Abstract:

This paper briefly reviews the development of electrolytic capacitors, and analyzes the high-voltage electrolytic capacitors in various kinds of electronic lighting power circuits.

The working state and the requirements of electrolytic capacitor performance are described. The working state of electrolytic capacitor in power electronic circuit with power factor

correction is expounded

Not only in the current to filter out 100Hz and its harmonic components. It mainly filters the AC current generated by the inverter and power factor correction circuit.

The high voltage electrolytic capacitor designed now is based on the parameters of 100Hz, while this high voltage electrolytic capacitor

will not adapt to the power factor. Finally, the development trend of high voltage electrolytic capacitor is put forward: high frequency, low resistance, and higher ripple current.

Keywords: high voltage electrolytic capacitor, ESR, life, high frequency low resistance

Preface:

Aluminum electrolytic capacitor has been the main component of electronic circuit since 1938, and its importance is no less than Source component. With the continuous update of active

components, electrolytic capacitors also continue to progress, the performance continues to improve. From early 55 degrees centigrade to now highest working temperature is 105, 125,

145 .

The rapid development of power electronic circuits has greatly promoted the development of electrolytic capacitors.

The demand for electrolytic capacitors by color TV and microcomputer makes the electrolytic capacitor raise the highest operating temperature from 55 to 85 centigrade

Even 105 degrees, the life also increased to more than 3000h

1, high voltage electrolytic capacitor life improvement

1.1 Energy saving and lamp LED lamp need electrolytic capacitor with higher maximum operating temperature and longer life

Because the negative electrode of electrolytic capacitor is electrolyte, the existence and the amount of electrolyte decide whether the electrolytic capacitor still keeps the capacitance

The electrolyte is especially easy to volatilize at high temperature, and the high temperature condition becomes an important index to measure the reliability of electrolytic capacitor.

In many cases, the life of electrolytic capacitors determines the reliability of electronic circuits. Therefore, the life of electrolytic capacitors has always been an important index of

capacitor performance.

In the energy-saving lamp and LED lamp, the driving circuit will work at high temperature because of the position of the drive circuit. Especially the application of high-power energy-

saving lamp makes the actual working temperature of electrolytic capacitor reach or exceed 105 degrees centigrade. Electrolytic capacitors are required not only to withstand high

operating temperatures, but also to have longer lifetimes.

The high voltage electrolytic capacitor used in our energy-saving lamp can reach 105 /16 000h, which satisfies the matching requirement of the ultimate life of the energy-saving lamp

and the life of electrolytic capacitor. In most cases, 105 /6 000h can meet the requirements of the general performance of energy-saving lamps life.

Theoretically, LED has longer lifetime than energy-saving lamps, and electrolytic capacitors should also have corresponding life to reflect the advantages of long life of LED. The

maximum working temperature of the driving circuit in the LED lamp will reach or exceed 75 degrees. Therefore, the life of the electrolytic capacitor in the driving circuit of the LED

lamp should be no less than 75 /50 000h, corresponding to 105 /10 000~16 000h. The super long life electrolytic capacitor suitable for LED lamp has been introduced in 2000, and the

contradiction between volume and life has been solved. In this way, the scheme without electrolytic capacitors has no advantage.

1.2 high voltage electrolytic capacitor needs withstand higher ripple current

In the special application environment of energy saving lamp, in order to reduce the cost and the three harmonic current, the capacitance of electrolytic capacitor is relatively low, even to

5W/ F. Thus, for a 20W energy saving lamp line, only 4.7~6.8 F of capacitance is needed. Figure 1 is the current waveform of filter capacitor for 40W energy saving lamp.

In the figure, the current value of the electrolytic capacitor is 8.2uf, and the current effective value is 343mA. In this way, the current per uf will approach 42mA! However, the

electrolytic capacitors in general switching power supply only need to pass through the current of less than 10mA per uf, and the difference between the two is about 4 times, which is

also the requirement that the energy saving lamp electrolytic capacitors have higher current rating requirements

The electrolytic capacitor in the energy-saving lamp should withstand two current shocks in the process of power supply: surge current surge and the current impact of the lamp tube. The

impact current of a 15 uf electrolytic capacitor will reach 50A! The duration is about 200 s, as shown in figure 2.

For 40W energy saving lamp starting time ,the peak current of the electrolytic capacitor will exceed 7A and the duration is about 300 s . The current waveform of the capacitor start up

as shown in figure 3.

The discharge current of the capacitor in the process of lamp discharge will reach 0.2A per uf! Therefore, the energy saving lamp electrolytic capacitor needs to withstand the impact

current and the continuous effective value current which is far greater than other applications, which is the working characteristics of electrolytic capacitors in energy-saving lamps and

electronic ballasts.

See from Figure 1, the effective value of current 0.307A 40W energy-saving lamp with 15 uf capacity corresponding to the corresponding per uf 20mA.

1.3 High voltage electrolytic capacitor need adapt to current

The driving circuit of LED lamp is arranged in the cap, thus requiring smaller components, for the electrolytic capacitor, not only to meet the volume of request, but also to meet the life requirements, LED lamp driving electrolytic capacitor in the circuit must be the best result of volume and performance.

Comparatively speaking, the current in the LED drive circuit electrolytic capacitor is slightly larger than the current through the electrolytic capacitor of the switching power supply, but far less than the current of the energy saving electrolytic capacitor. From this point of view, the LED electrolytic capacitor should have a small volume and long life .

BIT electrolytic capacitor manufacturers have introduced a high performance small volume electrolytic capacitor which can be used in LED drive circuit at 50 thousand h/75 centigrade.

Whether it is used for energy saving lamps, electrolytic capacitors or LED electrolytic capacitors, the performance of electrolytic capacitors in China has reached the world famous energy-saving lamps, LED electrolytic capacitors performance, and can be directly replaced.

1.4 switching power supply and high power converter need high ripple current, high frequency and long life electrolytic capacitor

In switching power supply and high power converter, the selection of high voltage electrolytic capacitor is not based on the amount of capacitance required, but the electrolytic capacitor

can withstand the ripple current when operating. The selection of electrolytic capacitor capacity is much larger than expected, and even a few parallel connection is needed.

The ripple current of the high voltage electrolytic capacitor is about 50% higher than that of 10 years ago. For example, the constant ripple current of 400V/100uf electrolytic capacitor

ten years ago is only 0.7A, and now it is 1A. In the same application, the capacitance can be reduced by 30%. For the large capacity high voltage electrolytic capacitor, the electrolytic

capacitor price and the cost of the household can be reduced. High voltage electrolytic capacitors used in switching power supply and high power converters also need long life, and 105

/6000h products are produced.

2. Working state change of filter capacitor in power converter with power factor correction circuit

With the limitation of the power factor of switching power supply and electronic device, the switching power supply, electronic ballast (energy-saving lamp), LED lamp and so on should

have the power factor correction function in the future. In this state, the current component of the electrolytic capacitor will change, and new requirements for the different frequency

characteristics of the electrolytic capacitor are also required.

In the power factor correction state, the filter capacitor is separated from the rectifier, and the nonlinear current component produced by the rectifier and the filter capacitor is not present.

Because the filter capacitor is at the output of the power factor correction, the output power of the power factor correction circuit (before the filter capacitor ,neglect switching frequency

and its higher harmonic current) is:

Obviously, this is a time varying function, and the output of the power factor correction (after the filter capacitor) should be a constant current output, so the filter capacitor has to absorb all the AC current components from the power factor correction circuit. The power factor correction switch frequency and its harmonic component current will be 4~6 times of the 100Hz current component. In this state, the main current component of the filter capacitor flow is 40kHz and more than the current component. The concern is that the high frequency current flows through the high-voltage electrolytic capacitor and affects the electrolytic capacitor and its electronic circuit.

3. The high voltage electrolytic capacitor in China often is 100Hz or 120Hz parameter

The high voltage electrolytic capacitor is usually used in the power frequency rectification filter circuit. When the AC current component produced by the load is very small, the current that the capacitor receives is mainly due to the ripple current caused by the rectifier filter circuit. With the application of power electronic circuit more and more, more and more widely, the proportion of AC current component produced by power electronic circuit is also higher and higher. The filter capacitor not only flows through the AC current component produced by the power frequency rectifier filter, but also filters the AC current component from the power electronic circuit. It should be noted that the AC current components produced by power electronic circuits are different in different applications.

In the field of electronic lighting, due to the particularity of electronic lighting, the switching frequency of the electronic ballast is generally 30~50kHz, and the effective value of the switching current component is about 65% of the total effective value current of the filter capacitor, while the current component of the power frequency and its high harmonics is 76%. Because the high frequency ESR of electrolytic capacitor is lower than ESR of 100Hz, the main loss of electrolytic capacitor in this state is from the 100Hz AC current component and harmonic current component.

In the switching power supply without power factor correction, the main factor leading to the heating of the filter capacitor is also the 100Hz AC current component and its harmonic current component.

The switch frequency of the inverter is 2~4kHz, the main component of current flowing through the filter capacitor which is still in the rectifier filter circuit produces 300Hz (three-phase rectifier circuit) current and harmonic current component, the effective value of current component is about 3 times the inverter part of inverter AC current generated by the component. Therefore, the heating of the filter capacitor is caused by these current components.

To sum up, the traditional power electronic circuit, current flows through the filter capacitor mainly 100Hz (or 300Hz) current component and its harmonic components, so when the design of high voltage electrolytic capacitors ,consider 100Hz (or 300Hz) and the harmonic current components into effect, parameters of electrolytic capacitor or parameters in 100Hz conditions are main parameters.

4. The contradiction between high voltage electrolytic capacitor and its application requirement

With the increasing application of power factor correction technology, the high voltage electrolytic capacitor will take the high frequency ripple current as the main characteristics. If the electrolytic capacitor is designed with the parameters of 100Hz, the electrolytic capacitor is not suitable for the filter function of power factor correction, although it can be used.

If the high frequency characteristics of electrolytic capacitors are improved, the loss of electrolytic capacitors can be effectively reduced if the ESR of high voltage electrolytic capacitors at 40kHz and above frequency is reduced as much as possible. The experiment shows that the application of high voltage and low ESR high voltage electrolytic capacitor to power electronic circuit with power factor correction can effectively reduce the loss of electrolytic capacitor and improve the efficiency of power electronic circuit by about 1%. At the same time, the thin film capacitor can be omitted to filter high frequency components. In fact, the cost and volume of the conventional high-voltage electrolytic capacitor and film capacitor are higher than that of the high voltage low resistance electrolytic capacitor.

High voltage electrolytic capacitor current is considered parameters under the condition of 100Hz design now, In the high frequency (such as 40kHz) ,electrolytic capacitor will exhibit inductance characteristic, also use digital bridge test negative capacity phenomenon in the high-frequency condition, these characteristics will affect the working state of power electronic circuits, and may increase the loss power electronic circuit.

The loss factor of conventional and high-frequency low resistance electrolytic capacitors under 100Hz condition is basically the same, generally less than 0.2. However, under the condition of 40kHz, the loss factor of high frequency low resistance high voltage electrolytic capacitor increases little, while the loss factor of conventional high-voltage electrolytic capacitor varies with the manufacturing process and material, and the highest loss factor is nearly 15! Therefore, in a high frequency ripple current based power factor correction application, the conventional high-voltage electrolytic capacitor is far less than the high frequency low resistance high voltage electrolytic capacitor.

5, the development trend of high voltage electrolytic capacitor

High voltage electrolytic capacitors for power electronic circuits with power factor correction require large reductions in high frequency ESR values, which are not only required for low voltage electrolytic capacitors.

High voltage electrolytic capacitors should continuously improve the current withstand capacity. In many applications, the selection of electrolytic capacitors is restricted by the current flowing through the electrolytic capacitor. Therefore, in many applications, the capacity of the capacitor is too large. If the current withstand capacity of the high voltage electrolytic capacitor is improved, the capacitance of electrolytic capacitor can be lower than the traditional selection value, and even the capacitance can be reduced by half! In this way, the purchasing cost of electrolytic capacitor can be reduced and the volume can be reduced.

To improve the withstand current of high voltage electrolytic capacitors, advanced materials, advanced manufacturing technology and advanced electrolytic capacitor manufacturing concepts and processes are needed.