[introduction] the occasion that on power source design we use more is, stabilize from ” tall ” voltage gets one is stabilized ” low ” voltage. The DC/DC that this often says namely, the chip of power source stabilized voltage that uses more among them has two kinds, one kind calls LDO(low pressure poor linear manostat, the linear regulated power supply that says at the back of us, also be to point to its) , another kind calls PWM (power source of switch of wide modulation of arteries and veins, we also call it switch power source in the article) . The efficiency that we often hear PWM is tall, but the response of LDO is fast, is this why? Fasten anxious, let us view their principle first.

Power source is whole in circuit board a important, power supply is not steady, other what does not talk.

The occasion that on power source design we use more is, stabilize from ” tall ” voltage gets one is stabilized ” low ” voltage. The DC/DC that this often says namely, the chip of power source stabilized voltage that uses more among them has two kinds, one kind calls LDO(low pressure poor linear manostat, the linear regulated power supply that says at the back of us, also be to point to its) , another kind calls PWM (power source of switch of wide modulation of arteries and veins, we also call it switch power source in the article) . The efficiency that we often hear PWM is tall, but the response of LDO is fast, is this why? Fasten anxious, let us view their principle first.

A few academic knowledge can be involved below, but still very easy to read and understand understand easily, if you do not understand, hey, must check oneself foundation.

1, the working principle of linear regulated power supply

2, the working principle of switch power source

As above graph, to get Vo from tall voltage Vs, switch power source was used with the square wave Vg1 that occupies sky comparing certainly, vg2 drives fluctuation MOS to be in charge of, vg1 and Vg2 are in opposition, vg1 is tall, vg2 is low; When MOS canal is opened on, next MOS canals are shut; When next MOS canals are opened, MOS canal is shut on. Formed the square wave voltage that occupies sky comparing certainly in L Zun Duan from this, it is low that we can regard inductance L and capacitance C connect filter, the stable voltage Vo after because voltage of this square wave passes filter,filter wave getting after wave. Vo presses evacuation to enter an amplifier through cent of R1, R2 (error amplifier) the V+ that lose end, the output Va of error amplifier as the 2nd amplifier (PWM amplifier) carrying, the output Vpwm of PWM amplifier is one has the square wave that takes sky comparing certainly, through door logic circuit processing gets two in opposition the switch that square wave Vg1, Vg2 will come to to control MOSFET.

Of error amplifier carrying Vref is one constant tension, and the Vt losing end of PWM amplifier is signal of wave of a triangle, once Va compares trigonometry when wave is big, vpwm is tall; Va compares trigonometry wave hour, vpwm is low, because of the relation of this Va and trigonometry wave, decided Vpwm of square wave signal occupy sky comparing; Va is tall, occupy sky comparing low, va is low, occupy sky comparing tall. Through processing, vg1 and Vpwm are inphase, vg2 and Vpwm turn over photograph; eventually the Vp of square wave voltage of L Zun Duan and Vg1 are identical. Pursue as follows

When Vo rises, v+ will rise, va drops, vpwm occupies sky comparing to drop, through people after logic, of Vg1 occupy sky comparing to drop, of Vg2 occupy sky comparing to rise, vp occupies sky comparing to drop, this brings about Vo to reduce again, then the rise of Vo will be restrained. Vice versa.

3, comparative and linear regulated power supply and switch power source

After the working principle that understood linear regulated power supply and switch power source, we are OK and clear why linear regulated power supply has lesser noise, swifter transient state is answered, but efficiency is poor; And noise of switch power source is bigger, transient state is answered slower, but efficiency is tall.

Structure of interior of linear regulated power supply is simple, feedback annulus way is short, noise is accordingly little, and transient state is answered fast (when should outputting voltage to change, compensation is fast) . But press difference to fall on MOSFET entirely because of what input and output, its efficiency is so low. Accordingly, linear stabilized voltage is used in small electric current commonly, on tall to voltage precision requirement application.

And switch power source, internal composition is complex, the factor that affects performance of output voltage noise is very much, and way of its feedback annulus is long, because of this its noise function under linear regulated power supply, and transient state is answered slow. But the structure according to switch power source, MOSFET is in leave completely and close two kinds of position completely, besides drive MOSFET, besides the energy that with him MOSFET internal resistance wastes, other energy is used in output entirely (theoretic L, C is not of energy consumption, although be not actually such, but the energy that these using up is very small) .

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