What is oral counting. The use of various types of oral exercises in the lessons of m
By size, all light sources can be conditionally divided into two groups:
point,
linear.
A point light source is a light source whose dimensions are so small compared to the distance to the radiation receiver that they can be neglected.
In practice, a point source of light is taken to be one whose maximum size L is at least 10 times smaller than the distance r to the radiation receiver (Fig. 1).
For such radiation sources, the illumination is determined by the formula E \u003d (I / r 2) cosα,
where E, I - respectively, the illumination of the surface and the luminous intensity of the radiation source; r is the distance from the light source to the photodetector; α is the angle at which the photodetector has moved from the normal.
Rice. 1. Point light source
For example, if a lamp with a diameter of 10 cm illuminates a surface at a distance of 100 m, then this lamp can be considered a point source. But if the distance from the same lamp to the surface is 50 cm, then the lamp can no longer be considered a point source. Typical example point source of light - a star in the sky. The stars are huge, but the distance from them to the Earth is many orders of magnitude greater.
Halogen and LED lamps for recessed luminaires are considered to be point light sources in electric lighting.The LED is almost a point source of light,because its crystal is microscopic in size.
Linear radiation sources include those radiators whose relative dimensions in any of the directions are larger than the dimensions of a point radiator. As you move away from the plane of illumination measurement, the relative dimensions of such an emitter can reach such a value at which given source radiation turns into a point.
Examples of electric linear light sources: fluorescent lamps, RGB LED strips.But, according to the definition, all sources that are not considered point sources can be attributed to linear (extended) light sources.
If from the point at which the point source of radiation is located, the vectors of light intensity are set aside in different directions in space and a surface is drawn through their ends, then a photometric body of the radiation source will be obtained. Such a body completely characterizes the distribution of the radiation flux in space.
According to the nature of the distribution of light intensity in space, point sources are also divided into two groups. The first group consists of sources with a distribution of light intensity symmetrical about a certain axis (Fig. 2). Such a source is called circularly symmetrical.
Rice. 2. Model of a symmetrical radiator
If the source is circularly symmetric, then its photometric body is a body of revolution and can be completely characterized by vertical and horizontal sections passing through the axis of rotation (Fig. 3).
Rice. 3. Longitudinal distribution curve of the luminous intensity of a symmetrical source
The second group consists of sources with an asymmetric distribution of light intensity. For an asymmetric source, the luminous intensity distribution body does not have an axis of symmetry. To characterize such a source, a family of longitudinal luminous intensity curves is constructed corresponding to different directions in space, for example, through 30°, as in Fig. 4. Usually such graphs are built in polar coordinates.
Rice. 4. Longitudinal distribution curves of the luminous intensity of an asymmetric source
There are some serious things in the world
that one can only talk about them in jest.
Niels Bohr
Introduction
The power supplies you use to connect your laptop to 220V, for example, are called secondary power supplies. They are called secondary because the primary power source will be a generator at a power plant that generates current flowing through city power grids or chemical element nutrition. All power supplies can be roughly divided as shown in the diagram below.
Primary Power Sources
Primary power sources are converters of non-electric types of energy into electrical energy. For example, hydroelectric power plants, wind turbines, solar panels, chemical sources current, batteries, gas generators, etc. Primary sources are mainly engaged in energy and manufacturers of all kinds of batteries. They are not very interesting to me, for example. Or interesting ... Yes, sunny and geothermal springs I'm interested in energy!
Secondary power supplies
Secondary power sources themselves do not produce electricity, they simply convert it. For example, a laptop power supply converts 220V AC into constant pressure 19.2B.
Secondary sources are required to provide the devices with the specified parameters of voltage, current, supply voltage ripple, frequency. We don't pour oil into the gas tank, do we? So electronic devices are more convenient and safer to power properly.
Linear power supplies
So they are called due to the principle of work. The fact is that the regulation of the output voltage in them is continuous, i.e. linear. These power sources appeared in the world first. And they are built according to the classical scheme: transformer, rectifier, filter, stabilizer:
The block diagram shows a stabilized linear power supply. This means that it is built in such a way as to maintain a given voltage, even if the device connected to it will eat from it a current of 1A, then 5A.
And there are also unstabilized linear power supplies. If you close the “stabilizer” rectangle on the block diagram with your hand, then you get just such an IP. Here in it, at different loads, the voltage at its output can change slightly (or in particularly bad cases, not at all slightly) change (usually it decreases).
The transformer lowers the mains voltage to the required one, then the rectifier makes a pulsating voltage from the usual alternating voltage, which is then smoothed by the filter to a constant state, and the stabilizer is used to maintain the voltage at the load within the limits required by the load. For example, the load is powered by a voltage of 10V +/- 0.2V - here you already need a very good source power supply with good stabilization.
Advantages
They are quite easy to make at home, with a good filter they give out a supply voltage with a low level of ripple and, accordingly, do not interfere with the operation of devices that are powered by them. As well as galvanic isolation from the network.
disadvantages
Low efficiency, which decreases with increasing current consumption. The fact is that the more the device consumes from a linear source, the more the regulatory elements (usually either transistors or specialized stabilizer microcircuits) heat up in it, which means that a breakthrough of energy flies into the atmosphere in the form of heat. Another disadvantage of linear power supplies is weight. A good powerful transformer weighs like a weight and has decent dimensions, and its price is worthy of the weight.
Switching power supplies
Or otherwise IIP. These sources operate fundamentally differently than linear power supplies. At the same time, they can, with smaller dimensions, feed significantly heavy loads. The principle of their operation is based on PWM (pulse width modulation).
First, in the SMPS, the input voltage is converted to DC, and then the DC voltage is converted into pulses that come with certain frequency and duty cycle, and then to the transformer (for galvanic isolation of the network and the load) or directly to the load without any isolation.
The block diagram shows that SMPS are more complex than linear power supplies. But they can also still be assembled at home. Or even remake the ATX PC power supply. The web is full of such examples.
Advantages
Light weight, good efficiency (up to 90-98%), small size. It has a lower cost if we compare the SMPS and a linear source of the same characteristics. SMPS is everywhere around us: charging mobile phones, power supplies for computers and laptops, lamps, LED years and other devices.
disadvantages
Often they do not have galvanic isolation from the network. They are sources of high-frequency interference, which is practically impossible to completely eliminate. They also say that there is a limit on the minimum load power. The fact is that when the load is less than the required SMPS, it may simply not start.
In the next part I want to show concrete examples power supply schematics, and maybe even step by step create a linear or switching power supply. Add the entry to your bookmarks (Ctrl+D) and subscribe to the newsletter!)
- Revich. Entertaining electronics (chapters about power supplies)
- Borisov. Encyclopedia of a young radio amateur (chapters about power sources)
- Belopolsky. Radio power supplies
- Sanjay Maniktala. Switching Power Supplies A to Z
- Semenov. Power electronics (pulsed)
- Raymond Mack. Switching power supplies
- Moskatov E.A. Power supplies
- Efimov I.P. REA power supplies
- Microcircuits for linear power supplies and their application (reference book)
- Brown M. Power sources. Calculation and design
- Geitenko. Secondary power sources
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