AC-DC LCD TV Power Architecture
and
LED Backlight
LCD TV Power Architecture and LED Backlight
•
LCD-TV Market
– Power Reduction Trend
– Edge LED LCD TV Backlight
•
26” to 42” H-V LIPS Reference Design
•
46/47” Power Reference (PSU) for any Backlight solution
– Interleaved Frequency Clamp CrM PFC with NCP1631
– Quasi Resonance Valley lock out Flyback Converter with NCP1379
– ECO Standby SMPS Solution with NCP1053A
•
46/47” Backlight solution
– LIPS Inverter
– Edge LED Driver
•
Conclusion
LCD-TV Shipments by Size
Source: Displaysearch 2Q 09
Power Reduction Trend
•
Regulatory reduce power
consumption in active and
standby mode
•
New technologies focused
on improving efficiency
Source: Sharp
•
Proposed ENERGYSTAR TV regulations
(V4.0) will lower average power targets
Power consumption reduction ~ - 50% over 2 years
Proposed ENERGY STAR rev4.0 Standards
Very few LCD-TV pass
proposed new standard,
most are Samsung LED
Target Effective Date: May 2010
LCD-TV LED Backlighting
Source: DisplaySearch July 2009
LED TVs is forecast to grow to 20-32% (~64 M#) by 2012
Comparison of LED LCD TV Backlight Options
LED
driver
Merit
Concerns
Edge-lit LED BLU
Direct-type LED BLU
High voltage Boost, buck, linear with Vf
adjustment
Boost or Buck plus Multi-channel
linear
• High Power Efficiency
• Good system reliability independent
LEDs performance.
• Cost down of system
• Slim LCD TV
•
•
•
•
•
• System Noise & EMI
• Using lots of external components
(Inductor, capacitor, diode)
• Thermal limitations
• High system cost due to number
of LEDs and # of Drivers
• Picture artifacts
Edge LED > 90% ?
Deep blacks, better contrast
Local dimming
Scanning for higher frame rate
Low power consumption
Complex signal processing
Power Architectures Remain Varied
Signal Power
Flyback
Resonant HB
30 – 80 W
PFC
CRM
Interleave FCCrM
CCM
70 - 400+ W
ECO Standby
<5W
Backlight Power
Flyback / Resonant HB
24V / 150V+ for LED
HV-LIPS for CCFL / EEFL
50 – 300 W
Traditional 24 V Backlight and HV-LIPS approach
Thin TV design impacts solutions choices as well
32” HV-LIPS Reference Design
• For 32” (highest volume size) with possible extension to 26/42”
– Available since March 2009
– For CCFL ( >> 95% of backlight) with possible extension to EEFL
– Single PCB with LCD and Inverter Power Supply
• Very Cost effective solution
– No extra Standby SMPS
– Straightforward CrM PFC
• Key ON Semiconductor ICs
– NCP1607 as CrM PFC controller
– NCP1351 or NCP1219 as Flyback with low power standby mode
• LX6503 Microsemi Backlight controller
– Full Bridge High Voltage Inverter without High Side Driver (discrete circuit)
– Jin balance solution
32” HV-LIPS LCD TV Block Diagram
HV-LIPS LCD TV Complete Solution
12 CCFL
175 mm x 330 mm x 25 mm
All-in-one board with current balancer
Green Point Reference design documentation:
http://www.ONSemiconductor.com/pub_link/Collateral/TND3
60-D.PDF
46/47” Power Reference (PSU)
• Higher power LCD-TVs from 40/42” to 52”/55”
• Project focusing on power stage only
–
–
–
–
ECO standby “OFF mode”
Interleaved frequency clamp CrM PFC
Up to 70 W Flyback
Up to 200 W for backlight
• Low profile design
– 1st phase: < 13 mm
– 2nd phase: < 8 mm
46” LCD TV Power Block Diagram
46” LCD TV Power Solution Unit (PSU)
Low Profile design < 13 mm / 17.5 mm total
46” LCD TV PFC Solution
• Up to 300 W Interleaved Frequency Clamp CrM
PFC
– Better EMI and EMC
– Lower Irms for output C
– Better for SLIM design
– Standard parts (= 32”CrM)
• New controller NCP1631
• Easy SLIM narrow range version
Interleaved FCCrM PFC for > 200 W & SLIM design
PFC Summary
46” LCD TV PFC Schematic
3
BD1
GBU806
Gnd_Lug
CN401
D1
1
-
+
L2
200uH
C3
C1
0.47uF
450V
C4
Y 1nF
5
6 *
nc 9
8
7
11 *
2
50uH
2
L1
1
C2
0.47uF
450V
R1
1M
Y 1nF
R2
1M
3
4
10
9
7
6 *
D3
L3Q2
MUR550APF
275V
1
8.7mH
Q3
BC808-25LT1
R15
1M
CFS28
1
3
R42
1
68u
47
R3
X2 1uF
R12
NA
1K
O_UVP
275V
0.065 2 W 5%
2
C10
NA
R39
1K
INSTALL
1
C11
NA
R11
J106
MMSD4148
R28
1M
8.7mH
C12
Backlight
Input
Power and
Signal
R24
1K5
R30
24K
D8
3
L5
450V
47
R20
1M
4
CN003
4324-07S
1
2
3
4
5
6
7
8
450V
R13
1M
10K
R6
2
68u
C6
+
R7
10K
3
L4
Q4
BC808-25LT1
3
2
3
R10
1M
R43
1
R9
1M
4
C7
10nF 500V
1
3
D5 MMSD4148
C8
+
D6 MMSD4148
2
Q1 STP9NK50ZFP
2
R8
1M
2
PFC_OUT
R5
1M
Q2 STP9NK50ZFP
CFS28
1
NTC 2R5
PFC_OUT
2
X2 100nF
RT1
D2 MUR550APF
L2Q1
R4
1M
L3
200uH
2
1 *
C5
1N5406
4
FB_PFC
R16 22K
ZCD1_10
R17 150K
R18 150K
R19 150K
IC1
NCP1631
R14 22K
R23 150K
4
5
6
RELAY1
BO_PFC
RELAY2
7
8
C21
C13
Rt
DRV1
OSC
GND
Vcontrol
Vcc
Freq-Fall Back
BO
DRV2
Latch OFF
OVP/UVP
CS
VCC4
PFC-OK
14
R27
47k
13
Q6
12
11
C15
10
100n
1
2
4
3
220n
R29
120K
C19
C17
1nF
C18
220p
R31
20K
R41
270K
O_UVP
R33
39K
Q5
1
BC856ALT1
POWER_BOOST
BC856ALT1
9
680n
220n
R25
15K
1
R38
1K
C20
SW1
R26
2K2
2
R22 150K
16
15
10n
C22
R34
10K
NA
R37
1K
R36
10k
+
R35
0
C16
RELAY SPST
10u 50V
D11 1N4007
2
R21 150K
PFC-OK
3
3
ZCD1
FB
1
2
FB_PFC
ZCD2
2
1
3
ZCD1_1
PC001A
SFH817A
F1
FUSE 6A-250V
F2
4R7 1W
Standby_supply
LINE_NEUTRAL
RV5
90-264_VAC_INPUT
TVR10471KSY
L
FG
CN001
4333-W05ST
FG
FG
N
+
+
C24
3.3 uF 400V
C25
3.3 uF 400V
46” LCD TV QR Flyback Solution
• Flyback converter
– Up to 70 W max
– Up to 3 output with 4 A Max
• Quasi Resonance Flyback Converter
– Reduced EMI
– Best safety behaviors
• New NCP1379 controller
– Valley-lockout system
– Variable frequency mode for ultra low power mode
– Over current protection with auto recovery internal
timer
46” LCD TV PWM Fixed F Flyback Solution
• PWM Fixed Frequency Flyback converter
– 50 kHz Fixed frequency
– Allow natural CCM
• New NCP1252 controller
– Adjustable switching frequency with skip mode
– Adjustable soft start
– Over current protection with internal timer
• Alternative solution to previous QR mode
– Both designs
• on the same PCB
• with the same switching frequency
• with the same key parts
QR Valley lock-out or PWM Flyback SMPS up to 70 W
46” LCD TV Flyback Schematic
T200
750875731
1
PFC_OUT
R251
33K 2W
C200
10n 500V
*
D201
1N4937
do41d
11
P
3
P
R252
33K 2W
+
2
+
C207
D207
C208
N
1
N
*
470u 16V
470u 16V
3
D205
R203 33k
R207 4R7
+
C217
47u 25V
R213
470u 16V
P
Q201
BC858ALT1
BO
CS
VCC
Q203
STP5NK70ZFP
6
3
470u 16V
470u 16V
V1
+
8
7
CS
C225
+
2
Q205
BC858ALT1
Q204
BC808-25LT1
R222
1K
Regulation
V2
10M 2W
3
R236
4K7
D215
R226 1K
D217
1
VS-Stby
R227
1K
C230
470nF
2
R241
R231 16K2
2K2
1
MMSD4148
VS1
VS2
R238
10K
VS2
3
D219
2_5VREF
2
VS1
R233
2K49
D221
P
MMSD4148
R232 6K19
+
R242
2K2
MMSD4148
N
1
TL431BCLPRA
C232
470u 16V
VS1
Regulation
R228 1K
CN202
4324-03S
1
2
3
Backlight
controller
supply to
Backlight
board
Q207
BC858ALT1
3
2
MMSD4148
R237
10K
D216
IC201
VS2
MMSD4148
V1
SFH817A
R223
1K
1
R255
R209 100
PC101A
D211
MMSD4148
1
VCC4
SFH817A
C224
470u 16V
Y 1nF
3
4
R219
2K2
MBRF20L80CTG
Gnd_Lug
CN403
R221
0.47R 2W
R220
47k
1
10u 50V
470u 16V
3
3K3
100n
C216
470u 16V
1
3
C215
220p
C218
100p 1KV
2
1n
2
to220
R218
R249
8K2
VS1
+
C220
N
DRV
C212
10uH
2
+
C219
N
GND
D210
5
MMSD4148
C211
R211
1K
L202
1
R217 27
4
Regulation
10
9
*
R212
1K
P
C222
N
R215
MJD200 220
DPAK
R216
220
100n
R210
1K
+
C221
C214
7
D209
C210
68p
P
+
8
P
3
CS
FB
Q202
D208
MMSD4148
1
P
CT
470
N
ZCD
C213
330p
2
PC101B
R208
2K2
C209
470u 16V
N
470u 16V
5
P
1
VS2
+
ZD201
MMSZ6V8T1
IC200
NCP1379
2
C206
2
D206
MMSD4148
C205
N
ZD200
MMSZ15T1
R206
MMSD4148
10uH
+
N
R214
10k
D203
+
BAV21
470k
L201
1
N
*
*
P
PFC-OK
V2
12
6
VCC3
P
R205
1K
to220
MBRF20L80CTG
CN201
4324-11S
11
10
9
8
7
6
5
4
3
2
1
Flyback power to
Signal processing
and Audio board
46” LCD TV QR Flyback Waveforms
•
QR mode with valley lock-out
– With valley lock-out for low P
– With lower frequency by P Max
•
Top Trace
– Vin = 400 Vdc Pout = 34 W
– 1.75 A at 42.7 kHz
– V max = 572 V
•
Bottom Trace
– Vin = 400 Vdc Pout = 70 W
– 2.62 A at 39 kHz
– V max = 618 V
Valley lock-out is a Key improvement of QR mode
ECO Standby SMPS Solution (1)
• Dedicated 5W ECO Power Standby SMPS
– Pin < 90 mW for Pout = 40 mW @ 230 Vac
– Integrated High Voltage switcher NCP1053A (400 mA
/ 40 kHz Max)
• Hysteretic mode improves
• Low frequency mode allows DCM
• Limited current reduces possible noise issues
Hysteretic, Low Freq & DCM for ECO Standby SMPS
ECO Standby SMPS Solution (2)
• Standby relay
– Disconnect all “parasitic” standby load (~100-150
mW @ 230 Vac)
– Directly controlled by TV µP
• Optional ECO “ON / OFF switch”
– Low cost 2A / 10V non-isolated switch
– OFF mode: Pin < 20 mW by no load @ 230 Vac
ECO switch provides “ON/OFF” without Mains switch
ECO Standby SMPS efficiency
80
Efficiency (%)
70
60
50
Efficiency / 230V
40
Efficiency / 120V
30
20
0.03 0.04 0.05 0.10 0.25 0.50 1.00 1.50 2.00 4.00 5.00
Output Power (W)
OFF mode / no load: Pin < 20 mW @ 230 Vac (15 @ 120 Vac)
Standby / 40 mW Out: Pin < 90 mW @ 230 Vac (86 @ 120 Vac)
ECO Standby SMPS Waveforms
•
Drain Voltage and Current of
NCP1053A Switcher
– 200 V/div & 200 mA/div
•
For 5 V & 1 A = 5 W Output
•
Left: Hysteretic Burst mode
– (100 µs/div)
•
Right: Detailed cycle
– (4 µs/div)
•
Top Trace:
90 Vac
•
Middle Trace: 230 Vac
•
Bottom Trace: 264 Vac
ECO Standby SMPS Schematic
T100
750871014
3
D101 1N4937
D100
9
8
1
4
L100
1
+
MBR360
7
6
2
10uH
5
C102
PC100A
470µ 16V
R101
1K
2
C101
10p 1KV
R102
30K
SFH817A
1
VCC3
2
1
C103
47µ 25V
1
R105
10K
IC101
TLV431ASN1
3
R120 0
BAV21
MMSD4148
HV Barrier
R114
2K2
VS-Stby
4
PC200B
P
+
D102
VCC1
R113 4K7
100 n
1.25VREF
MMSD4148
D105
ON-OFF Switch
"Optional"
N
VCC2
C106
R104
10K
2
VCC4
CN100
4324-02S
VS-Stby
D104
Q101 BC808-25LT1
3
2
2
1
J100
INSTALL
1
C100
220p 400V
P
R100
100K 1/4W
N
Standby_supply
D109 MMSD4148
V1
3
SFH817A
Regulation
D108 MMSD4148
STANDBY
RELAY1
D110 MMSD4148
ZD101
MMSZ5V1T1
RELAY2
VS1
R103 8.2K
GND
PC200A
D106
MMSD4148
GND
7
R109
10K
R110
1K
D107
GND
R116 1K
R115 1K
BC848ALT1
R118
470
R117
4.7K
C107
10nF
VS-Stby
4
NC Power Drain
VS2
Q103
BC848ALT1
5
MMSZ15T1
R112
1K
MMSD4148
Q102
4
POWER_OK
PC001B
SFH817A
3
SFH817A
3
3
ZD102
Q100
BC858ALT1
R111
10K
2
4
Control in
R108
4.7K
1
SFH817A
2
PC100B
D103
MMSD4148
3
VCC
8
C105
47u 25 V
1
1
R107
4.7K
+
IC100
NCP1053P44G
2
R106
470
+
C104
10u 25 V
R119
22K
POWER_OK
VS-Stby
STANDBY
CN101
4324-05S
5
4
3
2
1
Standby power and signal
To Signal processing board
46” Flat TV PSU - Backlight Interface
• Interconnection on Power to any Backlight
solutions
–
–
–
–
400 Vdc / 200 W
PFC OK
5 V and 12 V
Power Good
• Separated & Dedicated Backlight solutions
–
–
–
–
High Voltage LIPS for CCFL / EEFL
High DC Output Voltage HB LLC for LED Driver
Classical 24 Vdc HB LLC
PDP dedicated Power converter
46”LIPS Inverter
• Higher power LCD-TVs
–
–
–
–
With extension to 40/42” or 52”/55” for both CCFL or EEFL
Follow on of 32” LIPS Reference Design
Full Bridge fixed frequency ZVS with possible synchronization
High efficiency, low EMI and sinusoidal lamp current
• Dedicated LIPS module
– To be interconnected with 46” Power Ref Design Step 1 < 13 mm
– Microsemi Backlight controller LX6503
• ON Semiconductor IC’s
– 2 High Side Drivers NCP5111
– 1 single signal driver transformer
• Low profile design
– < 13 mm on top of PCB
46” LIPS Inverter Block Diagram
LIPS - High Voltage Back-light Inverter
Full Bridge Inverter
2 x High Side Driver
NCP5111
OFF in Stand-by
Current
balancing
Board
Current
sensing
CCFL
I Lamp regulation
OCP, OVP
PWM 1
PWM 2
Open lamps
protection
Back-light
Controller
LX6503
ON/OFF, Dimming,Synchro
CrM Interleaved
PFC
NCP1631
400 Vdc
OFF in Stand-by
QR Flyback
SMPS
NCP1379
OFF in Stand-by
12 Vdc
5 Vdc
13 Vdc Audio
Power Good
Relay
St-by / ON
Bias
Mains Input
90-264 Vac
Stand by SMPS
NCP1053A
ON/OFF
5 VdcStand-by
Power (PFC + Flyback + Standby SMPS)
LCD TV
Signal
processing
and
Audio
amplifiers
46” LED Backlight Power
• Higher power LCD-TVs
– With extension to 40/42” or 52”/55”
– HB LLC dedicated to Backlight power
– High DC output voltage to power directly LED drivers
• Separate / Dedicated LED Power module
– To be connected with 46” Power Ref Design step 2 < 8 mm
• ON Semiconductor IC’s
– New NCP1397
– New
– New LED driver controller CAT4206
• Low profile design
– < 8 mm on top of PCB (< 12.5 mm total)
Multiple LED Linear Drivers with CAT4026
•
•
Up to 6 channels with linear bipolar transistors Linear:
“Vf monitoring and supply modulation & control”
Dedicated SMPS to support output voltage modulation
46” Linear Edge LED Driver TV Block Diagram
Dedicated
SMPS for
Backlight
with
Modulated
output voltage
46” Linear LED Driver Backlight Solution
•
•
Special technologies
PCB size: 250 mm x 165 mm
Ultra SLIM design < 8 mm / 12.5 mm total
HB LLC for Ultra Slim SMPS
• Limited number of components
• Zero Voltage Switching (ZVS)
• Zero Current Switching (ZCS)
• Higher power density
High efficiency and EMI friendly for low profile SMPS
Resonant Inductance Location?
External inductance
Benefits:
• flexibility
• EMI
• use resonant coil for OCP
Drawbacks:
• cooling
• insulation
Internal leakage inductance
Benefits:
• insulation
• cooling
• One component
Drawbacks:
• flexibility
• EMI + stray flux
• window utilization
External resonant coil is better for ultra slim design
Secondary Rectification
Push-pull configuration
Benefits:
• voltage drop
• Single diodes
Drawbacks:
• secondary winding
• matching
• window utilization
• Higher voltage rectifiers
Bridge rectifier
Benefits:
• one winding
• Lower voltage diodes
• Matching
Drawbacks:
• Higher losses
Bridge rectifier is better for HV output applications
NCP1397 - LLC Stage Controller
Features:
- operation from 50 kHz up to 500 kHz
- 600 V driver
- Startup sequence via an externally adjustable softstart
- Brown-out protection combined with latch input
- Disable input for ON/OFF control (skip mode)
Benefits for backlight application:
• No driver transformer
• Simple skip mode
• Simple OCP
NCP1397 is cost effective and highly safe solution
New OCP Implementation
• Adjustable delayed fault
• Short circuit protection with frequency shift
• New Double phase current information from auxiliary
winding of resonance coil
Res. Coil aux. winding provides accurate and fast OCP
Output Voltage Modulation
CAT4026 sinks
current from FB
divider to increase
output voltage
• Linear LED Drivers impact
– Dedicated SMPS to support output voltage
modulation
– Does not allow to get added auxiliary voltages for
Audio & Signal processing
Single Output Voltage modulated for Linear Driver
HB LLC Schematic for Linear LED Driver
HB LLC Waveforms
•
Strong load variation (0 to 100%)
on HB LLC with 100 Hz dimming
•
Traces:
– Top: Output current from 0 to 1
A (0.5 A/div)
– Middle: Primary current 2 A/div
– Bottom: Output voltage ripple
2 V/div (120 Vdc)
•
Top picture: 50% dimming
– HB LLC works in Burst
– Up to 3 Vpeak ripple on Vout
•
Bottom picture: 5% dimming
– HB LLC works in Burst
– < 0.5 Vpeak ripple on Vout
Edge-LIT LED Backlighting Trends
•
‘LED Light bars’ vary in configuration
– Single LED Strings of High Power (~ 200 V+ , 100 mA+)
– Multiple LED Strings (up to 4) of Lower Power (~ 100 V+ ,
50 mA+)
LED Driver solutions must handle from 4 to 16 channels
Existing Large Panel Backlight Solution
Loosely ~100V
For each LED channels!
Advantage: Independent Channel
Efficiency and LED-Fault handling
Loosely regulated input supply
Drawback: Cost and Complexity
Existing LED Driver Backlight Solution
•
•
Large-size panel power Module used for 6 Channel Edge-LIT LED TV
Each channel has a Dedicated Driver IC + inductive DC/DC boost + switch
6 Ch = 6 x ( DC-DC Boost +
additional switch )
6 Ch = 6 x Driver IC
Multi-channel “Linear” Edge-Lit Solution
•
Cost effective solution to address a wide number of channels
•
VF Monitoring to dynamically adjusts Anode voltage
•
Efficiency target range >90%, 94% typ. (varies with LED
mismatch)
•
Thermal dissipation addressed by external Power BJT’s
•
Address various LED string faults
“Linear LED Driver”: A cost effective solution for multiple channels
Multi-channel “Linear” Edge-Lit Solution
•
6 channel configuration shown
LED-Anode : dynamic adjustment
Fault diagnostics
LED Cathode OVP
LED Cathode regulation ~3 V
External power
devices (low θJA)
Multi-channel “Linear” Edge Driver Schematic
Connection to the 6 Edge LED segments
OVP
UVP
DPAK or TO220FP Power stage
Current sense
Optimized Dynamic LED-Anode Control
'LINEAR' POWER DISSIPATION
TYPICAL EFFICIENCY
100%
20
DISSPATION [WATTS]
200V
100V
EFFICIENCY
95%
90%
85%
15
10
5
0
80%
0%
5%
10%
15%
20%
LED STRING MISMATCH [Pk-Pk]
•
•
•
6ch: 200V, 100mA (120W)
12ch: 100V, 50mA (60W)
0%
5%
10%
15%
20%
LED STRING MISMATCH [Pk-Pk]
Efficiency depends on LED string matching
200V LED strings (with 10% mismatch) delivers ~ 94% efficiency
Thermal power dissipation levels : ~ 5 to 10 watt range
V modulation & control to limit overall Power dissipation
LED Channel Current Matching
0.6%
VARIATION vs BASE CURRENT
CHANNEL MATCHING %
1.0%
0.2%
MATCHING %
VARIATION %
0.4%
0.0%
-0.2%
-0.4%
-0.6%
0
2
4
6
BJT BASE CURRENT [mA]
VARIATION % .
0.4%
0.0%
-0.2%
-0.4%
Ch1 Ch2 Ch3 Ch4 Ch5 Ch5
-0.5%
CHANNEL
•
•
•
•
0.2%
0.0%
-1.0%
VARIATION vs LED CATHODE
0.6%
0.5%
Initial channel matching tolerance ~ ± 0.5%
Variation with BJT Base current : < 0.25%
Variation with Cathode to 30V : < 0.15%
Overall Channel matching less than ± 2%
-0.6%
3
6
9 12 15 18 21 24 27 30
CATHODE VOLTAGE [V]
Very good current matching < +-2%
Optimized Wide PWM Dimming Range
BRIGHTNESS vs PWM DUTY
CURRENT % [FSB]
100%
•
No concept limitation
for very short “ON”
time
•
CAT4026 Linear
Driver is optimized
for PWM dimming
•
Strong power
variation managed
directly by SMPS
10%
1%
0%
0%
1%
10%
PWM DUTY CYCLE
100%
Down < 1% for 400Hz PWM dimming
Edge LED Linear Backlighting Summary
•
Provides reduced total solution cost
•
VF monitoring minimizes & optimizes power dissipation
•
Minimizes EMI
•
Offers competitive Channel to Channel LED matching
•
Offers competitive wide range PWM dimming with good linearity
•
Supports Fault diagnostics against Open-LED and Short-LED
modes
The Linear is a easy to design and cost effective solution
Conclusion
• Complete roadmap of LCD TV solutions
– 32” LIPS
• A cost optimized solution for CCFL from 26” up to 42”
– 46” Power
• Power for any type of Backlight from 40” up to 55”< 13 or 8
mm
– 46” LIPS
• < 13 mm with separate LIPS
– 46” Edge LED
• SLIM < 8 mm with separate LED Drivers with very efficient
Linear Edge LED driver solution
• Approach
– Synergy by re-use solutions, speeding up the design process
For More Information
•
View the extensive portfolio of power management products from ON
Semiconductor at www.onsemi.com
•
View reference designs, design notes, and other material supporting
the design of highly efficient power supplies at
www.onsemi.com/powersupplies