Led converter circuit

At this time, the total on voltage is increased, resulting in very low power factor. When the current limiting resistor is connected in series, the number of LEDs in series is reduced and the power factor is improved, but the efficiency will be reduced because of the current limiting resistor. In order to solve the problems of low power factor and efficiency of AC LED and improve the frequency shown by the load structure, a new topology circuit of AC LED converter is proposed, and the topology circuit and control method are analyzed and studied.

In order to improve the power factor, Buck PFC circuit is used to correct the current waveform in this paper. The output voltage of Buck PFC circuit is converted into AC signal through half bridge converter, which is used as the input voltage of later stage LCC circuit and supplied to load led lamp.

As can be seen from Fig. Therefore, the capacitance has no impact on the life of the whole topology circuit; The fundamental frequency of the input and output AC voltage of the LCC resonant circuit is Hz, so the voltage frequency of the load led is also Hz, and the voltage flicker cannot be seen at this frequency.

I is the effective value of sinusoidal input current. From the relationship between the input voltage and output voltage of the converter:. For double transistor forward circuit, the relationship between primary side current and secondary side current of transformer is as follows:.

When the inductive current works in the continuous conduction mode CCM mode , the current ripple is:. Next, we analyze the calculation method of LCC parameters. Through the complementary conduction of switching tubes S2 and S3, the input of LCC resonant circuit is AC, and the working state is shown in Figure 2.

Von is the series on voltage of Because of the load shedding and lightning induction, all kinds of surges will be invaded from the power grid, and some surges will cause LED damage. Therefore, the analysis of the driving power of "Zhongke Hui Bao" should be deficient in surge protection.

As for the frequent replacement of power and lamps, the LED driver should have the ability to suppress the surge and protect the LED from being damaged. To meet the requirements of safety and electromagnetic compatibility, it is best to increase the LED temperature negative feedback in the constant current output, in addition to the conventional protection.

According to the driving mode, the common market-led lamp driver is divided into two kinds. One is constant current drive. The characteristic of a constant current drive is that the output current is constant. The output voltage is changed in one range. This means that the output voltage is in one of the output voltages.

The range, the current is how many ma. The output current of the constant current drive circuit is constant, but the output DC voltage varies in a certain range with the different sizes of the load. The load resistance is small, the output voltage is low, the greater the load resistance is, the higher the output voltage is. Constant current circuit is not afraid of load short circuits, but it is strictly forbidden to load fully open. The constant current drive circuit is ideal for driving LED, but relatively speaking, the price is higher.

Attention should be paid to the maximum withstand current and voltage used, which limits the number of LEDs used. And the other is the constant voltage drive. The constant voltage driving characteristic is that the output voltage is fixed, and the current is limited to the maximum value with the change of the lamps and lanterns.

The most common output voltages in the led market are 5V, 12V, 24V, and so on. When the parameters in the voltage stabilizing circuit are determined, the output voltage is fixed, whereas the output current varies with the increase or decrease of the load.

The voltage stabilizing circuit is not afraid of load opening, but load short circuits are strictly forbidden. A regulated drive circuit powers the LED. Each string requires a proper resistor to average the brightness of each string LED. The rectified voltage changes will affect the brightness. The input voltage and current are the two most important parameters.

The propagation lamp comes with a separate explanation on how to calculate the input voltage and current of the LED lamp. This is only a description of the LED lamp's input. People will be able to see the original driving parameters be sure to identify some driving false targets!!! We select the corresponding LED driver based on the lamp board's input voltage and current. For example, if the lamp board's input voltage is V and the input current is mA, the LED driver output voltage can be selected to include it, and the current is nearly the same.

The formula surface, as well as the voltage greater or lesser than all, must be included. Otherwise, there will be flickering. Low current is acceptable. Finally, we only need to press the positive and negative pole marked by the lamp plate to weld the drive or connection line.

It is necessary to note that the conventional LED-driven output line, the red is the positive pole. The black is the negative pole If it is a gray line, then the gray is the positive pole, the white is negative Blue brown line, the blue line is the negative pole, the blue line is the negative pole and so on Figure 1.

Let's see a video about how to make an LED driver:. How to Make a LED driver. Charge Pump Circuit. The charge pump circuit uses the accumulation effect of the capacitor on the charge to store electrical energy. It uses the capacitor as an energy coupling element and controls the power electronic device to perform high-frequency switching, allowing the capacitor to store energy during a part of a period, and the capacitor releases energy during the remaining time. This kind of circuit obtains different output voltages through different connection modes when the capacitor is charged and discharged, and the whole circuit does not need any inductance.

The charge pump circuit is relatively small, with fewer components, and lower cost. However, it uses relatively many switching elements. Under the condition of a certain input voltage, the range of output voltage change is relatively small. The relationship between the voltage and the input voltage changes.

When there are multiple LEDs, they must be driven in parallel. To prevent uneven current distribution in the branch, a ballast resistor must be used, which will greatly reduce the efficiency of the system. Switch Power Circuit. From the circuit point of view, compared with the charge pump circuit, it contains magnetic components, that is inductor or high-frequency transformer.

The switching power supply circuit can achieve a wide range of voltage output, and the output voltage is adjustable continuously, the output power is large, so the application range is wider, especially in the medium and large power situations. Linear Circuit. The linear control circuit regards the semiconductor power device working in the linear region as a dynamic resistor and realizes constant current drive through its control level control.

The disadvantage of the linear control circuit is low efficiency, but it has a fast response to the input voltage and load change. The circuit is relatively simple.

It is easy to control the current of LED directly, and it is easy to control the high precision of the current. The actual feedback control of the switching power supply is the output voltage, and the output current control is not easy to be accurate, and the LED lamp is easily damaged when the control of the switching power supply is biased; the efficiency of the linear circuit is not high. Based on the above reasons, a novel LED drive circuit is designed.

The circuit uses a single-end flyback switching power supply as the front stage control, and the linear pressure control constant current source is used as the post level control. After converting the single-ended flyback power supply, the DC voltage output can be obtained, which is used as the input of the post-stage voltage-controlled constant current source.

Because the input voltage of the constant current source is controlled by a high-efficiency single flyback switching power supply, the pressure control constant current source can accurately control the LED and can change the input voltage of the constant current source in a large range, so the efficiency and precision are guaranteed, and the power supply can be supplied by the city. At the same time, the two-level control is not easy to damage the LED lamp.

Figure 2. Novel Driver Circuit Design. The system circuit is shown in Figure 2. The transformer T1, the switch tube Q1, the diode D1 and the capacitor C1 constitute the single end flyback switching power supply, and the operational amplifiers U1, U2 and power transistor Q2 constitute the pressure controlled constant current source, and the MCU STC89C51 is the core control device.

When the gray value changes, the microcontroller generates a corresponding brightness control voltage based on the gray value obtained. The brightness control voltage is added to the same phase input of U1.

The output voltage of the U1 is the control voltage of the MOS tube Q2, which is known by the concept of the operational amplifier's deficiency. The reverse input voltage of the U1 is equal to the voltage on its forward input, that is, the current on the R12 is controlled by the brightness control voltage, and does not change with the change of the load. Single-chip produces a corresponding luminance control voltage according to the gray value it gets, and also produces a PWM signal.

Then the MCU changes the duty ratio of the PWM signal according to the LED current signal obtained and changes the output voltage of the switching power supply , that is to change the constant. The input voltage of the flow source reduces the voltage on the power tube Q2, so that it works in the adjustable resistance zone or near the adjustable resistance zone in the case of the constant output current, in order to improve the efficiency.

TL is the three-terminal adjustable shunt reference, where the existence of TL and its corresponding electric phase is to limit the maximum output voltage of the switching power supply and further improve the security of the system.

When the light is relatively good, the MCU controls the output of the luminance control voltage according to the gray value obtained, so that the output current of the constant current source is relatively small, and the energy-saving effect can be achieved. The design of an LED driver is not difficult, but we must have a good idea. As long as we do debug before calculation, debugging and aging after debugging, we believe that anyone can do well in LED.

As for the impact, there is no specific indicator yet. This is mainly for the high-voltage driver chip with a built-in power modulator, which not only reduces the power consumption of the chip but also does not introduce additional power consumption for heat dissipation.

The power consumption of the power tube is divided into two parts, switching loss and conduction loss. LED is an electric drive application, and the switch damage is much larger than the conduction loss. The switching loss is related to the CGD and CGS of the power pipe and the driving ability and working frequency of the chip. So solving the heat problem of the power pipe can be solved from the following aspects:.

MOS power tube can not be selected based on the size of the conduction resistance. The rest is frequency and chip drive capability. Here we only talk about the influence of frequency. Nowadays, companies rate bulbs through lumens as these give you a more accurate indication of how much light to expect from an LED.

Watts do not measure brightness but the amount of power used. My Account Log In Register. Lumens and Wattage Light bulbs bring objects to life, different lighting temperatures set the mood, they make it safer to walk across spaces and can even decorate and highlight specific locations.