Transformerless high power power supply for an amateur transmitter. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The tempting idea of ​​getting rid of the large and very heavy power transformer in the transmitter power amplifier power supply has long puzzled radio amateurs. Especially, this idea is attractive for the participants of radio expeditions, where every extra kilogram of equipment mass is felt as "its own hump".

In various amateur radio publications of past years, designs of transformerless power supplies were published. But these, as a rule, were relatively low-power devices, designed to power transmitters with a power of 100 ... 400 W, and in addition, they required protection against "incorrect" plugging of the power plug into the socket.

The use of modern small-sized electrolytic capacitors makes it possible to design and manufacture a powerful high-voltage power supply unit of small size and weight. The proposed version of the power supply is designed for a power amplifier on a GU-43B lamp, connected according to the common cathode circuit with an output power of 1,5 kW (supply - 3 kW). Using the inclusion of a lamp according to the scheme with a common cathode, with this power supply scheme, the input signal to the control grid is supplied through an RF transformer, and nothing else.

If, however, a signal is simply applied through a capacitor, then due to the fact that the output circuit of the driver is galvanically connected to its case, an alternating component of the mains supply of 50 Hz will fall on the grid. In addition, this will lead to a disruption in the operation of the power amplifier. But in a common grid circuit, where the control grid is connected to the cathode, this problem does not arise. Some features of the circuit diagram of such a power amplifier with a transformerless supply are shown in Fig. 6.5.

The above method of switching on does not require additional protection against "incorrect" connection to the network (accidental rotation of the power plug, when "phase" and "zero" can be mixed up), because. there is no galvanic connection of the power circuits with the case (it is unacceptable in full-wave multipliers!). However, it should be reminded once again that this power supply generates high voltage, life-threatening.

According to safety regulations, the radio station housing must be securely connected to a good ground. For personal safety and the safety of others, work on high-voltage power supplies must be done with great care and should only be carried out by experienced and trained radio amateurs. This power supply is a transformerless tenfold voltage multiplier-rectifier.

With an AC supply voltage of 230 V, the constant output voltage is 32...40 V without load and 3000 V at a load of 1 A. The power consumed by the load is 3 kW. When testing, a set of powerful resistors with a total resistance of 3 kΩ and a total power of 3 kW was used as a load. This power can be consumed from the power supply for quite a long time without fear of overheating of its parts (for example, to work in FM mode). When operating in SSB or CW mode, the supply voltage drawdown has a significantly lower value and depends on the peak factor of the SSB signal or the duty cycle of the telegraph packets. The total mass of the power supply unit is 5,8 kg, which is much less than the mass of a similar transformer unit.

The multiplier circuit is symmetrical, full-wave (Fig. 6.6).

Each arm provides a fivefold multiplication of the mains voltage. To avoid trouble, the operating voltage of the capacitors used must be chosen with sufficient margin. Each capacitor, except for C1 and C1 ', consists of six capacitors in series-parallel connection, shunted with resistors (Fig. 6.7).

All capacitors that make up the combined capacitance are 470 microfarads each. Shunt resistors are used two-watt, 220 kOhm each. Rectifier diodes are designed for a reverse voltage of at least 800 V and an operating current of at least 7 A.

Turning on the power supply (see Fig. 6.6) is performed in two stages. First, the mains voltage is supplied through a limiting 50-watt resistor of 200 Ohm, then, after 5 ... 10 seconds, it is closed by the contacts of relay K1.1 either manual switches or toggle switches. Turning on the relay provides a simple self-locking circuit that creates the necessary delay (not shown in the diagram). Switching off can be done in reverse order or immediately. The mains voltage is supplied through a fuse or circuit breaker for a trip current of 15 A. To protect against some unforeseen circumstances, for example, an internal breakdown of a lamp, etc., high-voltage fuses for 2 A are installed between the power supply and the load and limiting fuses are constantly on 50-watt resistors of 20 ... 30 ohms.

All capacitors, except for C1 and C1 ', diodes and shunt resistors are placed on two printed circuit boards made of foil fiberglass, 2 mm thick. Moreover, each arm of the multiplier is assembled on a separate board. On fig. 6.8 shows one of the boards, on the other, the same board, there is a reverse polarity of capacitors and diodes.

The size of each board is 240x170 mm. The conductive tracks on the boards are duplicated (soldered) with a thick stranded wire. Electrolytic capacitors, from which C2...C5 (C2'...C5') are assembled, are used at 470 uF, 400 V. They have an outer diameter of 35 mm and a height of 50 mm. The boards are interconnected using ceramic racks, mounted inside. On the chassis of the amplifier, the capacitor unit is mounted on an insulating plate made of thick PTFE.

Capacitors C1 and C1' 3300 uF, 400 V must be well insulated from the case and installed separately. (Remember that you are dealing with a high voltage of 3000 V - good insulation is paramount here!). In power amplifiers, galvanic coupling of the supply circuits and the case is strictly not allowed.

Author: Semyan A.P.

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