Voltmeter - indicator for laboratory power supply. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Voltmeter - indicator for laboratory power supply. 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 simplest thing is to make a voltmeter on a pointer measuring head. But this is no longer so modern and not accurate enough, therefore, the next in simplicity is a DC voltmeter on an ICL7107 type chip (like the domestic K572PV2, only the switching circuit is slightly different). Voltmeter on a four-digit seven-segment LED display, with a maximum reading of "1999".

The figure shows a typical simplified circuit.

(click to enlarge)

The switch can select the measurement limits (it switches the resistors of the input divider). Trimmer resistor R6 adjust the device. One problem is with the power supply, since you need a bipolar voltage of ±5 V, and the input should not be "grounded" to the power buses or to a common wire.

There are descriptions of voltmeters that take special care, make built-in negative voltage sources, but in my case this was an unnecessary complication. But the fact is that the laboratory power supply was homemade based on a transformer. TS-180 from an old black and white tube TV.

This is a very good transformer, with a large set of windings, among which there are several H3.3V filament windings. Far from all of them were involved in the block circuit, at least one winding remained free. So it was decided to make a bipolar ± 5 V power supply on it.

The rectifier is half-wave, the diode VD2 rectifies the negative half-wave, and VD3 - positive.

Since not only the IC is fed with a positive voltage, but also the indicators, a relatively powerful 7805 stabilizer is used there, and the negative one does not require a lot of current, because there is a parametric stabilizer on a resistor and a zener diode.

Author: Mishakov P.A.

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