In Amateur radio the literature repeatedly it was suggested the need for the power from USC stable source power to provide a more natural it will sound. Indeed, when maximum output power amplifier ripple voltage unstabilized the source can achieve a few volts. Thus the supply voltage can significantly reduced through the discharge the filter capacitors. It quietly at peak the values of the output voltage higher sound frequencies, thanks sufficient capacity filter capacitors, but impact in the amplification low-frequency components great level, as in musical signal they have a long duration. In the result of the filtering capacitors have time be discharged, reduced the power supply voltage, and hence maximum output the power amplifier. If the reduced voltage leads to the decrease of the current rest of the output stage amplifier, this can lead to the emergence of additional nonlinear distortion.
Another hand, the use of stable source power, built in the usual scheme parametric stabilizer, increases consumed from the network power and requires the mains transformer the greater mass and dimensions. In addition, there the need to " drain heat dissipated output the transistors of the stabilizer. Often the power power dissipation output the transistors of USC equal to power dissipated output transistors stabilizer, i.e. half power is wasted. The switching regulator voltage high-efficiency, but quite complex in manufacture, have a great the high-frequency interference level and not always reliable.
If power supply not required stringent requirements for stability of voltage and the level of ripple, as the power source can to use the normal a bipolar power supply, schematic diagram of which is shown in Fig1.
Powerful the composite transistor VT7 and VT8, included as an emitter repeaters provide good enough filtering ripple voltage with network frequency and stabilization output voltage because of installed circuit bases of the transistors the Zener diodes VD5 - VD10. Elements LI, L2, R16, R17, C11, C12 eliminate the possibility of high-frequency generation, the tendency to which due to the large gain current composite the transistors. Value AC voltage, coming from the network the transformer is selected such that to a maximum the output power of USC (which corresponds to a current in the load 4A), the voltage on the capacitors filter C1 - C8 decreased approximately 46...45 V. In this if the voltage drop across transistor VT7, VT8 will not be to exceed 4, and dissipated the power transistors is 16 watts. When reducing of the power consumed by power source, increases drop the voltage at the transistor VT7, VT8, but dissipated in them power remains constant due to the reduction of consumed current. The power supply works as a voltage regulator with small and medium-load currents, and at a maximum current as transistor filter. In this mode output voltage may be reduced to 42...41, the level of ripple on the output reaches a value of 200 mV, the efficiency equal to 90 %.
As showed mock-UPS, fuses not can protect the amplifier and the power supply from over - current due to its inertia. For this reason, it has been applied the quick-release device protection against short circuit and the overcurrent load collected on a transistors VT1-VT6. And protection function in case of overload positive polarity perform the transistors VT1, VT2, VT5, resistors Rl, R3, R5. R7 - R9, R13 and capacitor C9, and a negative transistors VT4, VT3, VT6, resistors R2, R4, R6, R10 - R12, R14 and the capacitor C10.
Consider the operation of the device when the positive overload the polarity. In the original condition at rated load all transistors protection devices are closed. When the increase of the load current begins to grow fall the voltage across the resistor R7, and if it exceeds the allowable the value starts to open transistor VT1, and after him and transistors VT2 and VT5. Last reduce the voltage on the base regulating transistor VT7, and hence, the output voltage the power supply unit. Thus at the expense of positive feedback provided by resistor R13, reducing the voltage on the output of the power supply leads to accelerate further opening of transistors VT1, VT2, VT5 and quick closing transistor VT7. If the resistance of the resistor positive feedback R13 is small, after activation device voltage protection at the output of the supply is not recover even after disconnecting the load. In this the regime would need to provide a launch button, breaking, for example, a short time resistor R13 after tripping and the moment of switching unit power. However, if the resistance of the resistor R13 choose such that when short circuit load the current was not equal to zero, the voltage at the output of the block power will be to recover from the unit operates protection current reduction load to a safe value. Almost the resistance of the resistor R13 select a value at which provides reliable the unit is switched on supply with current limiting short-circuit value 0,1...0,5 A. the Current response security device determines the resistor R7.Similarly works the protection device block power in case of overload negative polarity.
Design and details
All the details of the block food placed on one Board. With the exception of the transistor VT7, VT8 block Titania posted on separate sinks with the size of the scattering the surface of 300 cm2 each. Coils LI, L2 power supply (Fig. 3) contain 30-40 turns of wire Sew-1 1,0, wound on the body resistor C5-5 or MLT-2. Resistors R7, R12 PSU are cut copper wire PEL, sew-1 or Pelsho diameter of 0.33 and a length of 150 mm, wound on the body resistor MLT-1. Transformer food is made on the toroidal magnetic circuit of electrical steel A, thickness 0.35 mm, width tape 40 mm, inner diameter magneto-wire 80, outer - 130 mm grid winding contains 700 turns of wire PELSHO of 0.47, secondary - G turns of wire PELSHO 1,2.
Each of transistors can KTH replace composite transistors CTG, CTG, and CTA - composite transistors CTG, CTG. Instead of Zener XA you can use connected in series Zener DA (B, C, D, E) and CSA.
Check the health of the PSU
For this purpose, replacing the resistors R7, R12 power supply more high resistance (about 0,3 0,2... Ohm), check the functionality of the unit power protection devices. It must operate at a current load 1...2 A. Sure normal operation of the unit power and USC set resistors R7, R12 rated resistance specified on the concept controlling the lack of the unit operates protection.
Literature
1. Lexine
Valentin and Victor. About visibility
nonlinear distortion
the power amplifier.- Radio, 1984,
No. 2, p. 33-35.
2. Solntsev Y. What Kg
let's say? Radio,1985, No. 2,pp. 26 - 28.
3. Solntsev Y.
High quality amplifier
power.- Radio, 1984, No. 5, p,
29-34.
4. Gumala E. Quality and
the circuitry of USC.- Radio, 1985,
No. 9, p. 31-34.
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