Digital modulation generator 1 Hz-150 kHz with breaker
For some research tasks required a breaker with the exact and stable parameters of frequency and duty cycle. And most cases, the required modulation of the main or carrier frequency, which, in turn, must also be stable. All these characteristics inherent to the generator, the circuit description and one of the design options set out in this note. It can generate the carrier frequency 1 Hz-150 kHz with a fill factor (duty) 1-99%, which can be modulated by a lower frequency in the same range of frequencies and duty. Depending on the position of a single switch SW1, this oscillator can operate in three modes. All these are shown on the diagram in the form of a waveform to the gate of the mosfet transistor VT1, which performs here the function of the circuit breaker.
The scheme involved two relatively inexpensive single-Board digital oscillator, which are characterized by good parameters, and completely determine the output characteristics of the device: DG1 — generator carrier frequency, DG2 generator modulation frequency. Their digital outputs (PWM) are switched through a chain of diodes, resistors and the switch SW1 to the input of the DA1 driver that controls output switch VT1. The switch has three positions and which determines the mode of operation of the circuit. The upper position closes its contacts 1-2 and the device generates promoborudovanie pulses as they are shown in the green waveform. Middle position — closes its contacts 2-3, and the output is only the carrier frequency (orange waveform). The lower position of the switch closes its contacts 3-4, and the device begins to generate promoborudovanie pulses as they are shown on the blue waveform.
The scheme assumes that the generator DG1 is always exhibited higher frequency than in DG2, but it will work just as well, if they are reversed. In addition, the circuitry of the switch and its harness provides protection from the constantly open key. Another protection is implemented using two suppressors — ZD1 and ZD2, the first protects the driver, and the second protects all nizkovoltnoy part of the circuit from voltage spikes on the power supply. Thanks to these devices the device is quite resilient and stable.
As the breaker fits many modern mosfet or igbt transistors. In their selection can be guided by such criteria: minimum resistance of open transition and closed maximum voltage. Last, you should choose based on the parameters of the connected load. For example, for strains in the load to 400V transistors are well suited 47N60 or IRFP460.
For a list of other elements of the scheme:
- DG1, DG2 — digital signal generator 1Hz-150kHz;
- DA1 driver TC4420 or TC4452;
- VD1, VD2 — diode 1N4148;
- VD3 diode UF4007;
- ZD1, ZD2 — suppressor 1.5KE18CA;
- SW1 — a three position switch, for example SS13F24;
- 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.
The design of the device can be any, because the requirements for high frequency are not applied. The author chose a bunk option, placed on the PCB 6х8см. On the second floor are two generators DG1 and DG2 and the ground — all the other elements. Appearance and some of the Assembly steps shown in the following photo: