When establishing industrial power source, a the commonnest challenge is alternating voltage power source changeover is volts d.c. power source. Almost all application needs volts d.c. of alternating voltage instead, from the small controller power supply that charges to be microwave oven for the mobile phone it is such. Will tell normally, have this kind of transition through using transformer and commutator, if pursue,1 is shown. In this circuit, through transformer step-down (one times at transformer primary with secondary coil v/LIT all over the ground number compares) .
Graph 1: Use transformer and LDO simplify AC is changed to DC
The solution has magnetism a few defect. You may know transformer to work through be flux changeover electric current. As a result of this kind of changeover, transformer can produce a large number of electromagnetism to disturb (EMI) . The output voltage of transformer is extremely noisy also, need large electric capacity comes filter divides noise. To low power application, can use simpler and the method with effective cost will remove magnetic element. Like how forming a voltage divider as two resistor, you can use capacitor to produce communication impedance (reactance) , its reduce tension before voltage reachs power supply. This kind of configuration calls capacitance pressing to fall normally solution.
Did not put through when load when, basic capacitor is pressed fall the electricity that the solution needs stabilized voltage diode to absorb applied place to need. Diode of this stabilized voltage is indispensible, because of this linear manostat (the input voltage of LDO) won’t exceed absolutely the biggest rating.
Graph 2: The form of primary electric capacity that takes LDO is pressed fall circuit, apply to 110 VAC, 5 VDC and 30 MA
Capacitance type is pressed fall develop attacks a defect of the structure is efficiency not tall, because a lot of power are met abreaction as the quantity of heat of resistor and LDO. Although LDO is not pressure regulating, but the energy that because stabilized voltage diode is medium,wastes, efficiency is not ideal still.
To improve the efficiency of this system, you need to optimize diode of resistor of surge of —— of 3 main component, stabilized voltage and LDO pressure fall. Formula shows the primary electric capacity that to how be calculated the graph shows 2 times 1 times to press fall the efficiency of the solution.
Because capacitance pressing falls,the solution is an electron metric the common power source configuration in waiting for industrial application with factory automation, because apparatus of this heart state developed dedicated at optimizing capacitance pressing to fall framework efficiency is mixed the component of solution dimension. TPS7A78 is compositive a lot of implementation capacitance type are pressed fall the discrete element that circuit place requires, be like active bridge-type commutator. TPS7A78 falls to use capacitance to press only circuit and design, but compositive a variety of functions, improve integral system efficiency. For example, TPS7A78 is compositive class of capacitance of a switch, can reduce input tension fourfold, reduce input electric current with same percentage thereby, conduce to use smaller electric capacity to press fall capacitance. This function can realize smaller solution size, reduce systematic cost and reduce bide one’s time power comsumption.
Graph 3: Use TPS7A78 is pressed in the 30mA capacitance when 30mA fall solution
The efficiency that demotes to go up with linear manostat is pressed in capacitance to understand use TPS7A78, the TPS7A78 solution that the traditional solution that we can show the picture 2 times and graph show 3 times undertakes comparative. In what use linear manostat tradition pressing falls in the solution, systematic efficiency is 11% . When configuration is same and laden power supply, because the input electric current of switch capacitance is reduced, and the surge resistance with less need, TPS7A78 can come true>The efficiency of 40% .