Interference-resistant power supply. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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This circuit design of the power supply is the result of experimental research aimed at creating an easy-to-configure IP with high efficiency, which has good noise immunity.

As can be seen from the diagram shown in Fig. 1, the source consists of three parts: AC voltage converter 220V 50Hz to DC 35...40V; pulse key voltage stabilizer with Uout = 7,6 V; linear stabilizer with Uout = +5 V. The circuit of the key stabilizer is based on the developments from the article by A. Mironov ("Radio", N4 / 87). Changes to the circuit are aimed at simplifying it, increasing the upper limit of the input voltage. The use of the 2D213A (VD5) diode instead of the KD219A recommended by A. Mironov (a diode with a Schottky barrier having a reverse branch of the current-voltage characteristic at a voltage of more than 25 V) makes it possible to ensure a sharp drop in the efficiency of the zener diode at input voltages of more than 28 V and, therefore, to raise the upper limit of the input voltage from 25 V to more than 45 V.

(click to enlarge)

The switching stabilizer modified in this way maintains the input voltage within the limits allowed for the input of a linear stabilizer assembled on KR142EN5A when the voltage at its input changes from 8,5 V to 45 V, which corresponds to a change in mains voltage from approximately 44 V to 220 V.

This is quite enough to ensure stabilization during a short-term decrease in the mains voltage (actually not lower than 70 V) due to the inclusion of powerful energy consumers (with a low quality of the network).

During the operation of the power supply, it was found that the impulse noise of the network only leads to premature switching of the key transistor and does not pass to the output of the stabilizer.

The use of the VD7, VD8, R8 and FU1 chain completely eliminates the possible troubles associated with the failure of a switching regulator, for example, during a breakdown of a key transistor. To ensure the output parameters indicated in fig. 1, the transformer is wound in such a way as to provide a rectified voltage in the range of 30 ... 35 V at a current of 0,4 A. Changing its output parameters downward only leads to a decrease in the noise immunity of the power source. The parameters of the inductor L1 are not critical (you can even not set it at all). The capacitance of capacitors C2 and C6 should not be chosen less than 200 uF and 600 uF, respectively, since this leads to an increase in the ripple level.

It is necessary to pay attention to the type of capacitors in these positions. Recommended type - K52, K53 or similar. You should not use K50-16, K50-35 - this will negate the result of all your work to ensure noise immunity.

The L2 inductor is wound on a TCHK-type core made of alsifer of size K24x13x7 and contains 26 turns of PEV-2 wire with a diameter of 1 mm. The dimensions of the core are not critical. However, it is still necessary to obtain an inductance of approximately 30 μH. The use of a ferrite magnetic circuit, as A. Mironov recommends, is undesirable, since this leads to a deterioration in the stabilizer parameters. When using an armored magnetic core, the choke contains 11 turns of eight PEV-1 0,35 conductors on a B22 2000 NM core.

Installation of a switching key voltage stabilizer is best done on a double-sided foil fiberglass (in this case, one side is used as a screen). It is desirable to reduce the length of the connection conductors along the circuits C2, VT3, VD5, L2, C6 to a minimum. The most optimal arrangement of elements is shown in Fig. 2. Blocking capacitors C4, C5 should preferably be placed directly on the terminals DA1 KR142EN5A or near them.

Establishing a power source comes down to installing a switching voltage regulator of the order of 7,6 ... 8 V at the output of a switching key voltage regulator with a resistor R6 at rated load. In this case, the operating frequency of switching should be monitored by an oscilloscope. The frequency should be within 30...40 kHz. If necessary, the frequency can be adjusted by selecting C3. It should be noted that depending on the selected capacitance C6, the value of the load resistance and the input voltage, the operating frequency can vary over a wide range. The optimal frequency for the rated load is 30...40 kHz. In the case of self-excitation of the switching regulator, it is necessary to install an additional capacitor C with a capacity of approximately 0,01 μF.

The value of R8 is selected depending on the parameters of the Zener diode VD7.

The input voltage of the power supply is easy to change by replacing VD6 with D818 (9V) and DA1 with KR142EN8. In this case, we get 12 V at the output at a current of up to 1,5 A.

To obtain several voltages, it is desirable to wind a separate winding on the T1 transformer for each voltage in order to "untie" switching regulators. With a current through the key transistor of more than 1,5 A, VT1 and VD5 must be installed on small radiators.

Long-term operation of several power supplies manufactured according to the described scheme showed their high reliability and noise immunity.

Author: P. Gribok, Belarus, Borisov; Publication: N. Bolshakov, rf.atnn.ru

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