Cleverly use the electronic ballast of waste energy-saving lamps as power supply transformer

The discarded SW electronic energy-saving lamp ballasts used should be those with only burnt filaments and intact electronic ballast circuits. The circuit board of the electronic ballast of the energy-saving lamp is round, with a diameter of about 30mm, so it can be easily installed in the space where the original transformer is located in the battery charger.

When modifying, first solder off (disconnect) the power cord on the electronic ballast and the four filament wires connected to the lamp tube, and take out the ballast. There is an E-type ferrite core inductor L with an enameled wire coil on the ballast (see the attached figure); one end of this inductor is connected to the oscillation circuit of the ballast; the other end is connected to the filament (the other end of the filament is connected in series with a capacitor C on the board and then connected to the oscillation circuit). The first step of the modification is to connect the two ends of the filament that were originally connected in the figure with a cross-over wire. The second step is to use an enameled wire or a thin plastic-skin insulated wire with a diameter of about 0.27mm, and use the method of threading and winding to add a set of 8 turns of coils on the skeleton gap outside the inductor coil, as the low-voltage output secondary induction coil of the "AC/AC converter". At this point, the AC/AC voltage converter modified from the ballast has been completed.

The next step is to connect the modified voltage converter to the battery charger circuit, that is, the secondary output of the converter is an induced voltage of about 25kHz, which is the same as the oscillation frequency of the electronic ballast circuit; because the voltage frequency does not match the working characteristics of the IN4001 low-frequency rectifier tube (D1, D2) on the battery charger, D1 and D2 should be replaced with FR107 high-frequency rectifier diodes, which can achieve good rectification and obtain the charging voltage required by the battery charger.

The modified "voltage converter" was used to replace the transformer of the original battery charger. After actual trial, the charging effect was very good. After long-term charging, the charger was only slightly hot, which showed that the working efficiency was greatly improved compared with the original iron core power transformer that was easy to heat up.