Economical power supply. Scheme, description

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Economical power supply. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Reducing the weight and dimensions and increasing the efficiency of power sources is one of the urgent tasks in the design of modern electronic equipment. The easiest way to solve this problem is to replace the traditional rectifier (with a mains transformer and capacitive filter) with a high-frequency converter, followed by rectification of the high-frequency voltage. Such power supplies, due to the fact that the voltage conversion occurs at a relatively high frequency (10 ... 40 kHz), have transformers and the entire structure of much smaller sizes and hence a higher power density, reaching up to 200 ... 400 W / cu. dm, which is several times more than traditional power supplies.

A schematic diagram of such a power supply is shown in the figure. At the output of the block, a bipolar voltage of 2x27 V is obtained at a load current of up to 0,6 A. The amplitude of the output voltage ripple at the maximum load current does not exceed 30 mV.

(click to enlarge)

The mains voltage rectifier is assembled on diodes V1-V4. The rectified voltage converter is made on transistors V6, V7 and transformers T1 and T2, and the increased frequency voltage rectifier is made on diodes V8-V11. The operating frequency of the voltage converter is 22 kHz. Capacitors C1 and C2 are necessary to protect the mains from interference; arising during the operation of the converter. Resistors R1 and R2, together with capacitors C3C4, are the primary filter and at the same time a voltage divider for the converter. Chain V5. R3, C5, R5 is used to facilitate the start of the converter generator. - Capacitors C6, C7 serve as a filter for the rectified high-frequency voltage.

The use of two transformers in the voltage converter made it possible to increase its efficiency. In conventional converters with one transformer, the latter operates in saturation mode. In a converter with two transformers, the output transformer T1 operates in a linear mode at much lower inductances than in a single-transformer converter. This makes it possible to reduce losses in the core and, consequently, to increase the efficiency of the converter. Saturable transformer T2 is designed only for the power consumed by the base circuits of transistors V6 and V7 and therefore has a small size. In converters with a single transformer, a significant surge of collector current appears at the moment of switching of transistors. In a converter with two transformers, this surge is practically absent, which significantly reduces the so-called dynamic losses and increases the overall efficiency of the converter.

The presence of a connection between the transformers through the windings III leads to the fact that at the right time the transformer T2 enters the saturation mode. This is necessary in order to fulfill the operating conditions of the converter, which were mentioned above. Transformer T2 is a switching element included in the base circuits of transistors V6 and V7. When the transformer T2 is saturated, its magnetizing current increases rapidly, as a result of which the voltage drop across the resistor R4 increases, and the voltage across the winding III decreases, and consequently, on the windings I and II, which leads to a decrease in the base current and the output of an open transistor into the active region and switching transistors. The switching frequency is determined by the magnetization reversal time of the core of the saturable transformer T2. Inductors Dr1 and Dr2 provide a delay in opening one transistor until then. until the other is completely closed. This is necessary to eliminate through currents and reduce losses when switching transistors.

Scheme designation	Winding- ka	Number of turns, winding method	The wire	Core
T1	I II II	160 29 + 29 5	PEV-2 0.33 PEV-2 0.57 PEV-2 0,33	Toroidal ferrite 200NM1 32X16X8 mm
T2	I II III	8 8 10	PELSHO 0,28 PELSHO 0.25 PELSHO 0,25	Two ferrite rings 016 W 10x6x2 mm
L1, L2		Turn to turn to fill	PEV.2 0,27	Resistor VS-0,5 R=100 kOhm

The data of transformers and chokes are placed in the table. A properly assembled power supply does not require adjustment.

Author: V. Tsikulsky, Ternopil; Publication: N. Bolshakov, rf.atnn.ru

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