Low voltage voltage stabilizer. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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In the stationary operation of high-quality equipment, CDs and audio players, there are problems with power supplies. Most power supplies mass-produced by a domestic manufacturer, (to be precise) almost all cannot satisfy the consumer, as they contain simplified circuits. If we talk about imported Chinese and similar power supplies, then they generally represent an interesting set of "buy and throw" parts. These and many other problems force radio amateurs to manufacture their own power supplies. But even at this stage, amateurs are faced with the problem of choice: there are many schemes published, but not all work well.

This circuit is presented as a variant of the non-traditional inclusion of an operational amplifier, previously published in [1] and soon forgotten. It differs from previously published ones in the extreme simplicity of the circuit, the use of non-deficient radio components, ease of setup and improved performance. With an output voltage of 3 V, the circuit (Fig. 1) provides a current in the load from 0 to 0,5 A, a stabilization factor of approximately 1500, a short circuit current of 0,85 A.

When the stabilizer is operating, the total current of the op-amp and the transistor flowing through R2 causes a voltage drop on it applied to the base of the regulating transistor VT1, and thereby ensures the operation of the stabilizer. A resistor is connected to the output of the op-amp DA1, which is a load resistance, approximately equal to Rh.mhh \u300d 1 Ohms, although DA1 also works at lower resistances. The non-inverting input DA1 is energized from a parametric stabilizer assembled on HL3 and R1, also powered from a stabilized voltage, which generally reduces the level of output voltage ripple, i.e. improves the performance of the stabilizer. The inverting input DA4 is connected to the output voltage divider of the stabilizer RXNUMX.

Transistor VT1 must be installed on a radiator to remove heat, the area of ​​\u1b\u837bwhich can be calculated based on the type of transistor and dissipation power. For example, for VT1,5 type KTXNUMX Pmax = XNUMX V. The power dissipation of the transistor is maximum in this circuit.

From the reference book we find the thermal resistance of the junction-housing Rthjc = 3,33 °C / W, the maximum allowable junction temperature TJMaKC = 125 °C.

We accept the maximum temperature of the atmosphere (environment) Ta.max=50°C. We calculate the thermal resistance Rtherm \u1d "P" max - Ta.max / Pmax / T125 \u50d \u1,5d 75 ° С - XNUMX ° С / XNUMX W \uXNUMXd XNUMX ° С / W.

We determine the thermal resistance of the cooling surface Ratherm = Rtherm - Rthjc = 75 - 3,33 = 71,67 °C/W, the required area of ​​the cooling surface (radiator) S = 1 / a Ratherm = 1/1,5 mW/(°C cm2 )0,07167°С/mW=10 cm2, where a - 1,5 mW / (°С cm2) - heat exchange constant for still air.

Details. As an op-amp, you can use any one that operates at ip = 2 ... 3 V, with a corresponding change in the circuit. I propose to use a widespread, non-deficient and inexpensive op-amp such as K157UD2, K157UDZ, in the case of which there are two op-amps that work normally at upit \u3d 2 V. An unused op-amp can be cut off to reduce the dimensions of the microcircuit case, as shown in Fig. 5, a. Bite off the 10th - 6th conclusions from the microcircuit, then carefully clamp the part of the op-amp housing with the cut-off conclusions in a vise at the level of the 9th - 5th conclusions and cut with a hacksaw blade exactly along the 10th - 2,6th conclusions. As a result, the new op-amp will have the pin numbering according to Fig. 1. At the same time, the above operation does not affect the operation and parameters of the OS in any way. The parametric stabilizer HL3 and R3 is not critical to the brand of the LED and the resistor R2. At a current of 10-1,5 mA, the stabilization voltage is within 2-XNUMX V.

Transistor VT1 can be replaced with KT814, KT816, KT818. Transformer T1 - of any appropriate power, providing a voltage at the input of the diode bridge VD1 of about 5,6-6 V, with a maximum load current of 0,5 A. The diode bridge VD1 can be replaced with diodes of the type KD208A, KD212 or similar, as well as at lower load currents KTS407A (1max = 300 mA), which is important for miniaturization.

Capacitor C1 is any with the appropriate voltage. It should also be borne in mind that the voltage on it in idle mode increases. At lower load currents, its capacitance can be reduced accordingly, as well as the overall power T1.

The printed circuit board of the stabilizer on the op-amp is shown in Fig. 3.

Establishment of a properly assembled stabilizer from serviceable parts consists in adjusting R4 (11out = 3 V) and checking the input voltage when connecting the equivalent load of the stabilizer: two 2 Ohm MLT-12 resistors connected in parallel, which should be within 6 V. Resistor R3 is selected for the nominal current used LED HL1. It is advisable not to reduce the capacitance of the capacitor C2, since some instances of the op-amp can be excited. Better to have it a little bigger. Without much effort, the stabilizer can produce 6; 9 and 12 V, you only need to increase the resistance of the resistors R3 and R4, respectively, as well as the operating voltage of the capacitor C4.

You can also assemble this stabilizer: with smooth adjustment in the range, for example: 11min \u3d 11 V, 12max \u4d 0,5 V, using instead of R1 a variable resistor with a handle and the simplest j graduated scale in increments of 4 or 16 V. R4 J brand SPZ- 0 b a board was developed for it. ; At the same time, in series with R11, turn on two I resistors, by selecting the values ​​​​of which, set 4min and 1max in the extreme positions of RXNUMX. At high load currents, a composite transistor can be used instead of VTXNUMX.

Literature

1. Shityakov A, Morozov M., Kuznetsov Yu. Voltage stabilizer at the OS // Radio.-1986.- No. 9.

Author: A.L. Danilchuk, Novograd-Volynsky, Zhytomyr region

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