Overview:
With the continuous development of power electronics technology, the application of frequency conversion speed regulation technology in the field of industrial transmission is more and more extensive, especially the application of AC-DC-AC frequency conversion speed regulation.
The AC-DC-AC variable frequency speed control circuit includes a rectification and inverter part, wherein the inverter part is typically 6 switching units (IGBT or MOS tube), 3 upper and lower arms, and some with a braking unit of 7 Switch unit. Since the reference ground of the control trigger pulse signals of the three units of the upper arm is suspended, the trigger pulses generally need four sets of power sources that are isolated from each other (the upper arm 3 units are respectively powered, and the lower arm shares a set of power sources). Of course, if the software cooperates with the control and gives a charging pulse, the power supply of the three units of the upper arm uses a bootstrap circuit, and only one set of power supplies can be used.
Only the case of using four sets of power supplies will be discussed here. The control auxiliary power supply of the inverter has three characteristics:
1) has multiple output voltages. The power supply described in this article has 5V, ±15V, four 16V trigger pulse power supplies, 12V bias power supply, and 24V total 9 output voltages. Among them, the 5V, ±15V output voltage is common, and the remaining output voltages are independent output voltages;
2) Four sets of pulse power supplies require better output voltage consistency and higher voltage regulation accuracy;
3) Four sets of pulsed power supplies are required to provide large instantaneous power, but the average power is small.
To meet the above requirements, it is simple and low-cost. It is a good choice to use the TOPSwitch series of American PI companies. TOPSwitch series products integrate MOS tube and PWM controller in one chip. The peripheral circuit is very simple. The power range covers several watts to hundreds of watts. The chip package is available in various forms. Some chips also have over-temperature and over-current. And input voltage overvoltage, undervoltage and other protection functions, can flexibly adapt to the design of many power supplies. PI also introduced auxiliary design software for the TOPSwitch family of products to allow users to quickly and accurately design the required power supply. When I was working on a servo controller project, the auxiliary power supply was designed with TOPSwitch products. As a typical example, the design method and key points are briefly introduced below.
(Please read the PDF for details)
Starlight mirror, also known as light mirror or scattering mirror, is a special filter. Different types of vertical and horizontal linear stripes are carved on the glass of starlight mirror by etching. Under the action of point light source, the bright points in the shooting scene can diffract, so that each light source point on the shooting photo emits light of a specific harness, To achieve a radiant effect.
According to the number of fine lines carved on the starlight mirror and the patterns composed of fine lines, it will produce star flashes with different effects. Common starlight mirrors mainly include: one character, cross, meter character, snowflake mirror, etc., and special ones include: Victor star, Polaris, etc. When shooting jewelry, water, starlight, lights and other scenes, you can get different types of light. The starlight mirror softens the image slightly, but its main function is to create a radiant effect around the light source. Starlight mirror is usually used to shoot the light of night scene or the reflection of objects to achieve a radiant effect and make the photos have a dreamy artistic effect.
Starlight lens is a kind of Color Filter widely used in commercial advertising photography. It can produce a radiant effect at the highlight of the subject. If the starlight mirror is used, soft starlight will appear in the high light parts of glassware and metal products, making the picture shining.
The light effect of starlight mirror in use is affected by focal length, aperture and light spot. The effect of using a telephoto lens is usually better than a telephoto lens. The aperture around F8 is better; If the aperture is too large, the light line will become an intermittent short line; The aperture is too small and the light effect is worse. The smaller and brighter the light spot, the better the light effect. The dark background is also an important condition to ensure the light effect, so the effect of using starlight mirror is particularly significant in night shooting, which can often make the night scene shine.
Star Filter,Cokin Star Filter,Cross Star Filter,Cross Screen Star Filter
shaoxing shangyu Tianya Photographic Equipment Factory , https://www.tianyafoto.com