CY8CLED04D01 25 W LED Driver Using CY8CLED04D01 Output 20 V; 350 mA with PFC, Universal AC Input 90 V to 264 V AC

Reference Design Guide Doc. No. 001-62217 Rev. **

Cypress Semiconductor 198 Champion Court San Jose, CA 95134-1709 Phone (USA): 880.858.1810 Phone (Intnl): 408.943.2600 http://www.cypress.com

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Copyrights © Cypress Semiconductor Corporation, 2010. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be used for medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges. Trademarks ®

®

PSoC Designer™ and Programmable System-on-Chip™ are trademarks, and PSoC and PowerPSoC are registered trademarks of Cypress Semiconductor Corporation. All other trademarks or registered trademarks referenced herein are property of the respective corporations. Source Code Any Source Code (software and/or firmware) is owned by Cypress Semiconductor Corporation (Cypress) and is protected by and subject to worldwide patent protection (United States and foreign), United States copyright laws and international treaty provisions. Cypress hereby grants to licensee a personal, non-exclusive, non-transferable license to copy, use, modify, create derivative works of, and compile the Cypress Source Code and derivative works for the sole purpose of creating custom software and or firmware in support of licensee product to be used only in conjunction with a Cypress integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or representation of this Source Code except as specified above is prohibited without the express written permission of Cypress. Disclaimer CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Cypress reserves the right to make changes without further notice to the materials described herein. Cypress does not assume any liability arising out of the application or use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress’ product in a life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges. Use may be limited by and subject to the applicable Cypress software license agreement.

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25 W LED Driver Using CY8CLED04D01 Reference Design Guide, Doc. No. 001-62217 Rev. **

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Contents

1.

Introduction ............................................................................................................................................................ 5 1.1 Reference Design Contents............................................................................................................................. 5 1.2 System Specification ....................................................................................................................................... 5 1.3 Output Characteristics ..................................................................................................................................... 5 1.4 Circuit Overview .............................................................................................................................................. 6 Document Revision History ....................................................................................................................................... 6

2.

Design Guidelines .................................................................................................................................................. 7 2.1

2.2 2.3 2.4 3.

Voltage and Current Characteristics .................................................................................................................... 11 3.1 3.2 3.3

4.

Input Voltage and Current (AC)...................................................................................................................... 11 PFC Stage Output Voltage and Ripple ........................................................................................................... 12 LED Driver Output Current and Ripple ........................................................................................................... 13

Performance Metrics ............................................................................................................................................ 15 4.1 4.2 4.3

5.

PFC Front End AC-DC Converter .................................................................................................................... 7 2.1.1 Design Specifications and Pre-design Choices .................................................................................... 7 2.1.2 Preliminary Calculations ...................................................................................................................... 8 2.1.3 Operating Conditions - Current ............................................................................................................ 8 2.1.4 Transformer ........................................................................................................................................ 8 2.1.5 MOSFET Selection ............................................................................................................................. 9 2.1.6 Catch Diode Selection......................................................................................................................... 9 2.1.7 Output Capacitor Selection.................................................................................................................. 9 2.1.8 Clamp Network Selection .................................................................................................................... 9 2.1.9 Multiplier Bias and Sense Resistor Selection ....................................................................................... 9 2.1.10 Feedback and Control Loop Component Selection............................................................................... 9 PowerPSoC LED Driver Circuit ........................................................................................................................ 9 Transformer Design Specification .................................................................................................................. 10 Schematic..................................................................................................................................................... 10

Efficiency ...................................................................................................................................................... 15 Power Factor ................................................................................................................................................ 16 Total Harmonic Distortion (Amps) .................................................................................................................. 16

EMI Compliance .................................................................................................................................................... 17 5.1

EMI Compliance............................................................................................................................................ 17 5.1.1 EN 55022 Class B, Line and Neutral Input (120 V, 60 Hz Input Voltage) ............................................. 17 5.1.2 EN 55022 Class B, Line and Neutral Input (230 V, 60 Hz Input Voltage) ............................................. 18

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1. Introduction

®

This reference guide describes a 25 W LED driver design using the CY8CLED04D01 PowerPSoC device. This design is capable of driving four channels of LEDs (string forward voltage of 18 V typical) at 350 mA. The design is tested for compliance with conducted EMI specification (EN 55022 Class B). Though the reference board is not certified for Underwriters Laboratories (UL) safety compliance, it is designed with due consideration of safety requirements. The objective of this reference design is to provide a starting point for designing constant current applications with power requirements in the order of 8 to 25 Watts.

1.1 1. 2. 3. 4. 5. 6.

1.2

Reference Design Contents Reference design guide (this document) Schematics Bill of materials PCB layout files (in Altium Designer format) PCB Gerber files Firmware

System Specification

This reference design works on AC mains voltage between 90 V and 264 V, 50/60 Hz. Table 1-1. System Specifications Symbol

Description

Min

Typ

Max

Units

VIN

Input AC voltage

90

120 / 230

264

Volts (V)

fAC

Frequency

47

50 / 60

63

Hertz (Hz)

Conducted EMI

Meets EN 55022 Class B

Dimming

TRIAC dimmable

1.3

Output Characteristics

This reference design drives a load of 6 white LEDs per channel, with typical forward voltage of 3 V per LED. The efficiency and power factor are functions of the input voltage. The following table lists the desired output characteristics: Table 1-2. Output Characteristics Symbol

Description

At VIN = 120Vac

At VIN = 230Vac

Units

Comments

VOUT

Output voltage

20

20

V

20 V maximum, 18 V typical

IOUT

Output current

350

350

mA

350 mA taximum

POUT

Continuous output power

25

25

W

25 W maximum

Efficiency

> 80

> 80

%

Peak efficiency

Power factor

> 0.98

> 0.92

PF

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Introduction

1.4

Circuit Overview

This LED driver circuit with CY8CLED04D01 uses a PFC stage as its front-end. This front-end AC/DC converter is based on flyback converter topology using L6562 transition mode (TM) power factor (PF) controller; with primary-side current sensing and secondary-side output voltage sensing for output voltage regulation. In addition to the primary and secondary windings, a third winding provides zero cross detection and power to the L6562. This transformer provides necessary isolation for the output from the AC mains supply. The switching frequency (fsw) of the PFC stage is controlled by the L6562. While regulating output voltage, the device operates in transition mode where TON is determined by the primary peak current and TOFF is determined by flyback transformer reset time. The LED driver stage, designed with Cypress’ PowerPSoC device, is used to drive 4 channels of LEDs in the floating load buck configuration. For more information on designing with PowerPSoC, refer AN52699 – Floating Load Buck Topology for HB LEDs and AN51012 – PowerPSoC Firmware Design Guidelines.

Document Revision History

6

Revision

Issue Date

Origin of Change

**

07/01/2010

SNVN

Description of Change New reference design guide

25 W LED Driver Using CY8CLED04D01 Reference Design Guide, Doc. No. 001-62217 Rev. **

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2. Design Guidelines

This section illustrates how to design the 25 W LED driver using CY8CLED04D01 for the specifications listed in Table 1-1 and Table 1-2 on page 5. The suggested component values provide a starting point and later help optimize the design for various criteria such as efficiency, power factor, or EMI compliance.

2.1

PFC Front End AC-DC Converter Figure 2-1. L6562 Based PFC Front-end AC-DC Converter

Figure 2-1 shows a L6562 based AC/DC converter configuration that uses the functionality of L6562 for performing power factor correction. This topology works in transition mode, that is, on the boundary of continuous and discontinuous inductor current mode. The input capacitance is small; so the input voltage is close to a rectified sinusoid. The control loop has a narrow bandwidth for minimum sensitivity to the double of mains frequency ripple appearing at the output bulk capacitor. The design equations given in application note ‘AN1059: Design Equations of High-Power-Factor Flyback Converters based on the L6561’ from ST Microelectronics, form the bases for the component values. The important design choices are mentioned in the following sections.

2.1.1 Design Specifications and Pre-design Choices 

Mains voltage range: VACmin = 90 Vac, VACmax = 264 Vac



Minimum mains frequency: fL = 47 Hz



DC output voltage: Vout = 28 V



Maximum output current: Iout = 1 A



Maximum twice line frequency output ripple: ΔVo = 3 V



Minimum switching frequency: fswmin = 100 KHz

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Design Guidelines



Reflected voltage: VR = 100 V



Leakage inductance overvoltage: ΔV = 70 V



Expected efficiency:

= 90%

2.1.2 Preliminary Calculations From the design specifications and pre-design choices, we can calculate the preliminary operating conditions. 

Minimum input peak voltage: VPKmin = VACmin x



Maximum output peak voltage: VPKmax = VACmax x



Maximum output power: Pout = Vout x Iout = 28 x 1 = 28 W



Peak-to-reflected voltage ratio: Kv = 1.233

2 = 123 V 2 = 372 V

2.1.3 Operating Conditions - Current Figure 2-2 shows the typical current waveforms. 

Peak primary current: IPKp = 2.030 A



RMS primary current: IRMSp = 0.585 A



Peak secondary current: IPKs = 6.53 A



RMS secondary current: IRMSs = 1.895 A Figure 2-2. High PF Flyback Current Waveform in Transition Mode

2.1.4 Transformer VPK min = 273 μH (1 K V ).fsw min.IPKp



Primary inductance: L p



The catch diode at the output has a typical forward drop of 0.85 V.



Primary to secondary turns ratio: n

8

( Vout

VR catch _ diode _ drop )

3.4

25 W LED Driver Using CY8CLED04D01 Reference Design Guide, Doc. No. 001-62217 Rev. **

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2.1.5 MOSFET Selection 

Maximum drain voltage: VDSmax = VPKmax + VR + ΔV = 542 V

An ST device, STP24NM65N, capable of withstanding 650 V (drain to source) is selected. The RDSon of this device at 25 oC is 0.19 max.

2.1.6 Catch Diode Selection 

Maximum reverse voltage: VREF max

VPK max n

Vout = 135 V

A 200 V Schottky diode, STTH4R02U, is selected to minimize conduction losses. The current rating of the device is selected to be 60% of the required peak secondary current.

2.1.7 Output Capacitor Selection The minimum capacitor value that meets the voltage ripple specification at 100/120 Hz ripple is Coutmin = 700 μF. Two capacitors of 470 μF, 50 V are used.

2.1.8 Clamp Network Selection With a proper construction technique, the leakage inductance can be reduced to less than 2% of the primary inductance. A clamp network comprises of a TVS and a blocking diode. The clamp voltage is VCL = VR + ΔV = 170 V. The TVS selected is P4SMA170A and the blocking diode is an RS1J-13-F.

2.1.9 Multiplier Bias and Sense Resistor Selection Assuming a peak value of 2.4 V (@Vac = 264 V) on the multiplier input, the peak value at minimum line voltage is 0.8 V which, multiplied by the maximum slope of the multiplier, 1.9, gives 1.52 V on the current sense. This is acceptable because the linearity limit is not exceeded. Considering 120 μA current for the divider, the lower resistor is 20 K and the upper resistor is 3 M . The sense resistor value should not exceed 0.492

. Its power rating is (0.585)2 x 0.43 = 147 mW if 0.43

is selected.

2.1.10 Feedback and Control Loop Component Selection The TL181-GB opto-coupler from Toshiba is selected. It is operated with 2.5 mA quiescent collector current. From the part’s datasheet, with 2.5 mA collector current, the diode current can be between 0.4 and 2.5 mA (1 < CTR < 6). An emitter resistor of 1 K gives the desired collector current. The bias resistor can thus be selected to be 10 K . The output divider can be selected to be 16.5 K and 1.62 K For the ZTL431 part that is biasing the opto-coupler with the feedback network of 7.4 μF and 4.7 K , the zero is at about 5 Hz. By selecting the feedback components of 120 K and 0.47 μF at the compensation pin of L6562, the open loop cross over frequency and phase margin is 1.7 Hz and 69.4o respectively. These components also ensure that the phase of o 100/120 Hz voltage ripple feedback signal is less than 180 which helps avoiding positive feedback of the ripple.

2.2

PowerPSoC LED Driver Circuit

The LED driver circuit is based on the CY3268 PowerPSoC Lighting Starter Kit design. The specifications of the driver circuit in this reference design are: 

Input voltage: 26 V minimum and 30 V maximum



LED output current per channel: 350 mA maximum



Expected efficiency: greater than 90%



Expected switching frequency: 800 kHz



Inductor current ripple: 30% of peak average current, that is, 30% of 350 mA = 105 mA

The schematic of the CY3268 kit is used in this design to achieve the stated specifications.

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Design Guidelines

2.3

Transformer Design Specification

The transformer specifications obtained from the above calculations may not always result in a feasible winding structure. Also, the primary magnetizing inductance may have to be increased in order to reduce the switching frequency and hence the switching losses in the system. The current sense resistance may have to be tuned based on the efficiency of the transformer and the accuracy of its turns-ratio. The transformer is one of the most important components in this LED driver circuit. The third winding is called the bias or sense winding. This reference design uses transformers manufactured by Renco Inc., USA. The specifications are as follows: 1.

Electrical specifications a. b.

2.

Materials a. b. c. d.

3.

Primary inductance = 0.32 mH at 10 kHz Primary leakage inductance ≤ 4.5 µH at 10 kHz

Core: EF20 (Ferrite material TDK PC40 or equivalent) Bobbin: LCP 4008 UL94-VO Magnet wires: Type Polyurethane Polymide-130oC NEMA MW 28, TEX E triple insulated wire Layer insulation tape: 3M Yellow Mylar or equivalent

Finishing a. b.

Varnish the complete assembly Flux band connected to pin 1 of transformer (Primary GND)

Renco Part Number: RL-9486 Figure 2-3. Transformer Schematic

2.4

Schematic

The stated guidelines provide a method to arrive at a first-pass schematic that can be used to prepare a prototype of this design. The final schematic of the 25 W reference design is in the document package.

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3. Voltage and Current Characteristics

This section documents the input and output, voltage and current characteristics of this LED driver reference design. Bench tests have been performed at both 120 V/60 Hz and 230 V/50 Hz. An LED load of 25 W is used for testing purposes.

3.1

Input Voltage and Current (AC)

Figure 3-1. Input Voltage and Current at 120 V, 60 Hz

Figure 3-2. Input Voltage and Current at 230 V, 50 Hz

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Design Guidelines

3.2

PFC Stage Output Voltage and Ripple

The waveforms in Figure 3-3 and Figure 3-4 show that the AC/DC front-end is controlling the output voltage ripple per design. Figure 3-3. PFC Stage Output Voltage and Ripple at 120 V, 60 Hz

Figure 3-4. PFC Stage Output Voltage and Ripple at 230 V, 50 Hz

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3.3

LED Driver Output Current and Ripple

The waveform in Figure 3-5 shows that the PowerPSoC device is able to regulate current to the set point. Figure 3-5. LED String Current, Channel 1

Figure 3-6. LED String Current Ripple, Channel 1

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Design Guidelines

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4. Performance Metrics

This section documents the system performance metrics of this reference design, including efficiency, power factor, along with notes on the key components that affect each of these metrics.

4.1

Efficiency

Efficiency is one of the most important performance metrics for any power supply system. Higher driver efficiency reduces the losses that are otherwise dissipated as heat. Based on validation of LED driver circuits built using the CY8CLED04D01, there are three key components that determine the overall system efficiency: 1.

Transformer

2.

Output Diodes

3.

Switching MOSFETs Figure 4-1. Variation in Efficiency With Input Voltage

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Design Guidelines

4.2

Power Factor Figure 4-2. Variation of Power Factor With Input Voltage

4.3

Total Harmonic Distortion (Amps) Figure 4-3. Variation of THD With Input Voltage

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5. EMI Compliance

This section captures compliance test reports from conducted EMI measurements of this reference design per EN 55022 Class B standard. The compliance test data is collected at a Cypress laboratory for pre-compliance testing.

5.1

EMI Compliance

Conducted emissions data for EN 55022 Class B is collected at 120 V and 230 V, 60 Hz input voltage. Data is collected separately for the Line and Neutral inputs but is presented in the same plot. When conducting the test, the output of the reference design is connected to four strings of six LEDs (forward voltage of about 18.3 V).

5.1.1 EN 55022 Class B, Line and Neutral Input (120 V, 60 Hz Input Voltage) Figure 5-1. EN 55022 Class B, Line and Neutral Input (120 V, 60 Hz Input Voltage) dBuV

80 EN 55022; Class B Conducted, Average EN 55022; Class B Conducted, Quasi-Peak

70 60 50 40 30 20 10

120V Line Peak 120V Neutral Peak

0 -10 -20 1 5/21/2010 6:47:42 PM

10 (Start = 0.15, Stop = 30.00) MHz

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5.1.2 EN 55022 Class B, Line and Neutral Input (230 V, 60 Hz Input Voltage) Figure 5-2 shows the conducted emissions measured on the Line and Neutral input for EN 55022 Class B and the peak measurements provide at least 11 dB margin from the limit line. Figure 5-2. EN 55022 Class B, Line and Neutral Input (230 V, 60 Hz Input Voltage) dBuV

80 EN 55022; Class B Conducted, Average EN 55022; Class B Conducted, Quasi-Peak

70 60 50 40 30 20 10

230V Line Peak 230V Neutral Peak

0 -10 -20 1 5/21/2010 6:54:53 PM

18

10 (Start = 0.15, Stop = 30.00) MHz

25 W LED Driver Using CY8CLED04D01 Reference Design Guide, Doc. No. 001-62217 Rev. **

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