Power supplies with PWM stabilizers. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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In practice, there are often cases when the existing power transformer does not provide the secondary winding with the voltage necessary for the normal operation of the stabilizer. In this case, you can use integrated pulse-width (PWM) stabilizers f.MAXIM, allowing you to "adjust" to the existing transformer.
The power supply unit (Fig. 1) uses MAX72X, which is available in two versions. MAX724 has a maximum output current of 5 A. MAX726 - 2 A. The permissible input voltage of the IC is 8 ... 40 V. The microcircuits have a fixed conversion frequency (100 kHz) and output current limit levels of 6.5 A for MAX724 and 2,6 A for MAX726.
The internal structure of microcircuits is shown in Fig.2. Microcircuits go on sale in plastic cases TO-220 (Fig. 3).
In the manufacture of the block, the calculation of the RF inductor L1 is required, which is a multilayer cylindrical coil wound with a wire that ensures the flow of the rated current. The calculation is made according to the formula
where d is the wire diameter, mm.
If the value obtained from (2) differs from (1) by more than 10%. the parameters are adjusted and the calculation is repeated. For example, for a power supply unit with MAX726 for a load current of 2 A and an input voltage of up to 50 V, L1 = 50 μH. The coil is wound with PEV-2 wire 00.5 mm on a paper frame 6 mm and 4 cm long. The number of turns is 140.
Author: I.Semenov, Dubna, Moscow Region
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A group of physicists from MIT and Princeton experimentally confirmed the ability of electrons to form a Wigner crystal - to line up in spatially ordered structures inside a semiconductor, and for the first time observed the melting of a crystal with increasing electron density.
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