Regulatory elements stabilizing the power supply with a large voltage drop on them dissipate more power, which is released as heat. Thereby, efficiency of power supply decreases and decreases its reliability. On the other hand, and the electrical network is not always stable, particularly in rural areas. Voltage fluctuations it is often up to 30 … 50 V or more, and forced to do by-pass voltage applied to the stabilizer so that he did not come out of the mode of stabilization at the minimum supply voltage.
Of course, applying the automatic adjustment of the mains voltage, for example, via ferroresonant AC voltage can improve the situation somewhat, but it does not solve the problem completely, and, in addition, complicates the design of BS.
In amateur conditions to provide easier adjustment of the stabilizer mode manually switching the taps of the primary winding of the power transformer. When winding of the power transformer T1 primary winding makes a number of taps, for example, for voltages of 190, 200, 210, 220, 230, 240 and 250 (logic 10 is quite acceptable in practice). Commuting bends switch SA2, you can choose the optimal thermal conditions of the PSU and its maximum efficiency. Protection from big jumps mains voltage is assigned to the fuse FU1. The capacitors C2 and NW — decoupling Nutrition (ceramic), relating to the stabilizer circuit. Switch SA2 should provide switching mains voltage, ie, have sufficient distance between the contacts and good insulation between them. Contacts themselves can be relatively thin.
In a second embodiment bends are made at the secondary winding of the transformer, although you can use a combination of taps to switch the primary and secondary windings. The switch must have powerful contacts, designed for operating currents issued by BP, but it can be a low voltage.
The third embodiment is applicable in the case when power transformer T1 is not possible to make the bends. The rupture of one of the tires (which is more convenient to constructively) coming from the rectifier to the stabilizer, the chain comprises a sequence of high-power silicon diodes (VD3. .VD9), Which are designed with a margin) for an electric current, and power supply are mounted on a separate radiator for heat dissipation. Switching diodes in the chain, you can adjust the input voltage regulator, thereby providing a gentle re-mode control element (transistor) VT1. The voltage drop across the diodes in the powerful currents of the order of 10 … 20 A 0.6 … 0.8 V at the instance of, respectively, the same amount would be «better» transistor. Instead of diodes can be applied to a set of powerful automobile lamps, wire resistors and the like, but it is not convenient in practice, as the use of the diodes.
At high output currents, BP (20 A) is useful to apply the parallel modules, consisting of regulating transistor and the inclusion of forward power diode. It is desirable that copies diodes and transistors were close to each other in the parameters for the uniform distribution of the current (power dissipation) nimi.Na between each module (VT1-VD3 and VT2- VD4) accounted for half of the current flowing through the stabilizer, ie transistors VT1 and VT2 (ideally) scatter half of the total power per stabilizer.
To reduce the heating control elements useful and consistent inclusion of several stabilizers. When this dissipated power is distributed to them in accordance with the voltage drop. For example, the stabilizer 1 issue 15, the stabilizer 2 — 9 B. When the input voltage is 18 V and a current of 10 A to the control transistor of the first regulator will dissipate power (18-15) 10 = 30 (W), the second — (15-9) U = 60 (W). If you use one stabilizer, then it would have dissipated power of 90 watts.
It is worth mentioning that the powerful BP ensure that the minimum thermal resistance between the control transistor and the heat sink. The best way to reduce it is soldered to the heat sink transistor (directly across the square leaving «tongue» of the transistor). On the plastic body of the transistor to be liberally apply thermally conductive paste and compress its spring metal bracket on the size of the body. The size of the radiator is better to choose a reserve or use fans. However, fans create quite annoying noise, so here it is necessary to evaluate the options.