supply efficiency. DN94 Datasheet


DN94 efficiency. Datasheet pdf. Equivalent


DN94


High performance rectifiers significantly improve server power supply efficiency
A Product Line of Diodes Incorporated

DN94
High performance rectifiers significantly improve server power supply efficiency
Dr Yong Ang, Diodes Incorporated

Introduction
Alternative appr oaches ca n improve the existing me thods of using Schottky diod es in h igh reliability, h igh ava ilability and low downt ime se rver sta ndby power su pplies. T wo dif ferent secondary circuit approaches, including syn chronous rectification a nd Su per Barrier Rectifie r (SBR™) were used to find the highest practica l efficiency in a +5VSB power supply capable of delivering 27W p eak p ower. Ef ficiency improvements were mea sured i n a n experimental converter, at 3.5% for synchronous rectification and 0.5% for SBR over the Schottky solution. This design note discusses the details.

Server standby power supplies
Desktop derived servers are de signed to ope rate in high re liability a nd availability a pplication environments whe re it must b e working continuously wit h ext remely low unsch eduled downtime. T ypically t he architecture of t he power supply fo llows a t wo st age conve rsion approach as show n in F igure 1. The front en d stage is a Continu ous Co nduction Mode active power factor correcting Boost converter and delivering a constant 400V DC rail to a downstream forward DC-DC converter processing the tightly regulated +/-12V, +5V and +3.3V rails required by the system.
AC ...



DN94
A Product Line of
Diodes Incorporated
DN94
High performance rectifiers significantly improve server
power supply efficiency
Dr Yong Ang, Diodes Incorporated
Introduction
Alternative appr oaches ca n improve the existing me thods of using Schottky diod es in h igh
reliability, h igh ava ilability and low downt ime se rver sta ndby power su pplies. T wo dif ferent
secondary circuit approaches, including syn chronous rectification a nd Su per Barrier Rectifie r
(SBR™) were used to find the highest practica l efficiency in a +5VSB power supply capable of
delivering 27W p eak p ower. Ef ficiency improvements were mea sured i n a n experimental
converter, at 3.5% for synchronous rectification and 0.5% for SBR over the Schottky solution. This
design note discusses the details.
Server standby power supplies
Desktop derived servers are de signed to ope rate in high re liability a nd availability a pplication
environments whe re it must b e working continuously wit h ext remely low unsch eduled
downtime. T ypically t he architecture of t he power supply fo llows a t wo st age conve rsion
approach as show n in F igure 1. The front en d stage is a Continu ous Co nduction Mode active
power factor correcting Boost converter and delivering a constant 400V DC rail to a downstream
forward DC-DC converter processing the tightly regulated +/-12V, +5V and +3.3V rails required by
the system.
AC input EM I f ilt e r
and
re ctif ie r
Ac tive
pow er
facto r
co rrecti o n
+400V
Cb ulk
Iso lated
DC- D C
co n ver ter
+12V, +5V,
+3.3V, -12V
4-ch an n el
seco n d ar y
moni to rin g IC
Auxiliary power supply
+12VC C_P ,
100m A
R1
100kΩ
C1
1nF
1kV
D1
S1M
R2
D2
C2
22μ F
O ption #2:
T1 A2 Super B arri er B 2
R ectifie r
L1
2.4μ H
C4
470μ F
O ption #1:
A1 Sync hr onous B1
R ectifie r
RTN
Aux
D3
U S1J
SM A
C6
47μF
U4
Z SR1200
Voltage
r egul ator
SO T 223
+5VSB, 5A
C5
470 μ F
C7
1μF
R3
Vcc HV
GND FB
U1
D
R4
200Ω
R5
+ 5V S B
C3
R6
5. 1kΩ
RTN
10kΩ
U2 0.1μF
C Y1
GND
U3
Z T L431
R7
4.7 kΩ
1nF
Figure 1 - Server power supply architecture diagram
A se cond f lyback DC- DC con verter is re quired to ge nerate a isolate d 5V ou tput wit h ±5 %
tolerance. Thi s voltage sou rce is active whe never the input AC vol tage source i s appl ied an d
remains operational even if the main output rails from the isolated DC-DC converter are disabled.
Issue 1 - November 2008
© Diodes Incorporated 2008
1
www.zetex.com
www.diodes.com
http://www.Datasheet4U.com

DN94
DN94
In the ‘standby’ or ‘off’ mode, it delivers power to the external circuits that perform soft power
control, Wake On LAN (WOL), Wake On Modem (WOM) or suspend state activities. If an external
USB device stimulates the server to transit from Standby to Active mode, the power supply could
be requ ired t o pro vide 5 A curr ent fo r a f ew second s, t herefore t he po wer sup ply must be
designed to that peak power.
A high level of integration is desirable for the standby circuit which is made feasible by using a
PWM regulator that incorporates a 650V MOSFET. The PWM regulator also provides over current
protection to en sure the +5VSB supply will not be damaged under output fault conditions. The
converter is nor mally designed fo r Critical Conduction Mode to red uce MOSFE T t urn o n
switching loss . Furthermore, the flybac k transf ormer size can be redu ced owing to the lowe r
average energy storage whilst its smaller ma gnetizing inductance also yields a b etter transient
line/load response. At light loads the IC will operate in skip cycle mode, reducing its switching
losses and ensuring high efficiency throughout the load range.
The seconda ry w indings of the tr ansformer a re re ctified and filtered t o pr oduce t wo o utputs,
where the +5Vstb main output channel is closed loop regulated through an optocoupler U2. The
low power +12VCC_S is used to supply the supervisory IC monitoring the 12V, +5V and+3.3V rails.
The superv isory IC w ill norma lly shut dow n the ac tive PFC st age and the m ain downst ream
forward converter if those outputs are not sensed at their nominal value. In the design example,
a third bias output +14VCC_P is capable of supplying 100mA to the P FC controller and forward
converter PWM regulator ICs during normal operation.
Critically, much of the flyback converter inefficiency is caused by the Schottky diodes normally
used fo r second ary side re ctification on t he +5VSB out put. Re placing the old ex isting diode
technologies with a more efficient rectifier is recognized as a clear means of drastically improving
power supply ef ficiency. Two diff erent secondary side rectif ier approaches in Figure 1 were
considered including synchronous MOSFET rectifier and the Super Barrier Rectifier.
High performance rectifier #1. Synchronous rectification with ZXGD3101
The ZXGD31 01 ca n emulat e t he performance of an idea l rectif ier by driving a sy nchronous
MOSFET effectively. Figure 2 shows a typical circuit configuration for low side rectification. The
controller can dr aw its power directly from the regulated +12 VCC_S output via emitter-follower
transistor Q1. In ot her cases wh ere a regulated v oltage above 8 V is una vailable, the
recommendation is t o provide a ded icated supply through auxiliary transformer wind ing. RREF
and RBIAS are chosen to be 3kand 1.8kwhich sets the controller turn-off threshold value to -
20mV.
+ 12 VC C_ S, 50 m A
A1
C8
1nF
R9
100 Ω
Q3
Q1
FM M T491
U5
DRA IN
Vcc
GATEL
GATEH GND
Z XG D 3101
R EF
BIAS
RR EF
R BIAS
B1
O ption # 1: Synchr onous r ec tifier
R8
10 kΩ
ZD1
C9
1 μF
Figure 2 - Synchronous rectifier control circuit
www.zetex.com
www.diodes.com
2 Issue 1 - November 2008
© Diodes Incorporated 2008




@ 2014 :: Datasheetspdf.com :: Semiconductors datasheet search & download site (Privacy Policy & Contact)