Microchip HV9861ADB1 Manual

Microchip Ikke kategoriseret HV9861ADB1

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Supertex inc.

www.supertex.com

HV9861ADB2

Doc.# DSDB-HV9861ADB2

A032713

General Description

Certain target markets for LED lighting require a power factor

of at least 90%. A power factor over 90% can be attained

using valley ll power factor correction with the addition of a

small boost converter.

The boost converter lowers line current distortion by adding

line current draw in the valley and lowering the peak

amplitude of the valley ll capacitor recharging current.

HV9861A LED Driver Demoboard

Boost Assisted, Valley Fill,

120VAC Input, 7W Output, 350mA, 20V, Power Factor ~ 93%

Basic valley ll circuit operation

A valley ll power factor correction circuit operates in two

distinctly different modes.

During a rst period, here referred to as the valley and

coinciding with line voltage being lower than half the peak

line voltage, the load is exclusively powered from two energy

storage capacitors. Consequently, in the valley the line

current is equal to zero. The valley, being characterized by a

line voltage less than half the peak line voltage, extends 30°

on either side of the line voltage zero crossing.

During a second period, coinciding with the line voltage being

higher than half the peak voltage, the load is exclusively

powered from the line and not from the valley ll capacitors.

Consequently, the line current is not zero. Furthermore, an

additional line current is drawn near the peak of the line

voltage for recharge of the valley ll capacitors. The two

line current components can clearly be identied in the

oscillogram of the line current.

Boost converter operation

The boost converter adds current draw in the valley, thereby

lowering distortion and raising power factor.

The boost converter switch, a bipolar transistor in common

base conguration, is driven indirectly by the current ow in

the valley capacitors. In the valley, current is extracted from

the valley capacitors during ON time of the main switch, each

capacitor contributing half of the load current. The capacitor

current in one of the capacitors develops a voltage of about

1.2V across two diodes in series. This voltage provides a

forward bias for the base emitter circuit of the boost transistor.

Current develops in the boost inductor, which subsequently

ows in to the valley capacitors during OFF time.

The boost converter develops a line current with an

amplitude which is line voltage dependent. When line

voltage is particularly small the boost converter operates

in discontinuous mode (DCM) and when the line voltage

approaches half the peak voltage the converter operates

in continuous conduction mode (CCM). The line current

amplitude increases nonlinearly with line voltage in either

conduction mode. The boost converter action results in

delivery of power to the valley capacitors thereby lowering

the amplitude of the capacitor recharging current during the

second period.

Circuit add-ons

PF 93. PF 90.6 % 8 %

without boost seconwith boost secon

Produkt Specifikationer

Mærke:	Microchip
Kategori:	Ikke kategoriseret
Model:	HV9861ADB1

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