Network power supply based on a solar battery. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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It is possible to make a low-power mains power supply with galvanic isolation, but without an isolation transformer, based on a small-sized solar battery and LEDs. The solar panel can be purchased separately or removed from a stand-alone LED lawn light, and the LEDs can be purchased from an LED flashlight or battery light.
Fig. 1
Such a power supply was assembled on a 25x25 mm solar battery from a lawn lamp of the Wolta Solar trademark and LEDs from the lamp. The block diagram is shown in fig. 1. LEDs EL1-EL14 illuminate the solar panel GB1, which generates a constant voltage. Its output current depends on the illumination, which, in turn, is determined by the parameters of the LEDs and the current through them. The LEDs are powered by a mains power supply with a ballast capacitor C1. The alternating voltage rectifies the diode bridge VD1 - VD4, the ripple of the rectified voltage smoothes the capacitor C2. Zener diode VD5 (with a nominal stabilization voltage of 56 V) in normal mode does not participate in the operation of the rectifier and serves only to protect capacitor C2 from breakdown. The fact is that if one of the LEDs burns out, the rectified voltage across capacitor C2 can exceed 300 V, which will lead to its failure. Resistor R1 limits the inrush current when the mains voltage is applied, and R2 ensures that the capacitor C1 is discharged after the power is turned off. Capacitor C3 at the output of the solar battery additionally smooths out voltage ripples with twice the mains frequency.
The average current through the LEDs, and hence the maximum output current of the solar battery, is set by selecting capacitor C1. By measuring the voltage on the LED Ud at the required average current Id and knowing their number N, calculate the capacitance of the capacitor C1 = Id / [4F (√2Uc
- N*Ud], where Uс - mains voltage; F - mains voltage frequency. The dependences of the output voltage of the power supply unit on the load current for various current values through the LEDs (1 - Id = 10 mA, 2 - Id = 20 mA) are shown in fig. 2.
Fig. 2
The design of the power supply is illustrated in Fig. 3. Most of the elements can be placed on a printed circuit board, the drawing of which is shown in fig. 4. The solar battery is installed directly on the LEDs and fixed along the edges with hot glue. You can do without a printed circuit board by using wired installation, fastening all the elements together with hot glue.
Fig. 3
Use an insulating material case for the power supply. The device uses resistors MLT, S2-23. Capacitor C1 must be designed to operate at an alternating voltage of at least 250 V; it is permissible to use the K73-17 capacitor for a rated voltage of 630 V. Oxide capacitors are imported. Diodes - any rectifier with a permissible reverse voltage of 300 ... 400 V and a direct current necessary to power the LEDs.
Fig. 4
The proposed power supply has small dimensions, which, of course, depend on the type of elements used and the mounting option. This device can be used to power various electronic devices with low current consumption, for example, multifunctional clocks, electronic thermometers, weather stations, which are powered by two galvanic cells or AA or AAA batteries.
By changing the number of LEDs and the current through them, you can change the output current of the solar battery. But it should be borne in mind that the maximum allowable current of most low-power lighting white LEDs does not exceed 20 ... 30 mA.
Author: I. Nechaev
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