Amateur radio power supply 1,5-24 volts 3 amps. Scheme, description

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Amateur radio power supply 1,5-24 volts 3 amps. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Sooner or later, a radio amateur faces the problem of making a universal power supply unit (PSU), which would be useful for "all occasions". That is, it had sufficient power, reliability and a widely adjustable output voltage, besides, it protected the load from "excessive consumption" of current during testing and was not afraid of short circuits.

It is proposed, in the opinion of the author, that the most satisfying these conditions is a fairly simple power supply for repeating, providing a stabilized voltage of 1,5-24 V at an output current of up to 3 A. In addition, it can operate in the current source mode with the ability to smoothly adjust the stabilization current within the limits 10-100mA or fixed currents 0,1A, 1A, 3A.

Rice. 1 (click to enlarge)

Consider the power supply circuit (see Fig. 1). Its basis is the traditional voltage stabilizer circuit, the "heart" is the KR142EN12 microcircuit, which is currently available to a wide range of radio amateurs. A rather powerful unified incandescent transformer TN-56 was chosen as a power transformer, which has four secondary windings with a permissible current of 3,4 A and a voltage of 6,3 V each. Depending on the required output voltage, the SA2 switch connects two, three or four series-connected windings. This is necessary to reduce the power dissipated in the control element, and, consequently, increase the efficiency of the device and facilitate the temperature regime. Indeed, in the most unfavorable mode, with the maximum difference between the input and output voltages (of course, if the output voltage corresponds to the range indicated by the SA2 switch) and the maximum current FOR, the power dissipated on the regulatory element will be: Ppacc.max = (Uvx.max-2Uvd- Uout.min)*Imax (1) Prass.max = (12,6-2*0,7-1,5)*3 = 29,1 W, where Uin.max is the maximum input effective voltage of this range; Uout.min - minimum output voltage of the given range; Uvd is the voltage drop across the rectifier bridge diode. It is easy to check that without dividing the output voltage into ranges, the power dissipated by the regulating element reaches 70 W.

The alternating voltage is rectified by the diode bridge VD1-VD4 and smoothed out on the capacitor C5. Fuse FU2 protects the transformer in case of failure of the rectifier diodes. Transistors VT1, VT2 serve to increase the output current of the PSU and facilitate the operation of the integrated stabilizer DA1.

Resistor R1 sets the current through DA1, opening VT2:

IDA1 \u2d Ubevt1 / R0,7 \u51d 0,014 / 2 \uXNUMXd XNUMX A, (XNUMX)

where Ubevt2 is the opening voltage of the emitter-base of the transistor VT2.

At a current of 14 mA, the DA1 chip can operate without a heatsink. To improve the stability of the output voltage, the regulating voltage is removed from the line of resistors R2-R4 connected to the output of the microcircuit and fed to the "control" output 01 DA1 through the decoupling diode VD6. The output voltage is adjusted by resistors: R4 - "GROUGH" and R3 - "FINE". The current stabilizer is made on DA1, current-setting resistors R5-R9 and a decoupling diode VD7. The choice of the required discrete stabilization current is carried out by the switch SA3. In addition, at the limit of "10-100 mA" it is possible to smoothly adjust the current with resistor R9.

If necessary, you can change the stabilization current by changing the values of the setting resistors using the formula:

R = 1,35/Istab, (3)
where R is the resistance of the current-setting resistor, Ohm; Istab - stabilization current, A. The power of current-setting resistors is determined by the formula:
P = I*I*R, (4)
where I - range stabilization current; R is the resistance of the resistor.

In reality, the power of the current-setting resistors is deliberately increased for reasons of reliability. So the resistor R8 of type C5-16V is selected with a power of 10 watts. In the current stabilization mode (switch SA3 in the "FOR" position), a power of 3,8 watts is dissipated on the resistor. And even if you put a five-watt resistor, then its power load will be 72% of the maximum allowable. Similarly, R7 type C5-16V has a power of 5 W, but MLT-2 can also be used. Resistor R6 type MLT-2, but you can put MLT-1. R9 - wire variable resistor type PPZ-43 with a power of 3 watts. R5 type MLT-1. These resistors should be positioned so that they are cooled in the best possible way and do not, if possible, heat other elements of the circuit, as well as each other. For clarity, the adjustment (set current) on the limb of the resistor R9 makes marks of 10, 20, 50, 75 and 100 mA, using an external milliammeter (tester), connecting it directly to the PSU sockets.

Additional convenience when working with a PSU is provided by a pV voltmeter, which is an M95 type microammeter with a total deviation current of 0,15 mA.

The resistance of the resistor R11 is selected so that the final value of the scale corresponds to a voltage of 30 V. You can also use any other measuring head with a total deviation current of up to 1,5 mA by selecting a current-limiting resistor R11.

As switches SA2, SA3 are used biscuit - type 11P3NMP. To increase the permissible switching current, the equivalent conclusions of the three biscuits are paralleled. The latch is installed depending on the number of positions.

Capacitor C5 is prefabricated and consists of five parallel-connected capacitors of the K50-12 type with a capacity of 2000 uF x 50 V.

Transistor VT1 is installed outside on a radiator with an area of 400 cm2. It can be replaced by KT803A, KT808A, VT2 can be replaced by KT816G. A pair of transistors VT1, VT2 can be replaced with one KT827A, B, C or D. Diodes VD6, VD7 are any, preferably germanium with a lower forward voltage drop and a reverse voltage of at least 30 V. Diodes VD1-VD4 type KD206A, KD202A, B, V or similar mounted on radiators.

When making the TV1 transformer yourself, you can follow the method described in [3]. The overall power of the transformer must be at least 100 W, preferably 120 W. In this case, it will be possible to wind another winding with a voltage of 6,3 V. In this case, another range of 24 - 30 V will be added, which will provide an output voltage regulation range of 3-1,5 V at a load current of 30 A.

Setting up the power supply carried out according to a known method and has no special features. A properly assembled PSU starts working immediately. When working with a PSU, first select the required output voltage range with the SA2 switch, set the required output voltage with the ROUGH and FINE resistors, guided by the readings of the built-in voltmeter. Switch SA3 select the current limit limit and connect the load. It should be noted that for all the simplicity of the circuit, this power supply combines two devices: a voltage regulator plus a current regulator. The PSU is not afraid of short circuits and can even protect the elements of the electronic device connected to it, which is very important when conducting various tests in amateur radio practice.

Literature

1. Nefedov A.V., Aksenov A.I., Elements of circuits for household radio equipment, microcircuits: Handbook.-M: Radio communication, 1993.
2. Akimov N.N., Resistors, capacitors, transformers, chokes, switching devices for REA: Handbook.-Minsk: Belarus, 1994.
3. Semiconductor receiving-amplifying devices: Handbook of a radio amateur / R.M. Tereshchuk, K.M. Tereshchuk.-Kyiv: Naukova Dumka, 1988.

Publication: cxem.net

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