AN3040
Application note
STEVAL-ILB008V1 4 x 18 W/T8 ballast driven by L6585DE
Introduction
This application note describes a demonstration board able to drive a 4 x 18 W linear T8
fluorescent tubes.
The ballast is controlled by the new L6585DE IC that integrates the PFC and half-bridge
control circuits, relevant drivers, and the circuitry that manages all the operating phases
(preheating, ignition and run mode) of the lamp. Protections against failures such as lamp
disconnection, anti-capacitive mode and PFC overvoltage are guaranteed and obtained with
a minimum number of external components. In addition to the description of the circuit and
design criteria, this document provides a short overview of the ballast performances.
Fluorescent lamps are driven more and more by electronic ballasts rather than by
electromagnetic ballasts, primarily because fluorescent lamps can produce around 20%
more light for the same input power when driven above 20 kHz instead of 50/60 Hz.
Operation at this frequency also eliminates both light flickering (the response time of the
discharge is too slow for the lamp to have a chance to extinguish during each cycle) and
audible noise. Electronic ballasts consume less power and therefore dissipate less heat
than electromagnetic ballasts. The energy saved can be estimated in the range of 20-25%
for a given lamp power. Finally, the electronic solution allows better control of the filament
current and lamp voltage during preheating with the unquestionable benefit of increasing the
average lamp life.
Figure 1.
4 x 18 W T8 ballast demonstration board
June 2010
Doc ID 16181 Rev 2
1/27
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Contents
AN3040
Contents
1
2
3
Basis of half-bridge inverter topology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Main characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Ballast design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1
3.2
L6585DE pin-by-pin biasing circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
PFC power section design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Boost inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Power MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Boost diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3
Design of the half-bridge inverter and choice of preheating inductor . . . . 14
4
Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1
4.2
4.3
4.4
Start sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Conducted emissions test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Guidelines for connecting the four lamps to the ballast . . . . . . . . . . . . . . 20
5
6
7
Automatic restart circuit for lamp replacement . . . . . . . . . . . . . . . . . . 21
Bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
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Doc ID 16181 Rev 2
AN3040
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
4 x 18 W T8 ballast demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Electrical architecture used for four-lamp electronic ballasts . . . . . . . . . . . . . . . . . . . . . . . . 4
Electrical schematic 4 x 18 W T8 - main wide range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
EOL circuit for first-series lamp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
L6585DE startup sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
One lamp ignition phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Lamp voltage and current in run mode condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Run mode, rectifying effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Ignition phase with broken lamps: case 1 (lamp 1 works, lamp 2 is broken, lamp 3 is
broken, lamp 4 works) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Ignition phase with broken lamps: case 2 (lamp 1 is broken, lamp 2 works, lamp 3 is
broken, lamp 4 works) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Conducted emissions at 110 Vac 50 Hz - line 1 peak detector . . . . . . . . . . . . . . . . . . . . . 19
Conducted emissions at 110 Vac 50 Hz - line 2 peak detector . . . . . . . . . . . . . . . . . . . . . 19
Conducted emissions at 230 Vac 50 Hz - line 1 peak detector . . . . . . . . . . . . . . . . . . . . . 19
Conducted emissions at 230 Vac 50 Hz - line 2 peak detector . . . . . . . . . . . . . . . . . . . . . 20
Connecting four lamps to the ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Automatic restart circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Doc ID 16181 Rev 2
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Basis of half-bridge inverter topology
AN3040
1
Basis of half-bridge inverter topology
The half-bridge inverter operates in zero voltage switching (ZVS) resonant mode to reduce
the switching losses and the electromagnetic interference generated by the output wiring
and the lamp. Voltage-fed, series-resonant, half-bridge inverters are currently used for
compact fluorescent lamp (CFL) ballasts and for many european tube lamp (TL) ballasts.
For this circuit, we have chosen a lamp-to-ground configuration with current preheating and
have implemented two parallel resonant circuits that each supply two lamps in series, as
shown in
Figure 2.
Figure 2.
Electrical architecture used for four-lamp electronic ballasts
4/27
Doc ID 16181 Rev 2
AN3040
Main characteristic
2
Main characteristic
The electrical specifications of the lamp ballast are shown in
Table 1.
Table 1.
Input and output parameter
Input parameters
V
IN
f
line
Input voltage range
Line frequency
Tube lamp
Number
Type
Power
4
T8
18 W
Expected output parameters
PF
THD%
η
%
Power factor
Total harmonic distortion
Efficiency
≥0.9
≤10
≈90
85 to 265 V
RMS
50/60 Hz
Doc ID 16181 Rev 2
5/27
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