Phase power regulator on substandard triacs. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Regulators of current, voltage, power

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Many instances of domestic triacs, for example, popular in the past KU208G, are characterized by low reliability and instability when working in an AC 220 V target. after a while, the lamp starts to flicker, and subsequently, it lights up at full power. Such triacs also behave unstable as "switches" when operating on a 220 V network, for example, in the absence of any triggering pulses on the control electrode (the load is de-energized), the triac starts to warm up, after which it either works like a semiconductor diode, or opens completely . Other scenarios of anomalous behavior are also possible.

The reason for the unstable operation of domestic triacs of medium power ("household") is that they "do not hold" the AC mains voltage of 220 V. Unfortunately, there are often cases when out of a dozen purchased triacs of the KU208G type, only one or two turn out to be conditioned, the rest or behave abnormally immediately after installation in the device, or after a relatively short time.

If high-voltage triacs "do not hold" the mains voltage, then you can try to turn on two such triacs in series. In this case, when the triacs are closed, the mains voltage applied to them is divided in two, which means that at the peaks of the mains voltage amplitude, a voltage of about 155 V instead of 310 V will be applied to each triac. At a reduced voltage, domestic triacs of the KU208 series work more reliably, which allows them to be used in various devices.

On fig. 1 shows a schematic diagram of a phase power regulator, which is designed to operate in a 220 V AC network with a load of 5 ... 400 W. The load of this regulator can be, for example, an incandescent lamp, a Christmas tree garland, an electric soldering iron, a small drilling machine with a commutator electric motor.

Fig. 1

Power triacs VS2, VS3 are connected in opposite series, which allows you to divide the mains voltage between the closed triacs equally. Resistors R9, R10 are designed to equalize the voltages on closed triacs, which form a voltage divider in two. The control node is implemented on a low-power high-voltage trinistor VS1. When the slider of the variable resistor R1 is in the lower position according to the diagram, the phase delay in opening VS1 is maximum, the minimum power is supplied to the load. When opening VS1, the current in the control electrode circuit of triacs VS2, VS3 increases sharply, VS2, VS3 open, the current in the load circuit increases sharply to the maximum. When the slider of the variable resistor R1 is in the upper position according to the scheme, the phase delay in opening VS1 is minimal, about 99% of the power is supplied to the load.

Resistor R2 is designed to set the minimum power level supplied to the load, resistors R5 and R6 protect the low-power trinistor from overload. To reduce the intensity of interference that a working phase power controller creates, LC filters L1V2R11 and L2C3C4RU1 are designed. In addition, the second filter reduces the level of impulse noise that enters the triac node from the network. This reduces the likelihood of a sudden power surge to the load, such as when the compressor of a nearby refrigerator is turned on. A fuse protects the device from overload.

The device can be mounted on a printed circuit board with dimensions of 20x80 mm, a sketch of which is shown in fig. 2.

Fig. 2

The design used mainly domestic parts. Resistors can be applied types MLT C2-23, C2-33 and other general applications. Varistor MYG20-471 will be replaced by FNR-20K431. If not available, it may not be installed. A variable resistor can be used such as SPZ-12, SPZ-Z0k with a resistance of 100 ... 300 kOhm. combined with a switch. A handle made of insulating material is put on the axis of the variable resistor. The housing of the variable resistor must be isolated from the metal housing (front panel) of the device. Capacitor C1 - oxide K50-35 K50-68 or equivalent. The remaining film capacitors are designed for an operating voltage of 275 V AC or DC not lower than 630 V, for example, polyethylene terephthalate K73-17-24 at 630 8. The KTs402B diode bridge can be replaced by. KTS402A. KTS405A. KTS405B or four identical diodes KD209A, KD105B, KD243G, 1N5395, 1N4005. Trinistor MCR100-6RL can be replaced by MCR100-8RL.

In place of the triac KU208G, KU208V can work in this device. With a load power of more than 200 W, triacs can be installed on a common heat sink, the use of insulating spacers is optional if the heat sink is isolated from the metal case of the device. Inductors L1, L2 are the same, contain 100 turns of PEV-2-0,51 wire wound on 400NN ferrite rods 50 mm long and mm in diameter. A ferrite rod of this length can be made from a magnetic antenna from an old LW / MW radio. Coils are wound on paper sleeves. Finished coils are impregnated with zaponlak. You can attach ready-made chokes to the printed circuit board using plastic clamps.

Triacs KU208G or. KU20VV are designed for operating current up to 5 A. In this device, the load current is limited to 2 A. This is due to the fact that two triacs connected in series dissipate twice as much power and for a high-current load it would be more appropriate to use one high-quality triac, for example, imported MAC15A6FP .

Setting up the device consists in selecting the capacitor C1 in such a way that when the adjusting knob of the variable resistor R1 is fully turned, the power supplied to the load changes from minimum to maximum. When setting up and operating the device, it should be taken into account that all its elements are under mains voltage.

Author: Butov A.L.

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