On-board network voltage indicators. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices
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Analyzing the voltage indicator circuit on a two-color LED [1], I came to the conclusion that the device can be significantly simplified if the pulsed glow mode is abandoned. This made it possible to assemble the indicator on just one microcircuit (see the diagram in Fig. 1).
Fig. 1
Two voltage comparators are assembled on the op amp DA1.1 and DA1.2. As long as the voltage across the capacitor C1 is less than the stabilization voltage of the zener diode VD1 (and, consequently, VD2), a high level voltage is present at the output of the comparators, both crystals of the HL1 indicator are lit. Transistor VT1 is closed.
If the voltage on the capacitor C1, increasing, exceeded the stabilization voltage of the zener diode VD1, a low level will appear at the output of the comparator DA1.1 and the "red" crystal of the HL1 LED will go out; only green light is on. Transistor VT1 is still closed.
When the voltage on the capacitor C1, continuing to increase, exceeds the stabilization voltage and the zener diode VD2, the output of the comparator DA1.2 will also appear low and the "green" crystal of the HL1 LED will go out, but the opening transistor VT1 will turn on "red".
Thus, when the voltage of the on-board network is reduced against the norm, the HL1 LED shines yellow-orange, when it is normal, it is green, and when it is increased, it is red.
Fig. 2
For those who prefer to build their homemade products on digital microcircuits, I suggest an indicator according to the diagram in fig. 2. The indication algorithm of this device is the same as that described above. The indicator is based on an LED voltmeter [2]. The calculation of the resistor voltage divider R1-R3 is borrowed from the same article.
Inverter DD1.1 switches from a single state to zero when the voltage at the input of the device is 12 V, and DD1.2 - at 15 V. Thus, at a voltage less than 12 V, the outputs of inverters DD1.1 and DD1.2 are high level, at the output of DD1.3 - low, transistors VT3 and VT4 are open, VT2 is closed, therefore both crystals of the HL1 indicator are lit.
When the input voltage exceeds 12 V, the high voltage level at the output of the inverter DD1.1 changes to a low one, the transistor VT3 closes and the "red" crystal goes out. Transistor VT2 is still closed.
When the voltage rises above 15 V, the output level of the DD1.2 inverter also becomes low, the VT4 transistor closes and the "green" indicator crystal goes out. However, a high-level voltage appears at the output of the inverter DD1.3, which opens the transistor VT2, which turns on the "red" crystal.
Both devices do not require adjustment and, with error-free assembly from serviceable parts, they begin to work immediately. Sometimes only the first of them requires a selection of zener diodes according to the limiting voltage values \u1b\u6,1b(VD7,5 - 2 ... 7,4V; VD9 - XNUMX ... XNUMX V).
Fig. 3
The printed circuit boards of the indicators are made of foil fiberglass 1 mm thick. Board drawings are shown in fig. 3 and 4. The boards are designed for the installation of MLT-0,25 resistors and imported oxide capacitors.
Fig. 4
In the first indicator, any op amp can work with the appropriate correction of the pattern of the printed circuit board conductors. Zener diodes - any low-power ones for the corresponding stabilization voltage. The transistor is suitable for the specified series with a letter index from Zh to M. In the second indicator, the transistors can be of any appropriate structure and power, the zener diode can be any for the corresponding stabilization voltage. The LED is suitable for domestic or imported two-color with a working current of 5 ... 20 mA.
Literature
- Nechaev I. LED voltage indicator. - Radio, 2004, No. 8, p. 55
- Kleshtsos O. On-board LED indicator. - Radio, 1998, No. 2, p. 54, 55, 60.
Author: Gusev V., Leninogorsk, Tatarstan; Publication: radioradar.net
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