Current trend of design of LED drive power source, use capacitance step-down principle to finish the product that drive circuit designs, had established firm calcaneal in the market gradually. Introduce the product of LED power source of this kind of design, all have better stability, and cost is expended inferior. In today’s article, we will spread out brief analysis and introduction with respect to the capacitance step-down principle in LED drive power source.

 

In the circuit of LED drive power source that use capacitance step-down principle and makes, following plan institute show the block diagram of its step-down principle. When U(of alternating current source of a sine here is with the commonnest 220VAC, 50HZ exemple) when bringing to bear on to go up in capacitance circuit, capacitor the charge on two plate, the electric field between plate is the function of time.

That is to say: The virtual value of electric current of the voltage on capacitor and amplitude follow Ohm’s law likewise. The voltage amplitude that is added on capacitance namely is certain, when frequency is certain, can have shed the Ic of sine alternating current of a stability. Value of smaller electric capacity jumps over capacitive reactance big, the electric current that has shed capacitor is bigger, establish ties on capacitor an appropriate load, can get a voltage source that reduce, can pass rectification, filter wave, stabilized voltage output. An issue that the attention needs here is, in this circuit system, capacitance just takes in and send out in large quantities in circuit energy, and do not waste energy, the efficiency of capacitance step-down circuit is very so tall.

 

Block diagram of principle of step-down of capacitance of LED drive power source

 

Normally the circumstance falls, use the LED power source that capacitance step-down principle designs, its main drive circuit will be mixed by wave of filter of step-down capacitance, current limliting, commutate the circuit composition such as stabilized voltage billabong. Among them, step-down capacitance is equivalent to the step-down transformer in circuit of common stabilized voltage, in receiving return of alternating current source directly, bear almost U of all alternating current source, should choose the metallic film capacitance that does not have polarity.

Adding up to the instant of electrify source, be U likely or the peak that loses half weeks – peak value, instantaneous electric current will be very right now big, because this needs to establish ties in loop resistor of a current limliting, in order to assure the safety of circuit, this is the main reason with current limliting indispensable circuit. The design of part of circuit of rectification filter wave asks, the requirement with circuit of common dc regulated power supply is identical. And need circuit of stabilized voltage billabong, because voltage step-down loop is medium,be, I of voltaic virtual value is stable, do not suffer the effect that load current size changes, because this is in stabilized voltage circuit, want to have billabong return, change in order to answer the size of load current.