There is a class of experimental tasks in which you want to apply the pulses to the coil inductance LC-circuit or a transformer just before the end of the transients. Depending on the connection of the output key possible solution and inverse problems. For this purpose, a generator of the pulse train or, as it is called, the breaker sparks. From these the device features a stability of output parameters and work wide range. This is achieved by building a scheme for high-speed logic 74HCXX.
The generator allows you to:
- to adjust the frequency of pulses is 1 kHz .. 1 MHz, the duration of the single pulse can reach a value in the 20ns;
- to change the duty cycle of pulses of 6.25 .. 50%;
- adjusting the repetition frequency of packs of pulses — 300 Hz .. 50 kHz;
- to change the number of pulses in a pack of 1 .. 8.
Usually, these settings are sufficient for such tasks; on the advanced features of the generator will be discussed below.
The scheme involved 2 circuits performing logic 2I-NOT — DD1, DD2, two shift register DD3, DD4, and DA2 driver for amplifying the output signal. If the output key (in the diagram, not drawn) sufficient output power logic circuits, the driver DA2 and a resistance R6 can be removed. Food logic provides PWM-stabilizer DA1.
The logic of the scheme is. Specifies the generator on DD1.1, DD1.3, DD1.4 supplies pulses to the clock input of the shift register DD3. With its outputs, we take the pulses to the output of the inverter and the clock emulsy for the following shift register. Depending on the position of the switch SA3 output inverter on DD2.1, DD2.2, DD2.4 time to 1 .. 8 pulses of the master oscillator. After the emergence of logical units on the 13th leg DD3, on the D-input of the first register begins to receive a logic zero, so the second 8 pulses of the master oscillator sequentially fill the output registers with zeros; the output inverter is in its closed condition. As soon as a zero appears on his 13th leg, the next shift register DD4 will receive a clock pulse, and the first repeat.
His work will be repeated until then, until the entrance of DD2.3 will not appear. Its appearance determines the switch SA4, which connects the entrance of the element DD2.3 to one of the outputs of the second register. The number of repetitions and is equal to the number of pulses that corresponds to the output number in DD4. This unit will switch the output of DD2.3 to zero, which will stop the oscillator and start the process of discharging capacitor C4(C5) through the resistors R3, R4.
While there is a discharge of the capacitor the entire system "falls asleep" and does not consume power for internal switching. This time — pause between bursts of pulses. As soon as the voltage on the capacitor reaches a logic zero, the register DD4 will be reset and the whole cycle will repeat again.
The series of chips К1564 (КР1564) is a complete analog 74HC imported. Therefore 74HC164 can be replaced by К1564ИР8, 74HC00 — К1564ЛА3. Pyativoltovy stabilizer LM7805 is replaced by КР142ЕН5А, and is diode 1N4148 , you can install any ultrafast — faster than he is, the better. TC4429 can be replaced by TC4420, but because this version of the chip signal is not inverted, the 2nd leg of this driver must be connected to the leg 6 DD2.2.
The diagram does not show the power pins of chips. They are standard: 7 — negative supply (common), 14 — plus. All the cons need to connect and be connected to GND and to Gnd of the stabilizer DA1. All positive findings — Out to his (or +5V).
If you did decide to use the driver DA2, then connect two tanks by 0.1 UF directly on the findings of this chip: 1-4 and 8-5. Also, shunt capacitance (0.1 µf) is recommended to be install on the power pin of the oscillator, in other words connect it to the findings 7-14 of the chip DD1.
If everything is assembled correctly, the device begins to work immediately. Trimming resistor R1 is necessary to set the upper limit frequency adjustment of the pulses so that at the output of the oscillator, with the minimum variable resistance R2 was correct rectangular pulses.
There are several options.
Connection to X2. This output allows you to connect a powerful enough n-p-n transistor in circuit with common emitter. The output is connected directly to its base and to the collector may include various types of inductive loads or a parallel LC-circuit. This connection is characterized by steep fronts of the impulses.
Connecting to X3. In this case, because the intermediate driver, the front of the pulse will be flatter, but the X3 allows you to connect a MOSFET is the key to any current and voltage. This option not only allows to solve the problem of the buildup of inductance, and of energy extraction with oscillating system or the tank. In the circuit of common-source X3 is connected directly to MOSFET gate key.
The scheme allows to obtain such pulses only the output X2. The switch SA1 must be in the far left (under the scheme) position, and SA3 should be in position with connected the 3rd leg in DD3; R1, R2 must have a minimum value. Passport frequency IC 74HC00 — 100 MHz, and therefore, a single pulse could theoretically have a duration of 10 NS, is almost stable 20 NS. The duration between pulses, as in the General case, is regulated by a variable resistor R4.
If a scheme to add two more shift register, then the device capabilities are expanding. In the diagram below, the increased ranges of the two parameters: the duty cycle of the pulse in the stack is adjustable from 6.7 to 80%, and the number of pulses can be from one to 16.
Also, the open circuit power of the entire diagram, you can insert another voltage regulator, for example, LM7818 or LM7815. In this case, the upper limit supply all the device voltage increases from 20 to 36 Volts.
The circuit breaker sparks PLL for the Tesla coil, see here.
Vyacheslav Gorchilin, 2014
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