Research And Design Of Constant Current Intrinsically Safe Switching Power Supply

With the rapid development of coal industry, more and more electrical equipmentis applied to the coal mine, at the same time, higher requiements are put forword forsafe use of electrical equipment. As the core of electrical equipment, the safety ofpower source is very important and it must meet the requirments of anti-explosivem,intrinsical safety is the optimal means for anti-explosive. As the fourth-generationlighting, LED lighting has broad application prospects in the coal mine. In order toobstain the desired brightness requiements and ensure consistency of brightness andchromaticity for multiple LEDs, constant current driving is needed. However, atpresent, intrinsically safe switching power supply with constant voltage output ismostly researched which is not suitable to dirve LED, so the research of constantcurrent intrinsically safe switching power supply has important academic significanceand practical application value.First, working principle and working modes of constant current flybackconverter were analyzed, critical inductance values and output ripple current underdifferent working modes were derived. Through analyzing output ripple currentwithin the whole dynamic operating region, the minimum inductance value wasobtained which made the maximum output ripple current get the minimum value.Energy transmission process of flyback converter in case of output short circuit modewas analyzed. The most dangerous output short circuit moment and the maximumoutput short circuit discharge energy were obtained. Bsaed on the minimum ignitionvoltage curve of capacitive circuit, intrinsically safe performance of the converter isevaluated.Following, means of improving the power of intrinsically safe converter wereanalyzed including chaging output characteristics of source, decreasing equivalentinductance value or capacitance value and shorting spark discharge time. Against themeans of decreasing equivalent inductance value or capacitance value, mathematicalmodel of different distinct circuits were built. Spark current, spark power and otherrelated expressions were decuced. Then simulate the circuit with mathematicalanalysis software Mathcad to verify validity of means. Analysis of means ofimproving the power was useful for designing large-capacity intrinsically safeswitching power supply.Then, over design of constant current intrinsically safe switching power supply was given including main circuit, control circuit and output protection circuit.Transformer and output filter capacitor were designed combined electric performanceparameters with intrinsically safe performance parameters; using LM358to realizeconstant current controlling and output over-voltage controlling; current rate ofchanging detection and totem pole driver were selected for the output protectioncircuit to speed up the protection speed which can shorten spark discharge time so asto improve the power of intrinsically safe conver.At last, system hardware platform was constructed. The results of simulation andexperiment verified the correctness and validity of theory and design.