TK11830M データシートの表示（PDF） - Toko America Inc

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TK11830M

POSITIVE-TO-NEGATIVE DC-DC CONVERTER

Toko America Inc  

TK11830

CIRCUIT OPERATION (CONT.)

POLARITY-INVERTING OPERATION

VSAT

VF

IL

IC

ILOAD

VL

Power Transistor Saturation Voltage

Diode Forward Voltage Drop

Inductor Current

Capacitor Current

Load Current

Inductor Voltage

where:

VL = L x (diL / dt) and VL = a constant value: IL = (VL / L) x t

During the charge cycle:

ILPK = [(VIN - VSAT) x tON] / L

(1)

During the discharge cycle:

ILPK = [(|VOFF| + VF) x tOFF] / L

(IL = 0 after tOFF)

(2)

From (1) and (2):

tON / tOFF = (|VOUT| + VF) / (VIN - VSAT)

(3)

VSAT

VIN

OSCILLATOR

CONTROL

VF

IL

L

ILOAD

VOUT

IC

COUT

+

ON

OFF

VIN - VSAT

-(|VOUT| + VF)

IL

ILPK

tON

CHARGE

tOFF

DISCHARGE

When IL = IC + ILOAD and output voltage are in a steady

state, the change of the charge/discharge must be

equivalent, so:

And:

∆Q+ = ∆Q1- + ∆Q2-

ILPK = 2 x ILOAD x [(tON / tOFF) + 1]

(4)

Ripple Voltage:

VRIPPLE = ∆Q+ / COUT

= (ILPK - ILOAD)2 x tOFF / 2COUT x ILPK

~ ILOAD x tON / COUT

(5)

IC

∆Q1-

ILPK - ILOAD

∆Q+

∆Q2-

ILOAD

VRIPPLE

Page 8

January 1999 TOKO, Inc.

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