Specifications

CONSTRUCTION
circuit has a high-voltage winding for
the EHT of the picture tube. This EHT is
connected to the electrode (aluminium
foil) of the ozone discharge tube.
The LOT used should be two-limb
type, i.e, the low-voltage windings should
be on the left limb of the ferrite core, and
the EHT winding (primary and second-
ary), which is generally epoxy potted, on
the right limb. The LOT should have an
external EHT diode and not an inter-
nally wired EHT diode, as is common in
colour television LOTs. The reason be-
ing that only AC voltage is needed here.
Further, it is necessary to remove any
coupling between the two limbs, which
may be present in the LOT windings. A
connection from the left limb to the right
limb is used to increase the mutual cou-
pling. In the circuit presented here that
coupling leads to over-currents in the
event of any discharge tube sparking,
thereby damaging the IRF840 instantly.
It is therefore necessary to cut off the
connection linking the two limb windings
before installation. Preferably, a 1,00-
ohm, 2#W resistor may be wired in the
place of this cut, if an improved perfor-
mance of ozone generation is desired.
Lab. note. During testing of EFY
Lab, transformer stamped as LOT 2070
obtained from the market was found to
be single limbed and could generate about
34kV peak voltage at 120V AC input.
Therefore a double-limbed Leader brand
transformer 2095 was procured and used
after removal of the encased TV20 recti-
fier diode, in a manner exactly as de-
scribed by the authors. This transformer
could produce about 30kV peak with AC
input of 120V. The corona discharge
across EHT secondary was prominent
with an air-gap of up to 125 cm. At only
80V AC input to the circuit, 100pA space
current was measured using the meter-
ing circuit described below.
The metering circuit (Fig. 5). This
employs a simple low-cost 100uA meter
used as VU-meter in audio amplifiers
and is freely available. Either the edge-
mounting type or the plain type may be
used. It has a
clear front
plastic case of
25 sq. cm which
is easily
mounted on the
front side of the
plastic box,
with a suitable
small cut made int he box with drill and
fret saw.
The meter has a top which can be
easily removed and replaced, as it is
snug fit. Removal of the meter top ex-
poses the meter scale, which can be re-
drawn in per cent of 0-1 gm/hour O3.
The meter shows the discharge cur-
rent through the ozone-generating tube
The earth side of the discharge tube
(aluminium tube) is connected through
a 1-kilo-ohm, 1W resistor to ground. The
EHT wire is connected to the electrode
(aluminium foil) on top of the glass tube
The 1-kilo-ohm resistor develops a volt-
age in approximate proportion to the
ozone that would have been generated.
A series combination of 4.7-kilo0-ohm
resistor and a diode (1N4001) supply
current to the meter coil.
LED indicator (Fig. 6). The indica-
tor LED on panel gets its current through
a single turn wound on the top limb of the
ferrite transformer. The current is recti-
fied by a 1N4003 diode and filtered by a
10uF, 16V capacitor which supplies the
current through 1-kilo-ohm series resis-
tor to the LED. The glowing of the LED
indicates that the circuit is working.
Lab. Note: At EFY Lab, about eight
turns of insulated wire around top limb
of LOT were used.
AC input. The AC mains supply is
at 230V AC and has a fuse of 500 mA in
series. A switch can be wired in series
with the same, though the same is not
shown in the circuit here. (Please note
that at EFY, 12V AC input was used as
mentioned earlier.)
Testing
Prior to operation of the circuit board
for ozone generation, it is required to
test the circuit properly. This can be
done as follows:
1. The low-voltage pulse generation
part has to be tested first. For this, in
place of the mains-derived 12-volt sup-
ply, a separate 12V supply, derived using
an external 12-0-12 volts, 1-amp trans-
former, and a 7812 voltage regulator, can
be used. The two oscillators should have
frequencies in the specified range and
the presets should be able to adjust them
over the range mentioned. Otherwise,
slight alteration of resistor values may
be needed. The 3300pF capacitor used
should be of good ceramic or polyester
type, with a rating of 100V or more.
2. Then, using a CRO, the pulse train
should be observed at the junction of two
bipolar transistors. Next, MOSFET IRF
840 is connected in the circuit.
3. Now apply 12V supply to the end
PARTS LIST
Semiconductors:
IC1 (N1-N5) - CD4069 hex inverter
IC2 (N6-N7) - CD4011 quad 2-input
Nand gate
T1 - 2N2222 np transistor
T2 - 2N2907 pnp transistor
T3 - IRF840 n-channel
MOSFET
D1-D4, D9 - 1N914 detector diode
D5-D6, D8, D11 - 1N4007 rectifier diode
D10 - BA159 switching diode
D7 - 12V, 1W zener
D12 - 1N4001 rectifier diode
D13 - Green LED
Resistors (all 1/4-watt, +_ 5% carbon,
unless stated otherwise):
R1, R4 - 100-kilo-ohm
R2, R6, R10 - 10-kilo-ohm
R3 - 110-ohm
R5, R15, R17 - 1-kilo-ohm
R7 - 2.2-ohm, 10 watt fusible
resistor
R8 - 10-kilo-ohm, 10-watt
R9 - 6.8-kilo-oh,m
R11 - 15-ohm
R12 - 100-ohm, 10-watt
R13, R14 - 47-ohm, 10-watt
fusible resistor
R16 - 4.7-kilo-ohm
VR1 - 10-kilo-ohm preset
VR2 - 1-kilo-ohm preset
VR3 - 1-kilo-ohm potmeter
Capacitors:
C1 - 3300pF ceramic disk
C2, C7 - 0.1uF ceramic disk
C3 - 100p, 400V electrolytic
C4, C5 - 0.47uF, 400V polyster
C6 - 100uF, 35V electrolytic
C8 - 3.3 kpF, 300V polyster/
mica
C9 - 10u, 16V electrolytic
Misellaneous:
X1 - LOT 2070 EHT
transformer (without
EHT diode) or Leader
brand LOT 2095 (diode
to be removed)
- Al tube, length=20cm,
diameter=1cm
- Glass tube, length =
17cm, diameter=1.2cm
- HT electrode
- Aluminium full
- M-seal, small packet
- Teflon tape, two rols
- Cork, two numbers
- VU meter
- Short glass tube
- 1.5cm length, dia=5
mm, 2 numbers
- Flexible polythene
pipe 5mm diameterm,
one metre length
- Aquarium pump
F1 - Fuse, 500mA :
DC IN socket
Fig. 6: LED indicator
circuit
91