herunterladen
Application Note 1
Issue 2 October 1995
8 Watt Fluorescent Lamp Inverter
David Bradbury
The circuit shown in Figure 1 has been
designedto drivean 8W fluorescent lamp
from a 12V source, using an inexpensive
inverter based on the ZTX652 transistor.
The inverter will operate from supplies in
the range of 10V to 16.5V, attaining
efficiencies up to 78% thus making it
suitableforuseinon-chargesystemssuch
as caravans / mobile homes/ RVs as well
as periodically charged systems such as
roadside lamps, camping lights or
outhouse lights etc. Other features of the
inverterarethatitoscillatesataninaudible
20kHz and that it includes reverse polarity
protection.
Circuit Operation
The 270Ω and 22Ω resistors bias a
ZTX652 transistor into conduction,
where the positive feedback given to the
transistor by W1 drives it into saturation,
thus applying the supply voltage across
W2. This causes a magnetising current
to build up in W2 until the transformer’s
ferrite core saturates. When this
happens, the base drive given to the
transistor by W1 decays, causing the
transistor to rapidly turn off.
Until the fluorescent tube strikes, the
transformer is only loaded by the tube
heater filaments which present only a
minimal load. Thus when the transistor
ZTX
1/4W
22R
1/4W
2.2
1W
270
250V
0.068uF
250V
0.015uF
Polyester
W4
W5
W3
W2
W1
652
8W TUBE
Eg. SYLVANIA F8W/W
OR PHILIPSTL8W/33
+12V
0V
0.22uF
Polyester
Polyester
Figure 1
8W Invertor.
AN 1 - 1
Compact DC to AC Inversion for Efficient Lighting Systems
