Two voltages from one source. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Two voltages from one source. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Sometimes, to power various radio devices, it is required to have two bipolar voltages of +12 and -12 V (or +9 and -9 V) from one source - a battery or a mains transformer with one winding. Such voltages are necessary for the operation of operational amplifiers and some other circuits. In this case, the main current consumption by the circuit is carried out, as a rule, along a circuit with a positive voltage, and the "-" circuit is auxiliary.

The industry produces a specialized converter chip for obtaining a negative voltage: KR1168EP1 (input voltage 3 ... 10 V, and the output negative is the same value as at the input). But it is not yet widely available, and also covers a narrow voltage range.

Rice. 5.4 (click to enlarge)

On fig. 5.4 shows a diagram of a simple converter that allows you to receive an additional stabilized voltage of -12 V (-9 V when using the KR12EN9A stabilizer) from a +142 V (+8 V) source. The load current in the -12V circuit can be up to 15 mA.

The converter operates at a frequency of 50 kHz and remains operational when the supply voltage drops to 7 V.

Two voltages from one source
Fig. 5.5

Two voltages from one source
Rice. 5.6. The design of the transformer T1

The circuit consists of a self-oscillator on a transistor VT1, a voltage-up transformer T1 and an integrated stabilizer DA1.

When assembling, it is required to observe the polarity of the connection of the phases of the windings of the transformer T1, indicated in the diagram. From the secondary winding of the transformer, the voltage after rectification should be 15 ... 19 V, which is necessary for the normal operation of the DA1 stabilizer.

To configure the converter, first, instead of DA1, we connect a 150 Ohm resistor. During normal operation of the circuit, the voltage shape on winding 3 in transformer T1 is shown in fig. 5.5, When setting up, it may be necessary to select the capacitor C3 and the resistor R2.

Transformer T1 is made on an armored core of size B22 made of ferrite 2000NM (1500NM) and contains 1 - 80 turns, 2 - 15 turns, 3-110 turns of PELSHO-0,18 wire in the winding (Fig. 5.6). After checking and adjusting the circuit, fix the coil and ferrite cups with glue.

Capacitors C2, C4, C5 used type K50-29-63V, C1 and C3 - any small-sized, C6 - K53-1A-20V.

All elements of the circuit are placed on a printed circuit board with dimensions of 65x50 mm (Fig. 5.7). To reduce the height of the board, the installation is made in two levels - capacitors C4 and C5 are located above the elements VT1 and DA1. The circuit allows you to get a higher output voltage than at the input, if you use a negative voltage spike (Fig. 5.5).

If the device you have assembled is stationary and can be powered from the mains, then widely used small-sized transformers (designed in the form of a mains plug) can be used to obtain a bipolar voltage. They have one secondary winding, and in order not to rewind the transformer, it is convenient to use the circuit (Fig. 5.8).

Two voltages from one source
Rice. 5.7. Converter printed circuit board

Two voltages from one source
Fig. 5.8

Publication: cxem.net

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