# Two types of circuit for power conversion (Dc/dc,ldo)

Source: Internet
Author: User

First, the principle of DC circuit

(1) Buck type converter

Brief analysis: During the opening of the switching tube s, the current is charged to the capacitance C through the switch tube and inductance.

When the switching tube s is off, the filter capacitance C is charged to r, because the inductor current cannot be mutated, through the RC circuit, D discharge

Brief calculation:

When the switch tube is on, there is

Reduction can be obtained inductance current L i= (VIN-VO) DTs (d for switch tube duty ratio, TS for switching frequency)

When the switching tube is turned off, there is

Reduction can be obtained inductance current L i=vo (1-d) Ts

by the law of the Volt-second, you can get Vo=dvin

(2) Boost type converter circuit

Brief analysis: During the opening of the switching tube s, the output voltage has a filter capacitor C power supply, the input current to the inductance L charge

During the switching-off period, the current is charged with the capacitance C through inductance L, diode D

Brief calculation:

When the switch tube is on,

Simplification: L I=vindts

When the switch is turned off, the Vin-vo

Simplification: L i= (VIN-VO) (1-d)

Vo= disadvantage due to the volt-second law: High switching frequency leads to low power supply noise

Second, the Ldo circuit

Ldo:ldo is the abbreviation for low dropoutvoltage regulator, which is the lower dropout linear regulator

Features: Less peripheral circuit, no inductor, small footprint,

Schematic diagram:

Brief analysis: The sampling voltage is added to the comparator A's co-phase input, compared with the reference voltage uref at the inverting input, the difference between the two is amplified by amplifier A to control the pressure drop of the series adjustment tube, thereby stabilizing the output voltage. When the output voltage uout is lowered, the difference between the reference voltage and the sampled voltage increases, the drive current of the amplifier output is increased, and the pressure drop of the series adjustment tube decreases, thereby increasing the output voltage. Conversely, if the output voltage uout exceeds the desired setpoint, the output voltage is reduced by comparing the front drive current of the amplifier output to a lower value. During power supply, the output voltage correction is continuous and the adjustment time is limited only by the reaction speed of the comparator amplifier and output transistor circuit.

Disadvantage: Low efficiency, the output current is about equal to the input current. Supplementary: When the linear power supply is operating in the case of large voltage, high current, because of the presence of the switch tube pressure drop, loss of power is very large, general efficiency is not high

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