The electronic transformer (ET) appeared on the domestic market relatively recently, but has already gained popularity among amateurs and professionals. A large number of materials on electronic converters, presented by self-made sources and chargers of various types, are published on the Internet pages. They describe in detail how they work and how to connect to the network. In terms of their composition, these devices belong to typical network modules, in which ET is used as the main node. Due to their simplicity and versatility, these products are no more expensive than a Chinese power supply unit (PSU). Like him, when charging, they work from an industrial network of 220 volts.
Device and principle of operation of ET
Structurally, this element of the circuit contains the following nodes:
- multivibrator - master pulse generator based on powerful transistors;
- bridge assembled on high-voltage inductors;
- small-sized voltage transformer 220 12.
The function of the generator in the electronic transformer circuit is performed either by a diode thyristor or by transistors connected according to the scheme of high-power pulse switches (they are also called key ones). During the operation of this electronic unit, the generation frequency is set using a variable resistor and a storage capacitor (it can be adjusted in the range from 30 to 35 kHz). The inductors are partially bridged and wound on a small ring core.
This module provides a feedback loop to improve the stability of the master oscillator.
The circuit uses high-voltage bipolar transistors (usually of the MGE 13001-13009 type). The specific brand is selected depending on the power of the electronic transformer, the main purpose of which is to lower the output signal level to a predetermined value of 12 (24) Volts. Its main advantage is its small size and light weight, which makes it possible to reduce the corresponding parameters of the entire device.
The principle of operation of the transformer is that the generator generates a pulse voltage of the required amplitude, which, after conversion in the transformer, is reduced to the required level. For normal operation of halogen lamps, powerful current pulses with an amplitude of 12 or 24 Volts are quite enough.
Power supply unit based on electronic transformer
When manufacturing a full-fledged power supply unit based on a 12 Volt DC electronic transformer, a rectifier bridge with filtering elements is added to its circuit. This unit consists of 4 medium power valve diodes with a reverse voltage of up to 1 kV and a current of the order of 1 Ampere. After them, the DC voltage obtained as a result of rectification is smoothed (filtered) by an electrolytic capacitor and a powerful inductive choke.
Thanks to this, the unit manages to control the charging circuit of the variable resistor and capacitor included in the electronic transformer.
The advantage of the power supply assembled according to the considered scheme is its simplicity and reliability. The main disadvantage is the difficulty of obtaining a pulse current at the output of a sufficiently large amplitude.The circuit is only suitable for low-power halogen lamps installed in small lamps of the "night light" type.
Advantages of electronic converters
The main advantages of devices built on the basis of ET include the following features of the operation of the circuit:
- the output transformer of the power supply will not start without connecting a load to it - it will go into active mode, if only a lamp with a lamp is connected to it;
- in addition to the sparing mode of operation of the elements of the electronic circuit, this property of the ET allows you to save on consumed electricity;
- the product easily implements a protection system against dangerous overloads and short circuits.
More complex half-bridge circuits are often taken as a sample used for the homemade manufacture of a power supply unit on such a transformer. They are usually based on drivers such as IR2153 or similar electronic components. As an additional option, they have an indicator LED that signals the presence of high-frequency oscillations.
Some of the advantages of electronic converters are attributed by specialists to the disadvantages that interfere with their independent conversion into the simplest power supplies.
Disadvantages of ET models offered by the market
Despite the economical and well-developed scheme, power supplies on ET have a number of disadvantages, which are usually attributed to:
- lack of special overload protection in the simplest Chinese models;
- the resulting need for mandatory completion of the circuit;
- in many market samples there is no input filtering device, which makes it necessary to add a smoothing electrolytic capacitor to it (it is placed after the "powerful" choke).
The listed disadvantages are usually referred to as the "hard" mode of operation of high-voltage transistors, included in the key circuit.
In case of an accidental output short circuit (short circuit), these elements simply "burn out", which leads to the need for an urgent update of the entire electronic module. Often, the semiconductor diode rectifier also fails, which also needs to be replaced.
It is impractical to repair ET, since it costs almost a penny. It is much easier and cheaper to purchase a new module and remake it to fit your needs.
Electronic transformer power
The power indicator of ET is understood as the value of the current in the load, multiplied by the supply voltage of the halogen lamp. On the domestic market, there are various samples of transformer products with declared indicators from 25 to several hundred watts. The most widely presented models are designed for an output power of the order of 50-80 watts. It is allowed to connect two or even three 20-watt lamps to such converters. As a rule, they are all designed for an output voltage of 12 volts.
The considered power supplies are used only for their intended purpose - to power halogen light sources. To use them for LED lamps, for example, is prohibited by the instructions attached to the product.