Portable battery-powered AF generators. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Portable battery-powered AF generators. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Measuring technology

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The article presents two options for battery-powered audio frequency signal generators. They differ from the usual two power amplifiers (up to 1 W at a supply voltage of 15 V), from which two different signals can be received. The use of integrated circuits ensures the operability of generators in a wide range of supply voltages, and their modifications with frequency tuning will expand the scope of applications.

On fig. 2 shows a diagram of a signal generator with a frequency of 1 kHz. It generates two signals (triangular and rectangular) with adjustable amplitude. The oscillation frequency is determined by the parameters of the elements R4, C1. Op-amp DA1.1 works as a square wave signal generator (meander), its output voltage is set by a variable resistor R6. This signal is applied to the first channel of the TDA2822M.

Rice. 1 (click to enlarge)

Rice. 2 (click to enlarge)

The signal at point A (at the inverting input DA1. 1) has a triangular shape, and through the voltage buffer follower on the op-amp DA1.2 it enters the second channel of the TDA2822M amplifier. The output signal of a triangular shape is regulated by the level of a variable resistor R7.

Connecting the load between the outputs of the channels of the DA2 chip allows you to get the form of the output voltage on the op-amp DA1.2, it goes to the second channel of the TDA2822M amplifier. The output signal of a triangular shape is regulated by the level of a variable resistor R7.

Connecting the load between the outputs of the channels of the DA2 chip allows you to get the shape of the output voltage in the form of a bipolar "saw". Dividers at the outputs of the generator can reduce the output voltage by 20 dB (10 times).

In generators, instead of the TDA2822M chip, two LM386s can be used, although they are not a complete analogue. The LM358 chip can be replaced with analogues (NE532, KR1401UD5, KR1040UD1) or other op-amps with similar parameters. In frequency-setting circuits, it is desirable to use capacitors with a film dielectric, for example, K73-9, K73-17.

Both designs are operated with a rechargeable battery with a voltage of 6,6 V or with a battery of 6 V (4x1,5 V) galvanic cells, but the generators are operational at a supply voltage of 3 ... power supply from network adapters. In this case, a protective diode should be provided to prevent direct connection of the battery to the rectifier, or a connector with disconnection of the power supply circuit from the built-in battery should be used. In fact, the design of generators largely depends on the capabilities and requirements of users of such a device.

As a variant of the generator according to Fig. 2, a modification can be proposed in which the op amp DA1.2 is turned on by a voltage inverter connected to the output DA1. 1. Then at the outputs of the amplifiers DA2 there will be anti-phase voltages of a rectangular shape.

Returning to the issue of frequency tuning of generators (see Fig. 1), a combination of fixed and variable frequency generators is possible. For tunable sinusoidal signal generators, it is important to use in frequency-setting circuits dual variable resistors with a minimum spread and capacitors of equal capacity (the spread is not more than 1 ... 2%, achieved by a set of several connected in parallel).

Author: P. Petrov

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