Darlington), are often composite elements of amateurs structures. As is known, with such an inclusion, the gain of the current, as a rule, increases ten times. However, it is not always possible to achieve a significant reserve of operability for the voltage affecting the cascade. Flow amplifiers consisting of two bipolar transistors (Fig. 1.23) often fail under the influence pulse voltageEven if it does not exceed the value of the electrical parameters specified in the reference book.
With this unpleasant effect you can fight different ways. One of them - the simplest - is the presence of a transistor with a large (several times) reserves of a resource on the voltage collector-emitter. The relatively high cost of such "high-voltage" transistors leads to an increase in the cost of the design. You can, of course, purchase special composite silicon in one case, for example: KT712, CT829, KT834, KT848, KT852, KT853, KT894, KT897, KT898, KT973, etc. This list includes powerful and medium power, devices developed almost for the entire spectrum radiotechnical devices. And you can use the classic one with two parallel-enabled field transistors of the KP501B type - or use the devices KP501A ... B, KP540 and others with similar electrical characteristics (Fig. 1.24). At the same time, the shutter output is connected instead of the VT1 base, and the source output is instead of the VT2 emitter, the flow output is instead of the united collectors VT1, VT2.
Fig. 1.24. Replacing the field transistors of the composite transistor
After such an uncomplicated refinement, i.e. Replacing nodes in electrical circuits, universal use, current on transistors VT1, VT2 does not fail even at 10 times and more voltage overload. Moreover, the restrictive resistor in the VT1 shutter circuit is also increased several times. This leads to the fact that they have a higher input and, as a result, withstand overload with a pulse character of controlling this electronic node.
The gain of the current cascade obtained is at least 50. Increases directly proportional to the increase in the supply voltage of the node.
VT1, VT2. In the absence of discrete transistors of the type KP501A ... in can be used without losing the quality of the device, use the microcircuit 1014ct1B. In contrast, for example, from 1014T1A and 1014ct1B, this can withstand higher overloads on the applied pulsed voltage - up to 200 in constant voltage. COFCOLOGE Turning on the transistors of the microcircuit 1014ct1a ... 1014K1V is shown in Fig. 1.25.
As in the previous embodiment (Fig. 1.24), include in parallel.
Codolve field transistors in the chip 1014ct1a ... in
The author tried tens of electronic nodes included by software. Such nodes are used in amateur structures as current keys in the same way as composite transistors included software. To the features of field transistors listed above, you can add their energy efficiency, since in the closed state due to the high input, they practically do not consume current. As for the value of such transistors, today it is almost the same as the cost of the type of mediterranean type transistors, (and similar to them), which are used as a current amplifier to control the load devices.
If you connect transistors, as shown in Fig. 2.60, the resulting scheme will work as one transistor, with its coefficient β will be equal to the product of the coefficients of the components of the transistors. This reception is useful for latch-operating circuits (for example, for voltage stabilizers or output caps of power amplifiers) or for input cascades of amplifiers, if it is necessary to provide a large input impedance.
Fig. 2.60. Composite transistor Darlington.
In the Darlington transistor, the voltage drop between the base and the emitter is two times more than the usual, and the saturation voltage is at least the voltage drop on the diode (since the transistor emitter potential T 1 should exceed the potential of the emitter of the transistor T 2, by the voltage drop in the diode). In addition, the transistors are connected as one transistor with sufficiently low speed, since the T 1 transistor cannot quickly turn off the transistor T 2. Taking into account this property, usually between the base and emitter of the transistor T 2, the resistor includes (Fig. 2.61). Resistor R prevents the transistor of T 2 to the conduction area due to the leakage currents of T 1 and T 2. The resistance of the resistor is chosen so that the leakage currents (measured in nano-perfumers for non-signal transistors and in hundreds of microampers for powerful transistors) have created a voltage drop on it that does not exceed the voltage drop on the diode, and at the same time so that the current flowed across it. Small compared to the basic current of the transistor T 2. Usually, the resistance R is several hundred ohms in a powerful Darlington transistor and several thousand ohms in a small transistor of Darlington.
Fig. 2.61. Increase the shutdown rate in a composite transistor of Darlington.
The industry produces Darlington transistors in the form of completed modules, including, as a rule, an emitter resistor. An example of such a standard scheme is a powerful N-P - N - Darlington Type 2N6282 transistor, its current gain is 4000 (typical value) for a collector current equal to 10 A.
Connecting transistors according to the Sziklai scheme (Sziklai). The connection of transistors according to the scheme of the CHIKLAY is a diagram similar to that. which we just considered. It also provides an increase in the β coefficient. Sometimes such a compound is called the complementary transistor of the Darlington (Fig. 2.62). The scheme behaves like a N-P-N transistor, which has a large coefficient β. The scheme acts one voltage between the base and the emitter, and the saturation voltage, as in the previous scheme, is at least a drop in the diode. Between the base and emitter of the transistor T 2, it is recommended to include a resistor with a small resistance. Developers apply this scheme in powerful two-stroke output cascades when they want to use output transistors of only one polarity. An example of such a scheme is shown in Fig. 2.63. As before, the resistor is a collector resistor of the transistor T 1 Transistor of the Darlington, formed by transistors T 2 and T 3. behaves like one transistor N-P-N - type. With a large current gain. Transistors T 4 and T 5, connected according to the scheme of Shiklai, behave like powerful transistor P-N-P - type. with a large gain. As before, resistors R 3 and R 4 have a small resistance. This scheme is sometimes called a two-stroke repeater with a quasi-pharmaceutical symmetry. In the present cascade with additional symmetry (complementary) transistors T 4 and T 5, would be connected according to the Darlington scheme.
Fig. 2.62. Connection of transistors according to the scheme of Shiklai ("Supplementing Transistor of Darlington").
Fig. 2.63. A powerful two-stroke cascade, in which the output transistors are used only N-P-N - type.
The transistor with a super-high value of the current amplification coefficient. Composite transistors - the transistor of the Darlington and the like - should not be confused with transistors with a super-high value of the current gain coefficient, in which a very large value of the coefficient H 21E is obtained during the technological process of manufacturing the element. An example of such an element serves a transistor of type 2N5962. For which the minimum current gain is guaranteed, equal to 450, when the collector current is changed in the range from 10 μA to 10 mA; This transistor belongs to a series of elements 2N5961-2N5963, which is characterized by the range of maximum voltages U Ke from 30 to 60 V (if the collector voltage should be greater, then it should be reducing the value C). Industry manufactures consistent pairs of transistors with super-high values \u200b\u200bof the β coefficient. They are used in low signal amplifiers for which transistors must have consistent characteristics; This issue is dedicated to section. 2.18. Examples of such standard schemes are the schemes of type LM394 and MAT-01; they are transistor pairs with a large gain coefficient, in which the stress U BE is agreed to the shared of Milcivolt (in the most good schemes Approval to 50 μV is provided), and the coefficient H 21E is up to 1%. MAT-03 scheme is a consistent p-N-P pair - Transistors.
Transistors with a super-high value of the β coefficient can be combined according to the Darlington scheme. In this case, the base current of the offset can be made equal to only 50 PKA (examples of such schemas are operating amplifiers type LM111 and LM316.
Literally immediately after the appearance of semiconductor devices, let's say, transistors, they rapidly began to displace electrovacuum devices And, in particular, triodes. Currently, transistors occupy a leading position in circuitry.
Beginnaya, and sometimes an experienced radio amateur-to-constructor, it is not immediately possible to find the desired circuitry solution or understand the purpose of one or another elements in the scheme. Having at hand, a set of "bricks" with known properties is much easier to build a "building" of one or another device.
Without stopping in detail on the parameters of the transistor (this is sufficiently written in modern literature, for example, c), consider only individual properties and ways to improve them.
One of the first problems arising in front of the developer is an increase in the power of the transistor. It can be solved by parallel incorporation of transistors (). Curving resistors in emitter circuits contribute to the uniform load distribution.
It turns out that the parallel inclusion of transistors is useful not only to increase power when gaining large signals, but also to reduce noise when the weak is increased. The noise level is reduced in proportion to the root square of the number parallel to the transistors.
Protection against current overload is most simply solved by the introduction of an additional transistor (). The lack of such a self-protecting transistor is a decrease in the efficiency due to the presence of the current sensor R. The possible option of improvement is shown on. Thanks to the introduction of a gerony diode or a Schottki diode, it is possible to reduce the value of the R resistor several times, and therefore the power dissipated on it.
To protect against reverse voltage, parallel with the outputs of the emitter collector typically include a diode, such as, for example, in compound transistors of the type KT825, KT827.
When the transistor is running in the key mode, when it is required to switch it from the open state into closed and back, sometimes use the forcing RC chain (). At the time of opening the transistor, the capacitor charge increases its base current, which helps reduce the inclusion time. The voltage on the condenser reaches the voltage drop on the base resistor caused by the base current. At the time of closing the transistor, the condenser, discharge, contributes to the resorption of non-core media in the database, reducing the shutdown time.
Increase the transistor steepness (the ratio of changes in the collector current (drain) to the voltage change of its change in the base (gate) at a constant UK USI)) can be used using the Darlington scheme (). The resistor in the base of the base of the second transistor (may be missing) is used to specify the current current of the first transistor. A similar composite transistor with high input resistance (thanks to the use field Transistor) Present on. Composite transistors presented in Fig. And, collected on transistors of different conductivity according to the scheme of Shiklai.
The introduction of additional transistors in the Darlington scheme and the shiklai, as shown in Fig. and, increases the input resistance of the second cascade variable current and, accordingly, the transmission coefficient. Application of a similar solution in transistors Fig. and gives respectively the scheme and, linearizing the steepness of the transistor.
Broadband transistor with high speed is presented on. Increasing speed achieved as a result of the decrease in the effect of Miller in the same way.
"Diamond" transistor for the FRG Patent is presented at. Possible options Its inclusions are depicted on. The characteristic feature of this transistor-absence of inversion at the collector. From here and an increase in twice the load capacity of the scheme.
A powerful composite transistor with a saturation voltage of about 1.5 V is depicted in Fig.24. The power of the transistor can be significantly increased by replacing the VT3 transistor to the composite transistor ().
Similar arguments can be cited for the transistor p-N-P typeas well as a field transistor with a P-type channel. When using a transistor as an adjusting element or in key mode, two options for turning on the load are possible: into the collector chain () or in the Emitter chain ().
As can be seen from the resulting formulas, the smallest voltage drop, and, accordingly, the minimum dissipation of power is on a simple transistor with a load in the collector's chain. The use of a composite transistor of Darlington and Shiklai with a load in the collector's chain is equivalent. The Darlington transistor may have an advantage if transistor collectors do not combine. When the load is turned on in the Emitter chain, the advantage of the Shiklai transistor is obvious.
Literature:
1. Stepanenko I. Fundamentals of the theory of transistors and transistor schemes. - M.: Energy, 1977.
2. US Patent 4633100: Puber. 20-133-83.
3. A.S. 810093.
4. US Patent 4730124: Puber.22-133-88. - p.47.
1. Increase the power of the transistor.
Resistors in the Emitter circuits are needed for uniform load distribution; The noise level is reduced in proportion to square root from the number of parallel to the included transistors.
2. Protection against current overload.
Disadvantage-reduction of efficiency due to the presence of current sensor R.
Another option - due to the administration of a gerony diode or Schottki diode, it is possible to reduce the value of the resistor R several times, and less power will be dissipated on it.
3. Composite transistor with high output resistance.
Due to the cascading of transistors, the Miller effect is significantly reduced.
Another scheme - due to the complete junction of the second transistor from the input and power supply of the first transistor with a voltage proportional to the input, the composite transistor has even higher dynamic characteristics (the only condition - the second transistor must have more high voltage cut-off). The input transistor can be replaced with bipolar.
4. Protection of the transistor from deep saturation.
Preventing direct displacement of the transition-collector using a Schottky diode.
A more complex option - a Baker Scheme. When the voltage reaches the database transistor collector, the base current is reset through the collector transition, preventing saturation.
5. Scheme of limiting saturation relative to low-voltage keys.
With a database current sensor.
With a manifold current sensor.
6. Reducing the transistor on / off time by applying the RC chain forcing.
7. Composite transistor.
Darlington scheme.
Shiklai scheme.
IN integrated schemes And two types of composite transistors received a wide range of discrete electronics: according to the Darlington and Shiklaya scheme. In micromogenic schemes, for example, the input cascades of operating amplifiers, compound transistors provide large input resistance and small input currents. In devices operating with large currents (for example, power stabilizers or output storage stabes) to increase the efficiency, it is necessary to provide a high gain of powerful transistors.
Shiklai scheme implements powerful p-N-P transistor with a large gain with low-power p-N-P transistor with small IN and powerful n-P-N transistor ( figure 7.51). In integrated circuits, this inclusion is implementing high p-N-P horizontal transistor p-N-P transistor and vertical n-P-N transistor. Also, this scheme is used in powerful two-stroke output cascades when the output transistors of the same polarity are used ( n-P-N).
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Figure 7.51 - Composite p-N-P Transistor Figure 7.52 - Composite n-P-N According to the scheme of Shiklai Transistor according to the Darlington scheme
Shiklai or complementary transistor Darlington transistor behaves like a transistor p-N-P type ( figure 7.51) with a large current gain coefficient
Input voltage is identical to a single transistor. Saturation voltage is higher than that of a single transistor to the voltage drop in the emitter transition n-P-N transistor. For silicon transistors, this voltage is the order of one volt, in contrast to the share of Volta of a single transistor. Between the base and emitter n-P-N The transistor (VT2) is recommended to include a resistor with a small resistance to suppress unmanaged current and improving thermal resistance.
The Darlington transistor is implemented on unipolar transistors ( figure 7.52.). The current gain is determined by the product of the coefficients of the components of the transistors.
The input voltage of the transistor according to the Darlington scheme is twice as much as a single transistor. Saturation voltage exceeds the output transistor. Input resistance operational amplifier for
.
Darlington scheme is used in discrete monolithic pulsed transistors. On one crystal, two transistors are formed, two shunt resistors and a protective diode ( figure 7.53.). Resistors R.1 I. R.2 suppress amplification coefficient in low current mode, ( figure 7.38), which provides a small value of unmanaged current and increasing the operating voltage of the closed transistor,
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Figure 7.53 - Electrical circuit Monolithic Pulse Transistor of Darlington
The R2 resistor (about 100 ohms) is formed in the form of a technological shunt, like shunts of the cathode transition of thyristors. For this purpose, when forming - an emitter using photolithography in certain local areas, an oxidic mask is left in the form of a circle. These local masks do not allow to diffuse a donor impurity, and under them remain p-columns ( figure 7.54.). After metallization over the entire Emitter area, these columns are distributed resistance R2 and a protective diode D ( figure 7.53.). The protective diode protects emitter transitions from breakdown when reformed collector voltage. The input power of the transistor consumption according to the Darlington scheme is one and a half two orders of magnitude lower than that of a single transistor. The maximum frequency of switching depends on the limit voltage and current of the collector. Talk transistors successfully work in pulse transducers to frequencies of about 100 kHz. A distinctive feature The monolithic transistor of Darlington is a quadratic gear ratio, since IN-the ampere characteristic is linearly increasing with an increase in the collector current to the maximum value,
The Darlington transistor is composed of a pair of the standard transistors combined with a crystal and a common protective coating. Usually in the drawings for the mark of the position of such a transistor do not apply special characters, Only the one marks the standard type transistors.
A load resistor is attached to the emitter chain of one of the elements. The conclusions of the transistor of Darlington are similar to the bipolar semiconductor trigation:
- base;
- emitter;
- collector.
In addition to the generally accepted version of the composite transistor, there are several types of its varieties.
Couple Shiklai and Casco Scheme
Another name of the composite semiconductor trio is a pair of Darlington. In addition, there is also a pair of Shiklai. This is a similar combination of dads of the main elements, which is characterized in that it includes different type transistors.
As to the cusodic scheme, it is also an option of a composite transistor, in which one semiconductor trigode is turned on according to the scheme with OE, and the other according to the scheme with OB. Such device is similar simple transistorwhich is included in the OE scheme, but with a higher frequency indicators, high input resistance and a large linear range with smaller distortions of the translated signal.
Advantages and disadvantages of compound transistors
The power and complexity of the transistor of Darlington can be regulated through an increase in the number of bipolar transistors included in it. There is also, which includes bipolar and, is used in the sphere of high-voltage electronics.
The main advantage of composite transistors is their ability to give a large current gain. The fact is that if the gain of each of the two transistors is 60, then with their joint work in a composite transistor, the total gain will be equal to the product of the coefficients of the transistors included in its composition (in this case - 3600). As a result, it will take a rather small current base for the opening of the Darlington transiston.
The disadvantage of the composite transistor is considered to be low speed work, which makes them suitable for use only in the schemes of working on low frequencies. Often, composite transistors appear as a component of output cascades of powerful low-frequency amplifiers.
Features of the device
Composite transistors have a gradual reduction in voltage along the conductor at the transition base-emitter twice the standard. The level of stress reduction on the open transistor is approximately equal to the drop in voltage, which has a diode.
For this indicator, the composite transistor is similar to a downstream transformer. But relative to the transformer characteristics, the transistor of Darlington has a much greater power gain. Such transistors can serve the operation of switching frequency to 25 Hz.
The system of industrial production of composite transistors is established in such a way that the module is fully equipped and equipped with an emitter resistor.
How to check the Darlington transistor
The easiest way to check the composite transistor is as follows:
- The emitter is connected to the "minus" power source;
- The collector is connected to one of the outputs of the light bulb, the second output is redirected to the "plus" power supply;
- Through the resistor, the database translates the plus voltage, the light bulb is lit;
- By means of a resistor, a minus voltage is transmitted to the database, the light bulb does not blow.
If everything happened as described, the transistor is working.
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