What does the project present?
The neon lamp powered by this installation allows lighting in the absence of the electrical network (for example in camping conditions) or in case of damage to this network. The DIY electronic kit presented aims to familiarize the amateur electronics engineer with the construction and operation of a simple converter with transformer.
How does the project work?
Due to the fact that it does not require heating of the filaments, the assembly works perfectly with obsolete neon tubes in which one or both filaments are destroyed.
Figure 1 shows the diagram of the oscillating car converter equipped with a type power transistor SN 100 (2N3055). By connecting to the 12V battery, by resistor R1 and winding n2 of the transformer, a positive voltage is applied on the circuit formed by C2, R2, RV1 and the base-emitter junction of the transistor.
In the first moment, due to the existence of capacitor C2, the base current iB is high and decreases as this capacitor is charged, finally reaching a value determined by the equivalent series resistance R2 and RV1.
Existence winding inductor n1 it forces the collector current to increase linearly and at its terminals to find the input of the supply voltage. The transistor is at saturation.
As the base current decreases and the collector current increases, the transistor goes out of saturation when iC = Beta 1B.
The fact that iC no longer increases, cancels the voltage on the n1 winding and this variation is transmitted by winding n2 and circuit C2, R2 RV1 at the base-emitter junction. The base current decreases rapidly and then changes direction leading the transistor to lock.
The sudden decrease of the collector current leads to the appearance of an overvoltage at the terminals of winding n1 in the same direction as the supply voltage. This voltage, transmitted by a positive reaction in the n2 winding, accelerates the blockage. As the capacitor C2 is charged (in the opposite direction than in the direction of the conduction), the negation of the base decreases and when the base voltage reaches positive values, the transistor starts to conduct. Then the cycle repeats. Until the priming of the tube the overvoltage is very high, and transmitted to winding n3 reaches values of 500 - 600V, enough to prime it.
From this moment on, the overvoltage on the collector decreases. Capacitor C3 has the role of protecting the base, and capacitor C1 has the role of filtering.
In figure 2 the way of placing the parts on the surface of the printed circuit is presented. During soldering, a soldering hammer of max. 35W, or an electronic gun and the following rules will be observed:
- maximum gluing time - 5 sec.
- maximum length of the terminals after shortening - 5 mm
During the assembly, the following will be taken into account:
- the identification of the transformer windings is made according to the wire diameter, as follows:
- Primary winding (1-2) - 0.63 mm
- Secondary winding (3-4) - 0.5 mm
- Third winding (5-6) - 0.22 mm
- the connection of the transformer to the printed circuit is made with the help of two pieces of wire, as can be seen in Figure 2.
- resistors R1 and R2 are mounted at a distance from the printed circuit at 2-3 mm, respectively 5-6 mm.
- the power transistor is mounted on the radiator, and this by means of two insulating washers, on the plated support, the fastening being made on the other side, with the help of two nuts.
Putting into service
After all the components have been mounted on a printed circuit, it is checked for possible cold or short-circuit soldering between the tracks. It then connects a 14W neon tube at the terminals marked with a high voltage signal.
The assembly is supplied by means of a switch inserted on the conductor that goes to the "+" terminal of the battery with the voltage of 12V. Do not power the assembly without connecting the neon tube!
The brightness of the neon tube and the battery consumption can be adjusted with the help of the semi-adjustable resistor RV1. In general, it is desirable to work with a consumption of 0.7 - 1.2A. If we want a higher brightness, we can work with a consumption up to 1.5 - 1.7A, however the transistor must be mounted on a larger radiator.
List of required components (with recent equivalents):
- T1 - transistor SN 100 or 2N3055 / 2N3773 / MJE 3055
- R1 - 10 Ohm / 0.5W or 12 Ohm / 0.5W resistor
- R2 - 150 Ohm / 3W resistor
- RV1 - 250 Ohm / 0.5W potentiometer
- C1 - capacitor 100 uF / 16V or 68 uF / 16V
- C2 - 1.5 uF / 100V capacitor
- C3 - 4.7 uF / 63V capacitor
- Tr - ferrite transformer (N1: 5-7 turns, N2: 2-4 turns, N3: 140-180 turns; Core: the bar from an old radio. For more details see also the information in the comments.)
- Radiator Al. (for the recommended size, see image 2)
- Printed wiring or breadboard test board
- Tin or connecting threads
Download the original IPRS leaflet Baneasa 8605
Also, for a much clearer view of this electronic kit, I have attached a picture with assembled assembly and a small video material with its operation. Thank you Mr. Sandu Cristinel for providing the necessary materials. These helped to complete the article.