NCP1255 25 W Evaluation Board User`s Manual

NCP1255GEVB
NCP1255 25W
Evaluation Board
User's Manual
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EVAL BOARD USER’S MANUAL
resistive divider. A double hiccup on the VCC brings down
the average input power while in auto-recovery fault mode.
The NCP1255 features several novelties compared to the
NCP1250 previously released. The key feature of this
component lies in its ability to push the switching frequency
as the converter experiences a sudden power increase.
However, this available extra power delivery can only be
maintained for a certain amount of time. Beyond this
duration, the controller gives up and enters an auto-recovery
mode. This mode is perfectly suited for converters
supplying highly variable loads such as Haswell-based
notebook adapters or inkjet printers to cite a few possible
examples.
Board Description
The application schematic that appears in Figure 1 has
been optimized to limit the leakage inductance losses and
maximize the efficiency. For this purpose, the RDC
clamping network has been replaced by a TVS-based
circuitry, leaving enough swing to the 800 V MOSFET.
Again, a 600 V type could have been used but would have
hampered the drain voltage dynamics at turn off. A capacitor
in parallel with the TVS limits its peak current at the switch
opening and helps softening the radiated noise. Besides its
excellent performance in standby, the TVS approach helps
to maintain a safe clamping level given the wide output
power excursion.
The chip supply is brought in via pin 6. Please note that the
start-up resistances, besides cranking the controller, also
perform the X2 discharge function for free. Upon start-up,
for a voltage less than 18 V (typical), the internal
consumption is limited to 15 mA maximum. It suddenly
changes to a few mA as the controller starts to drive the
800 V MOSFET at 130 kHz when VCC reaches 18 V. The
auxiliary voltage can go down to around 9 V before the
controller safely stops the switching pulses. The first VCC
capacitor C3 must be sized so that the auxiliary winding
takes over before the UVLO is touched. The auxiliary
winding is tailored to deliver an auxiliary voltage above
12 V and it drops to 10 V in no-load conditions. This
guarantees a good no-load standby power performance as
you will read below. A low-valued resistance (R13) limits the
voltage excursion on this auxiliary voltage in short circuit
situations.
Regulation is ensured by pulling down the dedicated pin
via an optocoupler, driven from the secondary side by a
NCP431. This new device does not require a 1 mA bias
current as it was the case with the classical TL431. The
absence of this bias current greatly contributes to reducing
the no-load standby power.
General Description
The part is encapsulated in a SOIC−8 package but a
reduced-feature set version (no brown-out and timers are
internally set), the NCP1254, also exists in a tiny TSOP−6
package. Featuring a low-power BiCMOS process, the die
accepts to work with VCC levels up to 35 V, safely clamping
the drive voltage below 12 V. With its 15 mA start-up
current, a high-value resistive network can be used in offline
applications to crank the converter, naturally minimizing the
wasted power in high-line conditions. In nominal load
operations, the switching frequency of this peak-current
mode control circuit is 65 kHz.
When the power demand goes up, the controller increases
the peak current setpoint until it reaches the upper limit
(0.8 V over Rsense, no opp). At this point, the output power
demand increase can only be answered by further shifting
the switching frequency up until it reaches another limit,
130 kHz. The maximum power is thus obtained at this
moment. On the contrary, in light-load operations, the part
linearly reduces its switching frequency down to 26 kHz and
enters skip cycle as power goes further down. This mode of
operation favors higher efficiency from high to moderate
output levels and ensures the lowest acoustic noise in the
transformer. To improve the EMI signature, a
low-frequency modulation brings some dither to the
switching pattern. Unlike other circuits, the dither is kept in
foldback and peak excursion modes, continuously
smoothing the noise signature.
The part hosts several new protection means such as an
auto-recovery brown-out circuit. It is adjustable via a
 Semiconductor Components Industries, LLC, 2012
December, 2012 − Rev. 0
1
Publication Order Number:
EVBUM2160/D
L1
+
2
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3  330 kW
3  330 kW
85−260
Vac
F1
250 V
Type=2AT
R35abc
1 MW
C12 X2
470 nF
2  27 mH
Schaffner RN114−0.8/02
IC4
KBU406
R9abc
1 MW
IN
−
C10
C7
100 mF
47 pF
+
R15
1 kW
R16
331 kW
U2B
R19
820 kW
220pF
C4
C5
1 nF
R20
390 kW
C15
0.1 mF
1mF
C6
R5
80kW
5
6
4
7
3
8
10mF
C3 +
D3
1N4937
2
1
U1
Eris
R14
2.2 MW
2
D1
MUR160
R12
0W
C1
33nF
200V
1
6
R24
not wired
1 kW
R10
Q2
2N2907
Q1
STP7NK80ZFP
R6
22 W
5
R7
4.3 kW
D4
1N4148
+
C13
47 mF
R13
10 W
Aux.
D6
P6KE220
R2a
1.5 W
0.5 W
R2b
1.5 W
0.5 W
C8
100 pF
1 kV
11, 12
7, 8
C11
680 pF
C2
680 mF
+
D5
1N973
U2A
SFH−615A
Figure 1. The Typical Implementation of the NCP1255 in an Isolated Flyback
Converter Authorizing Peak Power Excursions
Y1
C14
2.2 nF
D2
MUR530
R18
80 W
U3
NCP431
C9
22 nF
R1
2.2 kW
R3
1 kW
R11
10 kW
R17
118 kW
0V
32 V
NCP1255PRNGEVB
NCP1255PRNGEVB
The Specifications
95
The evaluation board must deliver 32 V at a nominal
25 W output power (Iout = 0.8 A). When the frequency
increases to 130 kHz, the peak power is up to 35 W or a 40%
increase compared to the nominal value. The duration of the
peak is set by resistance R7 pulling pin 8 down to ground.
When set to 200 ms (tOVL) as in this board, the short circuit
duration (tSC) is internally limited to 50 ms: tSC = tOVL/4.
Should the output current further grow, as the frequency is
clamped, the feedback voltage rises up to its open loop value
( 4.5 V). In this mode, the delivered power increases to
41 W or a 64% peak compared to the 25 W nominal value.
The complete power supply specifications are as follows:
Vout = 32 V
Vin = 100 − 240 V rms
Iout, nom = 0.8 A (Continuous Delivery of 25 W)
Iout, peak = 1.3 A (Peak Power of 41 W)
Fsw, nom = 65 kHz
Fsw, max = 130 kHz
The transformer is built on a PQ26/25 type of core and
features the following characteristics:
Primary Inductance LP = 1 mH
Maximum Primary Peak Current at TA = 70C = 1.3 A
Turns Ratio, Np:Ns = 1:0.39
Turns Ratio, Np:Naux = 1:0.19
Continuous Primary rms Current = 0.8 A
Continuous Secondary rms Current = 1.9 A
IEC−950 Safety Compliant
Vin (100 V rms)
90
hĂ(%)
85
Vin (230 V rms)
80
75
70
65
60
0
5
10
15
20
25
30
Pout (W)
Figure 2. The Efficiency is Maintained in
Light-load Conditions Thanks to the Frequency
Foldback Technique
Typical Waveforms
Some typical signals have been captured on the operating
board. The start-up sequence at a 100 V rms input is clean,
exempt from output overshoot (Figure 3):
vout (t)
Electrical Performance
Some efficiency tests were carried on this board. The
current was set to its nominal value (0.8 A) and reduced in
a 20-step sequence. Efficiency was recorded at every step
and collected in Figure 2 graph. As you can see, the nominal
efficiency is slightly less than 90% at nominal and maintains
above 85% as the output power drops. The average
efficiency at a 100 V input is 88.3% and drops slightly less
than 85% at high line (230 V rms). Please note that these
measurements include a 1.5 m long dc cable. The light and
no-load numbers are as follows:
vcc (t)
Vin = 100 V rms
Figure 3. There is No Noticeable Output Voltage
Overshoot Upon Start Up at Low Line
In short circuit, the double hiccup (Figure 4) nicely
reduces the duty cycle in burst mode to less than 3%. This
greatly helps to reduce the average input power while in fault
mode.
The peak power behavior was also tested as shown in
Figure 5. In the left side, the peak power is 35 W and lasts
100 ms. The feedback voltage is around 4 V, the controller
considers an overload transient. The output voltage drop is
well contained in the allowable limits (5%). If the transient
load duration is reduced to slightly below 50 ms but the
power increased to 41 W, the controller lets the voltage drop
while authorizing the peak excursion. Should the duration
exceeds 50 ms, the power supply would protect itself and
enter hiccup mode.
Table 1. LIGHT AND NO-LOAD NUMBERS
Low Line, 100 V rms
High Line, 230 V rms
Pout = 0 W, Pin = 48.7 mW
Pout = 0 W, Pin = 100 mW
Pout = 0.5 W, Pin = 0.690 W
Pout = 0.5 W, Pin = 0.81 W
Pout = 0.6 W, Pin = 0.797 W
Pout = 0.6 W, Pin = 0.92 W
Pout = 0.7 W, Pin = 0.915 W
Pout = 0.7 W, Pin = 1.06 W
Iout = 0.8 A
These numbers are very good, furthermore if we consider
a low-voltage IC externally cranked by a resistive network.
The brown-out sensing network is another burden that
significantly impacts the performance as well. When the
start-up/X2 network and the brown-out divider are removed
while the converter delivers an unloaded 32 V output, the
input consumption is measured at 50 mW with a 230 V rms
input voltage.
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3
NCP1255PRNGEVB
VOUT (t)
vDS (t)
VCC (t)
2.5 s
Vin(100
= 100
V rms
VIN
V rms)
vout (t)
IOUT (0.8 A)
Vin = 100 V rms
Iout = 0.5 A
Iout,peak = 1.1 A
vFB (t)
50 ms
vout (t)
1.15 V
3.5%
2s
vDS (t)
Vin = 265 V rms
Vin = 100 V rms
Figure 4. The Double Hiccup Nicely Limits the
Input Average Power while in Burst
Iout = 0.5 A
Iout,peak = 1.3 A
vFB (t)
Figure 5. By Increasing the Switching Frequency
Up to 130 kHz, the Controller Authorizes Peak
Power for a Certain Amount of Time
Conclusion
transiently increasing the power capability without affecting
the transformer as the peak current remains constant. Packed
with a wealth of features, this SOIC package will let you
build safe and rugged power converters with a limited count
of surrounding components.
This evaluation board user’s manual shows the peak
power capability offered by the NCP1255 and the overall
good efficiency brought by the frequency foldback
technique. The frequency excursion offers a nice means of
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4
NCP1255PRNGEVB
Table 2. BILL OF MATERIAL FOR THE NCP1255 EVALUATION BOARD
Substitution
Allowed
Comments
Designator
Qty.
Description
Value
Tolerance
Footprint
Manufacturer
Manufacturer
Part Number
R1
1
Resistor
2.2 kW
1%
SMD0805
Multicomp
MCHP05W4F2201T5E
Yes
Not Wired
R2a, R2b
2
Resistor
1.5 W, 0.5 W
1%
SMD2510
Panasonic
ERJ1TRQF1R5U
Yes
0.5 W
R3
1
Resistor
1 kW
1%
SMD0805
Multicomp
MCHP05W4F1001T5E
Yes
−
R4a, R4B
2
Resistor
15 kW
1%
Through-hole
Vishay BC
Components
MRS25000C1503FCT00
Yes
0.6 W
R5
1
Resistor
80.6 kW
0.1%
SMD0805
TE Connectivity/
Holsworthy
RP73D2A80K6BTG
Yes
−
R6
1
Resistor
22 W
1%
SMD0805
Multicomp
MCHP05W4F220JT5E
Yes
−
R7
1
Resistor
4.3 kW
1%
SMD0805
Multicomp
MCHP05W4F2202T5E
Yes
−
R9a, R9b,
R9c
3
Resistor
330 kW
1%
SMD0805
Multicomp
MCHP05W4F3303T5E
Yes
−
R10
1
Resistor
1 kW
1%
SMD0805
Multicomp
MCHP05W4F1001T5E
Yes
−
R11
1
Resistor
10 kW
1%
SMD0805
Multicomp
MCHP05W4F1002T5E
Yes
−
R12
1
Resistor
0W
1%
Through-hole
Vishay BC
Components
MRS25000C2209FCT00
Yes
Strapped
R13
1
Resistor
10 W
1%
Through-hole
Vishay BC
Components
MRS25000C1509FCT00
Yes
−
R14
1
Resistor
2.2 MW
1%
Through-hole
Vishay BC
Components
MRS25000C2204FCT00
Yes
0.6 W
R15
1
Resistor
1 kW
1%
SMD0805
Multicomp
MCHP05W4F1001T5E
Yes
−
R16
1
Resistor
330 kW
1%
SMD0805
Multicomp
MCHP05W4F3303T5E
Yes
−
R17
1
Resistor
118 kW
0.1%
SMD0805
Multicomp
MCTC0525B1183T5E
Yes
−
R18
1
Resistor
80.6 kW
1%
Through-hole
Vishay BC
Components
MRS25000C8069FCT00
Yes
0.6 W
R19
1
Resistor
820 kW
1%
Through-hole
Vishay BC
Components
MRS25000C8203FCT00
Yes
0.6 W
R20
1
Resistor
390 kW
1%
Through-hole
Vishay BC
Components
MRS25000C3903FCT00
Yes
0.6 W
R24
1
Resistor
22 kW
1%
SMD0805
Multicomp
MCHP05W4F2202T5E
Yes
Not Wired
R35a,
R35b,
R35c
3
Resistor
330 kW
1%
SMD0805
Multicomp
MCHP05W4F3303T5E
Yes
−
C1
1
Capacitor
33 nF/250 V
10%
Through-hole
Vishay
MKT 1822−333//405
Yes
−
C2
1
Electrolytic
Capacitor
680 mF/35 V
20%
Through-hole
Rubycon
35ZL680MEFC12.5X20
Yes
−
C3
1
Capacitor
10 mF/50 V
10%
Radial
Panasonic
ECA1HHG100
Yes
−
C4
1
Capacitor
220 pF
5%
SMD0805
Multicomp
MCCA000335
Yes
−
C5
1
Capacitor
1 nF
5%
SMD0805
Multicomp
MCCA000351
Yes
−
C5a
1
Capacitor
470 pF
5%
SMD0805
Multicomp
MCCA000342
Yes
−
C6
1
Electrolytic
Capacitor
1 mF/16 V
20%
Radial
Murata
MURGRM31MR71C105K
A01L
Yes
−
C7
1
Electrolytic
Capacitor
100 mF/400 V
20%
Through-hole
Nichicon
UCY2G101MHD
Yes
−
C8
1
Capacitor
100 pF/1 kV
20%
Through-hole
Vishay
F101K25S3NN63J5R
Yes
−
C9
1
Capacitor
22 nF
10%
SMD0805
Multicomp
MCCA000374
Yes
−
C10
1
Capacitor
47 pF
5%
SMD0805
Multicomp
MCCA000326
Yes
−
C11
1
Capacitor
680 pF/100 V
10%
Through-hole
Vishay BC
Components
D681K20Y5PH63L2R
Yes
−
C12
1
Capacitor
470 nF
10%
Radial
Epcos
B32923C3474K
Yes
X2
C13
1
Capacitor
47 mF/25 V
20%
Radial
Panasonic
ECEA1HN470U
Yes
−
C14
1
Capacitor
2.2 nF/250 V
20%
Radial
Murata
DE1E3KX222MA5B
Yes
Y1
C15
1
Capacitor
0.1 mF
10%
SMD0805
AVX
08051C104K4T2A
Yes
−
D1
1
Ultra-fast
Diode
MUR160
−
Axial
ON Semiconductor
MUR160RLG
Yes
−
D2
1
Rectifier
MURD530
−
DPAK−4
ON Semiconductor
−
No
−
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5
NCP1255PRNGEVB
Table 2. BILL OF MATERIAL FOR THE NCP1255 EVALUATION BOARD (continued)
Substitution
Allowed
Comments
Designator
Qty.
Description
Value
Tolerance
Footprint
Manufacturer
Manufacturer
Part Number
D3
1
Rectifier
1N4937
−
Axial
ON Semiconductor
1N4937RLG
No
−
D4
1
Rectifier
1N4148
−
Axial
Fairchild
Semiconducotr
FDLL4148
Yes
−
D5
1
Zener Diode
1N973
−
SMDSOD80
NTE Electronics
1N973B
No
33 V Zener
D6
1
TVS
P6KE220A
−
DO15
Fairchild
Semiconducotr
P6KE220A
Yes
−
F1
1
Socket
forUse
PCB TR5 TE5
−
Radial
Wickmann
5590000000
−
−
F1
1
Fuse
2 A/250 V−T
−
Radial
Schurter
0034.6618 1
(Note 1)
Yes
−
U1
1
PWM
Controller
NCP1255
−
SOIC8
ON Semiconductor
−
(Note 1)
No
−
U2
1
Optocoupler
SF615A−2
−
SMD
Vishay
Semiconductor
SFH615A−4
(Note 1)
No
−
U3
1
Shunt
Regulator
NCP431
−
SMD
−
NCP431ACSNT1G
No
SOT−23
U4
1
Diode
Bridge
KBU4K
−
Through-hole
Multicomp
KBU4K
Yes
−
TR1
1
Transformer
750313495
−
Through-hole
Würth Electronic
Midcom
750313495
No
PQ2625
J1
1
Line Input
Connector
C8 SNAP IN 2P
−
Through-hole
Schurter
4300.0099
−
−
J2
1
Output
Voltage
Connector
−
−
Through-hole
Taiwan
Semiconductor
KBU406
−
−
Q1
1
HV
MOSFET
STP7NK80ZFP
−
TO220
ST
Microelectronics
STP7NK80ZFP
−
−
Q2
1
PNP
Transistor
PMBT2907A
−
SOT23
NXP
PMBT2907A
−
−
L1
1
Self
227 mH
RN114−0.8−02
−
Through-hole
Schaffner
RN114−0.8−02
−
−
J2
1
PCB
Terminal
Block
CTB5000/2
−
Through-hole
Camden
CTB5000/2
−
−
Holes
4
Plastic Feet
SFCBS−M4−
16M−01
−
Through-hole
Richco
SFCBS−M4−16M−01
−
−
1. This is a Pb-free device.
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6
NCP1255PRNGEVB
TRANSFORMER SPECIFICATIONS
ON Semiconductor and
are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks,
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limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications
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EVBUM2160/D