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Hello everyone, today we are going to learn about the working principle of PWM circuit

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The pin that controls the upper tube G pole on the PWM chip is called the upper tube drive

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The pin that controls the lower tube G pole on the PWM chip is called the lower tube drive

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Common terms for these are HDRV, DRVH, or UGATE for the upper tube drive

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and LDRV, DRVL, or LGATE for the lower tube drive

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This pin connected to the back end of the inductor is called the feedback pin

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The output of the upper tube G pole and the lower tube G pole of the PWM chip is PWM pulse

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The PWM chip outputs PWM pulses to the G poles of the upper and lower tubes

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First, let's look at the pulse at the G pole of the upper tube

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It is divided into high level and low level

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Upper tube G pole outputs high voltage level, control upper tube conduction,

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output low voltage level, control upper tube cutoff

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This high and low level can be understood as intermittent direct current

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It means that the PWM chip intermittently outputs high level to the G pole of the upper and lower tubes,

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and intermittently controls the MOS tube to turn on

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We divide the pulse into T1 and T2 periods

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And then every subsequent period we're going to repeat this T1 time and T2 time

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Firstly, before time T1, the G pole of the upper tube does not output high level,

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and the G pole of the lower tube does not output high level either

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The G poles of both the upper and lower tubes are in a low state,

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which we refer to as "dead time".

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During the dead time, both the upper and lower tubes are cutoff

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because there is no high level in the upper and lower tube G poles

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Therefore, the front end of the inductor is also dead before T1 time period

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When entering the time period T1,

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the G-pole of the upper tube changes from low level to high level,

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and the upper tube will conduct

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The G pole of the lower tube remains low,

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so the lower tube is cutoff

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At this point, because the upper tube is conducting the common point voltage through

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Therefore, the front end of the inductor is also high in time T1

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After the high level comes over, it flows to the rear stage through the inductor,

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and the inductor is in the state of charging, similar to a battery charging,

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positive on the left and negative on the right

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When entering the time between T1 and T2,

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the G pole of the upper tube changes from high level to low level,

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and the upper tube will cutoff

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After the upper tube cutoff, the current flowing through the inductor suddenly disappears

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The inductor has a reverse electromotive force, which changes from a charging state to a discharging state

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Between T1 and T2, because the G pole of the lower tube hasn't had time to go from low to high

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So the lower tube is still cutoff

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When entering the T2 period,

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the G pole of the upper tube is still low,

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and the G pole of the lower tube becomes high,

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and the lower tube is conduction

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When the lower tube is switched on, a discharge loop is formed for this inductor

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If the lower tube is not in conduction, the charge in the inductor can not be discharged

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During this discharge, the lower tube acts as a switch

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When the switch is disconnected,

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the negative terminal of the battery is not connected to the negative terminal of the load,

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so the load does not work

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When the lower tube is on, forming a discharge loop for the inductor

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Therefore, the working principle of PWM circuit,

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is by the PWM chip to meet the working conditions,

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keep the output of the tube drive pulse,

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to drive the upper tube and lower tube turn on and off,

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produce a continuous supply of power output

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The inductor is constantly charging, discharging, charging, discharging......

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The front end of the inductor is a pulse,

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and so are the G poles of the upper and lower tubes

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The back end of the inductor is a continuous direct current output

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Okay, so this is how a PWM circuit works