Simple laboratory power unit

Once rather powerful and reliable source of a food with target tension regulated largely was necessary for the author of this article. Having studied available literature, he came to a conclusion that devices offered for repetition have shortcomings: at linear stabilizers big dimensions (because of need of use of oksidny high-capacity condensers and heat-conducting paths), at ShIM of stabilizers the range of regulation is quite narrow and at target tension there are high-frequency pulsations, and devices with the improved consumer qualities (restriction on a current, indication of modes, switching of windings of the transformer etc.) are rather difficult. It was necessary to look for other decisions and as a result the power supply, free from the called shortcomings was developed.

In the offered laboratory power supply is applied by p two-level transformation of the straightened tension: ShIM transformation to intermediate tension and subsequent linear stabilization. Main technical characteristics of the device following: limits of regulation of target tension - from 1,3 to 30 In, factor of instability on tension - 0,07 % / In, instability on a current of loading of 0,1 %, the maximum entrance (variable) tension - 27 In, transformation efficiency at the maximum current of loading - not less than 70 %. Possibility of change of a threshold of restriction of a current to 1,2 is provided And, there is not trigger protection against short circuit with light indication. The source differs small dimensions, the minimum thermal losses (at a loading current to 0,3 And heat-conducting paths are not required). the Block diagram of the device is shown to p by

on fig. 1. Entrance tension of Uвх is transformed ShIM-preobrazovatelem by DA1 to intermediate Uпр which, in turn, is entrance for the analog DA2 stabilizer. Feedback through the differential DA3 amplifier supports power failure necessary for DA2 (for LM317 - 2,5 In) thanks to what thermal losses on DA2 are minimum.

the Schematic diagram of the power supply is represented by p on fig. 2. The straightened tension from an exit of Bridge VD1 smoothes out the C1 condenser and moves on an entrance of ShIM of the converter assembled on the elements DA1, VT2, VD2, L1. The circuit of inclusion of DA1 - standard lowering [1]. Application of chip КР1156ЕУ5 minimized number of passive elements, but imposed restriction on the maximum entrance tension which in such inclusion should not exceed 40 Century of ShIM by means of an accumulative throttle of L1 and the VD2 diode forms intermediate tension of Uпр on the C4 condenser.

On the microcircuit DA2 stabilizer is accurate a linear regulator of tension. Regulate it the variable R12 resistor. VD3 and VD4 diodes protect a chip from return currents and negative tension and are entered according to recommendations about its application [2].

of OU DA3 and R7-R10 resistors form p the differential amplifier who is watching power failure on the DA2 stabilizer. The factor of strengthening of DA3 is chosen equal 1,5 that allows to support the established value in all interval of tension and currents, including at short circuit of an exit. The tuning R2 resistor regulate power failure at adjustment.

On the elements VT1, HL1, R1 is executed by p a signaling device of a short-circuited condition of an exit. In a normal mode the VT1 transistor is open, and power failure on it does not exceed the several tenth shares of volt. At a voltage reduction on a source exit to 0,7 In and less the VT1 transistor is closed and the light-emitting diode of HL1 starts to be shone. About the included condition of the power supply HL2 light-emitting diode signals.

is Very interesting to p a R5 resistor role. At tension on it more than 120 мВ (the average value defined by practical consideration) comes into effect the internal limiter of width of impulses of a chip of DA1, turning it into a current source. This Kr1156eu5 property can use for restriction of the maximum current of loading. So, for example, at the resistance of this resistor equal 0,1 Ohm, the source is capable to give out in loading a current to 1,2 And, and at R5 = 1 Ohm - only to 120 мА. Having established the resistor resistance of 0,5 Ohm and having limited to that a loading current value 240 мА, it is possible to refuse a heat-conducting path for a chip of DA2 and from external that key of ShIM of the converter (having excluded the VT2 transistor, the R3 resistor and having connected a conclusion of 2 DA1 to a point of connection of a throttle of L1 and the VD2 diode). In this case dimensions of a product will be not much more match a box.

as a key of VT2 can apply any transistor with static factor of transfer of a current of base more than 30 and an admissible current of a collector not less than 3 A.Avtor used КТ805АМ. It has quite good frequency properties therefore losses when switching are small. Very well "conducts" itself on this place the field IRF3205 transistor - the heat-conducting path is not necessary to it at a current to 1 And.

Inductance of a throttle of L1 can be any from 40 to 600 мкГн, the unique requirement - it should be calculated on not less than 1,5 A.Rezistory's current - MLT, C1-4 with a resistance permissible deviation from face value ±10 in %, the tuning R2 resistor - multiturnaround wire SP5-2VB or similar, variable R12 - any type resistance 4,7... 6,8 kiloohms. Condensers C1 and С4 - oksidny K50-35 in capacity 220... 470 мкФ with rated voltage 63 In, the others - ceramic (KD2, K10-7, K10-17it. item) .

Adjustment of the power supply is reduced by p to installation by the tuning R2 resistor of tension 2,5 In between conclusions of 2 and 3 DA2 (at 50 percent loading).

Sources

1. of Unsociable persons of S.Preobrazovateli of tension on chip КР1156ЕУ5. - Radio, 2001, No. 11,0.38,39,42.
2. Integrated chips: chips for linear power supplies and an ikhprimeneniye. - M: Dodeka, 1996.

Author: Village MURALEV, Dimitrovgrad Ulyanovsk Region