Instrukcja obsługi Microchip HV9861ADB1
Microchip
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HV9861ADB1
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Supertex inc.
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 identied 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 conguration, 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 seconwith boost secon
Specyfikacje produktu
| Marka: | Microchip |
| Kategoria: | nieskategoryzowany |
| Model: | HV9861ADB1 |
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