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stabilization in this way is very popular because it provides a steady voltage precision. The circuit of Sch.8.19 shows the typical circuit voltage stabilization TE. This is done through anasyzefxi Rr
Figure 8.19. Stabilize voltage TE
RL V0
Because TE does not give high output current, make the circuit with a transistor power pnp, as shown. The power transistor has the potential to give the desired load current IL connected to the voltage V that we want to stabilize. The transistor is behaving like a big RV resistance similar to that of b Sch.8.15
Demonstrated, the analysis of TE (Chapter 4) that the output voltage is given by:
(8.9.1)
Therefore, the steady-state output voltage V0 can be adjusted at will through the Rf of the Ri
8.10 Stabilization of an integrated circuit
Generally, two basic parts of an advanced stabilizer is the element that gives the reference voltage and the voltage controlled amplifier. These parts can easily be combined into an integrated circuit so that we have very good stability and low volume.
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Stabilizers are commercially voltage integrated circuit (IC) for many applications and provide stabilization from 0.01 to 1%. Usually, the integrated amplifier contains a setup and a Zener diode on the same chip. Often the transistor is not contained within the integrated circuit to not cause large changes in voltage V and current IL by temperature. These changes resulted in large error stabilization.
Many integrated circuits are designed to stabilize specific fixed output voltages, eg 5 V logic circuits to 15 V for the operational amplifiers. The Sch.8.20 shows one such circuit, the MVR5V, to stabilize the output voltage of 5 V dc. The maximum load current is 600 mA and rate stabilization, S = (D ^ / AVo) x 100, is 1%.
Transformers. 8-12 V
Figure 8.20. Integrated Circuit Voltage to 5 V dc
The decoupling capacitors C2 and C3 are used to the circuit has low output impedance to all frequencies. Note that the output impedance of all stabilizers increases at high frequencies, while strengthening the regulatory amplifier (error) is reduced. The electrolytic capacitor C2 has a low resistance in the middle region of high frequencies, while the capacitor C3 (polystyrene or ceramic) operates at high frequencies to lower the output impedance in this region.
With MVR5V must use an external heat sink if you want to capitalize on the region of maximum current of 600 mA which is able to give. If the power
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the burden is less than 100 mA, the capacitor C1 can be 1000 MP the transformer can be the classic transformer of 6.3 V and does not need heat sink.
If we want an output voltage of 12 Vtha should use the integrated circuit (IC) MVR12V. The input voltage must be at least 14.5 V. MVR15Vdinei The output voltage of 15 V input voltage at least 17.5 V. The maximum input voltage for MVR12V MVR15V and is 27 V and the MVR5V is 20 V.
The Sch.8.21 shows a variation of the circuit Sch.8.20 with which we can have adjustable stabilized output voltage. The circuit uses MVR5V, but can use other IC to have greater control range of output voltage. O MVR5V stabilizer maintains stable voltage 5 V at the ends of the resistor R1 and through the voltage divider R1 and R2, the output voltage is given by:
So, by changing the resistance of potentiometer R2, may regulate at will the stabilized output voltage Vo.
(8.10.1)
Figure 8.21. Regulated stabilization circuit
output voltage to the IC MVR5V
The Sch.8.22 IC shows a basic circuit voltage stabilization, the mA723 (or L123), which gives out a regulated output voltage from 7 V to 27 V. To mA723 has the following components:
adjustable
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1. A Zener diode reference. The diode was powered by a constant current source. The diode including an amplifier anasyzefxi used to degrade the output impedance.
2. An error amplifier. Both the inverting input and the non-inverting have their own external akrodeketes. O compensation capacitor CC, strengthening degrades at high frequencies to avoid instability on those frequencies.
Figure 8.22. Regulated voltage stabilizer 7-27 Vme the ICmA723
3. A voltage amplifier following average power with T1. The transistor that limits the power losses of the regulator, which corresponds to the maximum (600 mA) in this case. But this limit can be increased if we use external resistance.
4. A transistor T2, current limit. The transistor is "held by ¬" the potential difference at the ends of resistor RSC and begins to conduct when it reaches 0.6 V. As the T2 conducts, contact shorted base emitter voltage of the following inert and makes cutting the supply voltage.
Another category is monolithic IC circuit and the series 78CHCH 79CHCH which give exit to a steady trend. While the first series, 78CHCH, at the output of stabilized positive trends, the second of the series 79CHCH gives a steady negative trend.
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Integrated circuits have these three terminals, which is the terminal of the input, output and common. These units can be connected in a circuit without having to connect external additional other ingredients except the input and output capacitors to filter the output voltage of the rectifier.
The Sch.8.23 shows the format of the integrated circuit on a KC. The next two numbers indicate the code stabilized output voltage, eg the 7805 means that the IC at the output of a stabilized voltage +5 V, while the 7905 gives -5 V. Similarly, the 7812 gives as + 12 V, while the 7915 gives -15 V.
Output (out) The
Common (shared) C
Input (input) I
Figure 8.23. IC voltage stabilization 78XX and 79XX series
Sch.8.24 The complete circuit is a +5 V power supply for powering digital integrated circuits.
TO3
Figure 8.24. Power supply voltage +5 V stabilized
To Sch.8.25 shows the complete circuit of a power supply ± 15 V power supply for linear integrated circuits.
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220 V
Figure 8.25. Stabilized voltage power supply ± 15V
8.11 Converter DC / DC
Sometimes we want to convert a dc voltage level to another level again dc. Eg if we have a system that has a positive supply voltage +5, we can use a converter DC / DC and transform these into a +5 V output voltage of +15 V. This way we will have available two tofodosias trends for the electronic device, ie, +5 and +15 V.
The converters DC / DC have great performance. This is what, to them, the transistors work as switches (on-off), so power loss significantly degraded. The typical performance of these converters ranging from 65 to 85%. A large class of converters DC / DC usually called palmotrofodotika (see below).
8.11.1 Converters DC / DC without stabilization
In a typical converter DC / DC without stabilization, the dc input voltage is applied to a square pulse oscillator. The peak voltage-to-top of a square pulse is proportional to the input voltage. The square pulse is used to drive the primary of a transformer, as shown in Sch.8.26.
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The
Figure 8.26. Structural diagram of a converter DC / DC without stabilization
The higher the frequency of the oscillator, the smaller is the transformer and filter data smoothing. But if the frequency is too high, it is very difficult to get pulses with steep fronts (ie with short rise and fall of the pulse). Usually, the most appropriate frequency of square pulses of the oscillator is between 10 and 100 kHz.
One common converter DC / DC is one that converts voltage +5 V to + 15 V. The voltage is +5 V supply voltage of digital integrated circuits, while the voltage is +15 V supply voltage multi-linear electronic circuits and IC with IS. For this case there is an economic trade converter DC / DC low power that converts the dc voltage of +5 V at dc voltage of +15 V.
There are too ways to design a converter DC / DC. The design of this depends on whether we use bipolar transistors (BJT) or power FET, the frequency of the oscillator and whether the transformer is lifting or relegation.
The Sch.8.27 shows an inverter circuit, DC / DC using BJTischyos. The circuit is as follows: O square pulse oscillator generates pulses whose frequency is determined by the elements R and C. The frequency of the oscillator is in the range of kHz, with a typical value of 20 kHz.
The square wave oscillator applied to a phase separator, T1, is a circuit which generates two square wave with a phase difference of 180 °. The pair of square pulses are input to an amplifier push-pull class B which stimulate the transistors T2 and T3. The transistor T2 is conducting during the half cycle and T3 during one of the other half cycle. The primary current of the transformer is square wave. The pulse square pulse is induced in the secondary of the transformer, as mentioned previously.
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This trend goes into a bridge rectifier, where it is rectified and then filtered. Thus, the output dc voltage we get a different level than the dc input voltage.
In the market there are various converters DC / DC ¬ poetry without a fixed number of companies with a yield of 65 to 85%. Eg There are cheap converters DC / DC conversion of +5 V to +12 V with current of 375 mA, +5 to +9 V with a current of 200 mA, +12 ± 15 V at a current of 250 mA, etc. All these converters require a constant input voltage because it does not include voltage stabilization. Also, these converters using oscillation frequency from 10 to 100 kHz. Given the frequency that contain shielding against radio frequency (RFI). Some of them have the inverters lifetime 200 000 hours.
8.11.2 Palmotrofodotika
The palmotrofodotika under the general category of penis ¬ converter DC / DC, because they convert a dc input voltage to another dc voltage output, either elevated or degraded. In addition, however, contain the palmotrofodotika system voltage stabilization. This system has a pulse width modulator to control the timing of an on-off transistor. Changing the working time of pal-
Electronic
high-current switch
Figure 8.28. Basic structure of a palmotrofodotikou
(8.11.1)
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ture these, palmotrofodotika can maintain the output voltage constant.
The Sch.8.28 depicts a block diagram palmotrofodoti-
Mr. As we see consists of a comparator amplifier, a reference voltage source, VR, a pulse width modulator, a high current electronic switch and a low frequency filter (FSF). The operation of this circuit is as follows: O error amplifier circuit compares the fraction of the reference voltage VR to the regulated output voltage Vo. The reference voltage VR from a series of small power stabilizer. Because the stabilizer is using small current, consumes little power and interior provide an accurate reference voltage. The output of the modulator amplifier, VC, used to control the electronic switch high currents. This control voltage, VC, is a square pulse waveform with period T.
Stabilizer series
Error amplifier
Pulse width modulator
FTT
O high current electronic switch provides in rotation or non-stabilized voltage V; either zero voltage, thus creating a square pulse period T. The voltage VS through the FSF, which filters the trend, provided the / LC is very greater than T/2p. Eventually, the price of VR stabilized at mid VS.
It turns out that the stabilized output voltage Vo is given by:
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The steady trend depends on the exact value of
reference voltage VR, the ratio of resistors R2/R1 and the
how good is filtration.
To function correctly palmotrofodotika should apply
Example 8-4
Calculate the resistors R1 and R2 of the palmotrofodotikou Sch.8.28 if we want the output voltage is 12 V, with a reference voltage 5 V.
Solution
We use Eq. (8.11.1) and to solve the ratio R2/R1, so we
R2 V0 12
Ri Vr 5 *
Since we know the ratio of resistors, the resistors count freely. Assuming for example a R1 = 4.7 kQ, the above relationship to calculate R2 = 1.4R1 6.6 kQ (6.8 kQ, E12 series).
