Use waste energy-saving lamps to transform switching power supplies

Since energy-saving lamps were widely used, a large number of discarded energy-saving lamps have appeared. The author used the waste energy-saving lamp circuits to transform them into switching power supplies for powering the Walkman, and the results were satisfactory.

The modified switching power supply circuit is as shown in the figure. The left part of transformer B2 is the original energy-saving lamp component, which will not be repeated. The original high-frequency ballast inductor coil has been replaced by a self-made high-frequency transformer. B2 and the components on the right are newly added. . B2 uses E5×7 magnetic core, the primary is wound with 110 turns of 019mm enameled wire, and the secondary is wound with 16 turns of 031mm enameled wire with a center tap; VD3 and VD4 use Schottky diodes or rectifier diodes with higher operating frequency, avoid using 1N4001 ~4007 and 1N5392 and other ordinary rectifier diodes, otherwise even if a 10A ordinary rectifier diode is used, it will be seriously heated and cannot be used; the voltage stabilizing integrated block can be optional 7805, the maximum output current is about 15A, and the output voltage is 5V; B3 is a high-frequency choke circle to reduce radiation interference, choose a magnetic ring with a high magnetic permeability of 10, and use 041mm enameled wire to double-wrap and wind 10 turns in parallel.

If you take the voltage directly on C5 during use, there must be no short circuit, otherwise V1 and V2 will have to be burned. The reason is that when a short circuit occurs, the current of coil L0 in feedback transformer B1 increases sharply, the voltages of coils L1 and L2 rise suddenly very high, and the current fed back to V1 and V2 also increases sharply, resulting in strong positive feedback. Finally, due to V1, V2 was burned due to the limited power consumption. The feedback of this circuit is a series current feedback and has an open circuit protection function. However, when the load increases, the feedback also strengthens, and even the frequency decreases with the increase of the load. The internal resistance of the entire power supply is extremely small, so it is easy to burn in the short term. Power triode.

The author once used an 8-13W straight fluorescent tube to replace the energy-saving lamp tube (still using the original high-frequency ballast inductor coil). When the power is turned on, the lamp just lights up or stays on for a short time, and the power triode of the energy-saving lamp Burning occurs. The voltage drop of the straight fluorescent tube is lower than that of the original U-shaped tube, which is the same reason why the transistor is overloaded and burned due to mismatch.

Other common self-oscillation power supplies on the market, such as special electronic transformers for spotlights, have no dedicated feedback transformers, and their feedback windings are on the same magnetic core as the secondary windings connected to the load. When the load increases, the feedback winding On the contrary, the voltage decreases. When there is a short circuit, the feedback amount is smaller, the self-oscillation frequency increases, and the internal resistance of the entire power supply becomes larger. It is like a spring that can be elastically adjusted within a certain range, so the power transistor is not easy to burn in the output short circuit.

Since the output voltage waveforms of V1 and V2 of energy-saving lamps are approximately square waves, as shown in the figure, there is a certain amount of harmonic interference. The Walkman is full of noise when listening to medium wave, but there is no effect when listening to FM, short-wave high-end or tape. In comparison, its interference is smaller than some pulse width modulated regulated power supplies.

The above are the author's experimental results, and some of the experiences and lessons may be of some reference to everyone.