Power regulator for soldering iron. Encyclopedia of radio electronics and electrical engineering

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

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For soldering radio components, it is recommended to use a low-voltage, low-power soldering iron. In reality, such soldering irons are rarely used by radio amateurs. There are many reasons for this, and the large weight of the transformer, and the relatively high price of such a soldering station. Therefore, most often in the arsenal of a radio amateur there is a set of soldering irons for 220 different powers - from 15 W to 100 W. The most running - 25 watts.

The tip of the soldering iron is sharpened to work with mini-printed circuit components. But, the thinner the tip of the soldering iron, the higher the temperature it heats up. To maintain the required thermal conditions, you need to adjust the power of the soldering iron.

To adjust the power of the soldering iron to 200 V, you can use the regulator, the circuit of which is shown in the figure. This power controller can be used with any heating appliance from 10W to 440W. Power adjustment step, ten steps. 100% power in position "10" of switch S1.

The principle of operation of the regulator is based on the periodic skipping of a certain number of periods of mains voltage. The number of missed periods depends on the position of switch S1. The lower its position (according to the diagram), the more periods of mains voltage will be skipped, the more. accordingly, the power supplied to the load will be less.

Functionally, the power regulator consists of a pulse source with the mains frequency, a decimal counter, an output key and a power source.

The power supply is made on a low-power power transformer with a double secondary winding of 12 V AC on each half. Such transformers, made in China, are often on sale, they are designed to power portable equipment. The secondary winding always has a tap from the middle, as it is designed to work with a two-wave rectifier (on two diodes). Here, one half of the winding is used to power the circuit - a half-wave rectifier on the VD2 diode and capacitor C2 is connected to it. and the second half of the secondary winding is used as a 50 Hz frequency generator. The alternating voltage from it through the circuit R1-C1 is supplied to the counting input of the counter D1.

Zener diode VD1 does not allow this voltage to exceed the threshold of 12 V. Positive half-waves are fed to the counter input. In order for these half-waves to take the form of pulses, even if of an arbitrary shape, they first enter the transistor cascade on VT2, which, working as a key, generates pulses of positive polarity. The counter is switched by negative pulses, in sequence.

That is, taking into account the inversion introduced by the transistor VT2, it turns out that the counter is switched in place near the zero mark of the sinusoid of the mains voltage that feeds the soldering iron. Accordingly, the soldering iron is turned on at this mark, which reduces interference from the operation of the regulator to a minimum.

From the zero output of the counter, the level goes to the base of the transistor VT1. When the logical unit is here, this transistor opens and passes current through the LED of the VS1 optotriac pair. The current through the LED is limited by resistor R3. The diode VD3 together with the capacitor C3 minimizes the effect of the current surge when the transistor VT1 is opened on the power supply of the meter, so there are no malfunctions in the meter when the load is turned on.

When current is applied to the VS1 LED, the VS1 triac opens and supplies power to the load, that is, to the soldering iron.

Switch S1 is connected between the outputs of the counter and its reset input. When the switch is in position 8 shown in the diagram, the unit from the output "0" of the counter goes through it to the input "R" of the counter. That is, the counter is held fixed at the zero position, and the output "0" is constantly held at a logical one. Transistor VT1 is open and voltage is supplied to the soldering iron continuously.

When the switch is switched to other positions, the number of missed periods of the mains voltage increases accordingly, during which a logical unit is kept at the output "0" of the counter.

Resistors C1-4, C2-23 MLT can be used in the device. Non-polar capacitor types K10-17, KM-5, KM-6, or imported analogue. Oxide capacitors of types K50-35, K50-24 K53-19 or imported analogues, in general, capacitors are suitable for almost any "consumer" type. The voltage for which they are designed should not be lower than 12 V, but it is better if with a margin, that is, not lower than 16 V. Instead of the Zener diode D814D, you can use any Zener diode for a voltage of 12 ... 15 V, for example, KS212 KS215, D814E, or imported zener diodes marked "12V", "15V". The zener diode should be low power. Diodes 1N4004 can be replaced by any rectifier diodes, for example, KD209, KD105, 1N4007. As VD3, you can also use 1N4148, KD522, KD521. KT3102 transistors with any letter index. You can use transistors KT315, KT503 and many foreign analogues, characterized as "ordinary npn".

The CD4017 chip can be replaced with the K561IE8 chip. The optotriac pair S202T02 is designed to operate on an alternating voltage of 220 V at a load current (current through the triac) of no more than 2 A. Therefore, the maximum load power should not exceed 440 W. But at more than 150W, the optocoupler requires a fairly efficient heatsink. Therefore, I would not recommend using this optocoupler with a load power of more than 150-200 W, although 440 W is acceptable. Another note, the minimum current of the optocoupler triac is 25 mA. This means that with a power of less than 5 watts, most likely it will not work. In reality, to ensure reliable switching, the load power must be at least 10 watts. However, I have not seen soldering irons for 220 V with a power below 15 W.

If you need to switch large loads, for example, if you use this circuit in conjunction with some kind of electric heater, then you need to redo the output stage accordingly, replacing the S202T02 optocoupler with a more powerful optotriac (or an output key circuit on the optocoupler and a powerful triac).

The power supply is made on a purchased transformer of low power and dimensions. The transformer has a 220 V primary with a 110 V tap (tap not shown in the diagram) and a 24 V secondary with a center tap. The maximum current of the secondary winding, according to the data stamped on the clamping plate, is 150 mA. This is quite enough. It is possible to use another transformer. For example, you can take the TVK110L transformer from the frame scan of an old tube TV. This transformer has two secondary windings, one wound with thick wire and the other thin. The one wound with a thick wire can be used to power the circuit, and the one wound with a thin wire can be used to receive pulses with the mains frequency.

Virtually no tuning is required. With serviceable parts, everything starts working after the first inclusion.

Author: Karnaukhov D.A.

See other articles Section Regulators of current, voltage, power.

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