LED voltage indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Indicators, detectors
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In the practice of a radio amateur, a situation often arises when it is necessary to monitor the readings of a particular parameter. I propose a diagram of an indicator LED "line". Depending on the input voltage, more or less LEDs are lit, arranged in a line (one after the other).
Allowable voltage range - 4 ... 12V, i.e. at an input voltage of 4 V, only one (first) LED will light, and at 12 V, the entire line.
The capabilities of the circuit can be easily extended. To track the alternating voltage, it is enough to install a diode bridge of low-power diodes before the resistor R1. The supply voltage can be varied from 5 to 15 V by selecting resistors R2 ... R8 accordingly. The brightness of the LEDs mainly depends on the supply voltage of the circuit, while the input characteristics of the circuit practically do not change. In order for the brightness of the LEDs to be the same, resistors should be selected as follows:
where Ik max - collector current VT1, mA;
R3=2R2; R4=3R2; R5=4R2; R6=5R2; R7=6R2; R8=7R2.
Thus, when using the transistor KT312A (lK max \u30d 2 mA), R33 \u1d 1 Ohm. Resistor R1 is included in the voltage divider and regulates the operation of the transistor VT7. Diodes VD103 ... VD105 can be replaced with KD220A, KD1, D8, LEDs HL102 ... HLXNUMX - with ALXNUMX.
Resistor R9 limits the base current of the transistor VT1 and prevents the latter from failing when a large voltage enters the circuit input.
Author: A.Kashkarov, St. Petersburg
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