Switching anode voltage stabilizer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Switching anode voltage stabilizer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The proposed simple switching anode voltage stabilizer is designed to power the lamp UMZCH. The UMZCH lamp mode for direct current was selected for the best sound quality at an anode voltage of 250 V. But the mains voltage is unstable, its deviations from the nominal value take the lamps out of the optimal mode, which causes a noticeable deterioration in the UMZCH sound. Stabilization of the anode voltage maintains the optimal mode of the lamps and, accordingly, high sound quality.

In recent years, interest in tube technology has renewed among radio amateurs, especially in UMZCH. The reliability of the lamp UMZCH can be increased, and the sound quality can be improved if their anode circuits are powered from a stabilized voltage source. Using modern circuit solutions and elements, it is possible to manufacture a simple and cheap switching anode voltage stabilizer.

Switching anode voltage stabilizer

The scheme of the proposed device is shown in the figure. The input of the stabilizer is connected to the output of the diode bridge, which rectifies the voltage from the anode winding of the low-frequency network transformer available in the UMZCH. Capacitor C1 smooths out the ripple of the rectified voltage. This and other capacitors also ensure stable operation of the stabilizer and suppress the high-frequency noise generated by it, preventing it from penetrating into the load and the power supply network.

When the power is turned on, a voltage of 1 V is set on the zener diode VD15, which opens the switching transistor VT1. A linearly increasing current flows through this transistor and inductor L1, charging the output capacitors C3 and C4. The pressure on them increases. When it exceeds the total stabilization voltage of the VD3-VD5 zener diode circuit, the emitting diode of the optocoupler U1 turns on. The phototransistor of the optocoupler opens and shunts the zener diode VD1. The voltage between the gate and source of transistor VT1 decreases to almost zero and becomes insufficient to keep the transistor open. The transistor closes, the diode VD2 opens, the inductor current L1 flows through it, which feeds the load and charges the output capacitors C3 and C4. The energy accumulated in the magnetic field of the inductor L1 is transferred to the stabilizer load connected to its output.

Further, as the output capacitors are discharged to the load, the voltage across them decreases, the zener diodes VD3-VD5 and the emitting diode of the optocoupler close. As a result of this, the phototransistor of the optocoupler also closes and stops shunting the zener diode VD1. But the transistor VT1 cannot immediately open, since its gate capacitance is discharged. This capacitance (about 1 nF) is charged by the current flowing through the resistor R1 (about 1 mA). Within a few microseconds, the voltage between the gate and source of the transistor VT1 rises to the level of 4...5 V, which is necessary to open it. After the opening of the transistor VT1, the diode VD2 closes and the process of energy accumulation described above in the magnetic circuit of the inductor L1 is repeated.

The use of film capacitors C2 and C4 greatly facilitates the pulsed operation of oxide capacitors C1 and C3 and increases the reliability of the device. This is also facilitated by the internal diode of the transistor VT1, which limits the voltage of the reverse polarity pulses on the transistor to a safe level.

The stabilizer is assembled on a universal breadboard with dimensions of 60x25 mm and placed in the basement of the UMZCH chassis. All parts are installed on the board, except for the capacitors. Oxide capacitors C1 and C3 are mounted side by side on the chassis. The terminals of capacitors C2 and C4 are soldered to the terminals of capacitors C1 and C3, respectively.

There are no special requirements for details. Resistors and oxide capacitors can be of any type Capacitors C2 and C4 - K73-17. Zener diodes - any low-power, both domestic and imported. A selection of zener diodes VD3-VD5 set the required output voltage. Transistor VT1 is a powerful field switching transistor with an internal diode, an insulated gate and an induced n type channel, for example, IRF730, IRF830, IRF840. It must have a maximum allowable drain-source voltage of at least 400 V. The transistor is attached to the UMZCH metal chassis through a mica gasket using KPT-8 paste.

Diode VD2 - pulsed with a permissible forward current of at least 1 A and a reverse voltage of at least 400 V. for example, FR207, FR307 or domestic KD226G, KD226D. Optocoupler U1 - any transistor collector-emitter with a permissible voltage of at least 20 V, for example, 4N32, 4N33, MOS8101, MOS8102, PC817, AOT128A, AOT128B. The inductor L1 is wound with PEL wire with a diameter of 0,46 mm until the frame of the magnetic core of size Sh5x5 is filled from ferrite 2000NM1. It is assembled with a gap of two layers of writing paper. The throttle is impregnated with paraffin.

The stabilizer does not require adjustment. Its pulses can be monitored with an oscilloscope on resistor R2. If the stabilizer does not enter the pulsed mode, it is necessary to turn on a capacitor between the gate and the source of the transistor VT1, the capacitance of which (several nanofarads) is selected experimentally. By selecting this capacitor, you can, if necessary, change the frequency of the pulses.

The stabilizer is used to power a stereo amplifier with single-ended output stages based on 6PZS beam tetrodes. The current consumed by the amplifier does not exceed 150 mA.

Author: K. Moroz

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