LOW-VOLTAGE POWER FROM THE NETWORK

LOW-VOLTAGE POWER FROM THE NETWORKCompact consumer electronic devices gadgets such as watches, alarm clocks, radios, toys, weather stations and other similar devices are available in almost every home. Regularly and everywhere, home owners have to ensure their power supply batteries with a nominal voltage of 1.5 V (“AA” AA and “mizinchikov”, “AAA”) or of the disc type CR, AG, etc. – with a voltage from 1.5 to 3 V. considering the fact that the power supply elements (batteries) are increasing in price (like everything else), the author offers a more rational solution for the cost-conscious owners, namely, to apply to the food in the house and (or) a favorite with owners of devices powered by household electrical outlet using the AC adapter. Thus, the cost for the family budget significantly reduced, since do not have to constantly buy batteries.

 
Of course, there is another way of saving or rational life support: replacement battery – batteries – batteries of the same size and form factor, since they are available and differ in energy intensity. This path is also justified from the point of view of Economics of the household. But it is less cost-effective and universal, relative to what is suggested below in the article, because the batteries will need a charger (an additional expense), there are good batteries with an energy of more than 2 h And more than 300 rubles apiece, and in addition, it is not always possible to effectively replace it instead of regular batteries, because the batteries of the described form factor have a full charge voltage of 1.2… of 1.25 V, while the battery is 1.5 V. When connecting these elements in a serial electric circuit, a difference arises in the equivalent voltage and for some electronic devices this is a significant factor affecting their normal operation.
 
For example, if the majority of remote controls for consumer equipment, the appropriate application of accumulators with nominal voltage 1.2 V each, instead of batteries with a nominal voltage of 1.5 V, each, then, for example, for the meteorological station of the Chinese manufacture a self-powered 2.4 V instead of 3 To is critical for the normal operation of the LCD device.
 
However, to solve the problem situation is not so difficult. This requires a network adapter.
 
Block diagram power supply the low voltage load through the stabilizer shown in figure 1.
 
Fig. 1. The power supply circuit of low voltage load using a circuit - stabilizer
 
Fig. 1. The power supply circuit of low voltage load using a circuit-stabilizer

 
Moreover, since the outbreak claimed the pathos of the article is to save budget, next will be considered not made, and available in almost every home AC charger for cell phones, of which – with the help of simple changes you can make adapter.
 
For this purpose quite suitable charger with switch mode power supply (inside the case), with a voltage range of 4.2…9 V and current more than 100 mA.
 
If you open the casing of most of these chargers cell phones, we can see their “guts”: a Board with a rectifier, a pulse transformer and voltage stabilizer (Fig. 2 photos).
 
Fig. 2 (photo). View of the inside of
 
Fig. 2 (photo). View of the inside of “content” using AC adapter – chargers for modern cell phones

 
These devices very much and almost all of them are organized on the same principle (made one wiring diagram). But today we will not even consider it especially because significant changes in it do not have.
 
To the scheme in figure 1, it is necessary to add only the additional stabilizer with fixed voltage. The most common and have a minimum retail price (9 rubles – as of the end of 2014) three-chip-type stabilizers L78LЗЗABZ-AR, which contain more than 20 discrete elements.
 
ATTENTION!
 
You need to make two serious fixes. First, the output current of modified stabilizer will be limited to a maximum current, which is calculated on the chip L78LЗЗABZ-AP, that is 100 mA.
 
And secondly, why it is recommended to use additional stabilizer adapter charger for cell phones (to power low voltage devices)? Because some devices such as weather stations (and others) applied with a constant voltage more than 3.7 V out of order, to prevent such situations, use instrumentation when debugging. And the wall charger for cell phones, containing the switching power supply have output voltage (depending on model and intended use) range from 4.2 to 8 V. This charger to most described gadgets can’t be connected. For example, the station “will to fight” and to show on display – LCD all segments at once, and with long-term influence of increased supply voltage will inevitably fail, which is not part of our plans. Therefore, we need additional low-power regulator with a fixed voltage.
 
LOW VOLTAGE STABILIZER
 
This linear regulator is the chip L78LЗЗBZ-AP. It is implemented in different versions, including in the housing to-92 -with three pins. The Pinout of the stabilizer in this case are shown in figures 1 and 3.
 
Fig. 3. The Pinout of the IC L78L33ABZ-AP
 
Fig. 3. The Pinout of the IC L78L33ABZ-AP
 
Fig. 4. Typical scheme of connection of the stabilizer lineup L78 in an electrical circuit
 
Fig. 4. Typical scheme of connection of the stabilizer lineup L78 in the circuit
 
Figure 4 shows a typical circuit for linear regulator.
 
In order not to bore the reader, I will not provide detailed electrical characteristics of the stabilizer (you can get free), I will only mention a few attractive aspects. For me it is, above all, price: 9 roubles per 1 corps (as of beginning of 2015). For a fixed output voltage stabilization 3.3 V output current 100 mA can be used in a wide range of low-voltage and low-power electronic devices for the replacement of staff and (or) Autonomous elements of food, which, by the way, are quite expensive. For example, a “disc” battery type CR2032 with a nominal voltage of 3 In the production Durasel will cost about two hundred rubles, and its energy is not infinite.
 
Described in the example of the stabilizer, there are analogues, and with different price. For example, such (more expensive) is analogous to the stabilizer LP2950AC2-3-3, which also has a maximum output current of 100 mA and a modification in the three-case to-92.
 
Figure 5 shows a view of the charge charger for Nokia cell phones with sealed linear regulators L78LЗЗABZ-AP.
 
Fig. 5 (photo). The Board charger for Nokia cell phones with sealed linear regulators L78L33ABZ-AP
 
Fig. 5 (photo). The Board charger for Nokia cell phones with sealed linear regulators L78L33ABZ-AP
 
As can be seen from figure 5 (photo), stabilizer output – output 1 left “in the air”, and is soldered onto it (and closed a plastic tube) conductor (“+” supply), which then goes directly to the station.
 
In figures 6 and 7 (photo) presented the view of the main unit with display weather station made in China with connected conductor from the power adapter, which passes through the battery compartment of the weather station; the conductors are soldered to the battery contacts.
 
Fig. 6 (photo). View of the station with the network adapter connected
 
Fig. 6 (photo). View of the station with network adapter connected
 
Fig. 7 (photo). The view from the back side of the housing of the weather station on Explorer of food
 
Fig. 7 (photo). The view from the back side of the housing of the weather station on a conductor power
 
Of course, there are areas in which these batteries while there is no substitute (for example, automobile keys for remotes and alarms, SMOS PC, etc.). However, in most electronic devices designed for household use, this replacement power adapter on a network is more than justified.
 
CURRENT LIMITING WITH SEMICONDUCTOR DIODES
 
Another popular (among others) a variant of network power low-voltage and low-power electronic devices is to limit the current by using semiconductor diodes. As a silicon semiconductor diode the voltage drop in the DC link is nearly 0.6 volts electric chain of series-connected diodes of the same type will give a significant reduction of stress that it is appropriate to implement in low-voltage circuit. For example, consider the case when you need to provide power to the electronic device within 3.3 V and there is only adapter for charging cell phone (implemented under the scheme with a pulsed IP – this clarification is important) with an output voltage of 4.2 V, two diodes of type 1N4148, КД105 (or similar) with any alphabetic index, connected in series with the load completely solve this problem.
 
Option limit the current (and voltage) is presented in figure 8.
 
Fig. 8. The electrical circuit connections of the diodes as current limiting
 
Fig. 8. The electrical circuit connections of the diodes as current limiting
 
Another thing that you need to consider the current in an electrical circuit.
 
Semiconductor diode type КД105 included as a current limiter, you can use where current consumption of the device (load) does not exceed 20 mA. Therefore, this option is appropriate only when it’s appropriate.
 
It should be noted that it is desirable to set after the circuit current limitation (diodes or integrated stabilizer) oxide capacitor to smooth the noise in the power supply circuit at low frequency. This advice is particularly relevant in a situation when the length of the power wires from the adapter to the device is more than 1 m.
 
A. KASHKAROV, St. Petersburg

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