LED drive "application" problems and solutions
LEDs are widely used in E27, GU10, PAR lamps, MR16 and other fields. However, in the application of electronic transformer-driven LED-MR16, there are some problems. This is mainly caused by four reasons: First, the normal power of the MR16 lamp cup for LED is only 5W. The magnetizing current generated in the half-bridge circuit cannot saturate the internal transformer, and the electronic transformer works in an abnormal state. Second, MR16 has a large electrolytic capacitor after the rectifier bridge, which is equivalent to the load of the electronic transformer from the original pure group load to a large capacitive load. Third, in a 5W application, a capacitor larger than 487 (uF) is required for the Buck circuit to work properly. Such a large capacity capacitor is not possible in a very demanding MR16 lamp cup. Fourth, the output voltage of the electronic transformer is not a sine wave. It is a triangular-like wave with a minimum of 5.6V. If the working voltage cannot reach 5.6V or lower, a larger filter capacitor is needed, otherwise the LED output current will be lower at VCE. When the chip's operating voltage drops to zero, there may be a low frequency flicker of 100 Hz or a regular flicker of the time interval determined by the peripheral components of the IC's COMP pin. In view of the status quo of the above industries and the reasons for the flashing, we recommend the RICHTEK8479 solution, which is a Two-StageTopology (Boost+Buck) architecture, and has a wide operating voltage of 4.5Vto36V, which can easily solve the flash phenomenon and achieve stability. Output current and illumination. The power scheme adopts a 2-stage architecture, that is, after the voltage input from the electronic transformer is subjected to fast recovery rectification, the voltage is boosted, the voltage is raised to a constant voltage of about 20 V, and then passed through the second-stage circuit, and The buck conversion is performed in a step-down constant current mode to keep the output current constant over a certain output voltage range. Since the IC has two MOS tubes built in, the peripheral circuit is compact and simple, and since the scheme adopts a boosting structure, the input terminal does not need to use a large-capacity electrolytic capacitor to stabilize the input voltage, which is very suitable for application in the MR16 base, etc. Space is small. This power supply can achieve a good constant current effect from a wide input voltage range of 8V to 19V, regardless of AC or DC input status. LED-MR16 spotlights will replace the halogen spotlights. The electronic transformer-driven power supply solution for the M7-MR16 spotlight explores a way to achieve a very compatible drive power supply.
The task of the managed switch is to keep all network resources in good condition. The network management switch product provides a variety of network management methods based on the terminal control port (Console), based on the Web page, and supports Telnet to remotely log in to the network. Therefore, network administrators can perform local or remote real-time monitoring of the switch's working status and network running status, and manage the working status and working mode of all switch ports in a global view.
The switch is the most important network connection device of the LAN, and the management of the LAN mostly involves the management of the switch.
There are also managed switches that provide policy-based QoS (Quality of service). Policy refers to the rules that control the behavior of the switch. The network administrator uses the policy to allocate bandwidth and priority for application flows and control network access. The focus is on the bandwidth management strategy required by the service level agreement and the way of publishing the policy to the switch. Multifunction light emitting diodes (LEDs) used to indicate port status, half duplex/full duplex and 10BaseT/100BaseT at each port of the switch, and switch status LEDs that indicate system, redundant power supply (RPS) and bandwidth utilization A comprehensive and convenient visual management system has been formed. 1U Industrial Switch,L3 Ethernet Switches,24 Port Managed Switch,Managed Industrial Switches Shenzhen Scodeno Technology Co.,Ltd , https://www.scodenonet.com
The network management switch supports the SNMP protocol. The SNMP protocol consists of a set of simple network communication specifications, which can complete all basic network management tasks, has a small demand for network resources, and has some security mechanisms. The working mechanism of the SNMP protocol is very simple, mainly through various types of messages, namely PDU (protocol data unit) to achieve the exchange of network information.