The power unit with protection against KZ

This circuit represents the elementary power unit on the transistors, equipped with protection against short circuit (KZ). Its circuit is presented in drawing.

Key parameters:

• Target tension - 0. 12В;
• the Maximum target current - 400 мА.

the Circuit works with li as follows. Entrance tension of a network 220В will be transformed by the transformer in 16-17B, then becomes straight VD1-VD4 diodes. The filtration of pulsations of the straightened tension is carried out by the C1 condenser. Further the straightened tension arrives on a stabilitron of VD5 which stabilizes tension on the conclusions to 12В. The rest of tension is extinguished on the R2 resistor. Further tension adjustment by the variable R3 resistor to demanded level in limits 0-12В is carried out. Then the amplifier of a current on VT2 and VT3 transistors which strengthens a current to level 400 мА follows. As load of the amplifier of a current the R5 resistor serves. The C2 condenser in addition filters pulsations of target tension.

Protection works with p so. In the absence of KZ on an exit tension on conclusions of VT1 is close to zero and the transistor is closed. The chain of R1-VD1 provides shift on its base at level 0,4-0,7 In (power failure on open p-n diode transition). It is enough this shift for transistor opening at a certain level of tension a collector emitter. As soon as on an exit there is a short circuit, tension the kolektor-emitter becomes excellent from zero and equal to tension on a block exit. The VT1 transistor opens, and resistance of its collector transition becomes close to zero, and, means, and on a stabilitron. Thus, on the amplifier of a current zero entrance tension arrives, via transistors VT2, VT3 very small current will proceed, and they will not fail. Protection is disconnected at once at KZ elimination.

of the Detail.

the Transformer can be any with the area of section of the core of 4 cm ² and more. Primary winding contains 2200 rounds of wire PEV-0,18, secondary - 150-170 rounds of wire PEV-0,45. The ready transformer of a vertical sweep from old lamp TVs of the Tvk110l2 series or similar will approach also. VD1-VD4 diodes can be D302-D305, D229Zh-D229L or any on a current not less than 1 And and return tension not less than 55 V.Tranzistory VT1, VT2 can be any low-frequency low-power, for example, MP39-MP42. It is possible to use and silicon more modern transistors, for example, КТ361, Kt203, КТ209, КТ503, КТ3107 and others. As VT3 - germanic P213-P215 or more modern silicon powerful low-frequency КТ814, КТ816, КТ818 and others. At replacement of VT1 it can appear that protection against KZ does not work. Then it is necessary to turn on consistently with VD5 one more diode (or two if it is required). If VT1 is silicon, and diodes are better for applying silicon, for example, КД209 (A-in).

in summary should be noticed

that instead of p-n-p of transistors specified on the circuit it is possible to apply and similar n-p-n transistors on parameters (not instead of any of VT1-VT3, and instead of all from them). Then it will be necessary to change polarity of turning on of diodes, a stabilitron, condensers, the diode bridge. On an exit, respectively, polarity of tension will be another.

/>/>!>