"Fair effect tube characteristics and single-ended amplifier production
Author: Zhong Wenxiang
The principle of the field effect tube control the working current is completely different from the ordinary transistor, which is much more simpler than the ordinary transistor, and the field effect tube is simply utilized to use additional input signals to change the resistance of the semiconductor. In fact, the channel size of the working current flow is changed. And the transistor is to use the signal voltage applied to the transmitting junction to change the junction current flowing through the emission junction, and further comprise a minority carrier transcetheral region and enters the collector region and the like. The unique and simple effect principle of the field effect tube gives many excellent performance of field effects, which exudes the user with seductive glory. The field effect tube not only has the advantages of ordinary transistors and tubes, but also the advantages lack of the two. The field effect tube has bidirectional symmetry, the source and drain of the field effect tube, which can be interchangeable (no damping), the general transistor is not easy to do, and the electronic tube is not possible to achieve this. The two-way symmetry, for ordinary transistors, is the emitter and the collector interchange, the tube is interchanged, that is, interchange the cathode and anode.
First, the characteristic field effect tube of the field effect tube has the advantages of high input impedance, small noise coefficient, good thermal range, and high dynamic range than the ordinary transistor. It is a voltage controlled device, which has similar transmission characteristics with tubes, and thus has a wide range of applications in high-fidelity audio equipment and integrated circuits, which have the following features.
High input impedance is easy to drive, and the input impedance varies with frequency. The input knot capacitor is small (feedback capacitor), and the change in the output terminal is small to the input, the drive load capacity is strong, and the power supply utilization is high.
The noise of the field effect tube is very low, and the noise coefficient can be 1 dB, and now the noise coefficient of most of the field effect tubes is about 0.5 dB, which is difficult to achieve in general transistors and electronics.
Field effect tubes have better thermal stability and large dynamic range.
The output of the field effect tube is the 2 power function input, the distortion is lower than the transistor, which is slightly more than the bile duct. The distortion of the field effect tube is more harmonic distortion, good listening, high school low frequency energy distribution is appropriate, the sound is dense, the low frequency is deep, the sound area is more stable, the transparent moderate, the level, analytical force and positioning Feel a good performance, with good sound field space drawing capabilities, very good performance for music details.
When the ordinary transistor is in operation, since the input terminal (emitting junction) is positive bias, the input resistance is very low, and the input end (between the gate and the source) can be applied to a negative bias. That is, the reverse bias can also be added to the bias, thus increasing the variation and diversity of the circuit design. Usually, when the anti-directional bias, its input resistance is higher, up to 100mΩ, and this characteristics of the field effect tube compensate for the shortcomings of ordinary transistors and tubes in certain aspects.
The radiation protection capacity of the field effect tube is 10 times higher than the ordinary transistor.
Fast conversion rate, high frequency characteristics.
The voltage and current characteristic curve of the field effect tube are very similar to the five-pole output characteristic curve.
There are more varieties of field effect tubes, which can be generally divided into two categories of junction field effect tubes and insulated gate farms, and there are N-type channels (current channels) and P-type channels, each of them. Enhanced and exhausted total four categories. Insulated Gate Effect Tube, also known as the metal (M) oxide (O) semiconductor (S) field effect tube, referred to as MOS tube. According to its internal structure, it can be divided into two types of MOS tubes and VMOS, each of which there are two types of N-type channels and p-type channels, enhanced and depletion types. VMOS field effect tube, which is a V-tank MOS field effect tube, which is a new high-efficiency power switching device developed on the basis of a typical MOS field effect tube. It not only inherited the MOS field effect tube input impedance high (greater than 100mΩ), but the drive current was small (0.1ua), but also had a high pressure height (up to 1200V), the operating current is large (1.5 ~ 100A), high output power (1 ~ 250W), the cross-guided linear is good, and the switch speed is fast and other excellent characteristics. At present, it has been widely used in high-speed switches, voltage amplification (magnification of voltage amplification), radio frequency amplifier, switching power supply, and inverter. Since it has the advantages of tubes and transistors, the high-fidelity audio power is used in it, the sound quality is warm and sweet, and the music is favored, so there is a broad application prospect in the field of sound. The VMOS tube and the general MOS tube can also be divided into two types of N-type channels and p-type channels, enhanced and depleted four categories, and classification features are the same as the general MOS tube. The VMOS field effect tube has the following features.
Enter the impedance high. Since the gate source is a SiO2 layer, the DC resistance between the gate source is substantially SiO2 insulated resistance, generally up to 100mΩ, and the AC input impedance is basically the capacitive resistance.
The drive current is small. Due to the high input impedance, the VMOS tube is a voltage controlled device, and the voltage can be driven, and the required drive current is small.
The transconductance is better. It has a large linear amplification area, which is very similar to the transmission characteristics of the tube. A preferred linear means having a lower distortion, especially with a negative current temperature coefficient (ie, in the case where the voltage between the gate and the source is constant, the turning current will increase with the tube temperature. Therefore, there is no phenomenon caused by the tube damage caused by secondary breakdown. Therefore, the VMOS tube has been widely used.
Non-varying effect. The tubular capacitance of the VMOS tube does not change with the voltage, and there is no change in transistor of the transistor to avoid distortion of the beam effect.
Good frequency characteristics. Most carrier motion of the VMOS field effect tube belongs to the drift movement, and the drift distance is only 1 to 1.5um. The transition time limit is not limited by the transistor, so the power gain varies extremely small with the frequency, and the frequency characteristics are good. .
The switch is fast. Since there is no small storage delay time, the switch speed of the VMOS field effect tube is fast, and dozens of A current can be turned on or off within 20ns.
Second, the main parameters of the field effect tube and the use in order to properly safely use the field effect tube, prevent static, misoperative operation or storage, damage to the field effect tube, must be understood and mastered to the main parameters of the field effect. The parameters of the field effect tube are as many as those, and the main parameters and meanings are now listed in Table 1, as references.
Table 1 main parameters and meanings of field effect
symbol
name
meaning
BVGSS
Gate source withstand voltage
The SiO2 layer between the gate source is very thin, with a pressure of 30 to 40V.
BVDSS
Source leakage pressure
VGS = 0, the VDS value when the source leak reverse leakage current is 10ua
VP
Clamp voltage
In the source grounding, the gate source voltage is output to zero when the drain source current is output.
VT
Open voltage
When the IDs reaches 1mA, the voltage between the gate source
IGSS
Leakage current
The re-current in the gate tuning is applied under the reverse current, the junction tube is NA, and the MOS tube is PA.
IDSS
Saturated leakage source current
Leakage current at zero bias VGS = 0
RGS
Input resistance
The gate source insulation resistance, the resistance of the gate trench in the reverse bias, the junction tube is 100m Ω, the MOS tube is 10,000mΩ or more
RDS
Output resistance
Division of the slope of the drain characteristic curve, 1 / RDS = △ ID / △ VDS
GM
Transconductance
Indicates the control capability of the gate voltage on the drain current
Ids
Source leakage current
Be
PD
Dissipation power
Be
NF
Noise Figure
Noise is caused by irregular motion of the pipe internal carrier, and the field effect tube is much smaller than the transistor, and the smaller NF is smaller.
CGS
Gate source capacitor
The input capacitor, the smaller, reduce the distortion, and the favorable frequency characteristics are improved.
CDS
Leakage source capacitor
The output capacitor, the smaller, reduce the distortion, and the favorable frequency characteristics are improved.
CGD
Grid leakage capacitor
Feedback capacitance, smaller, reduce distortion, favorable frequency characteristics
The choice of field effect tubes should pay attention to the following points.
The parameters of the ID of the field effect tube are selected according to the circuit requirements, which can meet the power consumption requirements and slightly more than a margin. Don't think it is, the better the ID, the greater the CGS, and the high frequency response of the circuit is unfavorable. If the ID is 2a, the CGS is about 80 pF; the ID is 10a, the CGS is about 1000 pF. The reliability used can be guaranteed by reasonable heat dissipation.
Select the source and drain pressure of the VMOS tube BVDSS should not be too high, it can meet the requirements. Because BVDSS large tube saturation pressure drop is large, it will affect efficiency. The junction field effect tube should be as much as possible, because they are not high, generally BVDSS is 30 ~ 50V, BVGSS is 20V.
The BVGSS of the VMOS tube is as much as possible because the VMOS pipe is extremely delicate, it is easy to break through, store or operate cautious, prevent the static object to contact the pin. In the storage, you should take the short circuit, and package it with a metal box to prevent the external induction potential from breaking through the gate, especially paying that the pipe cannot be placed in a plastic box or plastic bag. In order to prevent the gate sensing breakdown, all instrumentation, electric iron, circuit board, and human body must have a good grounding effect in the installation and commissioning, before the pipe access circuit, all the pins of the pipe must be shorted. State, the short-fitting material can be removed after the welding is completed.
The pairing tube requires the same batch of the same factory, so the parameters are consistent. Try to use the twin-parallel parallelism to allow the tube's clamp voltage and the cross guide as possible, so that the pairing errors are less than 3% and 5%, respectively.
Use the audio special tube as much as possible, which is more suitable for the requirements of the audio amplifier circuit.
When installing the field effect tube, the location should be avoided near the heat generating element. In order to prevent the tube vibration, the tube is to be fastened, and when the pin lead is bent, it should be greater than the root distance 5 mm, to prevent the pin, or cause the air leakage to damage the tube. The pipe must have a good heat dissipation condition, and enough heat sink must be configured to ensure that the tube temperature does not exceed the rated value, ensuring long-term stable and reliable work.
Third, the audio amplifier art charm and evaluation audio amplifier can be divided into electronic pipe amplifier, transistor amplifier, integrated circuit amplifier, field effect tube amplifier, and two or more types of amplifiers, various amplifiers, various amplifiers, various amplifiers, and two or more types of amplifiers. The circuit and the components used are also five flowers, thousands of variables, thereby distinguishing sound quality on the sound source, it is difficult to say which amplifier can be partial, and the technical climb is a universal amplifier. The electronic tube amplifier acts on the transmission of space charges, and the tone is warm and soft, especially the string, and it is expressed as alcoholic and intriguing. Transistors and integrated circuit amplifiers have sharp analytical efforts, wide frequencies and strong dynamics, with vigor of vigor, and urgent enthusiasm. Field effect tube amplifier and mixed device amplifier, force map integrated tube and transistor audio characteristics, create a color, let the music pass god, let the sound perfect. In recent years, with the continuous development of electronic computer technology, various electronic synthesizers, various audio effects and biliary effectors software and virtual speaker technology are endless. This makes the development and popularity of the audio amplifier hardware and far can't catch the software speed. In the precision hardware, hardware is often can't catch the software. If the computer simulation 3D effect is much larger than the real 3D effect, the space and sound source synthesis of the listening room Limit, while saving the expenditure of putting hardware. Green audio, double fever - computer audio is likely to be the mainstream of the future, hardware is not software, implement hard and hard, powerful, concentrated in efficient, convenient, magical, and economic characteristics. If you set a virtual optical drive in your computer, each time you play the music, you don't have to start the physical optical drive, which not only reduces the wear of the waiting track time and the physical optical drive, but more importantly, the noise of the physical optical drive is eliminated, but the high-fidelity show. For another example, the biliary power amplifies softly sounds, and the production cost is not thin, and the items of the sound are more, and through the biliary effect software, we can create a "soft," in the computer, you can simulate Charging tone. At present, the computer multimedia audio is in advance, and has a bridge that communicates with the TV. The prospect is very beautiful! Computer and audio enthusiasts are a special level of time and effort, actively explore the pursuit of sound quality. Will continue to take a love responsibility, more sweet songs in life, and a little bit of a bitter dispute. Whether it is ordinary sound, or computer multimedia audio, the power amplifier is still an indispensable terminal that drives the speaker, and all kinds of amplifiers can achieve this function. However, modern people have a demanding demand that the audio (technical factors main, such as frequency response, distortion, signal-to-noise ratio, etc.) and music (art charm, if the sound is mellow, whether the sound of the sound is rich, whether the sense of hearing is full of hearing, etc.) The more and more high, many "golden ear" can hear the singer's teeth, mouth angles, and immersive, to the feeling of the scene, so the playback of the audio amplifier is also given a greater demand, and strive to distinguish the audio Fashion charming music atmosphere. Each type of audio amplifier has its own advantages and attributes, and there is a shortcomings, while the mainstream of the field effect tube amplifier has the advantage of both transistors and electronic pipes, and also has the advantages of the two. At the circuit, a large number of practices have proved that single-ended amplifiers are a model of efficiency and have unparalleled music charm. Many enthusiasts from simple pursuit of sound quality, anti-multiplexing, repeated comparative listening, eventually moving to the A class, seems to feel that there is no Class A, music is like lonely music.
Fourth, single-ended amplifier performance is generally generally divided into three categories: 1A class amplifier, but also known as a matrix amplifier; 2 AB amplifier; 3B amplifier, B-like amplifier. In these three types of amplifiers, the linear is best, the most tone is the Class A amplifier, and the single-ended Amplifier and the push-pull amplifier are designed in design, which is to use an enlarged device to enlarge the entire music waveform. The push-pull design uses two amplifier, and the positive and negative half weeks of the signal is zoomed separately, including some push-pull A amplifiers. Single-ended amplification and push-pull enlargement A significant different feature is that the enlarged music waveform is a full waveform that is very similar to the input waveform. It does not push a large-negative waveform, although the push-pull enlargement uses pairing The parallel of the accuracy of up to 2% error or even smaller errors, but this is only a piece of digital description, and the positive and negative waveforms are not possible to pass well, and the phase shift caused by the nonlinearity caused by the circuit components, the Duecent the distortion will be further Increased, of course, distortion and tone are not opposed to a certain extent, which depends on the use and goals of the design amplifier, not to push the excessive, and in the push-pull amplifier, due to multiple harmonics,However, the original positive and negative waveform is not handled, but harmonic handover cannot be negated, but it is difficult to compete with single-end waveforms. With regard to push-pull amplification harmonics, especially the even harmonic will offset each other, the author does not agree, only harmonic ingredients such as 180 ° or 360 ° have cancel each other. If the DC high pressure in the push-pull power amplifier is divided into two channels in the center tap of the push-pull transformer center, due to the opposite direction of the two arm coil, the difference is 180 °, the AC ripple is almost completely offset. Single-ended amplifiers have the most natural music, and its asymmetry is similar to air compression and expansion. Due to the maximum air content is the non-polar molecular nitrogen (N2), about 78%, so the air is a "single-ended" medium that makes a very high pressure, so that the single-ended A-music is the most passive, the most sound mellow.
V. Making Design Amplifiers in VMOS Field Effects SLR Amplifiers have two basic principles: one is simple, the other is linear. And the simplest amplifier line is a single-ended, simple is the only reason for the single-ended amplification, because the single-ended class has the most fascinating music. In Class A, Class B, AB line program, linear is the best of the classification, and the deficiencies are the lowest efficiency, about 20%, is a model of efficiency. There is also a payment of amplifier used in single-ended amplification circuits. The transistor has too low input impedance, and the input impedance of the tube is high, but its output impedance is also relatively high, and the electronic tube is not suitable for the power amplifier output tube, so the unique choice is the field effect tube. The field effect tube has a high input impedance and transconducting, and a large current can be output, which is suitable for applications in single-ended amplifiers. In numerous field effect tubes, single-ended amplifiers made with VMOS field effect tubes, more collaps, and unique charm. The high-end titanium film sound, the medium frequency is full of delicate and smooth magnetic sound, the elasticity is full of low-frequency bombings, don't have a hegemony. In the general design midfielder effect, it is not fully utilized, and even thinks that the sound is cold, and it is not the reason this is not the reason for the field effect. It is not good, on the one hand, people use it directly to change the transistors, the lines of the transistor cannot exert the characteristics of the appearance effect; on the other hand, these circuits typically use the bias of the AB class. Based on the velocity transfer characteristics, there is a serious nonlinearity in low bias, bringing serious distortion, and the solution is to make it work in Class A, especially single-ended Class A, excellent transient characteristics, sound quality Pure beauty, the occasional harmonics, the sound is pleasantly listening, and there is a beautiful tone of the tube. Circuit principle
Single-ended field effect tube power amplifier circuit five flowers, each characteristic, the motor circuit is shown in the drawings. In order to obtain a beautiful voice, take a concise first principle, more than one component is more distortion, and one line is more distortion. The principle of circuit principle is now a brick-to-jade, and the main features have the following characteristics. (1) In order to avoid the transmission of distortion, non-stable contact resistance, friction noise, and operationally exhausted exhaustion, this unit is referring to the audio control of the sound type low noise VMOS field effect tube IRFD 113. It has reduced some components with respect to the key-controlled volume circuit, and shields, so that the noise coefficient of the volume control portion reaches 1 dB (the VMOS field effect tube noise coefficient is about 0.5 dB), dare to be high-grade vacuum step potentiometer or no The source transducer potentiometer is counter-balanced, and the feel is more embarrassing. The VMOS field effect tube is high, and the voltage control device is connected between the gate and the source. Since the gate leakage current is small, the capacitive voltage can remain substantially unchanged over a period of time. When the tube operates in an adjustable resistance region, the drain source resistance will be controlled by the voltage of the gate source voltage, that is, the capacitor, which is equivalent to the voltage-control variable resistance, and when the finger resistance conductive conductive electrical conductivity) switch S1 Closed, ie, the capacitor is charged, and when the contact switch S2 is closed, the capacitance is discharged, thereby reaching the purpose of controlling the electrical resistance of the voltage by the voltage. Adjust the size of the volume in the acoustic device. S1 and S2 can be made of thin silver or thin copper sheet, with a spacing of about 2mm. After the debug is determined, the volume increase or decrease is set to ± 2dB. (2) The IRF510 is made of voltage amplifies, and the amplified audio voltage is fixed to the upper arm tube IRF150 for the expansion and active output. The lower arm pipe IRF150 constitutes a constant flow source, and the DC is a path, and the communication is open, so that the AC signal passes Output capacitor drives the speaker. (3) Since the VMOS field effect tube has a negative current temperature coefficient, in the case where the voltage is constant between the gate and the source, the on-current current will reduce the temperature rise, thereby avoiding the second attack of the pipe. Put on. However, the change in the temperature of the tube is very far from the change rate of the current. In order to prevent the negative temperature coefficient inertial delay, the normal temperature coefficient compensation resistance of the unit in the IRF510 cathode string is a proper resistance (100Ω / 2W) ) To play a buffer. The principle is that when there is no cathode resistor, the IRF510 gate source voltage is constant fixed bias, independent of the tube current change, and after the cathode resistance is added, the source potential is also lowered when the tube flow is reduced. Relative to the gate, the gate potential is improved so that the gate source voltage is increased. At this time, the tube current increases, thereby causing the amount of current steep slope generated by negative temperature coefficients. The cathode resistance resistance value determines the size of this role, which acts as an appropriate buffer, which is not current negative feedback resistance. (4) This unit does not use an OCL without output capacitor circuit after considering speakers. Second, the second considering zero-point offset voltage, in particular dynamically, the speaker voice circle generates DC bias magnetic displacement, directly affects the performance of the speaker, thus Determination sound quality. Since the large capacity output capacitance is more electrolytic capacitance, it is generally considered to be large, and in fact this is a signal-to-noise ratio. The key is what circuit is applied. If the electrolytic capacitor is used in the dynamic range, it is not Suitably, the dynamic range signal is only 2mV, requiring the amplification circuit to have a higher signal-to-noise ratio, and the electrolytic capacitor signal to noise ratio is low. The electrolytic capacitance is used for the active amplifier output, and the case is different, and the signal-to-noise ratio is greatly improved relatively low. Another point, the electrolytic capacitor is preferably energized before use, and is preferred, and then the sufficient cooker is made after it can reduce the noise coefficient. The components without noise are not, the key should be reasonably used, and take measures to achieve the necessary purpose. This machine in order to reduce the output electrolytic capacitor due to the effect of the induction resistance to the high frequency, use 3 electrolytic capacitors to reduce the sensing resistance, and connect the negative electrode of the speaker to the negative electrode to clamp the electrolytic capacitor leakage current. Line mapping magnetic displacement. (5) The airport effector bias is provided by the power supply module LM7812, and the power amplifier power supply does not take the voltage supply of the power supply to avoid the low frequency strength and dynamics of the loud sound, that is, reducing the voltage shift current, reducing the power trimming quality.
2. When making commissioning, the two channels are used to power the independent power supply to increase the separation, reduce interference, and enhance the working stability of each channel. The working point will be equipped with a direct coupling circuit, so it is necessary to complete a few times, and the IRF510 operating current is about 20mA, and the upper and lower two tubes IRF150 (paired) operating current is about 1.5A, and the gate source voltage is about 1.5A. For 3.8V, the two-stage bias resistance is repeated, and the midpoint voltage is L8V. Different origins, different batch tubes will be inserted, and the data is for reference only. It is best to use the oscilloscope to adjust it as the best working status of Class A. Otherwise, due to the discrete of the tube, even if the work point is adjusted by the parameter or the parameter given by the manual or the characteristic curve, it is not necessary to operate in the best Class A state. There are many field effects, different pipe parameters, characteristics and tone of different pipes. Table 2 lists several common pipe parameters for reference. The other components of this unit are selected for reference related information, and will not be described here.
Table 2 Main parameters of several common field effect tubes
model
use
Types of
Source leakage pressure / V
Source leakage current / a
Explement power / w
Remark
BS170
Low noise zoom
N
60
0.3
0.63
Be
2SK389
Low noise difference
N
50
0.01
0.2
Double pipe package
IRF510
Voltage amplification
N
100
2.5
20
Be
Irfdl13
Low noise zoom
N
60
0.8
1
Be
2SK1058
High frequency power amplification
N
160
Seduce
100
Complement 2SJ162
2SK413
High frequency power amplification
N
140
8
100
Complementary 2SJ118
2SK405
High frequency power amplification
N
160
8
100
Complementary 2SJ115
IRF130
High frequency power amplification
N
100
12
75
Complementary IRF9130
IRF540
High frequency power amplification
N
100
Twist
150
Complementary IRF9540
IRF150
High frequency power amplification
N
100
40
150
Complementary IRF9150
The single-ended circuit is a power consumption, the unit output pipe single tube heat loss is 30W, and the working voltage can also increase the output power, but the heat loss is also increased accordingly. Therefore, the tube must be mounted on a heat sink which is not more than 1kΩ / w, and the specification is not less than 200 mm × 200 mm × 6 mm, and the tube is applied to the appropriate position after smearing the tube with silica fat. 3. Parameter indicator measurement technical indicators are shown in Table 3.
Table 3 measured technical indicators
Input sensitivity
360mV
Maximum output power
8W (8 Ω, THD + N = 10%, 1kHz sine wave signal)
Maximum music output power
10W (8 Ω, THD + N <211%, 1kHz sine wave signal)
distortion
3.8% (1W / 8Ω, 1kHz)
Signal-to-noise ratio
88DB (unsight)
Frequently
18Hz ~ 165kHz
4. Assessment, the evaluation, the audio-listed equipment is as follows: (1) Philips (Philips) LHH-500 top CD player; (2) homemade direct heat pipe 3A5 pre-stage; (3) Italy Aoybacquer filament box; (4) American music ribbon super flanne Cable speaker line; (5) high wind ORTOFON AC-5000 8N oxygen-free copper signal line; (6) Hitachi 4N single piece of copper 3 × 3.5mm silicone rubber power cord; (7) g & w TW-05D type Audio dedicated power purifier. When taking the genuine Hugo CD, the sound field is wide and very good. Audiovon positioning, good analytical force, low frequency, control. The sound quality is very pure, which is unforgettable! "
Our other product:
