scr conduction angle and input voltage, thus gives the corresponding dimming signal. meanwhile, the program is no feedback signal, completely open-loop conol, the size of the original edge of the conol duty cycle to conol the size of the output power. theoretical basis for its conol are as follows: where: constant power conol mode are the first to predict the output power of led p, in theory, once after a good ansformer design, have determined that as long as the change in the size of the primary current, you can change the output power size. since then: where: u is added to the ansformer primary voltage, the input voltage; d is the duty cycle; is the switching frequency; for the ansformer primary inductance.
led scrolling signtab2.1 led elecical characteristic (t = 25 ° c) can be seen from the table 2.1, although the deviation of each led are not too large, but when the led in series, the total deviation can not be ignored. par lamps may be more than the actual power of 9w or less than 9w, directly reflected in the maximum brightness of the lamp is rated or not to be brighter than the rating. when the par lamp when the actual power of less than 9w, and drive the output power is still 9w, then the current flowing through the led has been over rated, long-term work on the led's life and color will have a certain effect. in addition, even if there is no bias led factory, as shown in figure .
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