MOS tube knowledge points sorted out, why it has become the protagonist of modern power electronics

吾妻思萌

MOS tube knowledge points sorted out, why it has become the protagonist of modern power electronics [Copy link]

 

Field effect transistor (FET) is a semiconductor device that uses electric field effect to control transistor current, so it is called field effect transistor. It is a semiconductor device controlled by input voltage . According to the basic structure, it is divided into junction field effect transistor and metal-oxide-semiconductor field effect transistor (also called insulated gate field effect transistor).

Field Effect Transistor Family Classification

Characteristics of field effect tubes : high input impedance , low noise, good thermal stability, strong radiation resistance and simple manufacturing process.

Since enhancement-type MOSFETs are mainly seen on the market and used in work, the following content will discuss this.

1. Basic knowledge of MOS tube

MOS tubes are divided into N-channel MOS tubes and P-channel MOS tubes (N-channel is more widely used).

The three poles of the MOS tube are: gate G, drain D, and source S.

Circuit symbols of N-channel MOS tube and P-channel MOS tube

Differences between N-MOS and P-MOS

MOS tube physical picture (TO-220 package)

Note: The manufacturing process of MOS tube will cause a parasitic diode to exist between the internal D pole and S pole. Its functions are: First, when there is a reverse voltage in the circuit, it provides a freewheeling current for the reverse voltage to prevent the reverse voltage from breaking down the MOS tube; second, when the voltage of the DS two-stage is too high, the body diode will be broken down first, thereby protecting the MOS; for high-speed switching occasions, the parasitic diode has a slow turn-on speed, resulting in the inability to turn on quickly after the reverse direction, thereby damaging the MOS, so a fast recovery or Schottky diode needs to be connected in parallel externally.

2. Main parameters of MOS tube

IRF3205 Data Sheet

IRF3205 Data Sheet

① Drain-source current ID: refers to the maximum current allowed to pass between the drain and the source when the field effect tube is working normally. The working current of the field effect tube should not exceed ID. This parameter will decrease as the junction temperature rises.

②Drain-source breakdown voltage VDSS: refers to the maximum drain-source voltage that the field effect tube can withstand for normal operation when the gate-source voltage VGS is 0. This is a limit parameter, and the operating voltage applied to the field effect tube must be less than VDSS.

③ On-drain-source resistance RDS (on): Under the conditions of specific junction temperature and drain current, the maximum impedance between the drain and source when the MOSFET is turned on. It is a very important parameter that determines the power consumption when the MOSFET is turned on. This parameter generally increases with the increase of junction temperature. Therefore, the value of this parameter under the highest operating junction temperature should be used as the loss and voltage drop calculation.

④ Turn-on voltage VT: refers to the gate voltage in the enhanced insulated gate field effect transistor when the drain and source are just turned on (specified ID value).

⑤ Maximum gate-source voltage VGS: refers to the maximum voltage that can be applied between the gate and source electrodes. It should be considered when designing the driver. It is generally: -20V~+20V. The reason why it can be positive and negative is because it covers N-type and P-type.

3. Application circuit of MOS tube

As a power device, MOS tube is mainly used in the main circuit in the switching state. In addition, it also has the functions of amplification, impedance conversion, oscillation, etc.

MOS tube is used as flyback power switch tube

Full-bridge inverter circuit composed of MOS tubes

MOS tube application amplifier circuit

maychang

After talking for a long time, there is still no explanation as to why MOS tubes have become the protagonist of power electronics.

maychang

The last picture is not a MOS tube at all, but a junction FET amplifier circuit. This picture has nothing to do with the title or the text, and the input and output polarities are wrong.

bigbat

The protagonist of power electronics is not MOS, but the composite tube IGBT of MOS+GTR. The withstand voltage of MOS is not enough for power electronics. The new silicon carbide MOS can partially replace IGBT.

秦天qintian0303

Good control

maychang

bigbat posted on 2023-6-2 10:51 The protagonist of power electronics is not MOS, but the MOS+GTR composite tube IGBT. The withstand voltage of MOS is not enough for power electronics. As for the new silicon carbide MOS...

In the era when there were only bipolar transistors, of course only bipolar transistors could be used. How high the frequency of bipolar power transistors can be, how high the frequency of the switching power supply can be, how large the power dissipation of bipolar power transistors can be, how large the power of the switching power supply can be. With the power MOS tube, it has a fast switching speed, a small on-resistance, and is easy to drive, so power MOS tubes have become the mainstream. After the birth of IGBT, because its current capacity is larger than MOS, it can produce higher power. In high-power applications, IGBT has become the mainstream. Silicon carbide is currently expensive, and silicon carbide will become the mainstream only after the price drops.

bigbat

maychang posted on 2023-6-2 14:47 In the era when there were only bipolar transistors, of course only bipolar transistors could be used. How high can the frequency of bipolar power transistors be, how high can the frequency of switching power supplies be...

Boss, you misunderstood. The post is about "power electronics". In this field, most devices are above 600V, usually with a current of more than 10A. It is basically difficult to find MOS tubes with a withstand voltage of 600V. The basis comes from the book "Motor Control Technology".

maychang

bigbat posted on 2023-6-2 17:41 Boss, you misunderstood. The post is about "power electronics". In this field, most of the devices are above 600V, usually with a current of more than 10A, MOS 600 ...

In the days before bipolar triodes, power electronics used vacuum tubes and gas-filled tubes.

[SCR] is also called [thyristor], [thyristor] is the abbreviation of [crystal thyristor], and thyristor is a vacuum electronic device. The voltage and current capacity of thyristor is not yet achieved by current thyristors.

maychang

bigbat posted on 2023-6-2 17:41 Boss, you misunderstood. The post is about "power electronics". In this field, most of the devices are above 600V, usually with a current of more than 10A, MOS 600 ...

It is very common to have a MOS tube with a withstand voltage of 700V. Most of the ordinary low-power switching power supplies that convert AC mains into low-voltage DC are flyback, and the MOS tubes used are usually 700V.

However, the current carrying capacity of such MOS tubes is not large. If you want a large current carrying capacity, then of course you should use IGBT.

bigbat

maychang published on 2023-6-2 18:39 MOS tubes with a withstand voltage of 700V are very common. Ordinary low-power switching power supplies that convert AC mains into low-voltage DC are mostly flyback. The MOS tubes used are usually...

The thyratron that the boss mentioned seemed to be seen on TV when I was a child. I remember it was about the size of a Coke can. At that time, I just wondered why these bulbs were not bright.

吾妻思萌

maychang posted on 2023-6-2 14:47 In the era when there were only bipolar transistors, of course only bipolar transistors could be used. How high can the frequency of bipolar power transistors be, how high can the frequency of switching power supplies be...

Boss, you misunderstood. The post is about "power electronics". In this field, most of the devices are above 600V, usually with a current of more than ten amperes. It is basically difficult to find a MOS tube with a withstand voltage of 600V. The basis comes from the book "Motor Control Technology".

Many MOS can now reach more than 800V. I have bought one on Taobao for 10 yuan or even less than 19 yuan.

bigbat

Azuma Simeng posted on 2023-6-3 09:41 Boss, you misunderstood. The post is about "power electronics". In this field, most of the devices are above 600V, usually more than 10A...

I have never seen a MOS with a high power. I heard from my colleagues that nowadays, high-power ones do not use MOS, but IGBT.

bigbat

maychang published on 2023-6-2 18:39 MOS tubes with a withstand voltage of 700V are very common. Ordinary low-power switching power supplies that convert AC mains into low-voltage DC are mostly flyback. The MOS tubes used are usually...

I asked a colleague about this and he said: Generally, MOS with a voltage exceeding 700V is ultra-high voltage MOS. The usual 220 circuit has a "rated voltage of 300V". Generally, 350V-500V MOS is selected for the circuit, and 600V-700V MOS is generally selected for the 380 circuit. Therefore, the voltage of MOS 700V is very small, and the power of MOS is not very large either, 3A is basically the limit, which is about 1 or 2A.

I don't quite understand it. My colleague makes chargers for trains, but I tend to believe what he says.

1. The peak voltage of 220V is 311V, why is the rated working voltage set at 300V? Isn't it too small?

2. The peak voltage of 380V is 537V. Is the rated working voltage not too much?

maychang

bigbat posted on 2023-6-3 12:17 I asked a colleague, and he said: General MOS with a voltage of more than 700V is ultra-high voltage MOS, and the usual circuit 220 circuit "rated voltage 300V" ...

[1. The peak voltage of 220V is 311V, why is the rated working voltage set at 300V? Isn't it too small?]

For single-ended switching power supplies, whether forward or flyback, the voltage resistance of the tube should not be 350V~500V, which is absolutely not allowed.

AC 220V is not an accurate 220V effective value from the power industry, but allows plus or minus 10%, that is, the maximum effective value is 242V. The 311V peak is the peak value of the 220V effective value. If it is 242V effective value, then the peak value is 342V. This is still a sine wave. If 220V contains certain odd harmonics, the peak value will be even larger.

For a single-ended forward converter or flyback converter, if it works ideally, the reverse voltage that the tube has to bear must be twice the DC power supply voltage, and twice 342V is 684V. How is it possible without using a tube above 700V?

maychang

bigbat posted on 2023-6-3 12:17 I asked a colleague, and he said: General MOS with a voltage of more than 700V is ultra-high voltage MOS, and the usual circuit 220 circuit "rated voltage 300V" ...

[2. The peak voltage of 380V is 537V. Is the rated working voltage not too much? ]

Multiply by the square root of 2, and you get the maximum voltage after rectification, which is 537 V. This is the value after rectification with capacitor input filtering and no load.

However, 380V is called 0.4kV system in the power industry. The 20V difference between 0.4kV and 380V is reserved for line loss. For example, China's electrified railways are 27.5kV from the substation and 25kV at the receiving end, i.e. the electric locomotive. The 2.5kV difference is reserved for line loss. The voltage drop of 2.5kV on the line is a bit incredible in the electronics industry, but it is normal in the power industry.

吾妻思萌

maychang posted on 2023-6-3 13:34 [1. The peak voltage of 220V is 311V, why is the rated working voltage set at 300V? Isn't it too small?] For a single-ended switching power supply, whether positive or negative...

My teacher told me before that twice the margin is the minimum. It turns out that odd harmonics can be so large. How should I calculate the harmonics of 220V?

maychang

Azuma Simeng posted on 2023-6-3 21:12 My teacher also told me before that twice the margin is the minimum. It turns out that odd harmonics can be so large. How should I calculate this harmonic for 220V?

Books on switching power supply design will definitely talk about how much the switching tube withstands depending on the AC mains voltage.

As for the odd harmonic content, my country's power standard is that the total harmonic should not exceed 5% and the odd harmonic should not exceed 4%.

器铭123

Very well said. Thank you.

振动试验仪器

MOS tubes have completely replaced triodes in high-current working environments because of their high voltage resistance, large output current, and greatly reduced failure rate under the same working conditions.

In high-power equipment, multiple components usually work in parallel. The parallel characteristics of triodes are poor, and MOS tubes work in a switching state, so there is no triode amplification factor that matches this project. In the triode era, the parameter consistency of high-power triodes was not very good, and the power of high-power power amplifiers could only reach 10KW. Therefore, before 2003, when domestic switch tube power amplifiers were not produced, the transistor power amplifiers of the vibration table were generally up to 6KW, and six KW power amplifier boxes worked in parallel.

A 1KW power amplifier box has 44 transistors in parallel for output. I heard that a vibration table manufacturer in Suzhou connected 10 power amplifier boxes in parallel. When the power amplifier was turned on to the output state, a big cannon was fired and all the high-power transistors were burned out.

The 10KW transistor amplifier imported from Japan at that time had to be cooled with water, which increased the possibility of failure.

You can make a 5KW amplifier with 20 200V50A MOS tubes. 20 tubes make up a power amplifier module. Putting 2 modules in a box can easily achieve an output power of 10KW. Air cooling is sufficient.

The last point is that the working efficiency of MOS is higher than that of transistor, so the heat generated by MOS with the same output power is much smaller than that of transistor.

The newly launched intelligent power amplifier uses high-power IGBT. The output power of the same box is about 30KW.

振动试验仪器

In the transistor era, the power of MOS tubes was very large, and the power of power amplifiers reached dozens of kW. Now the capacity requirements are even higher, and they are all in the hundreds of kW. The capacity of MOS is naturally smaller, and we have entered the IGBT era. In another ten years, there will be even larger tubes.

What kind of pipes are used in my country's ultra-high voltage power transmission?