Voltage converter + battery charger. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters

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Power outages in our homes, alas, have become not just a tradition, but have also acquired a certain trend. If they used to turn it off according to a schedule, now at times they turn it on according to a schedule. What about your favorite TV series? There is a way out if you have a car battery and a portable TV of the “Electronics” type with a 12 V power supply. And if the TV is stationary, then you can either buy another “Electronics” or assemble the converter described below.

Today, there are many options for circuits, but almost all of them require the independent manufacture of a power transformer, which is quite labor-intensive and, one might even say, a little tedious task, in addition, requiring some skills and experience from the radio amateur. This device uses a ready-made transformer of the TS-180 type (from a tube TV), which does not require any modifications.

When developing this device, the task was also to create a small-sized, high-efficiency mains voltage source that does not require complex settings, capable of delivering power of more than 100 W to the load.

High efficiency is achieved thanks to the design features of the inverter (Fig. 1). As a result, a pulsating voltage is supplied to the transistor switches with intervals between pulses equal to the pulse length (Fig. 2). Using an ordinary master oscillator for a push-pull switch as an inverter is fraught with overheating of the output stage, which means a drop in efficiency, and often failure of the transistors. After all, as you know, any system has inertia, and you can imagine a situation where one key has not yet closed, and the second has already opened, plus the self-induction of the transformer. That is why most circuits are often made using a single-ended circuit or using decoupling capacitors.

The master oscillator (Fig. 1) is assembled on elements DD1.3-DD1.5 of the K561LN2 and C1, R2, R3 microcircuits.

(click to enlarge)

The pulse repetition rate depends on the capacitance of capacitor C1 and the total resistance of resistors R2, R3. In this case, when using batteries with a voltage of 6 V, it is selected at 50 Hz, and when using a voltage of 12 V - 100 Hz. Let's consider the operation of the inverter together with the diagram (Fig. 2). Let's start from the moment the first pulse appears at the output of the generator (pin 6 of DD1).

Through buffer DD1.2 (pin 8) it is supplied to the counter input. Immediately the trigger goes into the log "1" state, in which a log signal "1" appears at the direct output (pin 1), and a log signal "2" appears at the inverse output (pin 0). The trigger remains in this state until the second pulse arrives. Then the trigger goes into the log "0" state, in which the polarity of the signals at its outputs has changed to the opposite. Identical states will be observed every two pulses of the generator. Depending on the state of the trigger and the pulses coming from pin 10 of DD1.1, the optocouplers will turn on at certain moments. This is easy to see from the diagram. Thus, we have achieved the desired result: the output switches will open alternately and with intervals between pulses equal to the pulse length.

The power part is assembled on powerful transistors VT1, VT2, which are controlled by optocouplers DA1.2, DA2.2 via switches VT3, VT4 (Fig. 3).

This circuit solution allows you to avoid failure of the output transistors in the event of an accidental failure of the master oscillator (MG). In the absence of pulses, transistors VT3 and VT4 are open and lock VT1 and VT2 with a deep negative voltage. As soon as the control pulse arrives at the optotransistor (for example, DA1.2), it unlocks and closes transistor VT3, as a result of which VT1 is unlocked by the positive voltage supplied through resistor R6. Fig. 3 shows the wiring of the T1 network winding at a supply voltage of 6 V; at a voltage of 12 V, only one half of the winding should be used (pin from the midpoint), for example pins 1 and 2 or 1` and 2`.

Construction and details. Most of the converter parts are placed on a printed circuit board (Fig. 4) measuring 46x52 mm. Output transistors and protection diodes are mounted on heat sinks made of duralumin and connected to the board with pieces of stranded wire, preferably with heat-resistant insulation.

The converter circuits through which a large current flows should be made with a wire with a diameter of at least 2 mm and as short as possible. This requirement also applies to the wires connecting the device to the battery.

Setting up a voltage converter consists of adjusting the frequency of the master oscillator to the selected frequency (50/100 Hz) by turning the slider of trimming resistor R3 or selecting the capacitance of capacitor C1. The frequency should be measured on one of the transformer windings. You can install (via a toggle switch) an additional capacitor, selecting the capacitance experimentally, and the converter can operate from both 6 V and 12 V without any frequency adjustment. The DD1, DD2 microcircuits are powered from the stabilizer Fig. 1,b. Capacitor Ssh is installed if an output voltage more similar to a sinusoidal one is required. However, for powering modern TVs with a switching power supply, this does not matter. The capacitance of the capacitor Csh is 1-2 µF and is designed for a voltage of at least 400 V.

Transistors VT1 and VT2 can be (and even recommend) replaced by KT827A, B, C.

References:

1. Panchenko V.A. DC-to-AC converters // Radioamator.-1998.-No. 3.С.26.

Author: S.V. prus

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