Research website of Vyacheslav Gorchilin
2020-02-02
All articles/Electronic circuits
Generator of bursts of short pulses with digital control
Dallask development of the generator of short pulses with a large duty cycle is the following diagram. Such a device may generate packets of pulses with the specified number in the bundle and with a given number of pauses between them. Unlike analog such generators, where the first and the last pulse in the packet can have different lengths, all pulses and pauses are processed correctly, that may be a very important parameter for many devices. At its output we get packs of pulses, the duration of which is regulated regardless of their frequency. The generator can be used both for research purposes and for the finished devices.
Generator parameters are the following. The pulse frequency is set in cifrova and is adjustable from 1 Hz to 150 kHz. The pulse duration in the pack is regulated by a variable resistance R1, depending on the position of the switch SW1 may be 70 ns 700 ns or 0.5 µs - 5 µs. The number of pulses in a packet, depending on the positions of the switch SA1 can be from 1 to 15. The number of pauses between bursts of pulses depending on positions of the switch SA2, can range from 0 to 15. Thus, duration of a pause equal to the pulse period.
As in the previous generator, this device also used a relatively inexpensive digital single-Board generator DG1. It is the clock for the entire rest of the circuit. To obtain the packs of pulses and pauses between them, the scheme used two inexpensive digital chips: DD1 and DD2. Clock pulses from DG1 (output TTL) is transmitted to the first (a dual input inverter DD1.1) and there formed with a locking signal from the outputs of the first counter DD2.1, connected through switch SA1. Depending on the provisions of the locking signal appears after 1 to 15 clock pulses. The same signal through the inverter DD1.4, enables the second counter DD2.2, the number of pulses at the output of the switch SA2 is also dependent on its provisions. After the appearance of a logical one at its output, resets the first counter, and with it the locking signal, and the cycle repeats again. To the output of DD1.1, via an RC-chain R1R2C1(C2), connected to one inverter DD1.3, which forms the duration of the output pulse depending on the position of the variable resistance R1. This pulse is supplied to the driver DA1 and the output switch VT1. Chain R6VD9ZD1 protects this key and driver and the rest of the scheme, from potential releases of EDS on its flow with inductive load.
The following are data on the number of output pulses and pauses depending on the switches SA1 and SA2. The position of switches is provided, as in the diagram. For example, the position "1100" from SA1 means that the contacts are closed at SA1.1 and SA1.2, and the other open; the generator thus produces a pack of three pulses. For DIP switch closed contact in the "on" position.
The position of the switches SA1 and the number of pulses
0000
1000 1
0100 2
1100 3
0010 4
1010 5
0110 6
1110 7
0001 8
1001 9
0101 10
1101 11
0011 12
1011 13
0111 14
1111 15
The position of the switches SA2 and the number of pauses
0000 0
1000 1
0100 2
1100 3
0010 4
1010 5
0110 6
1110 7
0001 8
1001 9
0101 10
1101 11
0011 12
1011 13
0111 14
1111 15
The position of "0000" from SA1 indicates that the generator generates the pulses (output disabled). The position of "0000" from SA2 means that the generator gives pulses without pauses between bursts, as it did familiar generator.
Connect to DG1
This item we have already described earlier, but still repeat some of the highlights. To get good front and decay of the pulse from single-Board generator DG1 is required to it two non-standard connection: TTL and +3.3 V. in addition to the above, connection +3.3 V in this embodiment, the generator is also used to power two additional circuits DD1 and DD2, which reduces the number of parts.
The photo above shows these two connections: TTL and +3.3 V. They also have and concept. +3.3 V is the internal single — Board power generator DG1, and the TTL output of the generator to the output inverter. Care should be taken to solder to these points of thin wires. This is best done by soldering iron with a fine tip.
Two other connections: VIN+ and VIN - are standard. First appears on the +12V circuits, and the second is connected to the common wire.
Details
As the output key are good "light" mosfet: IRF840 or IRF740. If the output required a lot of power, then it is better to apply high-speed IGBT. Driver DA1 optimally use the high-speed microchip TC4452, then the minimum pulse width is obtained in 60-70 ns. And fit more "slow" TC4420, but then the minimum duration of the output pulse is about 100 ns. By the way, this scheme can be applied to an inverting driver, such as, TC4451, but then the output of the resistance R1 (point A) to be connected not to the positive supply, as in the diagram, and to the common wire.
For a list of other elements of the scheme:
  • DG1 — digital signal generator 1Hz-150kHz;
  • DD1 chip is a binary logic 74HC02;
  • DD2 is a binary pulse counter 74HC393;
  • VD1-VD8 — diodes 1N4148;
  • VD9 diode UF4007;
  • ZD1 — suppressor 1.5KE18CA;
  • R1 — any variable resistor with plastic handle; R2 is any trimming resistor;
  • C1, C2 — capacitors with a small HEEL, better tubular;
  • SA1, SA2 — DS-04B, SWD14 (any DIP switch in 4 sections);
  • XS1 — standard connector to the power supply at 12V, for example, like this;
  • XS2 — any terminal block on the three pins, for example, like this.
Installation
It can be done in any convenient way. Need to be reminded that in the diagram the power pins of digital circuits (DD1, DD2) not specified, but they must be connected like this: 7 the output — to the common wire 14 output to the positive supply (+V in the diagram). In the power unit it is necessary to have the driver DA1, and all connections as close as possible to the output key VT1.
Setting
Setting up the circuit, as in the simpler version of this generator, comes down to setting the minimum duration of the output pulse, at which it is still observed on the oscilloscope connected to the DA1 output (6.7 output). This is done using a trimming resistor R2 with a minimum value of R1, an open SW1 key and setting the SA1-SA2 switches to the position: 8 pulses - 8 pauses (see table). Also, on a single-board generator DG1, you must set the maximum frequency (150 kHz) and the parameter "DUTY" equal to 50%. More parameter "DUTY" does not change. Otherwise, the scheme starts working immediately and does not require additional settings.
Design
The design of the device can be any, on your taste. The author chose the optimum for single Board generator DG1, bunk option, placed on a printed circuit Board 5x7 cm. On the second tier is a single Board generator DG1, and the first — all the other elements. Appearance and some of the Assembly steps shown in the following photo:
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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Reliable partner for PCB production
The author can send a set of parts and a manufactured printed circuit board for self-assembly of this device.
Applications for this generator can be found here or here.