Ultra-low voltage LED emitters. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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LED emitters are widely used as display elements. Until recently, the impossibility of powering LEDs from low voltage sources, usually below 1,6 V, was considered their noticeable drawback.
Figures 1-4 show a selection of circuits for powering LEDs with reduced voltage.
The first of the circuits (Fig. 1) uses the well-known principle of doubling the supply voltage in combination with an inductive-type voltage converter.
Fig. 1
The low-frequency pulse generator is made on multi-structure transistors (KT361 and KT315). Generator load - telephone capsule TK-67. The output voltage of the generator through the capacitor C2 is supplied to the connection point of the LED HL1 and the germanium diode VD1. When the capacitor C2 is periodically alternately connected to the power bus and the inductive energy storage device (telephone capsule), the voltage of the power source and the voltage accumulated on the C2 plates are periodically summed up. As a result, the HL1 LED starts to glow when the power supply voltage exceeds 0,7 V.
The pulse generator (Fig. 2) is made on series-connected transistors of different structures (KT361 and KT315), which form an active element with a section of negative dynamic resistance. The coil of the intermediate frequency circuit from the radio receiver "VEF" with an inductance of 260 μH was used as the load of the device. The device is covered by positive feedback through the HL1 LED, which simultaneously acts as a capacitance.
Fig. 2
A multivibrator based on series-connected germanium transistors of different conductivity with direct connections and a transformer load is shown in fig. 3.
Fig. 3
LED HL1 is connected to the power supply in series with the secondary winding of the transformer. A ferrite ring F1000 K10x6x2,5 was used as the core of the transformer. The primary and secondary windings of the transformer have 20 and 40 turns of PEV 0,23 wire, respectively.
An autotransformer-type voltage converter for low-voltage LED power supply is shown in fig. 4.
Fig. 4
By selecting the RC elements of the device (which may be absent), the number and ratio of turns of the transformer, the type of core, the use of a germanium transistor, the lower value of the supply voltage can be increased to 100-250 mV.
Author: Shustov M.A.
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