[Repost] Working principle and working mode of boost converter
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What is a boost converter? A boost converter is called a parallel switching converter. Unlike a buck converter, the boost inductor is at the input (switch) and the buck inductor is at the output. The output voltage Vo of a boost converter is always greater than the input voltage Vi. The explanation is relatively simple. When the switch is turned on, the diode D is turned off, and the node voltage between the inductor L and the switch is 0. When the switch is turned off, the potential across the inductor L is reversed, so the node voltage between the inductor L and the switch is greater than the input voltage Vl, and the inductor current continues to flow through the diode D, making Vo greater than Vi. It can be proved that Vo=Vi*[T/(T-Ton)], T is the switching pulse period, and Ton is the conduction time. The working principle of boost converter The main relationship and critical inductance of boost converter when working in CCM and DCM Based on whether the minimum current flowing through the inductor is zero (i.e. whether the inductor current is intermittent during the S shutdown period), the boost converter can also be divided into two modes: continuous conduction mode (CCM) and discontinuous conduction mode (DCM). For a given switching frequency, load resistance, input and output voltage, the boost converter has a critical inductance Lc. When L>Lc, the converter is in CCM: and when L The basic working principle is that when the input voltage changes, the internal parameters change, and the external load changes, the control circuit performs closed-loop feedback through the difference between the controlled signal and the reference signal to adjust the on (or off) time of the main circuit switch tube, so that the output voltage or current of the switching converter is relatively stable. To analyze the steady-state characteristics and simplify the process of deriving the formula, the following two assumptions are made: (1) The switch tube and the freewheeling diode are ideal components. That is, they can be "on" or "off" instantly, and the voltage drop is zero when "on", and the leakage current is zero when "off". (2) The inductor and capacitor are ideal components. The inductor I operates in the linear region and is not saturated, the parasitic resistance is zero, and the equivalent series resistance (ESR) of the capacitor is zero. Working mode of boost converter The boost DC-DC converter is also called the step-up converter. Its circuit topology is shown in Figure 2.1. The basic circuit of the BoostDC-DC converter consists of a power switch tube VT, a freewheeling diode VD, an energy storage inductor L, an output filter capacitor C, etc. Because the switching speed of the MOSFET tube is fast and the control logic is relatively simple, the switch tube VT generally uses a MOSFET tube. During the conduction period of the switch tube VT, the current in the inductor rises: during the cut-off period of the switch tube VT, the inductor current decreases. If the current in the inductor drops to zero during the cut-off period of the switch tube VT, and the energy stored in the inductor is also zero during the remaining time of the cut-off period, then this switching power supply is said to work in the discontinuous conduction mode (DCM); otherwise, it works in the continuous conduction mode (CCM). The following analyzes the two working modes of the boost DC-DC switching converter separately to facilitate system design. Working range of boost converter Assume that the input voltage range of the boost DC-DC switching converter is [V.min, V.max], and the load resistance range is [R min, RL.max]. On the RL-V; plane, the operating range of the switching converter corresponds to a rectangle. According to the expressions of the critical inductance Lc of CCM and DCM of each switching converter and the critical inductance Lk of CISM and IISM, the curves described by them are drawn. The RL-V; plane can be divided into two parts: CCM and DCM and CISM and IISM, as shown in Figure 2.5. It can be seen from Figure 2.5 that for Boost For DC-DC converters, the critical inductance LK of CISM and IISM has a monotonic relationship with the input voltage and load resistance, while the critical inductance Lc of CCM and DCM has a non-monotonic relationship with the input voltage and load resistance. On the RL-V plane, different inductance values will cause the Boost converter I to operate in different modes 34.12-131
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