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A Super-Efficient (96.5%) Modular Telecom Rectifier
A rectifier is the general term for a dc power supply that also charges batteries. The
rectifier produces a regulated dc output voltage suitable for telecom applications.
Rectifiers are usually designed to accept a wide-range of ac input so that the rectifier
can be used worldwide with ordinary ac mains.
A scalable dc power supply will include one or more identical rectifier modules
connected in parallel, a controller for monitoring the system, a battery, and a low
voltage disconnect (LVD) circuit to prevent over-discharge of the battery.
Fig.1 depicts a typical system.
In normal operation, the system is powered by the ac mains. The rectifiers convert the
ac power into a clean stable dc voltage suitable for both the operation of equipment
and the charging of the battery.
The battery is normally intended for use as a backup power source for the system load
(the equipment being powered by the system) until the normal ac power is restored or
a backup generator is operated.
The system controller enables the operator to monitor the system, and to diagnose any
problems that may arise. The controller can also be used to connect the power system
to the outside world via a LAN or a cellular net. In the best architectures, the
controller is an optional component of the system; the system can work normally
without it, but with reduced functionality.
When the ac input power is absent the rectifier modules are unavailable and the load
devices are powered by the system's battery. The battery is connected in parallel to the
normal rectifier output.
The battery discharges as it supplies the load devices. When the battery voltage falls
below a certain value the battery must be electrically disconnected from the system, to
avoid damage to the battery due to over-discharge. The disconnection is performed by
an LVD circuit in the form of a mechanical relay or an electronic switch.
In recent years efforts have been made to raise the efficiency of the rectifier to the
highest possible levels.
The efficiency of the rectifier module determines system efficiency, and is very
important for achieving:
 Low heat dissipation.
 Small size and weight.
 Improved reliability as a result of low component stress.
 Decreased air-conditioning.
Gamatronic Electronic Industries Ltd., POB 45029, J erusalem 91450 Israel
Tel: +972-2-5888222
Fax: +972-2-5828875 i n f o @ g a m a t r o n i c . c o . i l
www.gamatronic.com
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Electricity bills savings.
Indirect reduction in CO2 emissions (from the electrical power plant).
In the not-so-distant past ordinary rectifiers achieved 90 % efficiency, and especially
well-designed models could reach 92 % efficiency. Such units are usually comprised
of two power stages: a dc-ac (PFC) stage followed by a dc-dc stage. The first stage
corrects the input power factor and creates a high dc voltage link (400 Vdc). The
second stage converts this high dc voltage to the output 48 V (or 24 V in some cases).
Each stage has its own efficiency, and thus the total efficiency is the product of
efficiencies. This means that for a 92% overall system efficiency each stage must be
96% efficient. This is not an easy goal to achieve.
It must be understood that the improvement of efficiency from 92 % to 96 % is huge
and signifies the reduction of the losses to half. As an example let us assume a
rectifier of 1800 W. A rectifier with 92 % efficiency will dissipate 156 W, and if its
efficiency were 96 % it would dissipate only 75 W. The difference in losses is huge
although the efficiency ratings are very close to one another. Figure 2 is a curve
illustrating losses vs. efficiency. From it one sees that improvement in efficiency from
92% to 96% require a reduction in losses from 8.7% to 4.2% (more than half!).
Over time new power topologies were developed for the two stages comprising the
rectifier module. Bridgeless BOOST PFC (Figure 3) was used extensively for the
input stage. This topology exploits the absence of the input diode bridge, using
transistors to eliminate bridge losses. With careful design, efficiency for this stage
could reach 98 %.
Years later, the Interleaved BOOST PFC (Figure 4) architecture was developed. In
this scheme the power stage is split into two significantly smaller equal stages that
operate in anti-phase to each other. Using this arrangement the high frequency
currents are cancelled or minimized and input line current is almost free of high
frequency ripple currents.
The second stage of the rectifier is responsible for converting the 400 Vdc down to 48
Vdc, or 54 Vdc for charging a string of four VRLA 12 V cells. For this stage many
innovative topologies were developed. The classic Forward converter has now been
replaced with Resonant and Quasi-Resonant topologies of many kinds. Recently the
LLC resonant converter has been used extensively by many high-end equipment
vendors to provide high efficiency. Such a converter is described in Figure 5 and
contains two inductors (series and parallel) and a capacitor, forming a resonating tank.
The name is therefore after those components designated here as Ls – Lm – Cs.
To achieve even higher efficiency, synchronous rectification is used at the output of
the transformer that actually replaces the output diodes with very low Rds(on)
MOSFETs. This arrangement improves efficiency by about 2 %.
Gamatronic Electronic Industries Ltd., POB 45029, J erusalem 91450 Israel
Tel: +972-2-5888222
Fax: +972-2-5828875 i n f o @ g a m a t r o n i c . c o . i l
www.gamatronic.com
Gamatronic Electronic Industries has been developing rectifiers and chargers for more
than 40 years. Recently Gamatronic introduced modular rectifiers specifically
designed for telecom and similar applications.
These rectifiers employ Interleaved BOOST for the input stage and an LLC stage for
the output. Overall maximum efficiency of 96.5 % results from the extraordinary
efficiencies of 98.2% average for each stage. This novel design makes use of the latest
technology in the fields of power devices, magnetic components and control.
Udi Levy
R&D Manager
Fig.1
Gamatronic Electronic Industries Ltd., POB 45029, J erusalem 91450 Israel
Tel: +972-2-5888222
Fax: +972-2-5828875 i n f o @ g a m a t r o n i c . c o . i l
www.gamatronic.com
Percentage of losses out of output power vs. Efficiency
12.00%
10.00%
8.70%
8.00%
6.00%
4.17%
4.00%
2.00%
0.00%
90%
92%
94%
96%
98%
100%
Fig.2
Fig.3 (source: ST)
Gamatronic Electronic Industries Ltd., POB 45029, J erusalem 91450 Israel
Tel: +972-2-5888222
Fax: +972-2-5828875 i n f o @ g a m a t r o n i c . c o . i l
www.gamatronic.com
Fig.4 (source: TI)
Fig.5 (source: On-Semi)
Gamatronic Electronic Industries Ltd., POB 45029, J erusalem 91450 Israel
Tel: +972-2-5888222
Fax: +972-2-5828875 i n f o @ g a m a t r o n i c . c o . i l
www.gamatronic.com
Gamatronic Electronic Industries Ltd., POB 45029, J erusalem 91450 Israel
Tel: +972-2-5888222
Fax: +972-2-5828875 i n f o @ g a m a t r o n i c . c o . i l
www.gamatronic.com