212
3.
Маматов М.Ш., Ташманов Е.Б., Рахимов Б.Н.
Обработка сигналов на
основе Фурье преобразование // Вестник Фер.ПИ.-Фергана,2016.-№3.-
стр.131-133. (05.00.00; №20)
4.
Ташманов Е.Б.,Маматов М.Ш. О двух задачах управляемости
яркости
цифровых изображений описываемых дискретными уравнениями
второго порядка // Материалы научной конференции «Актуальные
вопросы геомет-рии и её приложения» Ташкент 27-28 октябрь 2014 г,
стр. 212-214.
TECHNIQUES TO IMPROVE EFFICIENCY IN SWITCHING POWER
SUPPLIES
Sh.D. Sultonov, Sh. Homidjonov
Fergana Polytechnic Institute
The reduction of losses is important to the efficient operation of a switching
power supply, and a great deal of time is spent during the design phase
to minimize
these losses. Some common techniques are described below.
The Synchronous Rectifier.
As output voltages decrease, the losses due to
the output rectifier become
increasingly significant. For V
out
= 3.3 V, a typical Schottky diode forward voltage
of 0.4 V leads to a 12% loss of efficiency. Synchronous rectification is a technique
to reduce this conduction loss by using a switch in place of the diode. The
synchronous rectifier switch is open when the power switch is closed, and closed
when the power switch is open, and is typically a MOSFET inserted in place of the
output rectifier. To prevent “crowbar” current that would flow if both switches were
closed at the same time, the switching scheme must be break-before-make. Because
of this, a diode is still required to conduct the initial current during the interval
between the opening of the main switch and the closing of the synchronous rectifier
switch. A Schottky rectifier with a current rating of 30
percent of the MOSFET
should be placed in parallel with the synchronous MOSFET. The MOSFET does
contain a parasitic body diode that could conduct current, but it is lossy, slow to turn
off, and can lower efficiency by 1% to 2%. The lower turn-on voltage of the Schottky
prevents the parasitic diode from ever conducting and
exhibiting its poor reverse
recovery characteristic.
Using synchronous rectification, the conduction voltage can be reduced from
400 mV to 100 mV or less. An improvement of 1-5 percent can be expected for the
typical switching power supply.
The synchronous rectifier
can be driven either actively, that is directly
controlled
from the control IC, or passively, driven from
other signals within the
power circuit. It is very important to provide a non-overlapping drive between the
power switch(es) and the synchronous rectifier(s) to prevent any shoot-through
currents. This dead time is usually between 50 to 100 ns. Some typical circuits can
be seen in Figure 1.