led driver load -- 63110a introduction working on better solutions

LED Driver Load -- 63110A

Introduction

Working on Better Solutions


Agenda

1. LED & LED Driver Introduction

2. Disadvantage of General E-load for Testing LED Driver

3. Chroma 63110A LED Driver Load Introduction

4. Conclusions


LED Driver E-load

LED Driver E-Load

LED Driver

LED

1. UUT ： LED driver2. LED driver powers the LEDs3. E-load simulates the LEDs

∥


The Category of LED

LED is classified by POWER and CURRENT

1. Traditional LED: For indicator light. Current: 10mA – 80mA Voltage: 0.7V Power 0.06W≦

2. Power LED: High brightness for lighting. Current: 350mA, 500mA, 700mA Voltage: 3.2V Power: 1W, 1.5W, 3W


Power/High brightness LED Application

Lighting: Use Power LED to be lamps and lanterns.

1. Outdoor lighting: Table lamps, Wall lamps, Ceiling lamps, Integrated

lighting.

2. Outdoor lighting: Garden light, Street/Road lamps.

Traditional lighting like halogen bulb/tube will be replaced by LED.

LCD backlight: Monitor, Notebook, TV.

1. Because of the low monitor cost and low notebook power(3-4W), their test

requirements are limited.

2. TV backlight: LED’s features include “lightweight, power saving (to meet the

requirement of Energy Star), RGB high chromaticity.” But it is more complex,

with high quality requirements, and therefore has greater testing requirements.


LED Driver Introduction

LED driver are required to power LEDs.Power LED driver: Classify by power

1. 1W-5W: a. Driven by IC directly, less components, integrated circuitry. b. Less test requirements.

2. ≥ 5W: a. AC or DC input, like general power supplies

b. Most LED drivers are designed as Constant Current, the

voltage will increase with LED numbers.

c. Probably independent product, more components and greater

testing requirements.


• LCD Backlight: TV– Including power supply outputs (4 channels) and multiple LED Drivers– Voltage＜ 500V (Commonly), Current ＜ 100 mA

• Indoor/Outdoor Lighting: Table lamps, Wall lamps, Ceiling lamps, Integrated lighting, Garden light, Street/Road lamps. (>5W)– Voltage ＜ 500V, Current ＜ 1A – If the LED Driver is CV+CC type, its current may be 1A≧ Even up to 20A.

63110A Target Market


LED Characteristic1. Nonlinear V-I curve.

2. Forward Voltage (VF).

3. Small Current (several hundreds mA).

4. Brightness decided by POWER.

5. Small equivalent capacitance.

≠�Rb

RL

VFVf

I

V

LED curve

Vo

Io Rd

LED Introduction


• LED driver Type• Voltage source

• Current source

• Voltage Source LED driverDisadvantage ： Due to the different LEDs having different forward

voltages(VF), the current flowing through the LEDs will vary, causing a difference in the brightness of the LEDs.

• Current Source LED driver• The brightness of the LED is determined by power, if Vf is fixed then the

brightness can be controlled by the current ( P= I ×V).

• Hence most LED driver designs are of the Constant Current type.




Power LED driver: CV+CC Type of LED driver1. The output is constant voltage under no load.2. When the loading current reaches a certain point, the output voltage drops

and the LED driver operates in constant current mode.3. Similar to DC Source design, and different from constant current LED

drivers.4. Has larger output current specification (>2A), and requires current

balance control circuit or device.

Can be tested using general E-Load by CV mode,but can not simulate “Turn on” status.

Use multi-channels of LED load simulator paralleling to get higher current.

Balance device


• 6% V error => 60% power error!!

• 6% I error => 6% power error!

• From the LED V-I characteristics a slight change in the voltage will cause a big change in the current.

• Hence most LED drivers are of constant current design.

Why LED Drivers are Designed as Constant Current？


LED Driver Structure

Dimming duty control

Current feedback

Power LED driver: CC Type of LED driver

Control output current, output voltage depends on LEDs, unlike SMPS with constant output voltage

OVP

LED in series


LED Driver Specification

Test Equipment

AC Source

Power Meter

LED Load Simulator

AC Source +Power Meter


• Temperature/aging of the LEDs may cause different test results

• Different series number of LEDs required for testing different voltage ranges of the LED drivers, not convenient

• Different types of LED have different VF 、 Rd values, users will need to prepare many different LEDs for verifying the LED drivers functions.

• More often than not if one LED of Light Bar is damaged during testing it may not be obvious.

• A LED Load Simulator is suggested to be a standard load for LED driver test.

Why LEDs are Not Suggested to Use for LED Driver Testing


Problems with General E-Loads (1)

I

V

LED curve

Vo

Io Rd

CR mode (R=Vo/Io) CV mode

Only able to test LED stable characteristics

1. Unable to test and verify LED driver startup characteristics and simulate different LED characteristics. 2. Unable to simulate the ripple current.

Stable operating point



Internal impedance of E-load may cause LED driver OCP or OVP.

General E-load

Resistance Load General E-load CR Mode

63110A

63110A

V/I overshoot

Overshoot then fail



General E-load response is too slow, it can not support to test PWM mode of dimming for LED driver.

63110A E-load has increased bandwidth to meet the test.

63110A LED modeLED load



General E-Load may encounter unstable voltage and current measurements.

First, check the UUT output is stable or not. Users can use Average

method for stable measurements

Max: 64 times

6310A series set the average times


LED Driver Load

Chroma designed an E-Load especially for LED Driver

Model 63110A: dual channel LED Driver Load Voltage Range: 0 ~ 60V / 0 ~ 500V Current Range: 0 ~ 0.6A / 0 ~ 2A Mode: LED mode, for simulating LED characteristics also included are CC, CR, CV mode (CC mode does not support dynamic loading)


Purpose of LED Driver Load

Purpose of 63110A: Simulate LED characteristics, and be used for verifying LED Driver.

1. Check the turn on condition for different LED. OCP/OVP is not allowed.

2. Check the inrush current when turn on. If over spec, it will damage LED.

3. Check if all spec is OK within the operating voltage range (LEDs in series).

4. Check the accuracy of output current when it stays on stable condition

5. Check the ripple current when it stays on stable condition

6. Check the operation is OK when PWM dimming. OCP/OVP is not allowed.

7. Check the current balance for PWM dimming of multi-channel driver


63110A designed to simulate LED characteristics, the following parameters are used to determine the loading characteristics

1. Vo: LED driver operating voltage

2. Io: LED driver operating current

3. Rd Coefficient: Operating resistor coefficient

4. Rr: High frequency resistor

Setting Parameters

LED mode

Turn ON “LOAD” before turn on Driver


1. Vo: operating voltage

2. Io: operating current

Press MODE key to choose LEDH (High V range) or LEDL (Low V range), then press ENTER to edit Vo and Io.

Vo & Io Setting


Rd or Coefficient: Operating resistor

coefficient

Press CONF. key, then press key to

choose Rd or Rd Coeff

Rd Coeff.: 1. Default.=0.1 2. Set range: 0.001 ~ 1.

Rd Coefficient Setting

V

I

Vo

Io

Vf


Definition:Vo: LED operating voltageIo: LED operating currentVF: LED Forward voltageRd: Operating resistor

What is Rd Coefficient？

VF Vo

Io Rd

V

I

The relationship of the four variables above can be described by the following equation

doFo RIVV

oF VaV 1aEg. ，

o

o

o

oddoodooo I

VCoeff

I

VaRRIVaRIVaV .)1()1(∴

Rd is therefore calculated as the ratio of Vo and Io multiplied by a coefficient (Coeff<1)


Method 1: Example: The V-I curve of a LED is shown in the diagram below. For a light

bar with 10 LEDs, the LED driver will need to output 350mA

How to get a suitable Rd Coefficient？

How is Rd calculated for a LED with operating current of 350mA, and a operating voltage of 3.44V?

From the V-I curve on the right, Rd can be calculated from the slope of the line

Rd of the one LED

7.13.04.0

35.352.3dR

Therefore the Rd Coeff. is:

173.0.7.135.0

44.3.. CoeffCoeff

I

VCoeffR

o

od


The Advantage of Setting the Rd Coefficient

Why set Rd Coefficient instead of the operating resistor Rd?

1. LED drivers are usually specified with an output voltage range (eg. 3~36V), this indicates that the LED driver can drive different number of LEDs in series.

2. When testing LED driver, the voltage range must be tested.

3. Different output voltage means different numbers of LEDs in series, hence it has different Rd values.

4. It is therefore inconvenient to change the value of Rd every time the output

voltage changes.


The Advantage of Setting the Rd Coefficient

Why set Rd Coefficient instead of the operating resistor Rd?

5. Because Rd is proportional to the output voltage, therefore by setting the

Rd Coefficient, 63110A will calculate the corresponding Rd value.

V

I

Vo1 Vo2 Vo3 Vo4

IoRd1 Rd2 Rd3 Rd4


7.13.04.0

35.352.3dR

287.0.3035.0

5.36. CoeffCoeffRd

33.04.0

5.38.3dR

173.0.1735.0

4.34. CoeffCoeffRd

Verifying Different LEDs

Different types of LED need to be considered when testing LED drivers.

A example: LEDs with 350mA current will have different Rd and Rd coefficient values. By setting the different Rd coefficients 63110A can simulate different types of LED for LED driver testing.



Method 2:LED driver designers sometime do

not know the character of LED they

used. So, they can not calculate Rd

Coefficient directly.

From the following two formula, V

I

Vo

Io

Vf1 Vf2 Vf3

Rd1/ Rd2/ Rd3

doFo RIVV

o

od I

VCoeffR . o

fo

V

VVCoeff

.We can get a new formula:

That means Rd Coeff can be calculated from Vf.



When output voltage is over Vf, the current stat to flow. Users can get Vf

value from the power-on waveform of LED driver.

From the formula , we can get Coeff = (42-37)/42 = 0.119o

fo

V

VVCoeff

.

Vo = 42V

Vf = 37V

V

I

Example:



Set parameters on 63110A, Vo=42V, Io=750mA, and set Rd Coeff = 0.119. The test result is very similar to the real LED load. Users can fine-tune Rd Coeff to approach and get better waveform.

If users set a wrong value of Rd Coeff (=0.5), they will get a different result.

V

I

V

I


1. 63110A will calculate and simulate the LED characteristics from the

Vo, Io, Rd coefficient settings, as shown in the diagram below, Vo and

Io are not the real loading values.

2. Io is determined by the LED driver, if the Io varies from the setting

value then Vo will also vary. This is different concept from CC and

CV mode of normal E-load.

doFo RIVV

VF Vo

Io Rd

V

I

Vo & Io Setting and Measured Vo & Io d


Vo & Io Setting and Measured Vo & Io d

1. For example, if Io is set to 100mA, and the real LED driver output Io’=110mA, then Vo will not be the setting value. So, the real Vo ’ will be higher than Vo.

2. User set the character of LED (by Vo/Io/Rd Coeff), then change the

parameter Vo for verifying current spec (±5%) in the voltage range.

V

I

Vo Vo’

Io’Io


Ripple Current of LED Driver

1. Under stable operation(Vo / Io), Iripple is caused by the LED driver Vripple and the

LED operating resistor Rd, Vripple / Rd = Iripple.

2. There are two kind of voltage ripple: 100/120Hz from main (50/60Hz), and

the switching frequency which can be as high as 100kHz.

I

V

LED curve

Vo

Io Rd

100Hz

100KHz


1. 63110A is an active load, the internal control circuits have a limited bandwidth. The Rd setting is able to simulate for 100/120Hz current ripple, but it is unable for the high frequency components (>100kHz).

2. Rr can be set similar value of Rd for simulating high frequency resistance. Then, it is recommended to use an oscilloscope to observe the ripple current while using LEDs as loading, and using 63110A adjust Rr to achieve the ripple current waveform as the LED loading.

Set high frequency resistor – Simulate Ripple Current

63110A as load


Rr: High frequency resistor

Press CONF. key, then press key to choose Rr, then press ENTER to setup.Rr: 1. Default. 2.Set. Rr range: 5Ω ~ 250Ω.

Rr is used to adjust the ripple current by adjusting the internal resistance of the

63110A. it is recommended that the Rr function is switched off to prevent the LED

driver from triggering OCP when turn on the power.

Only when testing ripple current should the Rr function be switched ON

Set high frequency resistor Rr – Simulate Ripple Current


Most general E-Load draw full load to simulate a short circuit test.

LED drivers have small output current, the 63110A is designed with internal relays for short circuit testing.

LED driver - Short Circuit Testing


1. The LEDs may have been packaged in parallel for some high power application. It needs LED Load Simulator connecting in parallel to provide high current or power.

2. The setting for Io of each channel of 63110A also need to be separated. For example, use two channels of 63110A to simulate a 2.8A of LED module. Each channel need to set Io=1.4A. But Rd Coeff still keep the same value.

3. When parallel, users may need to set 63110A a lower bandwidth if the loading current is unstable. There are 5 range of bandwidth to select in Config.

Parallel for higher Current

2.8A


1. Users can set the different value of parameters for each channel of 63110A. Therefore, it performs multi-section of LED I-V curve.

2. It can be used for simulating different type of paralleled LED. It also can simulate the nonlinear part of Vf.

Parallel for Different Type LEDs

V

I

V

I

V

I


• Most E-Load manufacturers have similar designs and are all unable to

simulate the I-V curve of the LED, as well as the internal capacitances

causing abnormal OCP, OVP. Unable to simulate LEDs, general E-Loads

are not suitable for testing LED drivers.

• 63110A was specifically designed to simulate LED characteristics and

therefore suitable for testing the functions of LED drivers.

• Can 63110A not only test stable conditions, it can also test turn on and

PWM dimming characteristics of the LED driver. The Rd value can be

adjusted according to the LED V-I curve making it ideal for LED driver

testing.

Conclusions

Thank you very much


Creation and InnovationCreation and Innovation

For more information contact ValueTronics 800-552-8258

Please visit our website www.valuetronics.com

http://www.valuetronics.com/

led driver load -- 63110a introduction working on better solutions

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