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High power drive controller The most common lamp in life is led lamp, but few people know that led lamp needs LED driver. The following is a guide to understand the relevant knowledge of LED driver controller. On May 29, Current Logic announced the release of the AL1665 single-stage flyback and buck-boost controller for commercial, online, dimmable LED lighting installations that can operate up to 100 W. Designed to drive external MOSFETs to control LED loads and maintain high power factors, the AL1665 also provides a small, high-efficiency solution that helps minimize additional components and maintain high switching efficiency. LED driver The AL1665 is designed for AC 1nput voltages between 85VAC and 305VAC and uses a primary side regulation (PSR) topology without optical isolation or a secondary side controller. Developers can use PSR to design smaller solutions with less PCB area and lower material costs while providing constant current regulation for the highest power LED lighting product applications. Dimmable fr0m 0.5% to 100% of high power output, the AL1665 is suitable for commercial LED product applications where lighting output levels can be adjusted for aesthetics or power savings, such as retail displays. The output voltage is compatible with ANSI approved dimmers and can be adjusted fr0m 0 V to 10 V using a dedicated PWM output or fr0m 0 V to 2.5 V using an analog 1nput voltage, simplifying the development of online lighting systems for local and remote management. The device uses boundary condition mode (BCM) switching and valley switching to significantly reduce losses and provide high efficiency at low EMI. The wide supply voltage allows the AL1665 to operate directly fr0m the mains in any region with line and load regulation of less than ± 2%, a power factor greater than 0.9, and a THD of less than 20%, enabling manufacturers to comply with all relevant regulations. The above is the relevant knowledge about LED driver chip DC-DC converter Power supply crossing frequency 1. Flyback power supply When choosing a system topology that can produce multiple outputs fr0m a single supply, a flyback power supply is a wise choice. Since the voltage on each transformer winding is proportional to the number of turns in that winding, each output voltage can be easily set by the number of turns. Ideally, if you adjust one of the output voltages, all the other outputs will scale by the number of turns and remain stable. 2. How to Improve the Cross Regulation Ratio of Flyback Power Supply In the real world, the parasitic components work together to reduce the load regulation of the unregulated output. I'll look further at the effects of parasitic inductance and how synchronous rectification can be used instead of diodes to dramatically improve the cross-regulation of flyback power supplies. For example, a flyback power supply can produce two 12V outputs of 1 A each fr0m a 48 V 1nput, as shown in the simplified simulation model of Figure 1. The ideal diode model has zero forward voltage drop and negligible resistance. The transformer winding resistance is negligible and only the parasitic inductance in series with the transformer leads can be modeled. These inductances are the leakage inductance in the transformer and the parasitic inductance in the printed circuit board (PCB) traces and diodes. When these inductors are set, the two outputs track each other because the full coupling of the transformer forces the two outputs to be equal when the diodes conduct during the 1-D portion of the switching cycle. Now consider what happens when you introduce a leakage inductance of 100 nH into the two secondary leads of the transformer and a leakage of 3 μH in series with the primary winding. These inductances can create parasitic inductances in the current path, including leakage inductances inside the transformer and inductances in the PCB and other components. When the primary FET is turned off, current still flows through the primary leakage inductor, and the secondary leakage inductor is turned on for a 1-D period with an initial condition of 0 A. A pedestal voltage appears on the transformer core and is common to all windings. This pedestal voltage ramps down the current in the primary leakage to 0 A and ramps up the secondary leakage current to deliver current to the load. When the two outputs are heavily loaded, the current continues to flow for the entire 1-D cycle and the output voltages are well balanced However, when one heavily loaded output and another lightly loaded output, the output capacitance on the lightly loaded output tends to peak charge fr0m the pedestal voltage; Because the current quickly goes back to zero, its output diode will stop conducting. See the waveform in Figure 3. The peak charging cross-regulation effects of these parasitic inductances are typically much worse than those caused by the rectifier forward voltage drop alone. Synchronous rectifiers help alleviate this problem by forcing current into both windings for the entire 1-D cycle, regardless of load. but with an ideal synchronous rectifier instead of an ideal diode. Since the synchronous rectifiers remain in good condition after the pedestal voltage drops, the two output voltages track each other well, even in the presence of a severely unbalanced load. Although the average current of the secondary 2 is very small, the root mean square (RMS) content can still be quite high. This is because, unlike the ideal diode in fig. 3, the synchronous rectifier can force a continuous current flow during the entire 1-D cycle. Interestingly, the current must be negative for most of this period to guarantee a low average current. Obviously, you are sacrificing better regulation to achieve a higher circulating current. However, this does not necessarily mean that the total loss will be higher. The forward voltage drop of a synchronous re DC-DC converter Common faults (1) Fuse blown In general, a blown fuse indicates a problem with the internal wiring of the power supply. Because the power supply works in the state of high voltage and large current, the fluctuation and surge of the grid voltage will cause the current in the power supply to increase instantaneously and cause the fuse to melt. The rectifier diode, high-voltage filter electrolytic capacitor and inverter power switch tube at the 1nput end of the power supply should be checked for breakdown, open circuit and damage. If the fuse is indeed blown, you should first check the various components on the circuit board to see if the appearance of these components has been burned and if there is electrolyte overflow. If the above situation is not found, use a multimeter to measure whether the switch tube has a breakdown short circuit. Special attention should be paid to: Do not start the machine directly after replacement when a component is found to be damaged. In this way, it is very likely that the replaced component will be damaged again because other high-voltage components are still faulty. It is necessary to conduct a comprehensive inspection and measurement of all high-voltage components in the above circuit before completely eliminating the fuse failure. (2) No DC voltage output or unstable voltage output If the fuse is intact, there is no output of DC voltage at each stage under load. This situation is mainly caused by the following reasons: open circuit and short circuit in the power supply, overvoltage and overcurrent protection circuit failure, auxiliary power supply failure, oscillation circuit does not work, power supply load is too heavy, rectifier diode in high-frequency rectifier filter circuit is broken down, filter capacitor leakage, etc. After measuring the secondary component with a multimeter and eliminating the breakdown of the high-frequency rectifier diode and the short circuit of the load, if the output is zero at this time, it is certain that the control circuit of the power supply is out of order. If there is a part of voltage output, it means that the front circuit is working normally, and the fault is in the high frequency rectifier and filter circuit. The high-frequency filter circuit is mainly composed of rectifier diodes and low-voltage filter capacitors to output DC voltage, in which the breakdown of rectifier diodes will cause no voltage output of the circuit, and the leakage of filter capacitors will cause unstable output voltage and other faults. The damaged component can be checked by measuring the corresponding component statically with a multimeter. For example, when a 24V DC motor power supply is powered on, there is no 24V DC output. Disassemble the power supply shell, observe that the fuse is not burned out and the circuit board has no obvious scorched or broken components. When it is not powered on, measure the AC 1nput resistance and DC output resistance to be normal, and measure the switch tube, rectifier bridge, rectifier tube and other important components to be normal. Therefore, it is judged that there is no possibility of serious internal short circuit, and it is estimated that the protection circuit acts. Maintenance Skills and Common Faults of DC-DC converter Switching power supply is a kind of power supply which uses modern power electronics technology to control the time ratio of switching transistor on and off to maintain a stable output voltage. It is widely used in industry, military, scientific research, communication, medical treatment and various household appliances. The development and application of switching power supply is of great significance in saving energy, saving resources and protecting the environment. Let's take a look at the circuit diagram and maintenance skills of the switching power supply. The main circuit of switching power supply is composed of 1nput electromagnetic interference filter (EMI), rectifier filter circuit, power conversion circuit, PWM controller circuit and output rectifier filter circuit. Auxiliary circuits include 1nput over-voltage and under-voltage protection circuit, output over-voltage and under-voltage protection circuit, output over-current protection circuit and output short-circuit protection circuit. Maintenance Skills and Common Faults of Switching Power Supply 1. Maintenance skills The maintenance of switching power supply can be divided into two steps: "Look, smell, ask and measure" in case of power failure Look: Open the shell of the power supply, check whether the fuse is blown, and then observe the internal situation of the power supply. If there is a scorched part or a broken component on the PCB board of the supply, you should focus on checking the components here and related circuit components. Smell: Smell whether there is a burning smell inside the power supply, and check whether there are burnt components. Q: Ask how the power supply was damaged and whether there was any illegal operation on the power supply. Measure: Measure the voltage at both ends of the high-voltage capacitor with a multimeter before powering on. If the fault is caused by the failure of the switching power supply to start oscillation or the open circuit of the switching tube, in most cases, the voltage across the high-voltage filter capacitor is not discharged, and this voltage is more than 300 volts, so be careful. Use a multimeter to measure the forward and reverse resistance at both ends of the AC power line and the charging condition of the capacitor. The resistance value should not be too low, otherwise there may be a short circuit inside the power supply. Capacitors shall be capable of being charged and discharged. Disconnect the load, and measure the resistance to ground of each group of output terminals respectively. Under normal conditions, the meter pointer shall have capacitor charging and discharging swing, and the last indication shall be the resistance of the discharge resistor of this circuit. Power-on detection After the power is turned on, observe whether the power supply burns the fuse and individual components smoke. If so, cut off the power supply in time for maintenance. Measure whether there is 300V output at both ends of the high voltage filter capacitor. If there is no output, check the rectifier diode and filter capacitor. Measure whether there is output fr0m the secondary coil of the high-frequency transformer. If there is no output, check whether the switch tube is damaged, whether it starts to oscillate, and whether the protection circuit acts. If there is output, check the rectifier diode, filter capacitor, and three-way voltage regulator tube at each output side. Some general rules of thumb for reducing winding leakage inductance Some general rules of thumb for reducing winding leakage inductance are longer windings, closer to the core, tight coupling techniques between windings, and close turn ratios (e.g., close to 1:1). For E-E cores, which are commonly used in DC-DC converters, the leakage inductance is expected to be 3% to 5% of the winding inductance. In an off-line converter, the leakage inductance of the primary winding may be as high as 12% of the winding inductance if the transformer is to meet stringent safety regulations. The tape used to insulate the windings makes them shorter and keeps them away fr0m the core and other windings. As will be seen later, additional losses due to leakage inductance can be exploited. In DC magnet applications, an air gap is generally required along the magnetic path of the core. In a ferrite core, the air gap is in the middle of the core, and the flux flows fr0m one end of the core to the other, although the flux lines diverge fr0m the center of the core. The presence of the air gap creates a dense region of magnetic flux that causes eddy currents to flow in the metal parts adjacent to the coil or close to the air gap. This loss is generally not very large, but it is difficult to determine. Overview of the Main Parasitic Parameters in Switching Power Supplies Parasitic parameters are unexpected electrical characteristics of the actual components inside a circuit, which typically store energy and react on their own components to produce noise and losses. It is a great challenge for designers to identify, quantify, minimize, or exploit these reactions. In the case of AC, the parasitic characteristics are more obvious. Inside a typical switching power supply, there are two main nodes with large AC values. The first is the collector or drain of the power switch. The second is the anode of the output rectifier. We must focus on these two special nodes. Main parasitic parameters in the converter There are some common parasitic parameters in all switching power supplies, and their influence can be clearly seen when observing the waveforms of the main AC nodes in the converter. Some of these parameters, such as the parasitic capacitance of the MOSFET, are even given in the data sheet of some devices. The main parasitic parameters of the two common converters are shown in Figure 3. Some parasitic parameters are well defined, such as the capacitance of a MOSFET, while other discrete parasitic parameters can be expressed as lumped parameters, making modeling easier. It is very difficult to try to determine the value of those parasitic parameters that are not clearly defined, and they are usually determined by an empirical value. In other words, in the design of soft switching, the se1ection of components is based on the principle of obtaining the best results. It is important to place the parasitic components in the right place in the circuit diagram Next Page |
