Nowadays, different battery powered devices typically use 3 V two-cell batteries. In old times, there was a “battery” of 9 V everywhere, both in the remote controls and in the desktop electronic clock with an LCD. By the way, as for the electronic clock, the author has exactly the same ones on the LCD and powered by battery, with Soviet melodies in the alarm clock. But, unfortunately, they consume significant current, and they do not have enough modern “battery” (6F22 battery) for more than a month. Therefore, it was decided to look for an alternative power source for them - a network one.First, an unsuccessful attempt was made to supply a voltage of 5.4 V from “charging” for a cell phone. The clock seemed to work, but it began to malfunction, for example, when switching from “23-59” to “00-00” the number “08-00” appeared immediately after which the clock went two minutes later, that is, every minute the reading increased by two minutes.
Then it was decided to make a compact voltage source of 9 V and mount it in a volumetric way in the battery compartment of the watch. The power supply is assembled according to the rectifier circuit with a step-down voltage stabilizer on the Zener diode VD5 and capacitor C1, the reactance of which takes on excess voltage (Fig. 1).
The output current of the power supply is not more than 20 mA, but this is more than enough to power the clock with the LCD. Capacitor C2 was taken with a relatively large capacity for good reason - it supports the watch’s power for several minutes, and therefore short-term disconnections from the mains do not disrupt the watch.In the circuit, the Zener diode D814V can be replaced by any zener diode with a voltage of 8-10 V. Diodes 1N4007 - any rectifier low-power, Capacitor C2 - the larger the capacity, the better. But it is possible and only 10-100 uF, - the circuit will work, but will not hold voltage when turned off from the network.
Based on the same circuit, a universal power supply was also made, from which various voltages can be obtained to power a variety of low-power equipment. The diagram of this power supply is shown in Figure 2. From this power source, voltages of 3 V, 6 V, 9 V and 12 V can be obtained. Moreover, even simultaneously.
The bottom line is that the zener diode in this circuit is replaced by a chain of four zener diodes in series of 3 V each. In total, they give 12 V, so if you remove the voltage from everyone, it will be exactly 12 V. But, if you take the voltage from only one zener diode, VD8, this voltage will be 3 V. With two zener diodes (VD8, VD7), voltage 6 In, with three zener diodes (VD8, VD7, VD6) there will be 9 V, on a with all four, as already mentioned, 12 V.
Naturally, the capacitor C2 should now be at a voltage of at least 12 V (in this case, 16 V).
As the Zener diodes VD5-VD8, you can use any zener diodes for a stabilization voltage of 3 V. For example, 1N59876, 1N4683, BZX84C3V0LT1 and others. You can use zener diodes for other voltages, for example, if you take zener diodes not for 3 V, but for 3.3 V, the output voltages will be 3.3 V, 6.6 V, 9.9 V and 13.2 V, respectively. Zener diodes can also have different stabilization voltages, and their it does not have to be exactly four. Accordingly, there will be different output voltages and a different number of outputs. In any case, the capacitor C2 should be at a voltage not lower than the largest of all output.
Author: Maykov S.
Additional warnings for mains-powered appliances/devices................
Considering the hazards that may occur during system installation and use,
maximum safety is only ensured if the product is installed in strict observance
of current legislation, standards and regulations.Ensure that all material to be used is in perfect condition and suitable for its
intended use.Before accessing internal terminals of the product, all power circuits must be
disconnected..........