MC33463 Просмотр технического описания (PDF) - ON Semiconductor

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MC33463

Variable Frequency Micropower DC-to-DC Converter

ON Semiconductor 

MC33463

MMBT2222ALT1

Startup Circuit

1.5 k

3.3 V

Vin

MMBT2907ALT1

1.0 k

100 µF

100

3

Lx

VO

MC33463H–33KT1

VLx Limiter

Drive

VFM

Controller

100 kHz

Oscillator

Vref

2

Output

100 µF

1 Gnd

Figure 21. Flyback Application

Calculation

Step–Down

Step–Up

Flyback

ton

D

D

fosc

fosc

L

ƪ ƫ t ton

(Vin * Vsat * VO)

(2IO)

t (n)(Vin)2(ton)

PO

D

fosc

t

(n)(Vin)2(ton)

PO

IL(avg)

IL(pk)

Vripple(pp)

IO

(Vin * Vsat * VO)(ton)

L

1

2

2

ȧȱȲǒ Ǔ ȳȴȧ DIL

1

16foscCO

) (ESR)2

Iin

(Vin * Vsat)(ton)

L

[ (ton)(IO)

(CO)

Iin

(Vin * Vsat)(ton)

L

[ (ton)(IO)

(CO)

The following converter design characteristics must be chosen:

Vin – Nominal Operating dc input voltage

VO – Desired dc output voltage

IO – Desired dc output current

Vripple(pp) – Desired peak–to–peak output ripple voltage. For best performance the ripple voltage should be kept to a low value

since it will directly affect line and load regulation. Capacitor CO should be a low equivalent series resistance (ESR) electrolytic

designed for switching regulator applications.

1. Vsat – Saturation voltage of the switching transistor.

n – Estimated circuit efficiency.

Figure 22. Design Equations

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