In practice, often there are cases when the available power transformer not provides the secondary winding of the voltage required for normal operation the stabilizer. In this case, you can use the integral pulse width (PWM) stabilizers f.MAXIM, allowing you to "tune" the existing a transformer.
In the power supply (Fig.1) applied MAHH produced in two versions. MAH has a maximum output current of 5 A. MAH - 2 Valid input A. voltage IC is 8...40 V. the Chips have a fixed frequency conversion (100 kHz) and the levels of the output current restriction 6.5 And MAH and 2.6 A for MUCH.
The internal structure of the chip is presented in Fig.2. Chips go on sale in plastic packages TO-220 (Fig.3).
In the manufacture of the unit requires the calculation of the RF choke L1 represents a multi-layer cylindrical coil, wire wound, providing the rated current flow. The calculation is made according to the formula
where d is the wire diameter, mm.
If obtained from (2) differs from (1) more than 10%. options adjusted, and the calculation is repeated. For example, for a PSU with MUCH on the load current 2 A and the input voltage to 50 V L1=50 µh. Coil wound wire sew-2 00.5 mm on paper frame 6 mm and a length of 4 cm Number of turns - 140.
Author: I. Semenov, Dubna, Moscow region.