Case Study Recom Power

Case study

Enabling a Major Leap
in Power Density
Implementation of Trench Schottky diodes leads
to compact, efficient AC/DC power supply design

The development of power supplies can often be a difficult process.
They are expected to reach heightened levels of efficiency, whether
that is for AC-powered or portable equipment, while still being as
compact as possible. Cost is another important factor, and it also
goes without saying that the power supplies must be reliable and safe.

One company facing and subsequently overcoming thesedesign challenges is Recom — a highly successful European
manufacturer of AC/DC power supplies and DC/DC
converters headquartered in Gmunden, Austria. For a recentproject, Recom wanted to develop an AC/DC power supply
which was intended for medical and other applications. The
goal was to create a solution which had double the power
density of the company’s previous model without sacrificing
safety, reliability, efficiency, or performance. To get there,
the development team had to use the latest advances inswitching controllers, topologies and components — andturned to Nexperia for help.

Strict medical requirements set the bar
The new Recom RACM1200-V power supply had tomeet the strict requirements of IEC60601-1, a series oftechnical standards for the safety and performance ofmedical electrical equipment. These requirements include
maintaining safety with the appropriate creepage andclearance distances on the PCB, while also keeping power
dissipation at a minimum.
The product parameters specified that the AC/DC power supply
needed to deliver a peak output power of 1.2 kW. As well as themain output, it was necessary to have two auxiliary outputs:
a 12 V/1 A supply to power an optional cooling fan, and analways-on 5 V/1 A output for control and monitoring purposes.
To minimize standby power consumption, the overall
efficiency had to remain high even when the main output was
switched off. It meant that the power supply needed to beefficient at both the 1.2 kW peak load and when delivering
5 W or less in active standby — this represented a difficult setof requirements to achieve in a single device.

Figure 1:
RACM1200-V, 1200 W AC
power supply by Recom PowerFeedbackLLCControl

RectiﬁerPFCConverter

PE

Primary
Control
Protection

Flyback
Control

LLC
Transformer

Flyback
Transformer

Rectiﬁer

Buck
Converter

MAIN
Control &Protection

FAN
Control &Protection+Remote Sense-Remote Sense

OutputFilter+Fan
Fan ADJFan RTN

Rectiﬁer

5V AUX
Control &Protection

Main
output(48 V)-Vout

OutputFilter

+5VSB

factory bridge

N

Fuse, Inrush
EMI Filter
Inrush Lim.

Isolation

L+VoutOutputFilter

5VSB RTN

Auxiliary
output(12 V)

Auxiliary
output(5 V)

Feedback

Communication

SecondaryControl
Protection

SignalInterface

PSU_GOOD
AC_OK
Remote Sense
Remote ON/OFF
Signal RTN

Figure 2: Block diagram of Recom’s RACM1200-V AC/DC converter

As well as targeting medical usage, the power supply
needed to be suitable for industrial, building automation,
IT and home appliance deployments too. In terms ofdimensions, it had to be compact and low profile, fitting
inside a standard 19-inch rack mount enclosure.
Trench Schottky diodes step up
The most challenging part of the design was the always-on
5 V output, as this meant a separate AC/DC power supply
would need to be included, and that would take up valuable
space. Due to the compact size of the design, the only option
for placement of this extra circuitry was near the main output
components, which would run hot when delivering theoutput current. This meant that overheating was a significant
risk, so it therefore needed to be given careful consideration
when the design was laid out.
At first, Recom tried fitting planar Schottky rectifiers forboth the DC/DC and AC/DC auxiliary power converters,
but overheating was still a problem (particularly underfull load conditions).
To solve this problem, Recom selected Trench Schottky
diodes from Nexperia. The Trench Schottky diode is a
development on the original concept of a Schottky diode.
The trench concept reduces leakage currents, thus increasing
thermal stability. It also improves switching performancecompared to planar Schottky diodes.
Nexperia’s PMEG100T20ELR device is now being used in thebuck converter of the RACM1200-V for its 12 V fan output(see Figure 2). Provided in a small and flat surface-mounted
package, this Trench Schottky diode can handle a maximum
forward current of 2 A, with a maximum reverse voltage of100 V. Furthermore, it has a very low leakage current.

2Case Study Recom Power

Figure 3: High density PCB of RACM1200-V including PMEG100T20ELR

Featuring low reverse recovery charge and high efficiency
The PMEG100T20ELR also features a low forward voltage
drop. This is typically 705 mV and the maximum value is only
800 mV at room temperature (590 mV typ. / 660 mV max. at125°C. It has a very low reverse recovery charge (Qrr) thatis typically only 8.5 nC. These characteristics proved pivotal
in minimizing the rectifier losses on each switching cycle ofthe converter (see Figure 4).

Reverse Recovery Behavior
3TrenchPlanar

20-1-2

Trench Qrr
Trench IRM-3-4-5-6-10.00

IF = 3A
VR = 48V
dI/dt = 1A/ns
tamb =85oC

Planar Qrr
Planar IRM
-5.00

0.00
t [ns]

5.00

10.00

15.00

20.00

25.00

Moreover, the selected Trench Schottky diode has a low
reverse leakage current of typically only 60 nA (at 60V reverse voltage). This was important from a DC/DC
conversion perspective — with the input-to-output voltage
ratio being low because the diode would be longer inits off-state, due to the high duty-cycle of the switching
MOSFET. Without this one component, Recom would have
had to change its power supply specifications to inferior
figures, and this would have resulted in a significant
compromise in performance.
Overall efficiency of Trench and Planar Schottky diodes isshown in Figure 5. This demonstrates how the benefits ofusing Trench diodes increase at higher switching frequencies.

96η in %

100
8040 V

60Rth(j-a)= 90 K/W40
20002550

75
100125Junction temperature (oC)

94.0
93.3

9392.292.356 %less PCB space

89.5

130250Frequency in kHz

500

Figure 5: Efficiency compared of Trench and Planar Schottky diodes

Case Study Recom Power

CFP3: 5.95 mm²
Footprint area

Figure 7: Nexperia Trench Schottky diode in CFP packaging requires
only half the PCB space of alternative solutions

9290

175

To make the design fit into a standard 19” rack mountenclosure, the maximum height had to be 40 mm or less.
The Nexperia Trench Schottky diodes have very low profiles
and require around half the PCB space of most competingdevices. This gave Recom more flexibility in terms of theother components placed on the board.

SMA: 13.57 mm²
Footprint area

93.5

150

Figure 6: Trench Schottky diodes are designed for a wide SOAPlanar

91

3

PMEG100T080ELPE

Trench95

89Competitor part
120

Figure 4: Trench Schottky rectifiers offer industry-leading switching
behavior and low Qrr

94

Improved thermal stability with a wide SOA
By leveraging Nexperia’s CFP technology, Recom could
design a PCB with low thermal impedance paths that would
dissipate the heat generated, without needing to use gap
pads or additional heat sinks for the power diodes. TheTrench Schottky configuration also means that the thermal
stability of the diodes is improved, with a wide safe operatingarea (SOA), as shown in Figure 6. This reduces the likelihoodof thermal runaway in the rectifiers. Consequently, Recomengineers were able to design a power supply capable ofdelivering full auxiliary power and 800 W main power at 50 °C
ambient temperature, without forced air cooling.

Max. reserve voltage (V)

I [A]

1

However efficient a component might be, it will always
dissipate some heat, so Recom engineers gave a lot ofthought to how the parts would be cooled. The Nexperia
Trench Schottky diodes use a copper clip-bonded FlatPower(CFP) technology to improve the heat conduction from thepackage to the board. This has a small, thin and light designformat, and delivers superior thermal performance.

In total, the Recom power supply design comprises over
70 Nexperia products — mostly diodes, transistors andlogic components, as well as three further Trench Schottky
diodes (part number PMEG40T20ER). During the project,
Nexperia power experts were available to support Recom
with technical advice, helping its engineers to make the best
design and component selection decisions.

Power supply offers high-power density and fan-lessoperation
Through working with Nexperia on this project, Recom
was able to launch a highly efficient, baseplate-cooled
power supply measuring just 228 x 96.2 x 40 mm in size.
Now available on the market, the RACM1200-V can deliver
a continuous power output of 1 kW with the baseplate
held to 80 °C. Peak output of up to 1.2 kW is available
for up to 10 s, or continuously with airflow. It achieves apeak efficiency of typically 95 %. Besides its wide range ofprogrammable functions, the high-power density and fanless operation of this unit makes it highly suitable for use ina variety of high-availability applications.

Figure 8: Medical application landscape for Recom power supplies

To meet all the design specifications envisaged for thisproduct, Recom found that Trench Schottky diodes were
the best route to take. These provided the required
combination of efficiency, switching performance andthermal stability, all in compact space-saving packages.

Steve Roberts, Innovation Manager at Recom explains:“We looked at products from different Trench Schottky diode suppliers, andafter giving each of them considerable scrutiny, came to the conclusion that
Nexperia’s components were the best choice. These offered enhanced thermal
performance and a larger SOA, which would both be critical features if we wereto meet the standards relating to medical applications. Additionally, the low
profile of these products was another key advantage.”

About RECOM PowerThe RECOM group is a power supply manufacturer
headquartered in Austria with over four decades ofexperience in developing and manufacturing the latest
standard and custom power converter technology, fromsub-1W to tens of kW. Customers worldwide have accessto our vast selection of DC/DC converters and AC/DC
power supplies along with a broad range of switchingregulators and LED drivers, all of which comply withinternational safety standards and carry the latest
certifications.
Find your regional sales contact here

About Nexperia
Nexperia is a leading expert in the high-volume
production of essential semiconductors that arerequired by every electronic design in the world.
The company’s portfolio includes diodes, bipolartransistors, ESD protection devices, MOSFETs, GaN FETs
and analog & logic ICs. Headquartered in Nijmegen, theNetherlands, Nexperia annually ships more than 100
billion products, meeting automotive standards. Theseproducts are recognized as benchmarks in efficiency – inprocess, size, power and performance — with industryleading small packages that save valuable energy andspace. Nexperia has over 12,000 employees across Asia,
Europe and the US.
Find your regional sales office here© 2021 Nexperia B.V.
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Date of release:
September 2021