RCCN WeChat QrCode
Mobile WebSite
As far as the current domestic LED drive power design trends are concerned, products that use the capacitive step-down principle to complete drive circuit design have gradually established a firm foothold in the market. The LED power products adopting this design have better stability and lower cost. In today's article, we will briefly analyze and introduce the principle of capacitor step-down in LED drive power.
In the LED drive power circuit made by the principle of capacitor step-down. When a sinusoidal AC power supply U (here, the most common 220VAC, 50HZ) is applied to the capacitor circuit, the charge on the two plates of the capacitor and the electric field between the plates are all functions of time. In other words: the effective value and amplitude of the voltage and current on the capacitor also follow Ohm's law. That is, when the amplitude of the voltage applied to the capacitor is constant and the frequency is constant, a stable sinusoidal alternating current ic will flow. The smaller the capacitive reactance, the larger the capacitance value, and the greater the current flowing through the capacitor. A suitable load can be connected in series with the capacitor to obtain a reduced voltage source, which can be rectified, filtered, and stabilized. One problem that needs to be noted here is that in this circuit system, the capacitor only handles energy in the circuit without consuming energy, so the efficiency of the capacitor step-down circuit is very high.
Under normal circumstances, the main driving circuit of the LED power supply designed with the capacitor step-down principle will be composed of step-down capacitors, current limiting, rectification and filtering, and voltage stabilization shunt circuits. Among them, the step-down capacitor is equivalent to a step-down transformer in an ordinary voltage stabilizing circuit. It is directly connected to the AC power circuit and bears almost all the AC power U. A non-polar metal film capacitor should be used. At the moment when the power is turned on, it may be the peak-to-peak value of the positive or negative half cycle of U. At this time, the instantaneous current will be very large. Therefore, a current-limiting resistor must be connected in series in the loop to ensure the safety of the circuit. This is the current limit. The main reason why the circuit is essential. The design requirements of the rectifier filter circuit are the same as those of the ordinary DC stabilized power supply circuit. The reason why a voltage regulator shunt circuit is needed is because in the voltage step-down circuit, the current RMS I is stable and is not affected by changes in the load current. Therefore, in the voltage regulator circuit, there must be a shunt circuit to respond to the load The magnitude of the current changes.
