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Figure 3. The electronic starter consists of only 8 components. The circuit ensures that the gas filling is heated and the ignitions take place very quickly one after the other. This eliminates the unpleasant flickering when switched on.
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parts list
Resistors:
R1=470k R2=100kaw R3=1k
R4 = 56N/%W
Capacitors:
C1 = 15n (see text) C2 = 100n/630V
Semiconductor:
D1 = Diac ER 900 Th1 = Thyristor TIC 106D
Before the electronic starter takes over its task, it is interesting to know how the fluorescent lamp is constructed and works with the conventional starting device.
Figure 1 shows the basic circuit diagram for this. The fluorescent lamp consists of an elongated glass tube containing a gas mixture of mercury vapor and argon.
The pressure inside the tube is very low. If now due to an electric field the
When the gas filling is ignited, a discharge takes place. The discharge mainly produces ultraviolet Light. The inner wall of the glass tube is covered with a layer
of phosphor, a fluorescent powder. the Fluorescent lights flicker during the ignition phase. The manufacturers are also aware of this problem, which is why they
looked for alternatives and found one. Special fast-starting fluorescent lamps. However, the relatively high acquisition costs prevent them from catching on everywhere.
But it is also possible without new lamps: The electronic starter ensures that the fluorescent lamp without to torches ignites. A welcome side effect of the new
starting system is the longer lamp life. is the ultraviolet radiation now stimulates this layer to glow, visible light is produced. The applied phosphor layer thus
works as a kind of light transformer that converts short-wave UV light into long-wave visible light. The light properties of the fluorescent lamps depend very much
on the phosphor layer. They are then also commercially available in different colors and with different light intensities (see also ”’Dimmers for fluorescent lamps’’
elsewhere in this issue). The noble gas argon is at the light generator. not directly involved; it just makes ignition easier. The ignition voltage required for gas
discharge depends very much on the temperature of the gas mixture: at a higher temperature, a lower ignition voltage is sufficient. For this reason, electrodes are
fitted inside the tube, which heat the gas during the ignition process and thus facilitate the escape of electrons during the gas discharge. If the first ignition
has taken place, a much lower one is sufficient Voltage to keep the lamp on continuously. The voltage required for this is the so-called "burning voltage". Above the burning voltage, the fluorescent tube behaves like a negative resistance; the resistance decreases, causing the current to increase prevent this, a choke is necessary (it is also known under the term "inductive ballast"). The choke is an inductive resistance; in contrast to the ohmic resistance, only very little electrical power is lost as heat,
The choke is used as an ignition coil and, together with the starter, generates such a high ignition voltage that the fluorescent lamp always ignites. The choke
takes on another task. It keeps the high-frequency interference caused by the gas discharge away from the mains.
The term "starter" has been used several times. However, not all of its tasks have been discussed. It is not only responsible for a sufficiently high ignition
voltage together with the choke, but also switches the current through the glow electrodes The starter usually consists of a glow igniter (glow lamp), a bimetal
contact (thermal switch), an interference suppression capacitor, two connection contacts and a housing (Figure 2). Before the fluorescent lamp is switched on,
the bimetal contact is open. If you now close the mains switch, the mains voltage via the choke and the glow electrodes also to the starter connections.
This voltage is sufficient to ignite the gas charge of the glow igniter (usually helium). A relatively low current of about 0.1 A now flows to the glow electrodes.
Through the gas discharge creates a certain amount of heat in the starter, which after a while causes the bimetallic contacts to close This results in a high
short-circuit current through the glow electrodes, causing the gas charge in the fluorescent tube to heat up considerably. The short circuit also ends the gas
discharge in the starter. The bimetallic electrodes now cool down and the contact opens again. The flow of current ends abruptly, so that the magnetic field in
the choke suddenly collapses. A voltage of several hundred volts is generated, which is sufficient to ignite the fluorescent lamp.
Once ignition has taken place, the lamp voltage drops to around half of the original value; one then speaks of the burning voltage. This voltage is too low to
close the starter glow igniter again activate. There is therefore no further gas discharge in the starter and the bimetallic contact remains open. An interference suppression capacitor is connected in
parallel with the starter, which is intended to suppress any interference with radio reception.
That's the theory. In practice, the ignition process looks a little different. Several attempts are always required to ignite a fluorescent lamp. There are two
reasons for this: 1. The temperature of the gas mixture in the glass tube is still too low at the first ignition attempt; 2. The instantaneous value of the current
can be zero when the bimetallic switch opens, so that no ignition voltage builds up. Several ignition attempts are therefore always necessary before the fluorescent
lamp is activated. Due to the mechanical inertia of the starter, the individual ignition processes are separated from one another by short pauses. And that is exactly
what causes annoying flickering.
In order to suppress the flickering during the starting process, you have to ensure that the gas charge in the glass tube is sufficiently preheated and that the
individual ignition processes follow each other quickly. The electronic starter takes over this task.
The circuit of the electronic starter is shown in Figure 3. The following initial situations apply to the functional description of the starter: Switch SI closed,
the anode of the thyristor is positive compared to the cathode. As long as the fluorescent lamp is not ignited, the instantaneous mains voltage is present at the
starter. The capacitor C1 charges up via the voltage divider R1/R2 until the breakdown voltage of the diac (approx. 30 V) is reached. Now the capacitor can discharge
and fires the thyristor. A powerful current flows through the choke and the glow electrodes. This current creates a magnetic field. If the mains voltage becomes
negative (the polarity reverses), then the positive current is initially maintained through the choke. The current picks up
reference : https://archive.org/details/elektor-1982-06-v-138/page/n55/mode/2up?view=theater
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