Another term used in defining a power supply is a DC power supply. What is this mechanism? This is a kind of device that allows you to get an acceptable stable constant voltage. Well, or just a constant current. When, say, a 24v DC power supply does the job and is in stabilization mode voltage, it is initially able to maintain the required specified indicator of the current even in the case and some change voltage.
- 1 Features and power classification
2 Types of power supplies
- 2.1 Secondary unit
- 2.2 Transformer unit
- 2.3 Impulse unit
Features and power classification
The most common classification principle for power supplies is power classification. That is, the number of devices functioning from electricity that the unit is capable of supporting.
If the device exceeds the permissible limit of current consumption, the unit reduces the consumption of the network, thus preventing the breakdown of devices and equipment breakdown. If you need provide electrical equipmentcontrol systems, surveillance systems (video surveillance), as well as all sorts of other devices that need electricity and constant voltage, then such blocks are the best fit because often designed for stationary application.
The main points that stand out and the qualities that interest us in such blocks are:
- long service life unless extreme situations and impacts occur
- high efficiency
- natural air convection
- output voltage adjustment has a potentiometer
- can be mounted either on a DIN rail or on a wall
- high reliability of the device
- protection that trips in case of overload, overvoltage
- workmanship - high
Types of power supplies
In general, power supplies can be divided into several types:
- secondary power supply;
- transformer or, as it is also called, a network power supply;
- switching power supply.
In short, their differences can be described as follows. The secondary power source is a kind of device designed to provide power to the appliance with energy, taking into account the voltage and current, by converting the electrical energy of other sources. According to the rules of GOST, when defining in documents and papers the word “secondary” is prudently omitted.
The power supply is capable of being integrated into some general scheme. It either happens in simple devices, or in variants when a voltage drop on some the lead wires, even a minor one, are unacceptable - the motherboard of any computer, eg.
The built-in voltage converters that it has to power the processor are responsible for this. The source can also be executed and located generally in a separate room. A common example for this case is arrangement in a separate room of the food shop. The source can be made in the form of a certain version of the power supply rack module, the most common unit common in associations and views of many.
Often, and in the most common aspects, secondary units convert energy from an AC power line of ordinary power frequency. If we consider different countries, in the Russian Federation it is 220 V and 50 Hz, and in America - 120 V and 60 Hz.
Transformer power supply is the most classic. It is also called network. Usually it consists of an autotransformer or, as an option, a step-down transformer. In this case, the primary winding is designed for mains voltage, followed by a rectifier.
This device converts alternating voltage into pulsating unidirectionalIn standard terms, it is permanent. The rectifier in this structure consists of a single diode in most cases. Or four diodes that form a diode bridge. It happens that more rare, other schemes are used, for example, if we interact with a rectifier with voltage doubling.
When the rectifier is already at the right place, then the filter goes on, smoothing the oscillations, which are simply called pulsations. As a standard option, this device is simply a somewhat large capacitor in terms of capacity used. In the scheme, in addition to the above, there may be protection against short-circuit, filters of high-frequency noise, as well as surge (varistors), current and voltage stabilizers.
Transformer sources have their advantages. And regarding them, we can say the following. They are well accessible element base. They are simple in their unique design. Their reliability is one of their highest and most important priorities. Transformer power supplies, however, have their drawbacks and you can tell the following about them. They are weakly resistant to voltage surges and loss of neutral, which in the final case leads to the formation of phase voltages. They have large dimensions and weight, they are metal-consuming. To ensure stability, they need a stabilizer, which introduces its additional losses.
Switching power supplies are essentially an inventory system. AC input voltage is initially rectified in pulsed blocks.
The voltage that is received initially, is converted into rectangular pulses, their frequency is increased, and the duty cycle is defined, which are fed to the transformer or to the output low-pass filter.
In the case when the switching power supply units are galvanically isolated directly from the mains, then the rectangular impulses are fed to the transformer, and if the pulse power supplies are not galvanically isolated, then filter.
Small-sized transformers can be used in pulse power supply units. The effectiveness of the work, as can be determined, with increasing frequency increases and, accordingly, decreases the requirement for the dimensions of the core, its cross-section, which is necessary to transfer sufficient required equivalent power. It explains everything. In the greatest number of cases, such a core is made of ferromagnetic materials and, therefore, quite different from the cores of low-frequency transformers. They are made of electrical steel.
Voltage stabilization in them is maintained by means of negative feedback. Negative coupling allows you to maintain the desired output voltage, while regardless of input oscillations, as well as load values, at a relatively fairly constant level. If the pulse source is galvanically isolated, then the most popular method is to use one of the output windings or an optocoupler can be used. This is how feedback is organized.
Depending on the magnitude of the signal, which depends on the output voltage, the pulse duty cycle varies at the output of the PWM controller. In this case, a resistive voltage divider is used, as a rule, if isolation is not required. This power supply maintains the desired stable voltage in this way.
Impulse sources do not create radio interference due to harmonic components, unlike transformer ones.