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Kacher voltage converters. Generalization
Previously different types of kacher voltage converters (KVC) were introduced, well generating both individual impulses and oscillations of various shapes. In the same note, we will try to bring them into a single system and consider KVC with a common emitter, with a common collector and with a common base. Also, here we will derive some properties and features of a particular KVC circuitry.
Note that in this series of notes we are discussing KVCs in which there is no inductive feedback, and the two coils (chokes) used in all the circuits presented here are not inductively connected in any way. This fundamental point is very important, since, according to the author, it is he who distinguishes the kacherny method of voltage conversion [1] from the blocking oscillator method [2]. In addition, the absence of such a connection increases the efficiency of devices assembled on this principle.
Recall also that all the generators presented here will not work in online simulators, because they do not include quality effects in p-n junctions. In reality, these generators are quite efficient and can be used in various areas of radio electronics.
Fig.8. KVC with a common emitter (a), with a common collector (b) and with a common base (c)
Figure 8 shows KVCs with a common emitter (a), with a common collector (b), and with a common base (c). Each such circuitry solution has its pros and cons, and has its own optimal scope. Let's consider them separately.
KVC with common emitter
This circuitry option is the most versatile and, to some extent, combines the advantages of all the others (Fig. 8a). A KVC generator with a common emitter is easily self-excited; high-voltage and relatively short pulses are very easily formed at its output, it can work both with a lumped inductor and with a long line.
Devices based on such circuitry were presented by the author here and here. They are distinguished by their simplicity and reliability. Next, we will tell you how to apply such a KVC for a long line, but for this you need to slightly improve the circuit and apply protection for VT1.
The kacher principle of excitation of oscillations has one big drawback - at sufficiently high values ​​of the voltage at the output X1, the p-n-junction of the transistor VT1 can gradually degrade or even fail completely due to sudden surges of back EMF, or back waves when working with long lines. To protect against these phenomena, you can apply a fairly simple protection: install a ZN1 suppressor between the base and the emitter, and between the collector and the emitter there is a diode in the reverse connection D1 (Fig. 9). The latter is required for transistors that do not have a built-in flyback diode.
Figure 9. KVC with a common emitter and voltage protection
The protective suppressor ZN1 is selected based on the maximum reverse voltage of the base-emitter of the transistor VT1, usually referred to in reference books as VEBO. For example, for the BUL128A transistor it is 9 volts, then the suppressor is also selected for this voltage, in this case, P6KE9.1CA.
The same protection can be applied to subsequent KVC options, especially where a high impulse voltage will be present at the output.
Now, instead of the L2 coil, you can connect a long line and, in general, any other load.
KVC with common collector
Such a circuitry has not been described anywhere before, because. represents a certain difficulty in identifying the mechanisms of self-excitation. In this regard, the most "mysterious" the scheme of all KVC is this one - with a common collector (Fig. 8b).
A common-collector KVC generator can produce both pulses and pure sine waves at output X1, but the latter will require the condition \[L_1 = L_2\] and also, - selection of resistance R1. As in all other switching on of the transistor, the selection of this resistor can bring the generator both into the stable continuous oscillation mode and into the pulse burst mode. The frequency of sinusoidal oscillations can be approximately calculated using the following formula: \[ f \approx {1 \over 2 \pi \sqrt{L_2 C_3}} \] At the same time, at the output X1, we will receive oscillations with an amplitude equal to twice the supply voltage of the circuit. The supply voltage itself can start from 1.5 V and end with the maximum reverse voltage of the VT1 transistor, divided in half. By the way, this way you can achieve extremely low energy consumption. For example, if the circuit is without load, then with L1 = L2 = 220 μH and a supply voltage of 12 V, the current consumption can be only 0.3 mA.
In particular, the lower (according to the diagram) output of the capacitor C3 can be switched to the power plus.
Common Base KVC
The scheme of such inclusion is shown in Figure 8c, and the device based on such a circuitry is presented by the author here. There is also a description and features of his work. The generator can participate in several modes and give out bursts of pulses, single pulses for resonance of the second kind, as well as - sinusoidal oscillations.
All KVC circuits presented in this work can be controlled from an external low-frequency modulator. To do this, the upper terminal of the resistor R1 must be connected to the output of such a modulator. The modulator itself must have at its output unipolar pulses with an amplitude equal to the supply voltage.
Element base
For this technology, the ideal transistor is a pulse transistor, with which you can squeeze the maximum out of it. In practice, the following brands were tested: BUL128A, BUL128D (with flyback diode), C5027-R, TIP41C, E13009L, E13009D (with flyback diode). But in principle, any npn transistor will do, except for a common collector circuit, where you want to get sinusoidal oscillations.
Chokes L1 and L2 can be either axial or radial type, for example: 470uH, 220uH. But the ideal solution would be homemade chokes wound with a gap between the turns, which will give them a minimum throughput capacity.
Pay special attention to capacitors. The first thing that is required of them is to work under the maximum impulse voltage that can be obtained on the inductance L2. Since the KVC can generate an amplitude on it that exceeds the supply voltage by 10-15 times, then the maximum voltage of the capacitors should not be less. This is especially true for KVC with a common emitter. The second thing that is required from capacitors is the minimum losses when smoothing pulses. To do this, it is necessary to use high-frequency capacitances, for example, MKP brands.
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Materials used
  1. Brovin V.I. The generator of breaks in the electrical circuit is a driver on a transistor. RU2444124C1.
  2. Wikipedia. Blocking Generator.