Table lamp stabilizer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Table lamp stabilizer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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At present, it would seem that the problem of instability of the voltage of the lighting network is not so acute. Almost all modern electronic household equipment can operate in a fairly wide range of supply voltage. For example, some modern TVs, according to the operating instructions, can operate from a mains voltage of 90 to 280 V. However, there is still a problem, especially for technically simple devices that are not equipped with stabilized sources, such as a table lamp.

When the luminaire is operated with a conventional incandescent lamp, when the mains voltage drops to 180 V and below, not only the brightness of the light decreases, but also its spectrum deteriorates, becoming harmful to vision, and with increased voltage, the lamp quickly burns out.

Of course, you need a stabilizer. But now there are no AC voltage stabilizers on sale, but use them. LATR for powering a 75 W light bulb is not only inconvenient, but also unprofitable (it takes on significant power by itself).

The figure shows a diagram of a simple power supply for an incandescent lamp, which has several important advantages. Firstly, it provides a stable nominal glow of the lamp in a fairly wide range of input mains voltage (170 ... 260 V). Secondly, the lamp is powered by direct current, therefore, its light is not modulated in any way, which significantly reduces eye fatigue. Thirdly, the source-stabilizer consumes minimal power.

The only drawback is that this circuit is only suitable for powering lighting devices, and is not suitable for powering electronic equipment and other devices designed to operate on alternating current.

Table lamp stabilizer

The circuit is based on a phase power regulator on the KR1182PM1 chip.

This microcircuit is widely used in various regulators-switches of lamps with a power of up to 150 watts. The disadvantage of the typical KR1182PM1 circuit, however, like most other similar regulators, is that the regulator assembled on it regulates the voltage on the pump only from the minimum to the mains, and cannot raise it above the mains.

Here, in order to increase the effective voltage on the lamp, the lamp is connected at the output of the regulator through a bridge rectifier on diodes VD1-VD4 with a smoothing capacitor C4. As you know, at the output of such a rectifier, the DC voltage will be approximately 1,4 times higher than the AC voltage applied to its input. But incandescent lamps work equally on both direct current and alternating current. Therefore, there is a real possibility of increasing the brightness of the glow of the pump, in comparison with the power supply directly from the network.

Let's consider a diagram. The phase regulator on A1 is connected according to the typical circuit, but instead of the regulating resistor between terminals 3 and 6, the R4-C3-R5 circuit and the phototransistor of the optocoupler U1 are connected.

The resistance R4 is chosen so that the maximum output power is provided. The resistance R5 is chosen so that when it is connected in parallel with the resistor R4, the brightness of the lamp decreases by about three times.

Capacitor C3 ensures smooth heating of the lamp after switching on and smooth adjustment of the stabilizer.

From output A1, the voltage to the lamp is supplied through the rectifier VD1-VD4-C4.

To control the output voltage that feeds the lamp, there is a cascade on the transistor VT1. Resistors R2 and R3 form a measuring DC voltage divider that feeds the lamp.

With an increase in the output voltage, the voltage at the base of VT1 also increases and it opens, supplying current to the LED of the optocoupler U1. The brighter LED U1 lights up, the more the phototransistor U1 opens, and the less the resulting resistance between terminals 6 and 3 of A1 becomes, and the voltage at output A1 decreases. If the output voltage (at the lamp) decreases, the voltage at the base of VT1 also decreases and VT1 closes. The LED of the optocoupler U1 goes out, and the phototransistor closes, increasing the resistance between pins 6 and 3 of A1. The lamp voltage increases.

When adjusting, the stabilization point is set by adjusting the resistor R3, so that the constant voltage on the lamp is 220 V. And by selecting the resistance of the resistor R5, the adjustment range is set downward.

Now for the details. All capacitors must be rated for voltages not lower than those indicated in the diagram.

The PC817 optocoupler can be replaced by any similar low-power one, consisting of an LED and a phototransistor.

Zener diode VD5 - D814A-E in a metal case. It is undesirable to use glass (D814D-1), as it can easily fail from overheating. The zener diode limits the maximum voltage in the collector circuit VT1.

Transistor VT1 can be replaced by any general-purpose silicon transistor that allows a collector current of up to 30 mA.

Many parts are used from the power supply circuit of old domestic semiconductor TVs (2-3-USCT). In particular, these are rectifier bridge diodes, capacitor C4, a low-resistance resistor with a power of 8 W (R6), a network noise filter inductor L1. Of course, new parts can also be used here, and the L1 choke can be wound on a ferrite ring with a diameter of 30-40 mm (100-200 turns of wire with a cross section of 0,5-0,6 mm).

Adjustment consists in setting the adjustment range (R5) and setting the output constant voltage (220 V) by adjusting R3.

In the event of a self-oscillating process (a periodic change in the brightness of the lamp), it is necessary to replace the capacitor C4 with a serviceable one (removed from the old TV power supply may suffer from loss of capacitance or high internal resistance).

Author: Nazarov V.S.

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Comments on the article:

Vasya
The scheme is crazy, it should not be repeated. In this mode of operation, the microcircuit cannot work, large pulse current overloads bring the microcircuit out of storage, and the inductor does not save the situation in any way. Well, it is not designed to work with a reactive load, which is the capacitor C4. So, if you need to make a stabilizer, then you should consider the option with a PWM controller and a high-voltage MOSFET transistor.

Fyodor
For Vasya. Everything works fine if you put a triac or two thyristors at the output.

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