High-Frequency Current-Voltage Characters Measurement

Summary: Fluorescent high-frequency measurement techniques have been widely accepted, after the measuring methods and instruments turn up which were recommended by national standard GB/T10682 2002.This article discusses the two measuring methods used by the present light industry, that is “national standard method” and ”constant-current method”.

Key words: Electronic ballast tester, High-frequency current source, High-frequency current-voltage characters measurement, Negative impedance characteristics, Constant power

Foreword 

Since the advent of high-frequency electronic ballast last century, various new lights which can work in the high-frequency condition turn up continuously.  However, how to design the light source which conform to the international standards?  How to measure the characters of fluorescent lamps in the high-frequency condition?  How to validate the match relationship between light tube and ballast?  This question always troubles the domestic engineers who research and develop the electronic ballast and the fluorescent lamps manufacture enterprises.  T5 light tubes come out and the execution of the standard GB/T10682 2002, make the problems more emergency.

Through a lot of experiments, it is prove that work condition of low pressure gas discharge lamp has a strong correlation with light frequency.  Because of lacking simply and efficient approaches and equipments, lamp designer can only choose the commercialization of the electronic ballast as high frequency source, measure the current-voltage characters of light tubes, then adjust the parameter and craftsmanship of light tubes and setting them. Electronic engineers quite understand that electronic ballast input and output terminals can combination by various circuit ways, and a variety of output waveforms they produce, which make lots of error on both ends of the light tubes current-voltage characters, resulting the different light parameters.  Say simply, high-frequency source which is not concide with standards, get the different datum, because unreasonable designs, produce unqualified productions.  The “standard crisis” holds a long time.

The engineers have tried many circuit programs, so as to reflect the light tubes work in high- frequency state correctly observing national standard GB/T10682 2002.  The representative method is the mothed formulate by national standards (the following named ”GB” for short), and the method to control the working current of light tubes (the following named “CC” for short).

Briefly analysis of two methods:

“GB” light tube current-voltage characters measurements: 

Basic structure and measurement: sinusoidal voltage E from 20 kHz ~ 26 kHz high-frequency voltage source, and ballast the tested light tubes through the noninductive resistance.  Setting the datum of E and R according to the requirements of tube test standards before measurement, judging from the table according to the light tube UL and IL and value W when measuring.

IL tube current

UL tube voltage

RL=UL/IL

Tubes equivalent resistance

Figure 1 “GB” measurement equivalent figure

From figure 1 Circuit derive tubes current-voltage formula:

W L = U L * I L *F ———– 1

Fluorescent high-frequency power factor F about 0.97~0.99. The formula set F = 1

Formula 1 simplified as: W L = U L * I L = ( (E/ I L ) -R )* I L 2 ——— 2

U L = R L * I L = ( (E/ I L )-R )* I L ——— 3

From formula 3, Tubes equivalent resistance R L ＝ U L / I L ＝ (E/ I L )-R, because the power constant pressure value E, R L has negative resistance properties.

 

Figure 2

Figure 2 lists the calculation results curve of tubes, after the T5 series of tubes with “GB” wiring.

Take T5 HE 28W as an example. Change a group of value I L by formula 2. Simulate changes of light tubes characters, so as to change the tubes equivalent resistance R L, ( slope K= -950), calculate value W L.

Table 1 “GB” T5 28W character calculated value

Figure 3

Figure 4

Analyze table 1, we can find that when the equivalent impedance R L almost doubled, the light tube power (quadratic function) changes little, the tested light tubes present “Constant Power” condition.

Figure 3 takes T5 14W and 18W as examples, draw the power curve of tubes equivalent impedance, from figure, we can find that when the current range from 0.15A to 0.19A, curve in top flat area, power basic unchanged.

After calculating the GB data and testing the experiment of T5 14W~80W, in the range of measuring this series of light tubes, the corresponding values of tubes W are in “constant power” condition.

Figure 4 shows in the “GB”, the variety track of volt-ampere characteristics of the tested tubes (take the light tubes of GE company as an example).   Lots of experiments demonstrate that T5 tube in any case; the changes of tube voltage drop should not appear the results which over the highest value as standard, in order to avoid the electronic ballast super power output state.

Lisun Group meet the GB of the testing instrument: DYJ：Adjustable Reference Ballast

 

” CC ” tube current-voltage characters measurement:

Basic structure and measurement: Constant current—- when loading impedance changes, the current in the circuit is not changing.  That is current changes independent of loading.  Constant current source should have the characters of high voltage and high resistance. Measure the light tubes, the sine wave current generator must accord with the requirement of GB/T10682 2002.  Confirm the current refer to the GB data table after lighting, and read the tube voltage value, at the time, tube pressure and the tube power are fluctuating along with the environment temperature and tube characteristics, but the tube current is almost not drift move (similar to the practical state of tube).  The changes of dynamic pipe pressure which has been tested, we can draw curve with recorder to prepare for analysis.

Figure 5 ” CC ” measurement equivalent figure

When we measure the tube T5 28W by “CC”, the value of tube pressure falls in the vertical line of lamp current (figure 6, the left), because the current value has been steadied by instrument.  When the state of the tube input / output changes, we can find that the tube pressure and the power are changing accordingly, due to the slight variations of tube impedance R L.  Pay attention to the values of negative impedance slope K and “GB” K, they are different (Show in figure 6 , the right).

Figure 6

Lisun Group meet the testing instrument of “ CC “: HCS-102A：Adjustable High Frequency Reference Ballast 

Analysis of “GB” and ” CC “

A. Advantages of “GB”:

1.In the measurement, tube loading works in the small sector of power curve peak ( first derivative = 0 ), “Constant power” state makes the measurement of tube light parameter more convenient.

2. The structure of circuit is simple, it can be combined by universal instruments, also be made of special equipment.

3.As the issued GB/T10682 2002, we must adopt “GB” in the product reviews and assessing.

B. Disadvantage of “GB”:

1.When the current adopts the pure resistance as “reference ballast”, get the measurement result similar to “Standard” just address to “standard tube” .

2. It is a disadvantage for the analysis of current-voltage characters (big error with the actual negative resistance of the tube), when the tube presents the state of “constant power”,

3. The variety of the many kinds of tubes outside the promulgated by《Standard》, due to the users have not deduced and calculate the value E、R by themselves. The measurement will be ended.

C. Advantages of “CC “:

1. Measuring equipment similar to electronic ballast which have excellent characteristics. Measurement similar to actual state.

2. Apply to all kinds of tube measurement, no limit to the boundaries of the varieties which is promulgated by “Standard”.

3. When measure the constant current, V-W is a variate, it is convenient to be used to analyze the electrical characteristics state of products.

4. Low cost of the measurement system structure.

D. Disadvantage of “CC “:

1. Measuring method is different from the “GB”, the tested numerical value should be equal to the “Standard” when necessary.  (Take T5 28W as an example, details in figure 7 )

 

Figure 7

Explanation of figure 6: measure the tube voltage value (0.17A,179V) by constant current source, push to the left from the tube negative resistance, and intersect with negative resistance line from “GB”, Intersection point value (0.15A,184V) .  Same Argument, constant current (0.17A,155V) —national standard(0.188A,150V). Inference, “CC” voltage range (155V—179V), accord with the accepted tube pressure range 28W in the GB.

Conclusion: as we know, fluorescent tube is a gas discharge device which has negative resistance properties, when we restrict the current at working, it means ballasting.  As a result, the glow brightness (efficiency) is subject to the current size, ballast which works with is a kind of current control products.  So analyze the “CC” from principle is more close to the actual state, many occasions can be put into use.

“GB” come into use earlier than “CC”, as the executing “Standard” in the lighting industry, it must be abided by the insider.

Have to point out that the two kinds of measurements, does not opposite to each other. They can play the role of each different in the industry, demonstrate evaluation in its actual use.

The following is the suggest table (table 2) of the two methods used occasions, as the end of this article.

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Tags：Adjustable Reference Ballast , CC Method , Current-Voltage Characters , GB Method