Research website of Vyacheslav Gorchilin
2022-04-21
All articles/Electronic circuits
Pulse burst generator on a single transistor
Previous The circuit worked on a single mosfet transistor and produced short high-voltage pulses at its output. The author noticed that under some special conditions it can go into a very unstable mode of bursts of pulses. By sequential selection of elements, the author managed to isolate this mode, however, as a generator, this circuit design solution suggests a bipolar transistor that is more optimal in this case. Now the circuit can stably generate bursts of pulses, have any output load, and even switch to an ultra-economical mode, in which its consumption is not recorded by digital devices.
The pulse burst mode is set in the circuit (Fig. 5a) using the R1-R2-C2 chain, which charges the capacitor C2, which allows the VT1 transistor to generate high-frequency pulses in the initial section of the discharge. The latter, in turn, is made possible by the positive feedback ring L1, put on the wire going through the load D1. In this case, D1 is a 12V LED matrix, but it can be another load, such as a transformer.
Fig.5. Schematic diagram of a pulse train generator on a single transistor (a) and its switching circuit (b, c)
Such a circuit could be called a blocking generator if it were not for the amplitude of the pulses on the VT1 collector, which can exceed the supply voltage by several times. On the conductor passed through the ring L1, such an amplitude was not recorded, and if it weren't for the kacher properties of the p-n-junction of the transistor VT1, then it would simply have nowhere to come from.
Fig.6. Oscillogram of the circuit operation at a resolution of 20 µs
Figure 7. Oscillogram of the circuit operation at a resolution of 1 ms
Figures 6 and 7 show the oscillograms of the circuit operation: the blue beam is on the collector of the transistor VT1, the yellow one is on the capacitor C2. The supply voltage of the device is 12 volts. It is clearly seen that a periodic discharge-charge occurs on C2 (Fig. 7), which makes it possible to generate high-frequency oscillations in the form of a burst of pulses on the collector of the transistor VT1 (Fig. 6).
Is it possible to stop the counter?
The most intriguing part of this device is the mode in which digital devices do not record its consumption. For example, if the device is connected as shown in figure 5b, where PU is a digital power supply with a digital current and voltage scale, and GP is our burst generator, then with a certain mode selected by the resistor R1, zero consumption is observed. The same thing happens if you make the connection of the device a little more complicated (Fig. 5c), and add a WM wattmeter to the circuit, and use an AP adapter for 12 volts instead of a power supply. In this case, under a certain mode, the wattmeter can also show zero consumption.
In fact, the circuit will have consumption even with a special mode, although the latter turns out to be really very economical. More accurate consumption of this device can be tracked by pointer or analog devices.
Element Base
Only pulse (switching) high-voltage transistors are suitable for this circuit. The following brands have been verified by the author: BUL128A, BUL128D, C5027-R, ST13009.
Suppressor D2 serves to protect the p-n-junction of the transistor VT1 and is selected based on the passport value of the maximum allowable base-emitter reverse voltage (VEBO), which is usually 9 volts. From here, a suppressor is selected, designed for the same voltage. In this case it is P6KE9.1CA.
The load for the circuit is LED array D1 rated at 12 volts, power 10 W. In this case, any LED or a set of them can be used in general. It is only desirable that their ignition voltage does not exceed the supply voltage by 2 times. Generally speaking, for a given circuit, you can find the optimal set of LEDs by selecting them.
The most interesting detail of this device is the current transformer L1, which is simply put on the collector wire. It comes from two ferrite rings K10x6x4 with a permeability of 1000-2000 HM, which must be added together, and then - wind on them a copper insulated wire with a core diameter of 0.2-0.25 mm. It is best to use the MGTF wire here. The coils are wound in one layer, until full. A gap remains in the ring, into which a conductor is threaded coming from the VT1 collector. Rings can be of other sizes, but the smaller they are, the shorter the domain recovery time, which has a positive effect on the output parameters of the generator.
Capacitors C1 and C2 must be either propylene or ceramic. The time of the oscillation period of the pulse train depends on C2, so it must hold the pulse voltage drops well.
Scheme Setup
Before turning on the device, bring the tuning resistor R1 to the position of maximum resistance (in the upper position according to the diagram). After turning on the power, smoothly turn this resistor until the matrix D1 begins to glow - it should start blinking. This should be the minimum consumption mode of the device. If the matrix does not light up, then the transformer is connected incorrectly and you just need to swap its conclusions (or thread the collector wire into the ring in the other direction).
Resistor R1 regulates the threshold for the start of generation and the duration between bursts of pulses. In super-economical mode, this frequency is about 6-10 Hz. If it is small for you, then later, after tuning, it will be possible to reduce the capacitance of the capacitor C2 by 5-6 times.
 
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