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Dimming Circuit for Fluorescent Lamp Inverter

IP.com Disclosure Number: IPCOM000121278D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Nakano, M: AUTHOR

Abstract

Described herein is a dimming circuit for a fluorescent lamp inverter.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 74% of the total text.

Dimming Circuit for Fluorescent Lamp Inverter

      Described herein is a dimming circuit for a fluorescent
lamp inverter.

      In a conventional dimming circuit, the dimming effect is
achieved by changing the ratio of discharge-on time to discharge-off
time.  Discharge ON/OFF frequency should be designed between
inverter's oscillation frequency, such as, e.g., 20-50 KHz and
flicker-free frequency, such as, e.g., about 100 Hz and more to chop
intermittently discharge current.  This frequency limitation is a
weak point of the conventional method for a circuit designer.

      Fig. 1 shows a disclosed circuit diagram to control discharge
current of a fluorescent lamp which consists of a conventional
voltage resonance inverter, a switching device Q1 and a flywheel
diode D1.

      FL is a hot or cold fluorescent lamp.  Discharge current IFL
flows through into a fluorescent lamp.  A capacitor C2 is working as
a ballast capacitor to keep constant discharge current of FL.  C1 and
also C2 are resonance capacitors with a self inductance of main
transformer T.  These parts decide operating frequency of this
inverter.  Two transistors Q2 and Q3 are switching alternatively
on/off by feedback signals from sub-winding of transformer.  L is a
choke coil which has large impedance to limit current IL at operating
frequency of inverter. R1 and R2 are bias resistors to supply a base
current into Q1 and Q2.  D is a diode to keep current (IL) flowing
continuously. ...