Backup power supply for pocket flash player. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Backup power supply for a pocket flash player. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Batteries built into miniature mobile multimedia devices usually have a small capacity, and, as a rule, are designed to play audio recordings for no more than a few tens of hours with the display turned off, or to play several hours of video or several hours of reading e-books.

If the mains socket is unavailable or due to bad weather or other reasons, the power supply is cut off for a long time, then various mobile devices with color displays will have to be powered from built-in power sources. Given that these devices consume a lot of current, their batteries may be depleted before the moment when electricity from the wall outlet becomes available.

If you do not want to immerse yourself in primeval silence and peace of mind, then to power pocket devices, you can provide a backup autonomous power source that will help out both during a long trip into the wild, and in case of man-made or natural disasters, when your locality may be on several days or weeks without power.

The device, the scheme of which is shown in fig. 1 is a relatively powerful compensation type linear voltage regulator with low saturation voltage and very low intrinsic current consumption. As an energy source for this stabilizer, a battery of galvanic cells, a rechargeable battery, as well as a solar battery or a manual electric generator can be used.

Backup power supply for pocket flash player

The current consumed by the stabilizer with a disconnected load is about 180 μA at an input supply voltage of 6 V or 210 μA at a supply voltage of 9 V. The minimum difference between the input and output voltage is less than 0,2 V at a load current of 1 A. This is significantly less than the best integrated stabilizers from the IRU1010 1209 series. When the input supply voltage changes from 5,5 to 15 V, the output voltage changes by no more than 10 mV at a load current of 250 mA. When the load current changes from zero to 1 A, the output voltage changes by no more than 100 mV at an input voltage of 6 V and by no more than 20 mV at an input supply voltage of 9 V.

When the SA1 contacts are closed, the supply voltage is supplied to the voltage stabilizer.

Resettable fuse FU1 protects the stabilizer and battery from overload. The reverse-connected diode VD1 protects the device from polarity reversal of the lithium voltage.

As the supply voltage increases, the output voltage also tends to increase.

To maintain the output voltage stable, a control unit assembled on VT1, VT4 is used. An ultra-bright blue LED HL1 is used as a reference voltage source. which, simultaneously with the function of a micropower zener diode, is an indicator of the presence of an output voltage.

When the output voltage tends to increase, the current through HL1 increases, the current through the emitter junction VT4 also increases, and this transistor opens more and VT1 also opens more strongly, which shunts the gate-source of a powerful field-effect transistor VT3.

As a result, the open channel resistance of the FET increases (because the gate-source voltage decreases), the load voltage decreases.

The trimming resistor R5 can be used to adjust the output voltage, which must be in the range of 5,0 ... 5,3 V to recharge mobile devices via a USB cable. Capacitor C2 is designed to suppress the self-excitation of the stabilizer with an increase in load current. Capacitors C1 and C3 - blocking power circuits. Transistor VT2 is included as a micropower zener diode with a stabilization voltage of 8 ... 9 V.

It is designed to protect against high voltage breakdown of the VT3 gate insulation. A gate-source voltage that is dangerous for VT3 may appear at the moment the power is turned on or due to touching the terminals of this transistor.

Construction and details. Fixed resistors of any type are small-sized for general use. Trimmer - RP1-63M, SP4-1, miniature multi-turn SPZ-39, SP5-2 or similar imported. Oxide capacitors of the K50-35 type or imported analogues, non-polar - K10-17, K10-50, KM-5. The KD243A diode can be replaced by any of the KD212 KD243 KD243, KD257, 1N4001 1N4007 series. Instead of the KT3102G transistors, any similar collectors with a low reverse current will do, for example, any of the KT3102, KT6111, SS9014, VS547, 2SC1845 series.

Instead of the KT3107G transistor, any of the KT3107, KT6112, SS9015 BC556, 2SA992 series will do. A powerful n-channel field-effect transistor of the IRLZ44 type in the TO-220 package has a low gate-source opening threshold voltage, a maximum operating voltage of 60 V, a maximum direct current of up to 50 A, an open channel resistance of 0,028 Ohm. In this design, it can be replaced by IRLZ44S. IRFL405, IRLL2705, IRLR120N, IRL530NC. IRL530N, The field effect transistor is mounted on a duralumin or copper heat sink with sufficient cooling surface area for a particular application. During installation, the terminals of the field-effect transistor are short-circuited with a wire jumper.

The mentioned types of transistors "have differences in the pinout and different types of cases. The super-bright blue RL30-CB744PV LED in a round 3 mm case can be replaced with RL50-CB744D (blue, 5 mm), RL30-WH744D (white, 3 mm), RL30 -UV744D: (Purple, 3mm) RL50-GH744D (Green, 3mm) and others similar with direct operating voltage 2,5...3,2V. -110, LP120-30 etc. It is also possible to use traditional fuse-link Power switch - PKN110.

The device can be mounted on a printed circuit board with dimensions of 65x40 mm, a sketch of which is shown in fig. 2. As an independent power source, you can use, for example, four pieces of series-connected alkaline galvanic cells with a capacity of 4 Ah or more.

This option is preferable if you plan to use this construct relatively infrequently. The use of high-quality alkaline cells will ensure long-term storage of the battery, and the capacity of one cell, for example, 6 Ah, will be enough to autonomously power a pocket player for at least 130 hours while listening to MP3 / WMA phonograms (with a current consumption of 45 mA).

If you plan to use this device relatively frequently, or if your player draws significantly more current even when the display is off, then a rechargeable 6V battery, such as a sealed motorcycle battery or a large flashlight, may be worthwhile.

You can also use a battery of 5 or 6 pieces of nickel-cadmium batteries connected in series, for example, "Panasonic" type P400D, 4 Ah; "Varta" type 5520 (HR20), 5 Ah. When hiking, fishing, to recharge batteries and power a handheld device, it may be convenient to use a solar battery capable of delivering a current of at least 150 mA at an output voltage of 6 V.

When the player is powered from this stabilized energy source, it should be read that the regulating transistor is connected to the "minus" circuit, therefore, simultaneous power supply of the player and, for example, a small active speaker system is possible only if both devices are connected to the output of the stabilizer.

Author: Butov A.L.

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