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71128

更新时间： 2024-11-20 22:21:51

品牌	Logo	应用领域
威世 - VISHAY		转换器
页数	文件大小	规格书
7页	76K
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Simple Solution for Dynamically Programming the Output Voltage of DC-DC Converters

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71128 数据手册

AN731

Vishay Siliconix

Simple Solution for Dynamically Programming the

Output Voltage of DC-DC Converters

INTRODUCTION

Figure1showsatypicaldc-to-dcconverterconfiguration. Asin

many PWM controllers, the non-inverting input of the voltage

feedback error amplifier is internally connected to the

reference voltage, V_r. The output voltage of the converter is set

by a resistor divider network R1 and R2. This configuration

enables a fixed output voltage that is equal to or greater than

the reference voltage. But in many power conversion designs,

it is useful to vary the output to a value lower than the reference

voltage and to dynamically adjust the output voltage. The

op-amp circuit shown in Figure 3 gives designers a simple way

to do this. Scaling the output voltage with respect to a control

voltage V_Cis totally flexible. This application note describes

how to use this simple solution and provides a step-by-step

designproceduretoassistdesignersincalculatingthespecific

parameters required by their circuits.

DESIGN REQUIREMENT

Reference voltage, V_r

Control voltage: V_C= V_C1to V_C2

Output voltage: V_O= V_O1at V_C= V_C1, V_O= V_O2at V_C= V_C2

and V_Ois linear for any value of V_Cin its range.

These design requirements are shown in Figure 2. The output

voltage is a linear function with respect to the control voltage.

The function crosses two end points A = (V_C1, V_O1) and B =

(V_C2, V_O2).

(V)

Power Stage

PWM

OUT

B (V , V

)

–

A (V , V

)

PWM Controller

(V)

FIGURE 1. Typical DC/DC Converter Configuration

FIGURE 2. Output Voltage vs Control Voltage Requirement

Power Stage

PWM

OUT

–

PWM Controller

–

LM358

Op-Amp Circuit

FIGURE 3. Op-Amp Circuit Offers Programmable Output Function

Document Number: 71128

28-Jan-00

www.vishay.com S FaxBack 408-970-5600

12 3 4 5 6 7

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