Voltage stabilizer on a powerful field-effect transistor. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Voltage stabilizer on a powerful field-effect transistor. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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When building high-current voltage stabilizers, radio amateurs usually use specialized 142 series microcircuits and similar ones, "enhanced" by one or more bipolar transistors connected in parallel. If for these purposes a powerful switching field-effect transistor is used, then it will be possible to assemble a simpler high-current stabilizer.

A diagram of one of the options for such a stabilizer is shown in Fig. 3.28.a. From the secondary winding of the transformer, an alternating voltage of about 13 V (effective value) is supplied to the rectifier and smoothing filter. On the filter capacitors, it is equal to 16 V. This voltage is supplied to the drain of a powerful transistor VT1 and through the resistor R1 to the gate, opening the transistor.

Part of the output voltage through the divider R2, R3 is fed to the input of the DA1 chip, closing the OOS circuit. The voltage at the output of the stabilizer increases until the voltage at the control input of the DA1 microcircuit reaches the threshold, about 2,5 V. At this moment, the microcircuit opens, lowering the voltage at the gate of a powerful transistor, i.e. partially closing it, and thus the device enters stabilization mode. The best results can be obtained if the VD2 diode is connected to a rectifier bridge (Fig. 3.28.b). In this case, the voltage across the capacitor C5 will increase, since the voltage drop across the VD2 diode will be less than the voltage drop across the bridge diodes, especially at maximum current.

(click to enlarge)

If it is necessary to smoothly adjust the output voltage, the constant resistor R2 should be replaced with a variable or trimming resistor.

In the stabilizer, a powerful field-effect transistor IRLR2905 is used as a regulating element. Although it is designed to operate in a key (switching) mode, in this stabilizer it is used in a linear mode. The transistor has a very low channel resistance in the open state (0,027 Ohm), provides a current of up to 30 A at a case temperature of up to 100 ° C, has a high steepness and requires only 2,5 ... 3 V to control the gate voltage. Power dissipated transistor, can reach XNUMX watts.

The field-effect transistor is controlled by a parallel voltage regulator chip KR142EN19 (import analogue of TL431). Capacitors - small-sized tantalum, resistors - MLT, C2-33, diode VD2 - rectifier with a low voltage drop (germanium, Schottky diode). The parameters of the transformer, diode bridge and capacitor O are selected based on the required output voltage and current. Although the transistor is designed for high currents and high power dissipation, to realize its full potential, it is necessary to ensure efficient heat dissipation.

Establishing a stabilizer comes down to setting the required value of the output voltage. It is necessary to check the device for the absence of self-excitation in the entire range of operating currents. For this, the voltages at various points of the device are monitored using an oscilloscope. If self-excitation occurs, then in parallel with capacitors C1, C2 and C4, ceramic capacitors with a capacity of 0,1 μF with leads of a minimum length should be connected. These capacitors are placed as close as possible to the transistor VT1 and the DA1 chip.

The printed circuit board of the device is shown in fig. 3.29. This board is designed for the installation of small-sized parts in surface-mounted packages, including the KR142ESh9 chip that needs to be replaced with an imported analogue in the SO-8 package.

(click to enlarge)

If the field-effect transistor could not be found, the stabilizer can be made according to a different scheme (Fig. 3.30), on powerful bipolar transistors, using the same microcircuit. True, the maximum load current for this version of the stabilizer is not more than 3 ... 4 A. To increase the stabilization coefficient, a current stabilizer on a field-effect transistor is used, and a powerful composite transistor is used as a control element. The transformer must provide a voltage of at least 15 V on the secondary winding at the maximum load current.

Author: Semyan A.P.

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Comments on the article:

Sasha
Replaced with irfz44n! Polevik burns out when connecting a 40-watt light bulb!

amateur
The resistance of a cold lamp is 10 times less than that of a heated one. Therefore, a 40 W lamp at the first moment is equivalent to a 400 W load! And there is no overload protection in this circuit, so the transistor burns out. Without the introduction of such protection, the scheme is impractical.

Aprol
I put a field worker 40N03P, but it was not possible to get more than 6V. 17V comes from the bridge, for 1 leg TL431-2,5B. TL changed and nothing. So I did not understand anything. Polevik changed to FDP7030L - the same thing.

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