DN31

Design Note 31
Issue 2 November 1995
Design Note 31
Issue 2 November 1995
High Voltage Generation for Xenon Tube
Applications
R24
T1
D4
C13
C12
C10
C11
T2
TH1
R23
D5
D6 +12V
R7
C2
R10
R11
R13
R1
R4
Introduction
The ignition timing lights in common
use range from simple neon to complex
u n i t s . N e o n t i m i n g l i g ht s h a v e a
drawback that due to their low light
output, the user is forced to operate
them in subdued lighting. This becomes
a safety hazard as one tends to hold the
unit close to the timing mark and to the
“invisible” (or apparently stationary)
fan blades.
The ignition lights which use Xenon
filled stroboscopic tubes are much
better, since their light output is of much
higher intensity. The circuit described in
this note incorporates such a tube,
which has an anode voltage rating of 500
volts maximum and requires a trigger
voltage between 2-6kV.
The circuit was designed for a four
stroke engine. It will be seen later that
the unit can be converted for use as a low
power stroboscope with some slight
modifications.
The required high voltage for the tube
was achieved by using an inverter. The
inverter must drive a capacitive load and
also withstand the secondary being
shorted. Operating the inverter in the
flyback mode seemed the best choice,
since the energy transfer only takes place
when the switching transistor is off, thus
effectively isolating it from the load.
DN31-1
R19
TR5
R6
C4
ZD3
14
11
10
R5
TR10
R2
5
ZD1
R8
R15
R16
R9
SW1
R22
1
C5
ZD2
TR11
R20
IC1
TR2
C9
C7
C6
6
TR7
TR1
D3
TR9
TR4
R3
C1
In the circuit diagram shown in Figure 1,
the transistor Tr7 is the switching device.
The trans form e r T1, con ver ts the
voltages and also transfers the energy.
The capacitors C10 and C11 are used as
energy storage elements. When the tube
is triggered, this stored energy is
dis c ha r g ed in to t he tub e - w hic h
produces a bright flash of light. The
brightness of the flash depends on the
size of the storage capacitors and the
voltage to which they are charged. The
switching of Tr7 is controlled by the
Schmitt trigger, formed by Tr3 and Tr4,
which senses the ’current’ through the
primary and secondary. On switch on,
the transistor Tr3 will be off and Tr4 will
be on. Thus, turning on transistor Tr5
pulls the gate of the MOSFET transistor
up to approximately the supply voltage.
Whilst the MOSFET is on, the energy is
stored in the primary inductance of the
transformer. The current in the primary
increases as a linear ramp whose slope
is inversely proportional to the primary
inductance. The resistor R11 senses this
R18
R14
TR6
Circuit Action
D2
R12
C3
TR3
D1
R21
R17
347
TR8
RV1 RV2
M1
C8
0V
T3
Toroidal pick-up coil
Figure.1
Ignition Timing Light (Parts list in Appendix A)
current and when it reaches a pre-set
peak value, sufficient voltage drop is
developed across R11 to turn Tr3 on.
This in turn switches Tr4 off, which pulls
the bases of Tr5 and Tr6 to ground. The
gate capacitance of the MOSFET now
discharges through Tr6 turning the
MO SF ET trans i stor off. When Tr7
turns-off, the primary current
immediately ceases and the collapsing
magnetic field produces a current ramp
of opposite slope in the secondary
windi ng - cha rgi ng up the output
capacitors C10 and C11. The value of
this current is the peak value of the
primary current divided by the
turns-ratio of the transformer T1. This
secondary current is also sensed by the
same Schmitt trigger circuit. This is
achieved by connecting a resistor, R12,
in series with the secondary as shown in
the diagram. Note that this current also
flows through R11.
As the output capacitors C10 and C11 are
charged up by the secondary current,
the voltage across them gradually
incre ase s. A lso, as the secondary
current ramps down, the voltage drop
across R11 and R12 decreases. When the
upper threshold voltage of the Schmitt
trigger is reached, the transistor Tr3
again turns-off and the next cycle
begins. This action continues to dump
the energy into the output capacitors
until the output voltage reaches the
required value. When this has been
achieved, the potential divider formed
by R1 and R2 and the voltage sensing
elements Tr1 and ZD1 inhibit the inverter
DN31-2
Design Note 31
Issue 2 November 1995
Design Note 31
Issue 2 November 1995
High Voltage Generation for Xenon Tube
Applications
R24
T1
D4
C13
C12
C10
C11
T2
TH1
R23
D5
D6 +12V
R7
C2
R10
R11
R13
R1
R4
Introduction
The ignition timing lights in common
use range from simple neon to complex
u n i t s . N e o n t i m i n g l i g ht s h a v e a
drawback that due to their low light
output, the user is forced to operate
them in subdued lighting. This becomes
a safety hazard as one tends to hold the
unit close to the timing mark and to the
“invisible” (or apparently stationary)
fan blades.
The ignition lights which use Xenon
filled stroboscopic tubes are much
better, since their light output is of much
higher intensity. The circuit described in
this note incorporates such a tube,
which has an anode voltage rating of 500
volts maximum and requires a trigger
voltage between 2-6kV.
The circuit was designed for a four
stroke engine. It will be seen later that
the unit can be converted for use as a low
power stroboscope with some slight
modifications.
The required high voltage for the tube
was achieved by using an inverter. The
inverter must drive a capacitive load and
also withstand the secondary being
shorted. Operating the inverter in the
flyback mode seemed the best choice,
since the energy transfer only takes place
when the switching transistor is off, thus
effectively isolating it from the load.
DN31-1
R19
TR5
R6
C4
ZD3
14
11
10
R5
TR10
R2
5
ZD1
R8
R15
R16
R9
SW1
R22
1
C5
ZD2
TR11
R20
IC1
TR2
C9
C7
C6
6
TR7
TR1
D3
TR9
TR4
R3
C1
In the circuit diagram shown in Figure 1,
the transistor Tr7 is the switching device.
The trans form e r T1, con ver ts the
voltages and also transfers the energy.
The capacitors C10 and C11 are used as
energy storage elements. When the tube
is triggered, this stored energy is
dis c ha r g ed in to t he tub e - w hic h
produces a bright flash of light. The
brightness of the flash depends on the
size of the storage capacitors and the
voltage to which they are charged. The
switching of Tr7 is controlled by the
Schmitt trigger, formed by Tr3 and Tr4,
which senses the ’current’ through the
primary and secondary. On switch on,
the transistor Tr3 will be off and Tr4 will
be on. Thus, turning on transistor Tr5
pulls the gate of the MOSFET transistor
up to approximately the supply voltage.
Whilst the MOSFET is on, the energy is
stored in the primary inductance of the
transformer. The current in the primary
increases as a linear ramp whose slope
is inversely proportional to the primary
inductance. The resistor R11 senses this
R18
R14
TR6
Circuit Action
D2
R12
C3
TR3
D1
R21
R17
347
TR8
RV1 RV2
M1
C8
0V
T3
Toroidal pick-up coil
Figure.1
Ignition Timing Light (Parts list in Appendix A)
current and when it reaches a pre-set
peak value, sufficient voltage drop is
developed across R11 to turn Tr3 on.
This in turn switches Tr4 off, which pulls
the bases of Tr5 and Tr6 to ground. The
gate capacitance of the MOSFET now
discharges through Tr6 turning the
MO SF ET trans i stor off. When Tr7
turns-off, the primary current
immediately ceases and the collapsing
magnetic field produces a current ramp
of opposite slope in the secondary
windi ng - cha rgi ng up the output
capacitors C10 and C11. The value of
this current is the peak value of the
primary current divided by the
turns-ratio of the transformer T1. This
secondary current is also sensed by the
same Schmitt trigger circuit. This is
achieved by connecting a resistor, R12,
in series with the secondary as shown in
the diagram. Note that this current also
flows through R11.
As the output capacitors C10 and C11 are
charged up by the secondary current,
the voltage across them gradually
incre ase s. A lso, as the secondary
current ramps down, the voltage drop
across R11 and R12 decreases. When the
upper threshold voltage of the Schmitt
trigger is reached, the transistor Tr3
again turns-off and the next cycle
begins. This action continues to dump
the energy into the output capacitors
until the output voltage reaches the
required value. When this has been
achieved, the potential divider formed
by R1 and R2 and the voltage sensing
elements Tr1 and ZD1 inhibit the inverter
DN31-2
Design Note 31
Issue 2 November 1995
D1
+12V
BY206
C5
0.01u
R4
27
C1
1500p
R14
47K
TR2
D2
R2
1N4148
100
R1
5K6
R8
0.5
R7
100
ZTX
502
R3
5K6
TR3
TR4
ZTX
302
ZTX
302
TR1
R5
3K3
R6
1K2
ZTX
502
2.0
RM6
CORE
0.09mm
GAP
BYV
96E
TR6
ZVN
2110A
ZD1
15V
R11
91K
0V
R15
1M
R13
680K
226
36 SWG
44
36 SWG
TR5
C4
RV1
47K
R9
C2
470pF
ZTX
502
C3
22uF
450V
BTX18
400
BR100
R10
(560+27) K
0.01u
T2
PT56
ED75
ZTX
502
TR7
C5
0.068u
ZD2
47V
R12
820K
Figure 2
Xenon Beacon
by keeping Tr3 on. When the tube is
triggered, the capacitors are discharged
and the output voltage drops. The
transistor Tr1 turns-off and unlatches
the Schmitt trigger and therefore the
inverter action resumes.
The use of capacitor C3 enhances the
switching of the MOSFET. As Tr7 begins
to turn on, the C3-T1 node swings positive
by transformer action. This swing is
capacitively coupled via C3 to the gate.
The regenerative action rapidly switches
Tr7 hard on. When Tr7 begins to turn off,
the C3-T1 node swings negative. Again the
regenerative action rapidly switches the
MOSFET transistor off.
The Xenon flash tube is triggered by the
firing of the first spark plug in the engine
firing order. The transformer T3 is
placed over the spark plug and produces
a trigger pulse for the monostable every
time the spark plug is fired.
A single monostable circuit, a 74121, is
used for both the thyristor trigger and a
revolution counter. One of the outputs is
used to control the transistor Tr8, whose
collector is capacitively coupled to the
gate of the thyristor. This form of
triggering ensures a positive turn-off of
the thyristor in each cycle. Hence, the
possibility of it remaining in conduction
for more than 1 cycle is removed. Prior
to the thyristor triggering, the capacitor
C13 will be charged to the output
voltage. When the thyristor conducts,
C13 and the primary inductance of the
trigger transformer T2, form an
oscillatory circuit. The secondary of T2
produces the required high trigger
voltage.
The second output of the monostable is
used to drive the revolution counter
circuit, whose operation is as follows:
When the spark plug is fired, the output
DN31-3
Design Note 31
Issue 2 November 1995
of pin 6 goes high, the transistor Tr9
turns-off and Tr10 turns-on. The
capacitor C7 is charged up to the supply
voltage (approx.) through diode D2.
When the output goes low, Tr10 will turn
off and Tr9 will turn on. The capacitor C7
will now discharge through Tr9 and
Tr11. This gives rise to a mean collector
current in Tr11 which will depend on the
frequency of firing of the spark plug. The
use of Tr9 instead of a resistor allows the
quick discharge of C7 and also reduces
the power consumption, since the only
current flowing through Tr10 is the
charging current of C7.
With the component values shown, the
unit gives a bright light output up to
about 2500 revolutions per minute,
beyond which the light output starts to
fall. This is because the output capacitor
is not charged to it’s final value before it
is triggered again. The flash tube
dissipates about 4 Watts per flash.
micro-farads output capacitor, the tube
dissipates a maximum rated 1 joule of
energy per flash. The maximum possible
flash rate, with the component values
shown, is four flashes per second.
Above this, the brightness of the flash
will drop due to the capacitor not being
charged up to it’s final voltage before the
tube is re-triggered.
A diac is used to trigger the thyristor. As
the output voltage increases, the voltage
drop across RV1 increases. When the
voltage drop across RV1 reaches the
breakover voltage of the diac, it starts to
conduct. This provides sufficient gate to
cathode voltage to bring the thyristor
into conduction, and hence triggers the
tube. When the tube discharges, the
output voltage drops, taking the diac and
the thyristor out of the conduction mode
and the cycle begins again.
The unit can be easily converted into a
low power Stroboscope by simply
triggering the monostable with an
external square wave oscillator instead
of the pick-up coil.
Xenon Beacon
Another possible application for the
ZVN2110A MOSFET is a Xenon beacon.
Since the beacon flash rate is low, a high
value output capacitor can be used. This
allows more energy to be dumped into
the tube, giving an intense pulse of light.
The circuit diagram is shown in Figure 2.
The circuit is similar to that described
previously.
The output voltage generated in this
cas e is 320 volts and with a 20
DN31-4
Design Note 31
Issue 2 November 1995
D1
+12V
BY206
C5
0.01u
R4
27
C1
1500p
R14
47K
TR2
D2
R2
1N4148
100
R1
5K6
R8
0.5
R7
100
ZTX
502
R3
5K6
TR3
TR4
ZTX
302
ZTX
302
TR1
R5
3K3
R6
1K2
ZTX
502
2.0
RM6
CORE
0.09mm
GAP
BYV
96E
TR6
ZVN
2110A
ZD1
15V
R11
91K
0V
R15
1M
R13
680K
226
36 SWG
44
36 SWG
TR5
C4
RV1
47K
R9
C2
470pF
ZTX
502
C3
22uF
450V
BTX18
400
BR100
R10
(560+27) K
0.01u
T2
PT56
ED75
ZTX
502
TR7
C5
0.068u
ZD2
47V
R12
820K
Figure 2
Xenon Beacon
by keeping Tr3 on. When the tube is
triggered, the capacitors are discharged
and the output voltage drops. The
transistor Tr1 turns-off and unlatches
the Schmitt trigger and therefore the
inverter action resumes.
The use of capacitor C3 enhances the
switching of the MOSFET. As Tr7 begins
to turn on, the C3-T1 node swings positive
by transformer action. This swing is
capacitively coupled via C3 to the gate.
The regenerative action rapidly switches
Tr7 hard on. When Tr7 begins to turn off,
the C3-T1 node swings negative. Again the
regenerative action rapidly switches the
MOSFET transistor off.
The Xenon flash tube is triggered by the
firing of the first spark plug in the engine
firing order. The transformer T3 is
placed over the spark plug and produces
a trigger pulse for the monostable every
time the spark plug is fired.
A single monostable circuit, a 74121, is
used for both the thyristor trigger and a
revolution counter. One of the outputs is
used to control the transistor Tr8, whose
collector is capacitively coupled to the
gate of the thyristor. This form of
triggering ensures a positive turn-off of
the thyristor in each cycle. Hence, the
possibility of it remaining in conduction
for more than 1 cycle is removed. Prior
to the thyristor triggering, the capacitor
C13 will be charged to the output
voltage. When the thyristor conducts,
C13 and the primary inductance of the
trigger transformer T2, form an
oscillatory circuit. The secondary of T2
produces the required high trigger
voltage.
The second output of the monostable is
used to drive the revolution counter
circuit, whose operation is as follows:
When the spark plug is fired, the output
DN31-3
Design Note 31
Issue 2 November 1995
of pin 6 goes high, the transistor Tr9
turns-off and Tr10 turns-on. The
capacitor C7 is charged up to the supply
voltage (approx.) through diode D2.
When the output goes low, Tr10 will turn
off and Tr9 will turn on. The capacitor C7
will now discharge through Tr9 and
Tr11. This gives rise to a mean collector
current in Tr11 which will depend on the
frequency of firing of the spark plug. The
use of Tr9 instead of a resistor allows the
quick discharge of C7 and also reduces
the power consumption, since the only
current flowing through Tr10 is the
charging current of C7.
With the component values shown, the
unit gives a bright light output up to
about 2500 revolutions per minute,
beyond which the light output starts to
fall. This is because the output capacitor
is not charged to it’s final value before it
is triggered again. The flash tube
dissipates about 4 Watts per flash.
micro-farads output capacitor, the tube
dissipates a maximum rated 1 joule of
energy per flash. The maximum possible
flash rate, with the component values
shown, is four flashes per second.
Above this, the brightness of the flash
will drop due to the capacitor not being
charged up to it’s final voltage before the
tube is re-triggered.
A diac is used to trigger the thyristor. As
the output voltage increases, the voltage
drop across RV1 increases. When the
voltage drop across RV1 reaches the
breakover voltage of the diac, it starts to
conduct. This provides sufficient gate to
cathode voltage to bring the thyristor
into conduction, and hence triggers the
tube. When the tube discharges, the
output voltage drops, taking the diac and
the thyristor out of the conduction mode
and the cycle begins again.
The unit can be easily converted into a
low power Stroboscope by simply
triggering the monostable with an
external square wave oscillator instead
of the pick-up coil.
Xenon Beacon
Another possible application for the
ZVN2110A MOSFET is a Xenon beacon.
Since the beacon flash rate is low, a high
value output capacitor can be used. This
allows more energy to be dumped into
the tube, giving an intense pulse of light.
The circuit diagram is shown in Figure 2.
The circuit is similar to that described
previously.
The output voltage generated in this
cas e is 320 volts and with a 20
DN31-4
Design Note 31
Issue 2 November 1995
Appendix A
Component Values for Figure 1
R1
1M
C1
68nF
D1
1N4148
R2
120k
C2
1500pF
D2
ZDX1F
R3
5k6
C3
470pF
D3
1N4000
R4
100
C4
2.2µF, 63V
D4
BYV96E
R5
820k
C5
6.8µF, 40V
D5
1N4148
R6
5k6
C6
10µF, 25V
D6
BY206
R7
27
C7
10µF, 16V TANT
ZD1
47V Zener
R8
3k3
C8
1000µF, 25V
ZD2
15V Zener
R9
1k2
C9
470µF, 25V
ZD3
5V1 Zener
R10
100
C10
0.47µF, 1000V1
TH1
BT151
T1
Core RM6 FX3437.
Primary - 44 turns 36
S.W.G,
Secondary - 226 turns
36 S.W.G., Air gap
0.09mm.
T2
See Xenon tube
details below
T3
Core FX1589,
20 turns, 1mm wire
1
R11
0.5
C11
0.47µF,1000V
R12
2
C12
0.22µF
R13
130
C13
47nF,1000V1
R14
3k3
Tr1
ZTX214C
R15
2k2
Tr2
ZTX384C
R16
2k2
Tr3
ZTX214C
R17
18k
Tr4
ZTX214C
R18
4k7
Tr5
ZTX384C
R19
4k7
Tr6
ZTX214C
R20
2k2
Tr7
ZVN2110A
R21
2k2
Tr8
ZTX300
R22
4k7
Tr9
ZTX214C
Xenon Tube ED69 (Integral
Reflector and Pulse
Transformer T2)
R23
10k
Tr10
ZTX384C
M1
R24
100k
Tr11
ZTX214C
RV1
100
IC1
74121
RV2
220
Note 1:
POLYPROPYLENE
DN31-5
1mA F.S.D., 75Ω
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