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Simple high duty cycle pulse generator
Unlike the previous circuit, two small-sized and inexpensive microcircuits are used here, and the generator design itself, and its assembly, turns out to be very simple. Nevertheless, such a generator is capable of producing pulses with a huge duty cycle - 3000 or more, which cannot be achieved in standard microcircuits like TL494 . The shortest pulse duration is 300 ns, and its rise and fall do not exceed 80 ns. The longest - depends on the C5 capacitor and can be, in principle, any. The pulse duration is regulated by a variable resistance R4 and does not depend on the master frequency, which can be an important condition for experiments by free energy seekers (see Fig. 1).
The driving frequency of the generator is divided into two ranges, which are selected by the switch SW1: 1 kHz - 10 kHz and 10 kHz - 100 kHz. The frequency depends on the capacitors C1 and C2, is regulated by the variable resistance R1, and can, in principle, vary within wider limits. The supply voltage supplied to the XS1 input can vary from 12 to 38 volts. The VT1 key generates short pulses on the XS2 connector for the load connected between the X2 and X3 pins.
Fig.1. Schematic diagram of a high duty cycle pulse generator
The operation of the circuit is quite simple. The generator of rectangular pulses on DA1, through the C5R3R4 chain, feeds them to the input of the DA2 lower arm driver, which contains an internal comparator. It allows to form a rectangular pulse from the exponential pulse formed by this chain, which is amplified by this microcircuit, after which it is fed to the control circuit of the output switch VT1. Capacitor C9 provides positive feedback to obtain a small hysteresis, which additionally removes all transient noise and contributes to the formation of a clear output pulse.
The R5VD1ZD1 chain protects the output switch and the rest of the circuit from sudden voltage surges at the VT1 drain. The DA3 microcircuit generates a stabilized voltage of 12 V on the circuit and may be optional. In the latter case, 12 V is supplied to the circuit from a separate power supply.
Any MOSFET or IGBT transistors with an opening voltage of 12 V are suitable as an output switch, for example IRF840. If you need a very fast key response, then you can use a high-speed MOSFET like AOTF27S60.
List of other elements of the circuit:
  • DA1 - master oscillator microcircuit NE555;
  • DA2 - output key driver microcircuit TC4452;
  • DA3 - voltage regulator L7812. Here you can use a lower-power analogue L78L12, but then the maximum input voltage on XS1 will drop to 33 Volts;
  • VD1 - diode UF4007;
  • ZD1 - suppressor 1.5KE18CA;
  • R1, R4 - any linear variable resistors with a plastic handle;
  • C1, C2, C4 - small TKE capacitors.
By the way, if you use TC4451 as DA2, then the output will become inverted and the key will be open almost all the time. This mode is also sometimes necessary for some experiments.
To configure, you must first set the following values. Contacts SW1 must be closed, R1 and R4 at the minimum value. The oscilloscope must be connected at two points: point 1 - blue ray, point 2 - yellow ray (see points in Fig. 1). Then we should receive a pulse, as in Figure 2, and a sequence of pulses, as in Figure 3. By adjusting the pulse duration with resistor R4 (to the position of maximum resistance), you need to obtain an oscillogram, as in Figure 4.
Fig. 2. Gate pulse VT1 (maximum duty cycle)
Fig. 3. Pulses with maximum duty cycle, with a frequency of 12 kHz
Fig. 4. Pulses with a minimum duty cycle, with a frequency of 12 kHz
The design of the device can be absolutely any, according to your desire. But it is still desirable to place the capacitor C5 as close as possible to both DA1 and DA2, and make the R3-R4 chain as short as possible.
Industrial version: PCB (open)
The industrial version provides a set of documentation for the industrial production of the board: GERBER file for the production of a printed circuit board, BOM file of the specification of components and a schematic diagram showing the values of the elements. All this allows you to immediately order a PCB, for example, here, and then quickly assemble it.
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