The power conversion function in the voltage parameter can be performed by various devices like generators, chargers, and transformer devices. To one degree or another, all of them are capable of changing the characteristics of energy, but their application does not always justify itself in terms of technical and ergonomic qualities. This is partly due to the fact that the task of current transformation is not a key one for most regulators - in any case, if we talk about direct and alternating current. It was these limitations that motivated manufacturers of electrical equipment to develop a pulse converter, which compares favorably with its compact size and accuracy of voltage stabilization.
Device definition
Numerous radio engineering devices, automation and communication tools rarely do without power single-phase and three-phase devices for transforming current in the range from units to hundreds of volt-amperes. Pulse devices are used for narrower tasks. An electrical pulse-type converter is a device that transforms voltage in small time intervals with a duration of the order of 1-2 microns / second. The voltage pulses in this case have a rectangular shape and are repeated with a frequency of 500-20 000 Hz.
Traditional converters with the ability to adjust the output voltage usually control the resistance indicator of the device. It can be a thyristor or a transistor through which current flows continuously. It is his energy that causes the controller device to heat up, because of which part of the power is lost. Against this background, a pulse voltage converter looks more attractive in terms of its technical and operational properties, since its design provides for a minimum of parts, which leads to a reduction in electrical noise. The adjusting element of the converter is a key that works in different modes - for example, in open and closed state. And in both cases, the minimum amount of thermal energy is released during operation, which increases the productivity of the equipment.
The purpose of the converter
Wherever a change in electrical parameters is required, pulse transformers are involved in a particular operational configuration. At the first stage of wide distribution, they were mainly used in pulsed technology - for example, in triode generators, gas lasers, magnetrons, and differentiating radio equipment. Further, as the device improved, they began to be used in most typical representatives of electrical equipment. Moreover, this was not necessarily a specialized technique. Again, in different versions of the pulse converter can be present in computers and in televisions, in particular.
Another, but less well-known function of transformers of this type is protective. Pulse regulation itself can be considered a protective measure, but the goals for adjusting voltage parameters are initially different. Nevertheless, special modifications protect the equipment from short circuits under load. This is especially true for idle equipment. There are also pulse devices that prevent overheating and excessive voltage surges.
Instrument design
The converter consists of several windings (at least two). The first and main one connects to the network, and the second goes to the target device. The windings can be made of aluminum or copper alloys, but in both cases, as a rule, additional varnish insulation is used. The wires are wound on an insulating base, which is fixed on the core - the magnetic circuit. In low-frequency converters, cores are made of transformer steel or a soft magnetic alloy, and in high-frequency converters, based on ferrite.
The low-frequency magnetic circuit itself is formed by sets of plates of , or -shaped. Ferrite cores are usually made whole - such parts are present in the composition of welding inverters and galvanic isolation transformers. Low-power high-frequency transformers do without a core at all, since its function is performed by the air. For integration into electrical devices, the design of the magnetic circuit is provided by the frame. This is the so-called pulse converter unit, which is closed by a protective cover with markings and warning labels. If during the repair process you need to turn on the device with the cover removed, this operation is performed through an RCD or an isolation transformer.
If we talk about converters that are used in modern radio and electrical engineering, there will be a significant difference between them and classical voltage transformers. The most noticeable decrease in size and weight. Impulse devices can weigh a few grams, and performance remains at the same level.
Features of operational processes
As already noted, for regulating the current in pulse transformers, keys are used that themselves can become sources of high-frequency interference. This is typical for stabilizing models that operate in current switching mode.
At the moments of switching, sensitive changes in current and voltage can occur, which create conditions for out-of-phase and common-mode interference at the input and output. For this reason, a switching power converter with stabilizer function involves the use of filters that eliminate interference. To minimize unwanted electromagnetic factors, switching the key is performed at times when the key does not conduct current (when opened). This method of anti-interference is also used in resonant converters.
Another feature of the working process of the devices under consideration can be called the negative differential resistance at the input during voltage stabilization under load. That is, under conditions of increasing input voltage, the current decreases. This factor must be taken into account to ensure the stability of the converter, which is connected to sources with a high rate of internal resistance.
Linear Converter Comparison
Unlike linear devices, pulse adapters are favorably distinguished by higher performance, compact dimensions and the possibility of galvanic isolation of circuits at the input and output. To provide additional functionality with the binding of third-party devices, the use of complex connection schemes is not required. But there are also weaknesses in the pulse converter in comparison with linear transformers. These include the following disadvantages:
- Under conditions of changing the input current or voltage under load, the output signal is unstable.
- The presence of the already mentioned pulsed noise on the output and input circuits.
- After sharp changes in the voltage and current parameters, the system takes longer to recover during transients.
- The risk of self-oscillations that can affect the performance of the equipment. Moreover, fluctuations of this kind are associated not with network instability of the source, but with conflicts within the stabilization scheme.
DC / DC Converter
All types of pulsed devices of the DC / DC system are characterized by the fact that the keys are activated during the translation of special pulses in the direction of the transistor. In the future, due to the growing voltage, a logical locking of transistors occurs, moreover, against the background of recharging the capacitor. It is this feature that distinguishes the switching device of pulse DC-DC converters from similar devices in independent inverter equipment.
Typically, such devices monitor the DC voltage under load in the process of supplying direct current to the network. This kind of control is achieved by adjusting the voltage on the open key. Small current values make it possible to fix a high level of performance at which the efficiency can reach 95%. Setting peak performance indicators of the system is a significant advantage of pulsed current converters, however, the implementation of the DC-DC circuit is far from possible in every design. Initially, the contact network should act in the device as a source - in particular, this principle is used in rechargeable batteries and batteries.
Boost converter
Using this transformer, the voltage is increased from 12 to 220 V. They are used in situations when there is no source with suitable power parameters, but you need to provide power to the device from a standard network. In other words, an adapter must be introduced from a source with one characteristic to a consumer with different power requirements. Schematic designs of pulse voltage converters 12-220 V allow the connection of devices that operate at a frequency of 50 Hz. Moreover, the power of the equipment should not exceed the maximum power rating of the transformer. And even if the voltage parameters match, the consuming device must be protected against network overloads. This voltage correction method has several advantages:
- The possibility of a long working session at maximum load without interruptions.
- Automatic output power adjustment.
- The increased efficiency ensures both the stability of the operating mode of the device and the high reliability of the function of the electrical circuit.
Step Down Pulse Converter
When using low-frequency or low-power equipment, the need for lowering the voltage index may quite naturally arise. For example, this task is often encountered when connecting lighting devices - for example, LED backlight. To lower the converter closes the regulating switching key, after which "extra" energy is accumulated in it. A special diode in the circuit does not allow current from the supply source to the consumer. Moreover, in self-induction systems, rectifier diodes can pass negative voltage pulses. In the operation of pulse converters 24-12 V, the output stabilization function is especially important. Both linear and directly impulse stabilizers can be involved. It is more profitable to use devices of the second type with latitudinal or frequency modulation. In the first case, the duration of the control pulses will be adjusted, and in the second, the frequency of their appearance. There are also stabilizers with mixed control, in which the operator can, if necessary, change the configuration of the pulse adjustment in frequency and duration.
Pulse Width Converter
In the process, a device that stores energy as a result of transformation is used. It can be included in the basic structure or can be connected directly to the input voltage without reference to the converter. One way or another, the output will be an average voltage indicator determined by the value of the input voltage and the duty cycle of the pulses from the switching key. On the operational amplifier is a special computer that evaluates the parameters of the input and output signals, recording the difference between them. If the output voltage is less than the reference, then a modulator is connected to the control, increasing the duration of the open state of the switching key relative to the time of the clock generator. As the input voltage changes, the pulse converter corrects the key control circuit so that the difference between the output and reference voltage indicators is minimized.
Conclusion
In its pure form, without connecting auxiliary devices like rectifiers and stabilizers, the converter functions are significantly narrowed, although the efficiency remains at a high level. The transformation devices, which rarely do without additional equipment, include regulators in AC networks. At least in this case, you will have to install a smoothing filter and a rectifier at the input. Conversely, pulse converters of constant electric currents both at the input and at the output can independently support their main function. But even in such systems, it is important that the device can perform the task of stabilizing the voltage. Also, do not forget about possible interference with the active use of switching keys in the stabilizer system. In such circuits without grounding, it is recommended to connect a noise filter to the converter unit.