Power unit for portable teleradio equipment


 The power unit, is intended for a feed of portable teleradio equipment. Its nominal target capacity: 20 W, and efficiency at rated power - not less than 85 %. Working frequency of transformation - 68 kHz.

Characteristics of the block are optimized for the loading laying within the limits of 0,5...1 from rated power. It steadily works at change of mains voltage in limits from 170 up to 240 In, maintains short-term short circuits of an output (the current of short circuit measured 02><5B@>< 7-35, it is equal 6 ).



Fig. 1. A power unit for portable teleradio equipment.  The circuit


  The basic circuit of the block is represented on fig. 1. The specifying generator of the inverter is collected on the operational amplifier DA1 covered with a circuit of positive OS. As loading # the primary winding of pulse transformer T1 serves. Differentiating circuit R7C6 creates the forced front of switching of transistors VT2 and VT4.

The unit providing acceleration of process @0AA0AK20=8O not of the basic carriers of a charge in these transistors, will consist of elements VT1, VT3, VD8, VD9, R8. R9, !7-!10 and additional windings III, IV transformer T2. We shall consider work of unit by the example of the top shoulder under the circuit floor - bridge  the inverter.

Let transistor VT2 is open and sated. Thus transistor VT1 is closed and the voltage is enclosed to it about 6 In from a winding of III transformer T2. Condenser S9 is charged.
Upon termination of a half-cycle of switching polarity of a voltage on an output of the specifying generator and, hence, on all windings of transformer T1 in steps varies; LI ¦ - a voltage on a primary winding of transformer T1. Transistor VT1 opens, and due to differentiating circuit R8C7 this process occurs accelerated.
Under influence of a total voltage with windings of III transformer T2 and II transformer T1 begins forced @0AA0AK20=85 not the basic carriers of a charge from base of transistor VT2 on a circuit: a winding of III transformer T2, collector transition of transistor VT1, a winding of II transformer T1, the emitter  transition of transistor VT2, diode VD8. Through time tpac sharp reduction of a collector current of transistor VT2 begins. Thus transistor VT4 is in a stage of opening.
The voltage on windings of transformer T2 changes the polarity. The charge which has been saved up by condenser S9, supports a closing current of base of transistor VT3 before its full closing. Since this moment the return voltage on the emitter  transition VT2 decreases up to the value which are not exceeding 1 In, that positively affects reliability of work of the inverter.

As switching, except for specified on the circuit, it is possible to use transistors KT704B, "704, and also any of series "809; suit both others high-voltage low and mid-frequency transistors. Their installation on heat-conducting paths with the effective area of dispersion about 50 sm2 is desirable. Transistors VT1, VT3 - anyone silicon with a maximum permissible pulse current of a collector not less than 500 m and boundary frequency not less than 100 MHz.

:A84=K5 condensers S1, !, !4 - 50-12. 50-27; !11, !12-50-29, 53-25, 53-28; the others - anyone ceramic, glass or glass-ceramic . Condenser S5 should be groups TKE PZZ,  or 47. Resistor R1 - !5-16, the others - ".

Transformer T1 is reeled up on ring magnet -wire  standard size 10E6E4,5 from ferrite 2000. Winding I is executed by wire --2 0,1 and contains 52 coils, windings II and III - on 8 coils of the same wire. Transformer T2 is reeled up also on ring magnet -wire standard size 20E12E6 from ferrite 2000 1. Winding I contains 120 coils of wire --2 0,25, a winding II - 2E12 coils of wire --2 0,8, a winding III and IV-on 5 coils of wire --2 0,25. Throttle L1 is executed on armored magnet -wire (5E5 from ferrite 700. The winding contains 50 coils of wire --2 0,8. Between half magnet -wire throttle it is necessary to enclose a lining from a dense paper thickness of 0,3 mm.

Dimensional capacity of transformer T2 on frequency of transformation 68 kHz is equal 42 W, that allows to increase target capacity of the power supply up to the specified value. For this purpose its winding I, III, IV it is necessary to reel up wire --2 0,41, a winding II, and also a winding of throttle L1 - wire --2 1. Besides it is necessary to increase the area of heat-conducting paths of transistors VT2, VT4 approximately twice, to count capacity of condensers S1, !11, !128 inductance of throttle L1 according to the recommendations stated in [3]; resistance of resistor R7 should be reduced up to 680 Ohm, R1 - up to 10 Ohm.

Thus there can be a need for "amplification" of operational amplifier DA1 by an additional transistor step of amplification of a current, and also for increase in capacity of condensers S2, !1.

The collected design is necessary for placing in shielding box. The author's variant of a design of the block has dimensions 100E63E33 mm that corresponds to specific capacity about 105 W/dm3. At correct installation and serviceable details the source of adjustment does not demand and starts to work at once.


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 Edit. 06.06. V.F.Gajnutdinov

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