Charger on mobile phone adapter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Charger on mobile phone adapter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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The constant renewal of the cell phone fleet has led to the accumulation of network adapters that, due to their parameters and connector, cannot be used for other models.

The use of a non-standard charger may cause the cell phone battery to overcharge, swell and possibly explode with serious consequences. Therefore, these adapters are better off looking for another application. We decided to use an adapter that turned out to be "orphan" to charge powerful car batteries.

It is clear that direct connection of the adapter for charging will not give anything: the power of cell phone adapters does not exceed 3 ... 5 W, the low output voltage (within 4 ... 8 V) at a charge current of up to 200 mA is completely insufficient to charge a car battery voltage 12 V and capacity 50...240 Ah.

(click to enlarge)

When analyzing the circuits of flyback switching power supplies included in the adapters, we found that for the most part they contain a mains rectifier with a filter, a blocking generator with positive feedback from a separate transformer winding, and an output low-voltage rectifier.

Stabilization of the secondary voltage is usually performed using a phototransistor optocoupler, the LED of which is connected to the output circuit, and the phototransistor to the base circuit of the generator transistor. Switching power supplies for televisions, computer monitors and other electronic equipment are made according to similar schemes.

The convenience of using adapters from cell phones lies in the presence of a ready-made blocking generator, a pulse transformer and other elements, as well as in the development of the circuit and maintaining the generation mode with significant fluctuations in the mains voltage.

To obtain a powerful charger from a cell phone adapter, it is enough to supplement the rectifier circuit with a power amplifier with a separate rectifier. The compactness of the adapter printed circuit board makes it possible to obtain, even together with a power amplifier and an output rectifier, a small-sized charger, moreover, it is 15 ... 20 times lighter than chargers based on power transformers.

Resistor R1 protects the diode bridge VD1 from breakdown during surges of the charging current of capacitor C5. At the initial moment of charging the capacitor, its resistance is close to zero, which without a resistor can lead to a large current pulse and damage to the diode bridge.

At the end of charging, the maximum voltage on the capacitor C5 exceeds the voltage at the output of the diode bridge, and the thyristor VS1 opens, which shunts the resistor R1. Capacitor C4 eliminates the possibility of turning on the thyristor from impulse noise. When overloaded, the thyristor closes, and when it is turned on again, it shunts the current-limiting resistor R1 again. The varistor RU1 protects the circuit from mains voltage surges. The resistance of the varistor is restored after the voltage drops below its turn-on threshold. Input transformer T1 and capacitors C1...C3 form a noise filter.

The pulse generator on the transistor VT1 with external RC circuits (functional node A1) is taken from the adapter and may differ in layout (numbering of parts is conditional). Resistor R4 creates an initial bias based on transistor VT1 for stable generation with changes in mains voltage.

Capacitor C7 is charged through the diode VD2 to a reverse voltage amplitude that is greater than the stabilization voltage of the zener diode VD3, as a result of which the zener diode opens, the voltage at the base of the transistor VT1 becomes negative and prevents it from opening with a pause longer than the pulse time. The current flowing through the resistor R4 through the open zener diode VD3 enters the capacitor C7, discharging it. The voltage on this capacitor decreases, and on the base of the transistor it increases. When the threshold is reached (more than 0,4 V), the transistor VT1 opens, the pause ends, and a new generation cycle begins.

The positive feedback voltage from the winding III of the transformer T2 through the capacitor C6 and the resistor R5 opens the transistor VT1, the current through the winding I T2 increases like an avalanche, and the energy accumulated by the transformer T2 is transferred from its winding II through the capacitor C9 and the current regulator R8 into the base circuit of the power amplifier field effect transistor VT2. Resistor R7 creates an initial voltage at the gate of transistor VT2, resistor R9 protects the gate of the field-effect transistor from capacitive overcurrents. The transistor VT2 is powered by a mains rectifier on a diode bridge VD1 with a filter on capacitor C5.

The high-frequency transformer T3 from computer power supplies (type AT / TX) or from monitors is used in the charger without alterations. The primary winding (it has up to three terminals) is connected to the drain circuit of the transistor VT2, a damping circuit C10-R10-VD5 is connected in parallel to it to dampen reverse current pulses that can break through the transistor or the TK winding.

The power amplifier on the field-effect transistor VT2 through the transformer T3 transmits an amplified high-frequency signal to the load, which, after being rectified by the avalanche diodes of the assembly VD6, supplies the charging current to the battery GB1 The ammeter RA1 allows you to set the charging current of the battery with the regulator R8. The HL2 LED controls the polarity of the GB1 battery connection and the presence of voltage at the output of the device. At zero gate voltage, the transistor VT2 is closed and opens with a positive voltage pulse from the T2 winding. To reduce the emissions that occur when switching VT2, a damper chain C11-R12 is connected to the drain, and a resistor R11 is connected to the source.

Most of the radio components in the charger are used from disassembled power supplies for computers and monitors. Resistors - type P2-23, varistor RU1 - for a response voltage of 430 V. Oxide capacitor C4 - from Nichicon or NRZ. All diodes - impulse, with high speed. Rectifier diodes VD6 are interchangeable with KD213B. Transistor VT1 - with a maximum voltage of 400 V. current 1 A and a gain of more than 200. Field-effect transistor VT2 must be with a slope of more than 1000 mA / V, an operating voltage of 600 ... 800 V and a permissible current of 3 A or more. Suitable transistors of the 2SK1317 ... 2SK1460 or IRF740 ... IRF840 series.

Type transformers: T1 - EE-25-01 or ZRMSOTS210001 T2 - HI-ROT, T3 - HI-POT TNE 9945, VSK-01C, ATE133N02, R320. Transformer T1 is made on a 3x3 cm ferrite core and contains 2x30 turns of 0,6 mm wire, T2 also on a 3x3 cm core. Winding I contains 360 turns of 0,1 mm wire, winding II - 20 turns of 0,2 mm, winding III - 36 turns 0,1 mm. The T3 transformer uses a 12x12 cm core. Winding I has 42 turns of 0,6 mm wire, windings II and III - 2x6 turns of 01,6 mm.

The charger is assembled on a circuit board, the adapter board is installed on it on additional racks. The VT2 transistor is mounted on a 40x30x30 mm radiator. Terminals X1, X2 are connected to the battery with stranded copper wires in vinyl insulation with a cross section of approximately 4 mm2. Crocodile clips are attached to the ends of the wires.

Adjustment of the device begins with checking the performance of the adapter board. When the mains voltage is applied, its output should have a constant voltage of 4.8 V. The diode and the capacitor of the adapter rectifier are not used in the circuit, the signal to the power amplifier is taken directly from the winding II T2 through the coupling capacitor C9. When the battery is connected, resistor R8 sets a charging current of approximately 0,05C (C is the battery capacity). Charging time is determined by the technical condition of the battery and, as a rule, does not exceed 5...7 hours. With abundant boiling of the electrolyte, the charge current should be reduced.

Author: V.Konovalov, A.Vanteev, Creative laboratory, Irkutsk

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