Universal charger and power supply. Encyclopedia of radio electronics and electrical engineering

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To eliminate the consequences of negative time processes in Ni-MN batteries (AK) used to power various equipment, including the UB-201 tonometer, it is necessary to conduct periodic charge-discharge training cycles to maintain the uniformity of the physical properties of the structures that are inside the AK itself, for which you need a charger-discharge device.

One of the possible options for manufacturing a simple charger-discharge device is given in [1]. A more complex universal charger and power supply unit (UZPU) for the OMRON M2 Basic automatic blood pressure monitor model UB-201 is proposed, which can operate in the following basic modes:

• dynamic battery charging mode during the positive half-wave of the supply voltage with a stable fixed charge current of 100 mA at a frequency of 25 Hz:
• dynamic battery discharge mode (training) during the negative half-wave of the supply voltage with a frequency of 25 Hz, discharge current 10 mA:
• static discharge mode of the battery with a stable discharge current of 100 mA:
• network source mode for powering the tonometer, which is connected to it through a standard connector:
• luminaire mode with two sub-modes: operation of the light source from batteries (use of battery tonometer or galvanic batteries) and operation of the light source from the mains 220 V/50 Hz;
• multimode, has two switched submodes, when either a battery or a network source is used simultaneously for the operation of a tonometer and a lamp;
• DC source mode for powering external devices with a power of 4 ... 5 W.

Fig. 1

The scheme of the UZPU is shown in Fig.1. It consists of a network transformer T1, two rectifiers on a VD3 diode and a VD4 diode bridge, two current stabilizers on transistors VT1 and VT5, a compensation voltage regulator on transistors VT2-VT4. A half-wave rectifier based on the VD3 diode was used to organize a pulsed dynamic mode for charging the battery, or rather, a dynamic charge / discharge cycle mode with a duration ratio of 10/1. The charger circuit consists of elements R1, R3, VD1, VD2 and VT1.

A feature of its circuit is the use of the VD2 LED as a reference voltage source, the use of which, due to the positive TKSN, allows not only to improve the overall TKSN of the device, but also to get an indication of its operation, since the LED will glow only when a rechargeable battery is connected (which indicates the presence of all contacts between the AC in the cassette in which they are installed for charging). Diode VD1 is used to protect the LED VD2 from the possible application of reverse voltage.

The scheme works as follows. During the positive half-wave of the supply voltage, the current value through the current stabilizer is 112 mA, 12 mA of which branch off to the R5VD10VD9 chain, and 100 mA to the battery charge. During the negative half-wave, the battery is discharged with a current of 12 mA through the R5VD10VD9 chain. The VD9 LED, in addition to the load element during a dynamic discharge, also performs the function of a light indication of the presence of a dynamic discharge. Diode VD6 prevents the battery from discharging through the elements of the charge current stabilizer when the mains power is turned off.

The discharge device circuit is completely similar to the charger circuit and consists of a current stabilizer on VT5 and a load of white LEDs VD11-VD13 and VD16, VD17, which are connected in parallel. The total current through the load is 100 mA.

A feature of the circuit is the extinction of the reference LED VD8 of the discharge current stabilizer when the battery voltage drops below 4,0 V, which indicates the end of the discharge process. It should be noted that there is still some glow of crystals of white LEDs VD11-VD13 and VD16.

Measuring the voltage on the battery during discharge is possible by connecting an external voltmeter to the contacts of the connector XS1.1 and XS1.3. To power the tonometer from the mains, a compensation voltage regulator is used on VT2-VT4. A feature of the circuitry of such a voltage stabilizer is the presence of a trigger effect in the event of a short circuit in the output (at a current above 0,7 A).

To protect the electrical circuit of the tonometer from excess supply voltage, a device is provided on the elements R9, VD14, VD15, VS1, which is an analogue of the threshold element (dinistor) with a turn-on voltage of 6,7 V. When a voltage exceeding this value appears at the output of the mains power supply , the threshold element opens and closes the output of the voltage regulator, which, in turn, should cause it to go into the closed state. If the E-K transition of the regulating transistor VT4 is broken, then this state of the device causes the destruction of the fuse FU1.

The battery in the UZPU can be in three states: charging, just in storage and in the discharge mode with a stable current (submode "lamp").

Construction and details

Transformer T1 is assembled on a magnetic core made of transformer steel Sh14x58.

Winding I of transformer T1 has 1716 turns of PETV wire with a diameter of 0,15 mm, winding II - 78 turns of PETV wire with a diameter of 0,7 mm. The "idling" current of the transformer in the author's version is 7 mA. You can also use a ready-made transformer with an output voltage of 10 V and a current of 0,7 A.

Fixed resistors type MLT, power in accordance with Fig.1. Variable resistor R7 type SP5-2. Oxide capacitors type K50-35. Capacitor C2 type K73-17.

Mode switches SA1 MT-1 for two positions, and SA2 imported for three positions with an average neutral.

The front panel has dimensions of 87x55 mm and is made of fiberglass 1,2 mm thick. The cover of the UZPU is made of sheet steel with a thickness of 0,35 mm and has dimensions of 87x95x55 mm. The lower part of the body is made of plywood 5 mm thick. The body elements are connected to each other with screws 10 mm long.

The VT4 transistor is mounted on an aluminum radiator with an area of ​​150 cm2 without an insulating gasket. Transistors VT1 and VT5 of the 2SA1837 type are used in current stabilizers for reasons of convenience in their design, since they have a plastic case, which allows them to be mounted on the same radiator with the VT4 transistor without insulating gaskets. In the absence of such transistors, domestic transistors of the KT814-KT816 brands can be used, which will have to be attached to the radiator case through a mica gasket.

Fig. 2

The appearance of the UZPU without a cover is shown in Fig. 2, and the assembled one is shown in the photo at the beginning of the article.

Setting

Charge Current Stabilizer

First you need to set the current through the reference voltage source LED VD2. To do this, the R3VD1VD2 circuit, in parallel with the diodes of which an auxiliary capacitor of 100 μF 16 V is temporarily connected, should be disconnected from the charge current stabilizer circuit and connected in series through a milliammeter to the cathode of the VD3 diode. By selecting resistor R3, set the current in the circuit to 10 mA. Disconnect auxiliary capacitor.

Instead of resistor R1, you should temporarily turn on a 20 ohm variable wire resistor, having previously set it to maximum resistance, and connect a current stabilizer to the cathode of the VD3 diode. Connect an ammeter between the collector VT1 and the cathode of the VD6 diode.

Turn on the power supply. In this case, the VD2 LED should light up, and the ammeter should show a certain current value. Decreasing the resistance of the temporary variable resistor, set the current value in the circuit to 112 mA. When the milliammeter is turned off, the VD2 LED should go out.

Now it is necessary to set the current in the discharge circuit, for which it is necessary to disconnect the R5VD9VD10 circuit from the circuit, turn on a milliammeter in series with it and apply 5,6 V DC (1,4 Vx4) to it from an auxiliary source in the appropriate polarity. By selecting resistor R5, set the current in the circuit to 12 mA. Restore all connections in the circuit.

Setting the discharge current stabilizer is carried out similarly to the above method for setting the charge current stabilizer, in accordance with the values ​​\u1b\uXNUMXbspecified in Fig. XNUMX.

Setting note: The LEDs of the reference voltage sources of the mentioned current stabilizers should not light when the load is disconnected.

Fig. 3

Setting up a stabilized voltage source consists in setting an output voltage of 7 V using a variable resistor R6 and a current through the reference element (diode VD7) 17 ... 20 mA using resistor R6, as well as checking the operation of its circuit in short circuit mode (0,7 ...0,8 A).

Literature

1. Yolkin S.A. Charger-discharge device with independent functions of charge and discharge Electrician. - 2011. - No. 9. - P.52.

Author: Sergey Yolkin

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