Converter for powering fluorescent lamps from a car battery. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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To illuminate the room in field conditions, the use of fluorescent lamps is considered the most economical. When using a high-frequency converter to power the lamps, a more uniform glow is provided and there is less impact on eye fatigue.
The circuit shown in the figure provides power for two or three 40-watt lamps of the LB-40 type.
(click to enlarge)
The basis of the converter is the TL494 chip. It includes a master sawtooth voltage generator, the frequency of which can be roughly calculated by the formula f = 1 / (C7R10), in our case it is 50 kHz. The microcircuit is powered by a battery through an RC filter on the elements R1, C1, C2, VD1. It is necessary to protect the microcircuit from overvoltage and polarity reversal. The 5 V reference voltage source provides power to all functional units of the microcircuit. From output 14 it is used to set the threshold voltages of the comparators. Soft start of the converter is provided by the R3C5 chain.
Resistor R8 is needed to quickly discharge capacitance C5 upon restart. Comparator ER1 is used to maintain voltage feedback from the output of the converter, and thus the output voltage is stabilized. The output pulses from the R16R17 divider are rectified, smoothed by the VD4C6 circuit and fed to the +ER1 input of the comparator, and the 2,5 V reference voltage from the R5R6 divider to the ER1 input.
With a mismatch, the pulse width decreases, and the output voltage stabilizes. The ER2 comparator can be used to protect the device from overcurrent by using a shunt connected between pin 15 (D1) and ground, or a current transformer and then rectifying the voltage and feeding it to the same pin. Corrective RC chains R2C3 and R4C4 are necessary for the stable operation of the stabilizing converter. The output of the microcircuit is the emitters of transistors from the outputs E1, E2, and the collectors are connected to a voltage of 12 V.
The IC's push-pull output provides some delay between pulses to prevent current from flowing through the power transistors. The output switches use powerful 35-amp transistors connected in parallel, two in each arm.
Diodes VD5, VD6, VD8, as well as chains R15C8 and R18C9 are used to reduce impulse surges in the supply circuit and load.
The device is assembled on a printed circuit board with dimensions of 100x130 mm and is located in a case from a computer power supply with forced airflow from a fan. Transistors VT1-VT4 and diodes VD5, VD6, VD8 are mounted on a radiator measuring 60x90x20 mm through mica gaskets. Transformer T1 is wound on M2000NM grade ferrite, size Sh12Ch15. The primary winding contains 184 turns of PEV-2 wire with a diameter of 0,6 mm. The secondary and third are wound with a bundle of ten wires with a diameter of 0,6 mm and contain 2x5 turns.
The current flowing through the lamp can be changed by selecting capacitors C10, C11. Indirectly, it can be judged by the current consumed from the battery.
References:
- Fields I. Converter for powering household equipment//Radio. - 2003. - No. 1.
Author: S.M. Abramov
See other articles Section Voltage converters, rectifiers, inverters.
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