There are schemes of bass amplifiers, transmitters, and other devices that require power not only from the bipolar source, but also from two galvanically unleashed sources that are not connected to ground or common associated the chains. To organize the power of that device in stationary conditions very just so as to be powered by the grid, which means there will be power or a pulse transformer. Enough to do two secondary windings, connected to other circuits, and variable voltage to submit them on a separate independent rectifiers.
More difficult to arrange the power supply galvanically isolated from two sources if the power source should serve as a constant current source, for example, side network of car or boat.
The figure is a diagram of a flyback pulse source, the output which has two galvanically isolated voltage 15 V, with the maximum the allowable current of 1 A. If you want a conventional bipolar power these outputs can be Daisy - plus one minus the other, and the point the connection will be shared neutral conductor.
The scheme has already become a standard, a source of direct current, pulsed generator, pulse transformer, the rectifiers in the secondary circuit.
The voltage from 12 V car battery is supplied to the chip type A1 LT1070 (flyback DC-DC Converter). Chain C1-C2-L1-C3-C4 bars the way interference that may penetrate from the systems of the car or boat.
Chip A1 generates a pulse frequency of about 40 kHz. The output of the chip there's a key displayed on the pin 4. He loaded the primary winding of the pulse the transformer T1. Chain C6-R3-VD1 negative emissions limits in the coil.
Is induced in the secondary windings. EMF. The coil 4 is a control. AC the voltage on it is rectified by the diode VD2 and through a trimmer R2 is supplied to the control input of the circuit A1 (pin 2). The stabilization system output voltage LN1070 works in such a way that the controller chip changes the duty cycle at pin 4 so that the voltage at pin 2 was equal to 1.24 V. that is, to get the voltage you need to remove the voltage from the secondary circuit and through the divider resistors to submit it to conclusion 2.
The ratio arms of the divider must be such that under normal the voltage at the output, at pin 2 of 1.24 V. In this scheme to relieve stresses stabilization system output is undesirable, as originally supplied the goal of creating a source with galvanically isolated output voltage as from each other and from the primary circuits. Therefore, there is a third secondary the source consisting of the winding 4 and the rectifier VD2-C7. It only serves to obtaining a control voltage. Since the coil 4 in the structure of the transformer, the voltage on it at the same depending on the duty cycle of the pulses, and the voltage on the other windings.
The transformer T1 is wound on a ferrite ring with a diameter of 28 mm Primary winding contains 40 turns of wire sew 0,47. She is wound first. Then, on her, in the same direction is needed to wind the secondary winding 2, and 3. Take the same wire and folded it in half 50 is wound coils. Winding 4 in the same direction and that the rest - 10 turns sew 0,12. The establishment comes down to setting the output voltage adjusting R2.
Author: Kozjanski. P.