The micropower power chips available on the market have the following control modes: PFM, PWM, chargepump, FPWM, PFM/PWM, and pulse-skipPWM, digitalPWM Common among them are PFM, PWM, chargepump and PFM/PWM. 1. PFM is a technique for realizing regulated output by adjusting the pulse frequency (ie, the operating frequency of the switching tube). Its pulse width is fixed and the internal oscillation frequency is varied, so filtering is more difficult than PWM. However, the PFM is limited by the output power and can only provide a small current. Therefore, PFM mode control can be adopted when the output power requirement is low and the static power consumption is low. 2. The principle of PWM is that in the case of input voltage, internal parameters and external load changes, the control circuit performs closed-loop feedback by the difference between the control signal and the reference signal to adjust the conduction pulse width of the internal switching device of the integrated circuit, so that the output The voltage or current is stabilized by the control signal. The switching frequency of the PWM is generally a constant value, so it is easier to filter. However, due to the influence of the error amplifier, the loop gain and response speed are limited, especially the loop gain is low, which is difficult to use for the LED constant current drive. Although many products currently use this scheme, there is a constant current problem. PWM mode control can be used in applications where the output power is large and the output noise is low. 3, chargepump charge pump solution is to use a discrete capacitor to send power from the input to the output, the entire process does not require the use of any inductor. The main disadvantage of chargepump is that it can only provide a limited voltage output range (the output generally does not exceed 2 times the input voltage), because when multi-stage chargepump is cascaded, its efficiency is significantly reduced. When driving more than one white LED with a chargepump, it must be driven in parallel, so it is only suitable for applications where the input and output voltages are not much different. 4, using DigitalPWM (digital pulse width modulation) through the digital management of independent digital control loop and phase, to achieve DC / DC point-of-load power conversion monitoring, control and management to provide a stable power supply, reduce the traditional power supply module The voltage amplitude causes instability of the system, and DigitalPWM does not require the use of traditional higher amounts of liquid capacitors for storage and filtering. DigitalPWM digital control technology enables the MOSFET to operate at higher frequencies, effectively mitigating the stress on the capacitor. digitalPWM is suitable for high current density, its response speed is fast, but the loop gain is still limited, and the current cost is relatively high. Therefore, its application in LED constant current driving still needs further research. 5. FPWM (Forced Pulse Width Modulation) is a constant current output based control method. Its working principle is that it always operates at a fixed frequency regardless of the output load, and the high side FET is turned on in one clock cycle. The current flows through the inductor, and the inductor current rises to produce a voltage drop across the inductive reactance. This voltage drop is amplified by a current sense amplifier. The voltage from the current sense amplifier is applied to the input of the PWM comparator and compared to the control terminal of the error amplifier. Once the current sense signal reaches this control voltage, the PWM comparator will restart the logic drive circuit that turns off the high side FET switch, and the low side FET will turn on after a delay. To operate at a light load, in order to maintain a fixed frequency, the inductor current must flow in the opposite direction through the low side FET. The FPWM technology driver chip currently only sees the chips used by MAXIM and National Semiconductor. As above, PFM and PWM use constant voltage driving to control LED, while FPWM and PFM/PWM are constant current driving mode control technology, which has proved to be more suitable for LED driving . WiFi 5 Outdoor Wireless AP is a wireless access point for outdoor environments. It is a device based on the IEEE 802.11ac standard, also known as WiFi 5. The device has a number of features and advantages that make it ideal for wireless networking in outdoor environments. WiFi 5 Outdoor Wireless AP,WiFi 5 Outdoor Wireless AP oem,the best WiFi 5 Outdoor Wireless AP Shenzhen MovingComm Technology Co., Ltd. , https://www.szmovingcomm.com
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