Network Krona, 9 volts 0,03 amperes. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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To power transistor receivers from the mains, attachments are usually used, consisting of a step-down transformer and a rectifier with a voltage stabilizer. However, using them as a separate structure is not always convenient. For portable receivers, you can make such a prefix (Fig. 1.30), which will fit in the power compartment.
The prefix is designed to power pocket radios or other devices that use the Krona battery from a 220 V network. The output voltage of the prefix is 9 V, the maximum load current is 30 mA. At a load current of up to 25 mA, the voltage is unchanged, and at a current of 30 mA it drops to 7 V.
(click to enlarge)
The prefix is insensitive to short circuits in the load (short circuit current 35 mA). The main parts of the console are a transformerless rectifier on diodes VD6 ... VD9 with quenching resistors R3 ... R7, a voltage converter (VT1, VT2 and T1) and a rectifier on diodes VD2, VD3 with a parametric stabilizer. The alternating voltage of the network is rectified, the direct voltage is converted into an alternating frequency of increased frequency, and, finally, the latter is rectified again. Due to the presence of a transformer, the input and output of the set-top box are galvanically isolated, and a sufficiently high frequency of the converter allows you to make a transformer, which means. and the entire prefix is small.
One of the circuit features of the set-top box is that the role of the ballast resistance of the output voltage stabilizer is performed by quenching resistors R3 ... R7. It happens in the following way. As the output voltage increases, the current flowing through the zener diode VD1 increases, causing an increase in the current drawn by the converter. In this case, the voltage on the quenching resistors increases, the supply voltage of the converter drops, reducing the output voltage. The stabilization coefficient of such a stabilizer is very high (about 1000 at a load current of up to 20 mA). Zener diodes VD4 and VD5 do not take part in the operation of the set-top box and are only needed to limit the voltage on the converter and on diodes D6 ... D9 in the event of a generation failure.
Transformer T1 is wound on a ring core made of ferrite 700NM (size K20x10x5). Windings 1-2 and 2-3 contain 85 turns each, 4-5 and 9-10 - 25 turns each, 6-7 and 7-8 - 100 turns of PEV-2 0,2 wire each. As VD1, you can use any zener diode with a stabilization voltage of 8 ... 10 V. Instead of D9V diodes, you can use any diodes of the VD9 series (except D9B), KD102, KD103. In the console, you can use transistors KT312B, KT315 with any letter index, KT342A ... KT342G. Zener diode KS156A can be replaced with D814A. Establishing the attachment comes down to the correct connection of the transformer windings and the selection of the resistor R1, at which the current of the zener diode VD1 is maximum.
Author: Semyan A.P.
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