Laboratory transformer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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The described design can serve as an alternative to laboratory autotransformers (LATRs), which are widely used in amateur radio practice. In addition, this device has an undeniable advantage - there is no galvanic connection of the output voltage with the network. The use of a laboratory transformer increases electrical safety when supplying and setting up transformerless devices.

The laboratory transformer is designed to step change the output voltage.

Basic device parameters

• Input voltage, V.....20
• High-voltage output voltage, V.....111...269
• Number of voltage steps.....30
• Load power, VA.....72
• Load current, A, not more than ..... 0,42
• Low-voltage output voltage, V.....5...65
• Dimensions, mm.....240x150x140
• Weight, kg.....6,5

Laboratory transformer (Fig. 1) consists of transformers T1, T2, output voltage switches SA1-SA7 and auxiliary elements. Transformers used are unified TPP281-127 / 220-50: T1 is turned down, and T2 is turned up. Accordingly, the primary winding of the transformer T1 is connected to the network, T2 - to the output of the device. Switches SA1-SA3 and SA5-SA7 switch their primary windings, switch SA4 - secondary transformer T1. The output voltage values ​​of adjacent steps differ by 2...8%. In the initial position of the switches SA1-SA7, shown in the diagram, the output voltage is equal to the input.

Sockets XS1, XS2 form a low-voltage switching block. The voltage at its contacts within 5 ... 65 V is changed by switches SA1-SA4: between contacts 2XS1, 2XS2 - in the range of 5 ... 10 V; on socket XS1 - 8 ... 15 V; between contacts 1ХS1, 2ХS2 - 13...25 V; on socket XS2 - 20 ... 40 V; and between the contacts 1XS1, 1XS2 - 33 ... 65 V. The load current of the low-voltage output is not more than 1,1 A. The number of voltage steps is 80. The laboratory transformer provides a higher accuracy of setting a small voltage value at the low-voltage output compared to the LATR autotransformer .

The device is assembled in a metal case. Holes for ventilation are made in the base and walls of the case. The designations on the front panel (Fig. 2) explain the control of the laboratory transformer and contain some of its parameters. Above each switch is indicated the transformation ratio switched by it. For example, if only switch SA3 is on (marked "(0,95"), this means that the device's transformation ratio is 0,95; accordingly, the output voltage is 209 V.

The long axes of symmetry of the sockets RD-1 low-voltage switch are parallel and located at an angle of 60 o to the horizontal. The distance between the centers of the mounting holes of the sockets is 19 mm. The centers of the upper contact of the left socket (1XS1), the upper contact of the right socket (1XS2) and its lower contact (2XS2) form the vertices of an imaginary equilateral triangle with a side of 19 mm - this is the distance between the contacts of a standard power plug. The low-voltage switch block provides five different plug connection options.

Depending on the required power of the laboratory transformer and the parameters of the low-voltage output, unified CCI transformers with a power of 1,65 ... For home-made transformers, a Sh207x127 magnetic circuit is used. Switches SA1-SA2 - microtoggle switches MT-25 or similar. The dual microtumbler MT-32 cannot be used when its two sections are connected in parallel. The non-synchronization of the operation of the sections will lead to the closure of the switched part of the winding at the moment of switching, therefore the permissible current of one section of the microtumbler (1 A) must be at least the current of the intermediate windings. The device can also use transformers TA, TN, TAN, having the designation "7/" [1]. Switching only the network windings of transformers CCI and TN provides 2 output voltage steps, TA - 3, TAN - 127. All CCI transformers allow switching of windings connected in a series intermediate circuit. Approximately 1% of TA transformers and 29% of VT transformers have groups of secondary windings designed for the same current values, and also allow them to be switched.

Literature

1. Sidorov IN et al. Small-sized transformers and chokes. - M.: Radio and communication, 1985, p. 32 - 109, 115 - 121.
2. unified transformers. - Radio, 1982, No. 1, p. 59, 60.

Author: A. Trifonov, St. Petersburg

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