Reducing the weight and size and increase the efficiency of the power supplies is one of the urgent tasks in the design of modern electronic equipment. Most simply, this task is solved by replacing the traditional rectifier (with a mains transformer and a capacitive filter) high-frequency transducer with subsequent straightening of the high-frequency voltage. Such power sources, due to the fact that the conversion occurs at a relatively high frequency (10...40 kHz), are the transformers and the entire structure is much smaller and hence higher power density as high as 200... 400 W/DM, which is several times more than traditional power supplies.
Schematic diagram of the power source shown in the figure. The output unit receives the bipolar voltage h In load current up to 0.6 A. the Amplitude of the output ripple voltage at maximum load current does not exceed 30 mV.
The mains rectifier is assembled on the diodes V1-V4. The rectified voltage Converter transistors V6, V7 and the transformers T1 and T2, and the voltage rectifier high frequency diodes V8-V11. The operating frequency of the voltage Converter 22 kHz. Capacitors C1 and C2 are necessary to protect the mains from interference; this occurs when the operation of the transducer. Resistors R1 and R2, together with the capacitors CS are the primary filter and also a voltage divider for the transmitter. Chain V5. R3, C5, R5 serves to facilitate starting of the generator Converter. Filter the rectified high-frequency voltage are the capacitors C6, C7.
The use of two transformers in the inverter voltage is allowed to increase its efficiency. In conventional converters with one last transformer operates in saturation mode. In the Converter with two transformers output transformer T1 operates in a linear mode at a much lower induction than in the mono-transformer Converter. This allows you to reduce core loss, and thus improve the efficiency of the Converter. Saturating transformer T2 is calculated only on the power consumption of the base circuits of transistors V6 and V7 and therefore is small in size. In converters with a single transformer when the switching transistors appears significant release of the collector current. In the Converter with two transformers this emission is practically absent, which significantly reduces the so-called dynamic losses and increases the overall efficiency of the Converter.
The link between the transformer windings III leads to the fact that at the right moment the transformer T2 is in saturation mode. This is required to satisfy the conditions of operation of the Converter, which are mentioned above. Transformer T2 is a switching element included in the base circuits of transistors V6 and V7. When saturation of the transformer T2 its magnetizing current increases rapidly, thereby increasing the voltage drop across the resistor R4 I reduced the voltage across winding III, and hence on the windings I and II, which leads to a decrease of the base current and the open output transistor in the active region of the n switching transistors. The switching frequency is determined by the time of reversal of the saturating core transformer T2. Inductors DR1 and dr2 do provide an opening delay of one transistor until then. while the other is completely closed. It is important to address cross-cutting currents and losses in the switching transistors.
The designation scheme
Obmat-
ka
The number of turns, the winding way
Wire
Core
T1
I
II lII
160
29+29 5
Sew-2 0.33
SEW-2 0.57 SEW-2 0,33
Toroidal ferrite NM HH mm
T2
I II III
8 8 10
PELSHO 0,28 PELSHO 0.25 PELSHO 0,25
Two ferrite rings 016 W mm Hg
L1,
L2
Turn to turn to fill
Sew.2 0,27
Resistor sun-0,5 R=100 ohms
Data transformers and chokes were placed in the table. Correctly assembled power unit does not require the establishment.
Author: V. Sykulski, Ternopil; Publication: N. Bolshakov, rf.atnn.ru