In this case, the difference between the input and output voltages of the stabilizer can be 2-3 volts (maybe less in general, but it is better not to risk it) while the level of ripple remains very, very small. Now - one subtlety that distinguishes this scheme from the standard one recommended by the manufacturer - to increase the efficiency of the stabilizer, that is, to reduce the voltage drop across the regulating element, a separate power supply of the reference source from the "watch room" is used. Its circuit is borrowed from the datasheet for the TL431 microcircuit, which is the source of the reference voltage for the applied stabilizer. Further, the rectified voltage is fed to the stabilizer itself.
To prevent burnout of the P2 relay contacts and failure of the rectifier diodes, a "soft start" device is used - initially the mains voltage is supplied through the series-connected resistor R1, which limits the starting current and is shunted by the contacts of the P1 relay only after the voltage on the capacitor C7 reaches the operating level relay. When you press the S1 (Power ON) button, a constant voltage through its contacts is fed to the gate of the transistor T4, it instantly opens, the P2 relay is triggered, which, with its contacts, connects the primary winding of the Tr1 transformer to the network. The presence of the "watch" voltage is indicated by the yellow LED2 (Ready). When connected to the network at the output of the rectifier appears constant pressure about 24 volts. A small power supply unit on the Tr2 transformer is permanently connected to the network, its task is to control the on / off control of the powerful part of the unit and generate an overvoltage to power the reference stabilizer. I had to introduce a soft start scheme for the power supply and what is called a "duty room" in computer power supplies. Since the inrush current of such a device can be very large, no, even a very powerful mechanical network switch will last long. Agree - a very valuable quality for a power supply. I have developed a power supply design for low-voltage equipment with a maximum current of up to 50A.Ī feature of this design is the function of disconnecting the load in the event of a short circuit or overcurrent. It seemed very tempting to apply this property of theirs in a high-current voltage stabilizer. It's no secret that powerful field-effect transistors (they are also mosfets) can work even with a very small voltage drop across them.
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