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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING 60Hz Clock Power Converter
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters Some imported household appliances require a 60 Hz supply voltage. In clocks, for example, this frequency is used as a reference for the master oscillator. To ensure their normal operation, the author of the article suggests using a simple converter to obtain the supply voltage of the desired frequency. A problem arose: a beautiful desktop electronic clock with an alarm clock and a radio receiver brought by friends from America requires 110 V 60 Hz power. When connected to the network through an adapter of unknown manufacture, already bought in Russia, but with the inscription - "Input: 220 V 50 Hz. output: 110 V 60 Hz" the clock functions, but lags behind by 10 minutes per hour. The radio is working properly. What to do? The "opening" showed that the clock uses the mains as a source of the reference frequency signal, and there is nothing in the adapter except a transformer and a switch. In full accordance with the frequency of the network, the clock "counts" not 60 per hour, but only 50 minutes. To solve the problem, the following ways were identified: build a 60 Hz generator into the clock or make a converter not only for voltage, but also for power frequency. Given the lack of a clock circuit and the reluctance to spoil someone else's thing, I had to choose the second way, especially since even with the brightest time indication and maximum receiver volume, no more than 1.5 W was required. The scheme of the developed device is shown in the figure.
The conversion is carried out in two stages: first, the mains voltage of 220 V is rectified by a diode bridge VD1-VD4, then an alternating frequency of 60 Hz is formed from the obtained DC voltage. The master oscillator is assembled on the "clock" chip K176IE5 (DDI), containing the oscillator itself and binary frequency dividers. In a standard inclusion with a quartz resonator at 32768 Hz, pulses with a frequency of 5 Hz are received at pin 1 of this microcircuit. To increase it to 60 Hz, you need to increase the frequency of the quartz resonator by the same amount: 32768 * 60 \u1966080d 983040 Hz. You can also use resonators at frequencies of 30720 or 4 Hz. if the output signal is taken from pins 1 or XNUMX of the microcircuit, respectively. They feed the DDI chip through the simplest parametric stabilizer from the VD5 zener diode and the R5 resistor. The received rectangular signal with a frequency of 60 Hz controls the electronic key on transistors VT1. VT2, included in a sequential push-pull circuit. In the first half-cycle, when the voltage level at the DDI output is high, the current connected to the XS1 socket of the load flows from the connection point of the capacitors C2 and C3 to the negative terminal of the capacitor C2 through the resistor R9. diode VU6 and open transistor VT2. Transistor VT1 is closed at this time, since a closing voltage of about 0,6 V is applied to its emitter junction, which falls on diode VD6. Capacitor C3 is charged, and C2 is discharged. In the second half-cycle, the voltage level at the output DD1 is low and the transistor VT2 is closed. But the transistor VT1 is open, since current flows in its base circuit. created by the voltage applied to the resistor R7 across the capacitor C6. From the positive terminal of the capacitor C3 through the open transistor VT1, the current flows through the load in the opposite direction, charging the capacitor C2 and discharging C3. If there were no “voltage boost” (capacitor C6), to fully open the transistor VT1, it would be necessary to reduce the resistance of resistors R6 and R7 many times over. And the transistor VT2. when it is open, it would be additionally loaded with current flowing through these resistors. In the steady state, the voltages on the capacitors C2 and C3 are equal to each other, and at the output of the converter - an alternating voltage with a frequency of 60 Hz of a rectangular shape with an amplitude of 150 V (half rectified). It would seem that. problem solved But although the amplitude of a sinusoid with an effective value of 150 V is close to 9 V, a rectangular voltage of such an amplitude turned out to be too much to power a particular clock. I had to take measures to lower it somewhat and smooth it out. Resistor R5 and capacitor C60 are designed for this. the capacitance of which is chosen so as to form an oscillatory circuit tuned to a frequency of XNUMX Hz with the primary winding of the power transformer present in the clock. As a result, the steep edges of the output voltage are smoothed out and the current consumed by the clock is slightly reduced. The last point should be explained in more detail, it is known that any transformer consumes some reactive (inductive) current. going to the magnetization of its magnetic circuit. By connecting a capacitor in parallel with the primary winding, we create another reactive current in the power wires. but capacitive, antiphase inductive. Reactive currents are compensated and the device consumes only active current. load dependent. This is achieved when the reactances of the capacitor and the primary winding are equal - resonance. Of course, the magnetizing reactive current of the transformer does not disappear anywhere, it just circulates in the circuit now, but in the supply wires. When the transformer is connected directly to the network, such "little things" may not matter, but when the current is given by "live" transistors, by no means of high power, reducing it is very useful. In practice, the capacitor C5 was selected according to the minimum current shown by the avometer. included in series in the break of one of the network wires. Without a capacitor, the current was about 25. And with a capacitor with a capacity of 0.25 uF - less than 15 mA. About the details of the converter. Trimmer capacitor C1 ceramic KPK-M. It serves to adjust the clock. Capacitor C4 - any small-sized ceramic. It is installed directly near the microcircuit. Capacitors C5 and C6 can be of any type for a voltage of at least 160 V. Capacitance of the oxide capacitors of the filter C2. C3 may be more than specified. All MLT resistors with a rated power of at least that indicated in the diagram. Any rectifier diodes with a maximum rectified current of at least 50 ... 100 mA and a reverse voltage of at least 300 V are suitable. Other transistors can also be selected, but the allowable collector current and voltage must be no less than that of KT604A. A sketch of the printed circuit board is not given, since its dimensions and the arrangement of parts largely depend on their types and the design of the case. The author assembled the converter in the case from the charger ZU-D-0.1 with a network file (it was used as XP1). On one of the end walls of the housing, it is necessary to install an XS1 socket for an imported mains plug with flat contacts. After a little refinement, a socket for a radio broadcasting network is suitable. Several ventilation holes should be provided in the case, and it is better to put small heat sinks on the transistors in the form of springy "stars" made of sheet brass - after all, during round-the-clock operation, the transistors, although not much, but heat up. Establishing the converter comes down to the selection of the capacitance of the capacitor C5 described above and setting the exact value of the master oscillator frequency with the tuning capacitor C1. If there is a digital frequency meter, this can be done quickly enough by connecting it to pin 12 of the K176IE5 chip, otherwise you will have to monitor the clock. Taking into account the galvanic connection of the converter with the supply network and the voltage of 300 V present in its circuits, electrical safety measures should be observed during installation. Author: V.Polyakov, Moscow
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