Created by Bernie Weir

High Brightness LED Driver Solutions for General Lighting

2

Source: OSRAM

World of Lighting• ~ 20-22% of electrical energy is used for lighting of

which 40% is for incandescent lighting, this represents 2000 TWh/year

Restaurants, Retail and

Services 48%

Industrial 16%

Residential 28%

Streetlighting 8%

>70% of the Energy Usage is Outside of the Residential Market

3

LED Technology Forecast and Impact

US DOE January 2009

4

LED Optical Characteristics• Chromaticity

• Some defined “box” in the white area on or near the Black Body Locus

• Bin sizes (x, y coordinates) varies by supplier

• Brightness (luminus flux)– All the “light” output into a

sphere– Factors in human sensitivity to

light of different wavelengths

5

Challenges of Driving LEDs

– Forward voltage varies by color, current & temperature– “Color point” shifts with current and temperature, more pronounced with Red and Amber

Nichia RigelNJSW036AT

All areWhite LEDs

6

Operating RelationshipElectrical, Optical & Thermal

Luxeon Rebel White

OSRAM PlatinumDragon

Seoul Semiconductor

Z1

1) Increasing drive current, increases flux

2) Higher current,

increases Vf & power

3) Higher power raises Tj,

reduces flux (light out)

1 2

3

7

Thermal Path is Critical to LED Lifetime

• 5mm lamps have almost no thermal path

• Rth >350 ºC/W typical• Chip (TJ) and phosphor can

essentially cook themselves

• Lighting-class LEDs are designed for high temp operation

• Rth <10 ºC/W typical• Lamp can stay within data sheet

parameters with good thermal design

Thermal path

Lighting-class LED5mm LED

No Thermalpath

8

LED Lifetime

40%

50%

60%

70%

80%

90%

100%

110%

0 10 20 30 40 50 60 70 80 90 100

Operating Time (k hrs)

Lum

en O

utp

ut

(%)

100 W Incandescent5mm LED42W CFL50 W Tungsten Halide400 W Metal Halide25 W T8 FluorescentLighting-class LED

• All conventional light sources dim over time, even LEDs• Standard light sources fail (open filament etc)• Properly designed LEDs dim gracefully

• End of life is based on Lumen Maintenance (L70) which is a function of operating temperature

Courtesy LRC, Rensselaer Polytechnic Institute

9

Application Drives LED Selection• What is the area/pattern to be lit?

– Linear strip or path– Spot– Area

• Optics considerations (narrow or wide beam)– Diffuser– Reflector– Lens

• Thermal density and heat removal

• Size and lit appearance

Reflector

Lens

10

LED Packaging Trends• Smaller size• Multi-high power chips• Multi-small chips• Phosphor coatings methods • Higher wattage packages• Deposited silicone primary lens systems

11

Arrangement of LEDs• Driving single strings of LEDs is highly preferred as it

provides ideal current matching independent of forward voltage variation, Vout “floats”

• Users do configure LEDs in Parallel/Series combinations – Requires “matched” LED forward voltages– If an LED fails open, the other LEDs may be overdriven– Cross connecting and multiple parallel techniques try to

mitigate the risk of a fault

Parallel

If a LED fails open, only 1 LED will be have 2x the drive

current

Series-Parallel Cross connect

Series

12

Example of a Low Current Driver

115 Vac25 mA 100 Ω

30 LEDs

110 V RMS, TP1 - 156 V P-P

TP2 - LEDs 108 V, 52% On

Current probe 25 mA

Features•Constant current as AC voltage increases•No delay in turn on after LED threshold voltage is reached•Bright LEDs at low voltages•LEDs protected from voltage surge

New family of simple 2 terminal Constant Current Regulators (CCR)• 20, 25, and 35 mA current• SOT123 and SOT223 packages• 45 V maximum operation

NSI45025

13

LED Driver Basics

• The main function of a driver is to limit the current regardless of input and output conditions across a range of operating conditions

• Ac-Dc power conversion and driver regulation can be merged together into a single driver or separated into two stages

• The arrangement of LEDs and the luminaire specifications dictate the fundamental driver requirements

• Isolated solutions means there is no physical electrical connection between the AC line voltage and the LEDs

Non-Isolated orIsolated Power

ConversionDriver

LED(s)

ACMains

14

Driver Operation

• Constant Voltage and Constant Current Regions

• Range of current and/or voltage regulation is driver/design specific

• Driver “constant” current behavior may not have a textbook relationship

• Some drivers are designed for constant power so LED forward voltage determines current

•Output can be designed to have tight current limited

•The output voltage depends on the LED forward voltage

Output is voltageRegulated or clamped

across a range of current

Constant Voltage

Constant C

urrent

15

Basic Configurations

• In a integral configuration, the power conversion and constant current driver are all within the light fixture

– Tight coupling of LED light source to the driver

– Optimum efficiency– Simplifies installation

• In a distributed configuration, the ac-dc power conversion is separate from driver (s)

– Modular applications like track and cove lighting

– Simplifies safety considerations– Increases flexibility

16

Offline LED Applications by Power LevelBased on Today’s LED Performance

• Low Power– 1-12 W

• Medium Power– 8-40 W

• High Power– >40 W

• Under-cabinet lighting• Desk Lamps• Accent• Appliances• A lamp Bulb Replacement

• Down Lighting• Spot Light (PAR38) Equivalent• Decorative Light Fixtures• Bollards• Ceiling Fans• Freezer and Refrigerator Lights• High Efficiency LED Supplies (ballasts) (24 V/ 48 V)

• Area Lighting– Street Lights– Fluorescent Lights– HID Replacement

• High Efficiency LED Supplies (ballasts) (24 V/ 48 V)

17

Factors to Consider• Output Power

– Range of LED forward voltage– Current – target, maximum– LED arrangement

• Power Source– 115 Vac, Universal (US/EU),

Industrial – 208/277 Vac or other– Low Voltage Lighting (landscape,

track etc)– Solar / Battery

• Functional Requirements– Dimming – PWM, 0 - 10 V, Triac,

Wireless, DALI, Proprietary, Other– Analog, Digital, or multi-level

dimming– Lighting Control – occupancy,

motion, timer

• Additional Requirements– Efficiency– Power Factor– Size – Cost– Fault handling (short circuit, open

circuit, overload, over temperature– Standards – Safety (UL,CSA,VDE)– Energy Star– Reliability

• Other Considerations– Mechanical connections– Installation– Repair / Replacement– Lifecycle– Logistics

18

Isolated Topology by Power Range

Increasing power & Power D

ensity

flyback

LLC HB resonant topology

Flyback is the best choice forLow power and LLC is bestchoice for highest efficiency

19

Offline LED Specific Standards• ENERGYSTAR™ SSL Specification (Version 1.1 -2/2009)

– Luminaire based limits, product specific requirements including power factor– No “off state” power requirement rules out standard wall plug adapters, exception are

devices with smart controls, standby < 0.5 W in those cases Electromagnetic & RFI per FCC 47 CFR Part 15/18

• IEC 61347-2-13 (5/2006) - Requirements for DC or AC supplied electronic control gear for LED Modules include:

– Maximum SELV operating output voltage <= 25V rms (35.3 Vdc)– “Proper” /Safe operation under various fault conditions:

• No LEDs testing and 2x the rated LEDs or modules• Output short circuited

– No smoke emission or flammability under malfunction

• ANSI C82.xxx LED Driver specification in development

• Safety – UL, CSA etc - UL1310 (Class 2) / UL 60950 / UL1012 – See appendix for more information

20

Basic Offline Topology

Flyback Controlleror converter

depending on power

Discrete orAnalog (NCP4300A)

implementation

21

20 W+ Universal NCP1351 Controllers

•Example based on NCP1351 20 W Universal input (DN06040)•Can support 350 mA to 1 A, design set for 700 mA, 33 Vdc

SimpleSecondary

Control

Variable Frequency

PWM Controller

ExternalHV FET

Discrete Regulator

22

NCP1351 LED Demo Board PerformanceEfficiency across Vf and Line (Iout = 700 mA nom)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0 5 10 15 20 25 30

LED Voltage (Vdc)

Effic

ienc

y (%

)

115 Vac230 Vac125 x 37 x 35 mm

23

Range of Low Power LED Driver Demo BoardsPout based on 90-265 Vac input range

0

5

10

15

20

25

Pout

(W)

NCP1013LED NCP1014LEDGT NCP1028LED NCP1351LED

IntegratedHV FET

24

Non-isolated Offline Buck Configuration

• Peak current controlled topology operating in deep continuous conduction

• Why:– Option to eliminate need for large electrolytic

output capacitor– Simple control scheme with “good” current

regulation– Can take advantage of the ON Semiconductor

DSS capability to power driver directly from the line

• Circuit should be optimized for the number of LEDs

25

Inverted Peak Current Control Buck

26

Regulate Peak – Control Valley

• Continuous Conduction Mode – Current is always flowing through the inductor

• L = (VIN,MAX – VOUT) * (VOUT / VIN,MAX) * (1/fs) *(1/ (%Ripple * Iout))

• Must respect minimum on-time (LEB + Tpd + MOSFET turn-off time)

27

Example: NCP1216 PCC Buck Circuit

• NCP1216 is directly powered from the ac mains simplifying startup and operation• Efficiency is a function of output power (current, # LEDs), external component

selection (FET, inductor, rectifier) and switching frequency• Dimmable through opto-coupler for safety isolation• DN06050 Design Note available demonstrates performance including EMI filtering

Iout = 500 mA (nom)

115 Vac

28

Considerations for 230 Vac Applications• Driving small strings of LEDs at high voltages results in extremely narrow duty cycles• Switching controllers have leading edge blank circuit of 200-400 ns before current is sensed• Switching frequency must be reduced for proper operation and input voltage is kept to a

minimum with a half wave rectified input circuit

100nFC1C2 1uF

C5

2.2uF

C3 1uF

C4 10uF

D1

D3MURA160T3

D2MMSD4148T1

R1

1R

R2

18k

LED

R4

10k

R3 2k

Q1STD1NK60 R5

2R2

L1

1mH

AC2

AC1

NCP1200U1

1

2

3

4 5

6

8

1/4W230Vac

400Vdc

16Vdc

MRA4003T3G

25Vdc

1/2W

1/4W

1W

1/4W

400Vdc

NCP1200 - 40kHz

0.2

0.25

0.3

0.35

0.4

195 205 215 225 235 245 255 265

Input Voltage (Vac)

LED

Cur

rent

(A)

29

Tapped Inductor ApproachExtends Duty Ratio, Increase Iout

30

Power Factor Requirements for Offline LED Drivers

• IEC (EU) requirements dictate THD performance for Lighting (over 25 W), other international standards apply depending on the region

• US DOE ENERGY STAR™ includes mandatory PFC for Solid State Lighting regardless of the power level. This is a voluntary standard and applies to a specific set of products such as down lights, under cabinet lights and desk lamps for example

– >0.7 for residential applications– >0.9 for commercial applications

• While not absolutely mandated in the for lighting in all countries, it may be required based on the application:– Utilities drive major commercial uses to have high PF at the facility level– Moreover when utilities owns/service the streetlight it is in their interest to have

good power factor, typically > 0.95+

31

Class C Limits

Harmonic Order nMaximum Value expressed

as a percentage of the fundamental input current23579

11 < n <= 39

230*λ

10753

λ is the circuit power factor

This class applies to lighting equipment exceeding 25 W

The standard equates to a THD<35% (PF around 0.94).In practice, lighting equipment suppliers may target THD<20%.

32

Improving Power Factor for Flyback Circuits • Traditional Flyback converters have a PF of ~0.5-0.55

• Improving this to > 0.7 for low power applications does not require new topologies, just circuit optimization

– Passive technique (Valley-Fill)– ONSEMI “haversine” flyback optimization– Critical Conduction Mode Flyback

• For high power applications like street lights, a dedicated PFC boost stage is normally used

D7 D5

D6 D4

D2

D1D3

R2

C2

C1

1 VF := 0

VF := 0VF := 0

VF := 0

VF := 0 VF := 0VF := 0

1u

1u

1k

33

NCP1014GTG Demo BoardR1 4R7

D1

MRA4007

D2

MRA4007D3

MRA4007

D4

MRA4007

J2-5

LED Cathode

1

R14820

R121K

R247K

R15

1K

T1C

E2- TESTPOINT

1

R6 1R8

C1100nF

C2220nF

L1 2.7mH

C4100nF

C5

2.2uF

Q1BC857

T1A

R11

100

Optional dimming components

T1B

5.1V

D8

C7 2.2nF

+C81000uF

+ C91000uF

J1-1

Line

1

24V

J1-2

Neutral

1

Q2BC846

R9 10R

R8 10R

3

2

C647uF D9

D5MURA160

R4200

U1

NCP1014

VCC1

FB2

DRAIN 3

GND4

1

4

Off

boar

d

C31.5nF

R3

3.3K

FL2

FL1

R52.2K

U21

234

Fly Leads

R7 1R8

8mm Primary-Secondary Boundary

J2-1

1

1

J2-6

- TESTPOINT

1

D7 MURS320T3

D6

MMBD914LT1

R1010K

C1010nF

E1+ TESTPOINT

1

R1310K

J2-2LED Anode

1

Slow loop responseto improve power factor

Reduce bulkcap to improvepower factor

Reduce cap toincrease dynamic

self supply frequency for improved EMI

Output capacitance Increased

34

Performance of “Haversine” Flyback

•DN06051 design note illustrates how to modifying the NCP1014 for higher PF > 0.8 using the “haversine” flyback optimization which easily meets US Residential Energystar Requirements

35

Demo: NCP1014GTG Portable Desk Lamp

Desk Lamp Magnetic Transformer

4 LED Cree MC-E Multichip Array

35 W Halogen

NCP1014 LED Driverwith PF Correction

795

744

Illuminance(Lux)*

0.96141.7 WHalogen(35 W bulb)

0.857 10.9 WQuad LED

PowerFactor

Pin (W)@ 120 Vac

Light Source

Summary of Results* Illuminance measures at 0.5 m

36

Achieving High Power Factor and Low Distortion

Secondary side controlis not draw for simplicity

High voltage dc node

NCP1652PFC

Controller

37

Area Lighting Considerations

• Light output varies significantly– Poll Height and Spacing– Type of Traffic Flow (residential, city center)

• Significant range of power and light levels required for area lighting

• One basic design can be scaled up or down in light output by adding LED light bars

• With a modular approach light bars are field upgradeable

LEDModulew/ CCR

PWM

DimmingControl

LEDLampw/CCR

PWM

LEDLampw/CCR

PWM

Power Supply

PFC IsolatedDC-DC

AC

Two Stage Modular ApproachAC-DC + Constant Current Stages

NCP1652

DCOutput

38

NCP1652 48 V Fixed Output SchematicIdeal for Fixed Voltage Area Lighting

R16

100, 1/2W

1

3 2

4

+

_

NCP1652 90 Watt LED Supply 48V, 2A Out, 90-265VAC Input

ACIn

48V2A

F12.5A

C1 C2L1

R1T1

3.3uH

12345

678 9

10111213141516

L2

L3

D1 - D41N5406 x 4

0.47"X"

0.47"X"1M

0.5W0.1uF400V

C3

D5

MRA4007T

1.5K

E440

AZ1R2560K0.5W

C422uF400V

D6

D7 D8

Z2

Z3

NCP1652

U1

U2

U3

Q1

2K 100

100

R3

R4

R5R8

R7 R6

R9 R10 R11

R12

R13 R14

R15

R17

R18 R19R20

R21

R22

R23

R24

R25

R26

R27

R28R29

R30

C5 C6

C7

C8

C9 C10

C11C12 C13

C14

C15 C16 C17 C18

C19 C20 C21 C22

C23

C24

C26

C25TL431A

10K

3.3 ohm

10

0.1 0.1

24K 1uF

102K

5.6K

2.7K

1K

0.1

100,63V

680uF,63V x 3

MMSZ5248B

MMSZ5245B

D9 MMSD4148T

MURS120T

MURS160T

1/2W

C27

2.2nF "Y"

36K3W 100nF

400V

SPP11N80C3

100uF35v

470uF35V

0.1u

F

76.8

K

49.9

K

39K10nF

100K

33nF

2.2K

470pF

7.32

K

8.6K

1nF

+

4.7uF25V

0.10ohm0.5W

680p

F

365K 365K

365K332K30.1K

Notes:

1. Crossed schematic lines are not connected.2. Heavy lines indicate power traces/planes.3. Z2/D9 is for optional OVP (not used).4. L1 is Coilcraft BU10-1012R2B or equivalent.5. L2 is Coilcraft P3221-AL or equivalent.6. L3 is Coilcraft RFB0807-3R3L or equivalent.7. Q1 and Q2 will require small heatsinks.

SFH615A-4

1

2

5

61nF

0.11nF

0 ohm

NC

0.1

(6:1)

D10

MR

A400

7T

D11

MMSD4148T

MUR860

R31

3.3K1/4W

Z4 (24V)MMSZ5252B

27K

8

11

39

NCP1652 Efficiency ResultsConfiguration: 48 V / 2 A

80

82

84

86

88

90

92

94

10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

% of Full Load

Effic

ienc

y (%

)

115 V ac230 V ac

40

Modifying Secondary Side for CC/CV Operation

Vf = 45 Vdc

Efficiency

41

NCL30000 CRM Isolated Flyback• Low Power (5-20 W) also need high power factor

– LED Drivers/Ballasts– Downlights / Spot Lights / Outdoor Lighting

• Key Objectives– Directly drive LEDs with tight constant current output regulation– High Power Factor >0.9, IEC Class C Harmonic Content– Greater than 80% efficiency at low power levels 5-15 W Pout, 83% typical– Scale-able to handle a range of power LEDs and current levels– Can support existing dimming solutions (TRIAC and Trailing Edge)

• Design approach to achieve high power factor in a single stage uses a critical conduction mode (CrM) fixed on-time flyback topology

42

NCL30000 Basic Application Diagram

Q1

EMI FILTER

1

2

3

4

8

7

6

5

Cin

RCS

D1

C1

Ccomp

Ctim

Ry

RLED

RZCD

RL

R2

R1

RSU

MFP

COMP

Vcc

DRV

GND

ZCD

CT

CS

AC Line Input

Dout

COUT

Rc

Rt

Ra

RbRx

GND

4

3

2

1

7

8

5

6

IN1+

NCS1002IN1-

IN2-

IN2+

OUT1

OUT2

VCC

NCL30000

+

-

+

-

Cc

Cv

43

Theory of Operation• Fixed on-time control

results in sinusoidal input current in phase

• Key Requirements– Input capacitance

must be very low– Control bandwidth

must be low (<20 Hz) to maintain constant on-time over a line cycle

• Secondary feedback controls on-time based on line and load

44

NCL30000 Demo Requirements • Intended to supply 350 mA and drive a wide range of LEDs (4-15) LED

driver applications. Component selections to support 700 mA or higher output current

• Reference design is targeting <20 W with this transformer, board can also support larger transformer for higher power

• Scalable solution for different power levels– 115 Vac Version - 90-130 Vac– 230 Vac Version 180-265 Vac– 90 – 305 Vac – Extended universal included 277 Vac - no Triac control

• For Triac Dimming, on time has to be adjusted for a specific number of LEDs to achieve best dimming performance. Default is 12 LEDs

• Robust Protection– Open LED, Shorted Output, Overload

45

NCL30000 Demo Board

Dual transformer footprints for 15 W / 30 W Designs

46

Efficiency and Current Regulation versus LoadNCL30000 115 Vac Demo Board

300

310

320

330

340

350

360

370

0 10 20 30 40 50 60

LED Forward Voltage (Vdc)

LED

Cur

rent

(mA

)

72%

74%

76%

78%

80%

82%

84%

86%

Effi

cien

cy (%

)

Efficiency ->

47

4

5

6

7

8

9

10

11

12

13

14

90 95 100 105 110 115 120 125 130 135

Input Voltage (Vac)

Inpu

t Cur

rent

TH

D (%

)

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

Pow

er F

acto

r (PF

)

THDPower Factor

Power Factor and Harmonic DistortionNCL30000 115 Vac Demo Board

48

Line Dimmable LED Drivers

• Triac dimmers (leading edge, phase cut) are intended for resistive loads and tend to behave badly when connected to an electronic transformer

• Some manufacturers have “specialized”dimmers –for electronic transformers such as low voltage track lighting

• Moreover for commercial applications there are also transistor based dimmers that have falling edge control (three wire connection)

• Triac dimming is common in residential a ndretail application

49

Matching LED Driver to Dimmer

•A typical switch mode power supply feedback system will attempt to maintain constant output over a wide range of input voltage by increasing duty cycle or in this case on time

•For line dimming, LED current should reduce proportionately to reduction of the RMS input voltage

•The maximum on time is set to limit the power at the nominal LED string power

•During dimming, the controller will not be able to increase on time, so natural dimming of the LED occurs in a predictable manner

50

Efficiency and Current Regulation versus LoadNCL30000 115 Vac Demo Board

0

10

20

30

40

50

60

0 100 200 300 400 500 600 700 800

LED Current (mA)

LED

Vol

tage

(Vdc

)

ConstantCurrentRegion

ConstantPowerRegion

LED PowerDimming Point

Short ProtectionRegion

51

NCL30000 350 mA Isolated Flyback 115 Vac / 12 LED / Triac Dimming Version

0

50

100

150

200

250

300

350

400

20 30 40 50 60 70 80 90 100 110 120 130 140

Input Voltage (Vac)

LED

Cur

rent

(mA

)

10%

20%

30%

40%

50%

60%

70%

80%

90%

Effic

ienc

y

52

NCL30000 350 mA Isolated Flyback115 Vac Line Dimming Control - 12 LEDs in Series

0

50

100

150

200

250

300

350

400

0 20 40 60 80 100 120 140 160 180

Conduction Angles (degrees)

LED

Cur

rent

(mA

)

Leviton SureslideLeviton ElectronicCooper AspireLutron SkylarkLeviton IllumittechLutron Digital FadeLeviton RotaryGE DI 61Lutron Toggler

53

Comments on Triac and Transistor Dimming• As illustrated, dimming range is highly dependent on the

characteristics of the wall dimmer

• Triac dimmers were originally designed for incandescent lamps and presented a much higher load (4-5x higher) than a LED replacement down-light

• Unfortunately each manufacturer has different dimmer characteristics

• As LED lighting enters the mainstream we would expect dimmer manufacturers to start optimizing their products to LEDs

54

6

7

8

9

10

11

12

13

14

90 115 140 165 190 215 240 265 290 315

Input Voltage (Vac)

Inpu

t Cur

rent

TH

D

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

Pow

er F

acto

r

THDPower Factor

Power Factor and Harmonic DistortionNCL30000 90-305 Vac Demo Board

55

300

325

350

375

400

90 110 130 150 170 190 210 230 250 270 290 310

Input Line Voltage (V ac)

Iout

(mA

)

70%

72%

74%

76%

78%

80%

82%

84%

86%

Effic

ienc

y (%

)

Efficiency and Current Regulation versus LoadNCL30000 90-305 Vac Demo Board (Vout = 12 LEDs, 37 Vdc)

Efficiency ->

56

EMI PerformanceNCL30000 Demo Board (90-305 Vac Version)

57

Isolated High PF Efficiency/Solutions

CRM + Resonant Half Bridge

CCM single stage NCP1652/NCL30001* (PWM dimmable)

85%

80%

90%

25 50 75 100Output Power

Effi

cien

cy

CRM Flyback

Output Current 0.3-3 A

Universal Input

NCL30000

* Available Dec 2009

58

100-200 W CRM/LLC High Power Streetlight Supply

NCP1397

59

50k hours of LED life is great but ….

Occasionally there can be failures

Caused by. . .

LED infant mortality

Assembly Partial Defects

Transients

Some Application Are. . .

Mission Critical

Safety Dependent

Difficult Access

60

NUD4700 LED Shunt Protection

•Protects operation in the event of an open LED fault

•Supports up to 1 A with proper heat sinking

CurrentSource

NUD4700 inPowerMite Package

61

LED Lighting Must be Approached as a System

62

Conclusion• Offline LED power solutions continue to evolve in a rapid

manner as new LEDs are introduced

• Variety of offline solutions depending on power level, features, and performance

• ON Semiconductor has a complete portfolio of PFC and PWM controllers and converters to address range of LED power applications

• Visit the ON Semiconductor website to see what new reference designs are being introduced optimized for specific AC line powered LED applications

63

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