Mobile phone charger with digital timer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Mobile phone charger with digital timer. 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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Long-term operation of batteries with non-compliance with instructions and charge-discharge modes leads to premature wear of the electrodes and the occurrence of a "memory effect" when sparingly soluble crystals-dendrites appear on the plates. Crystallization, causing an increase in the internal resistance of the battery, reduces the discharge current and voltage, which leads to malfunctions of the cell phone.

The pulsed current charging of batteries proposed in the article allows you to extend their service life, restore capacity and remove the "memory effect". In this case, there is no overcharging and overheating of the battery. In between pulses of the charging current, the battery is discharged with a current of 0,2 ... 5% of the capacity.

The amplitude of the charging current in the pulse reaches five times the average current, which allows you to "pump" power into the battery in a very short time (0,1 ... 1 ms) and speeds up the restoration of its performance. The energy consumption during charging with direct and pulsed current is almost the same, but in the latter case, the case temperature does not increase, since a short pulse and a sufficiently long interval between pulses allow the temperature to drop in a timely manner. The average battery charge current does not exceed the passport recommended by the manufacturer. To maintain the warranty period, the charging time must also meet the factory recommendations.

The charger circuit is shown in Fig.1. The device includes a digital timer on a DD2 chip, which is a 14-bit binary counter. Resetting the counter (setting all digits to zero) occurs when a high level appears at the reset input R (pin 11) DD2. The counter is incremented by the negative edge of the clock pulse.

(click to enlarge)

Clock pulses are generated by a multivibrator on the elements DD1.1 and DD1.2, performing logical operations 2OR-NOT. A high level at the output of each element occurs when both of its inputs are low levels. Variable resistor R2 changes the frequency of clock pulses and. hence the battery charge time. The operation of the counter DD2 is indicated by the LED HL1. When the supply voltage is applied, it lights up, at the end of the count of the 8th pulse it goes out, and after 8 pulses it lights up again, etc.

The output pulses of the counter DD2 through the inverter on the element DD1.3 are fed to the analog timer DA1, operating in the controlled multivibrator mode. This mode allows you to generate pulses at the output 3 DA1 synchronization with the state of DD2. The duration of the multivibrator pulses, first of all, depends on the resistances of the resistors R5, R6 and the capacitance of the capacitor C3.

In the initial state, output 3 of timer DA1 is high, transistor VT1 is open, and charging current is supplied to battery GB1. As the capacitor C3 is charged through resistors R5 and R6, the voltage at terminals 2 and 6 of DA1 grows, and when it reaches a level of 1/0,69 Un after a time t5 = 6 (R3 + R2) C3, the timer switches, appears at pin 3 low, the transistor closes and the charging current stops.

The internal discharge transistor DA1 at input 7 during the time t2=0,69R6 C3 discharges capacitor C3 to the level of 1/3 Un, the lower comparator at input 2 switches the internal trigger to its initial state, and capacitor C3 is charged again. The cycle is repeated. Resistor R6 allows you to set the required current when charging the battery.

The duration of the pulses at the output of the multivibrator DA1 with the specified values of the elements is 3,5 ... 35 s, which corresponds to a frequency of 1,2.0.12 Hz.

Resistors R8 and R9 create an initial bias based on transistor VT1, resistor R10 in the collector circuit limits the pulse current, reducing the likelihood of breakdown of transistor VT1. Overload indication is made on the HL4 LED with a current-limiting resistor R12.

In the emitter circuit VT1, to control the polarity of connecting the battery GB1, two LEDs HL2 and HL3 (green and red) are installed in anti-parallel. If the polarity of the battery is incorrect, the red LED HL3 lights up, if the polarity is correct, the green LED HL2, which additionally serves as a discharge circuit for the battery. To control the charging current, an ammeter RA1 is used, according to the readings of which one can judge the average charge current.

Pin 5 of DA1 is connected to the internal voltage divider of the timer and is used to control the pulse frequency of DA1. When the count ends, a high level appears at the output (pin 3) of DD2, which is inverted by the DD1.3 element, and "0" from its output switches DA1 so that the pulse frequency at output 3 DA1 drops. The battery charging current is significantly reduced, and the charger enters the buffer mode of charging the GB1 with a weak current. This allows you to keep the battery in working condition for a long time without recharging it.

A high voltage level from output 3 DD2 also goes to input 6 of element DD1.2 and stops the multivibrator on elements DD1.1 and DD1.2. Count pulses cease to arrive at the input. From counter DD2. To restart the multivibrator, the counter is reset with the SA1 "Reset" button or the power is turned off for a few seconds.

The output stage on the transistor VT1 in the circuit is powered directly from the power unit on the transformer T1, diode bridge VD1 and capacitor C4. Microcircuits are fed through a voltage regulator on the DA2 chip. The increased voltage on the capacitor C4 compared to the voltage of the battery being charged allows the formation of short current pulses of large amplitude to remove the crystallization of the electrodes.

Most of the memory parts are placed on a printed circuit board measuring 96x38 mm (Fig. 2), which is fixed inside the case.

Mobile phone charger with digital timer

The case is used factory, type BP-1. A transformer of the TN or CCI type with an output voltage of 2x12.2x15 V and a permissible load current of 1 ... 1,5 A is installed on the chassis tray. Switching terminals, ammeter, LEDs and regulators are installed on the front panel of the device. The battery is connected to the charger using clothespins.

The diode block VD1 corresponds to two pulse diodes of the KD213B type. Chip DD1 is interchangeable with KR1561LE5, 564LE5, CD4001B; DD2 - on CD4020, CD4040, K561IE20A, analog timer DA1 is replaced by KR1006VI1, stabilizer DA2 - by KR142EN8A(G). As an output transistor, you can use D333 or KT8116. Low-power resistors - C2-29, C2-34, R10 - type RWR-7W, 2R00JSYC or C5-37V, variables - SPO or SDR. Capacitors - KM.

Setting up the device should begin with a thorough check of the circuit for errors. When the supply voltage is applied (without a battery), the HL1 and HL2 LEDs should light up. When the battery is connected, the HL2 LED may light up with increased brightness, with a "reverse polarity" (incorrect battery polarity), the red HL3 LED should light up. Regulator R6 sets the battery charge current according to the ammeter (1/10 of the capacity indicated on the case), regulator R2 - recommended charge time.

With a minimum resistance R2, a high level at output 3 DD2 should appear after 60 minutes, with a maximum after 600 minutes. These values are adjusted by selecting the resistance R1. At the end of the charge, it is recommended to check the discharge current of the battery and determine the internal resistance.

Author: V.Konovalov, Irkutsk

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