New possibilities of microcircuit voltage stabilizers. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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Chip stabilizers are increasingly found in amateur radio designs. But their capabilities are much wider compared to those used by radio amateurs. In some cases, the stabilizer can become, for example, the basis of an AF amplifier, acoustic siren or modulator, in others - the basis of a powerful stabilizer built into the network adapter. This is discussed in the proposed articles.

UNUSUAL APPLICATION OF THE KR142EN12 CHIP

Integrated voltage stabilizers of the KR142, KR1157, KR1168 and similar series, described in the article by S. Biryukov "Microcircuit voltage stabilizers of wide application"("Radio", 1999. No. 2, pp. 69 - 71), are successfully used in the designs of linear voltage stabilizers and power supplies. Taking into account the features of a number of such ICs, it is possible to expand their scope. This, in particular, applies to adjustable stabilizers KR142EN12A, KR142EN12B.

DC or AC amplifier. As you know, to change the output voltage of the KR142EN12A (KR142EN12B) microcircuit, an adjustable constant voltage must be applied to its control output. Since the control output current is 50 ... 100 μA, and the output current reaches half a mountain of amperes, we can say that the current gain of the microcircuit is several tens of thousands and it is capable of performing the functions of a current amplifier. The scheme of such an amplifier is shown in fig. 1. According to its characteristics, it is similar to the well-known emitter follower.

If a DC amplifier is needed, the input voltage is applied directly to the control pin of the microcircuit. At the same time, a voltage of 1.2 V more will be established at its output. The maximum input voltage must be 3...3,5 V less than the supply voltage.

The load R (incandescent lamp, electromagnet, etc.) is connected directly to the output of the microcircuit. The maximum load current is determined by the maximum current of the microcircuit. Capacitor C3 is installed in case of self-excitation of the device.

To implement an AC amplifier, you will have to introduce capacitors C2, C3. By selecting the resistor R2, a constant voltage is set at the output, equal to about half the supply voltage. The value of the resistor R` is chosen so that a current flows through it, approximately twice the maximum load current R.

Capacitor C4 must be of such a capacity that it passes the currents of the lowest frequency of the amplified signal. Experiments have shown that the amplifier has a wide bandwidth - up to 200 kHz. In addition, the microcircuit worked stably for an active load without capacitor C3.

Modulator. The current through the control output of the microcircuit is relatively stable, so connecting a transistor cascade to it will allow you to get an AC voltage amplifier with a high gain. As a result, it will be possible to build a relatively simple modulator (Fig. 2) for a small-sized portable AM ​​radio station. Its amplification is such that when using a BM1 electret microphone of medium sensitivity, the amplitude of the alternating voltage at the output of the microcircuit is several volts. And this is enough to modulate the output stage of the transmitter.

By selecting the resistor R3, a constant voltage is set at the output of the microcircuit, equal to half the supply voltage. The transistor must have a base current transfer ratio of at least 200.

Amplifier 3H. Based on the design described above, an ultrasonic frequency converter can be assembled (Fig. 3). Here, the dynamic head BA1 is connected directly to the output of the microcircuit, and current constantly flows through it.

The sensitivity of the amplifier is quite high - when a signal with a voltage of 8 mV is applied to the input, the output voltage is 1 V. A dynamic head with a voice coil with a resistance of 10 - 16 ohms or more (or several low-resistance connected in series) should be connected to the output of the amplifier.

The supply voltage may be higher - 9 ... 12 V, but then it is necessary that the dynamic head be of the appropriate power. In addition, it is permissible to apply an unstabilized voltage, since the stabilization effect of the microcircuit is preserved. If necessary, install a resistor R' and a decoupling capacitor C4, as shown in Fig. 1.

powerful siren. Its scheme is shown in Fig. 4. A generator of rectangular audio frequency pulses is assembled on two transistors and a microcircuit, and a powerful dynamic head BA1 is used as an emitter. It is chosen based on obtaining maximum power at the available supply voltage. It should be borne in mind that the maximum current through the microcircuit should not exceed 1,5 A for KR142EN12A and 1 A for KR142EN12B.

Transistor VT1 must have a current transfer ratio of at least 30, and VT2 - at least 100.

Establishing a siren comes down to setting a stable generation with a tuning resistor R4. The generation frequency is changed by selecting capacitor C2.

Switching regulator. Due to the ability of the microcircuit to operate in a pulsed mode, it is possible to assemble a pulsed controller for the speed of rotation of a DC motor or the brightness of an incandescent lamp on it (Fig. 5).

A master oscillator operating at a frequency of about 1.1 kHz is assembled on the elements DD1.2 and DD1. The variable resistor R1 changes the duty cycle of the generated pulses (while the generated frequency changes slightly), which are fed to the buffer elements DD1.3. DD1.4, and from their outputs - to the control output of the DA1 chip. As a result, powerful voltage pulses are formed at the output of the microcircuit, the duration of which can be changed by resistor R1. The longer the pulse duration, the faster the rotation of the axis of the electric motor M1 or the greater the brightness of the incandescent lamp EL1.

Diode VD3 protects the DA1 chip from possible voltage surges when working with an electric motor. In the case of using the regulator only with an incandescent lamp, the diode is not needed.

The supply voltage in this device must be 2 ... 2,5 V more than the maximum voltage on the electric motor or incandescent lamp.

The regulator was used in conjunction with a small-sized electric motor DPM 30-N1-09 and a power supply unit with a voltage of 10 ... 11 V. The rotation speed of the motor shaft could be changed from several revolutions per second to the maximum.

In all the devices described, it is permissible to use polar capacitors of the K50, K52 series. K53, and non-polar - series KLS, K10-17, K73. Trimmer or variable resistors - SPO, SDR, SP4. If the chip will dissipate more than 0,5 W of power, it must be placed on a heat sink.

LOW-POWER VOLTAGE REGULATOR ICs IN POWER SUPPLY UNITS

When designing stabilized power supplies for various equipment, as a rule, microcircuit voltage stabilizers are used. A large range of such microcircuits [1] provides designers with a wide choice of them to create a stabilizer with the required parameters. In some cases, however, low-power microcircuits are quite applicable to building relatively powerful stabilizers. An example in this regard is the construction of a voltage regulator built into a network adapter.

In most cases, as is known, such adapters, especially imported ones, provide an output current of up to 0.5 A and do not contain a voltage stabilizer [2]. If a stabilizer is needed to improve the "quality" of the rectified voltage, you can use the IC chips specified in [1].

Today, the KR142 series microcircuits are the most accessible. To obtain an output voltage of 9 V, KR142EN8A is usually chosen. KR142EN8G. However, they provide load current up to 1 ... 1.5 A with an even higher short-circuit current (SC). Because of this, in the event of an emergency, the transformer and rectifier diodes of the adapter may fail.

To avoid this, you need a stabilizer with a load current of up to 0,5 A and a short-circuit current of not more than 0,6 A. But it is difficult to find microcircuits with such parameters and with an output voltage of 9 V.

There is a way out. It is necessary to use a low-power microcircuit and "power" it with a transistor (Fig. 1).

In such a device, with a load current of more than 20 mA, the voltage drop across the resistor R1 will be enough to open the transistor VT1. The current will flow "bypassing" DA1, the output voltage will be determined by its parameters, and the load current may exceed the permissible output current of the microcircuit many times over. True, the short circuit current will reach 1 ... 1,5 A, which is fraught with the above consequences.

It is not difficult to limit the short-circuit current by introducing another transistor (VT2 in Fig. 2). Then, with a load current of up to 20 mA, only DA1 will still work, and the transistors will be closed. When the current exceeds the specified value, the transistor VT1 will open and the current will flow through it. As soon as the current reaches a value of 400 ... 500 mA, or a short circuit occurs in the load circuit, a voltage will appear on the resistor R1, which will open the transistor VT2. Now both transistors will start working in the current stabilizer mode.

The resistor R1 sets the approximate value of the stabilization current: lct = 0.6/R1. In this case, the short circuit current will be: lkz \u3d lce + lkzms where lkzms is the current KXNUMX of the microcircuit.

In both devices, transistors VT1 are any of the KT814, KT816 series. Transistor VT2 should be with a low collector-emitter saturation voltage, so it is advisable to use, in addition to that indicated in the diagram, transistors KT208A-KT208M, KT209A-KT209M, KT3107A-KT3107I, KT3108A-KT3108V. Capacitor C1 is the adapter filter capacitor.

Literature

1. Biryukov S. Microcircuit voltage stabilizers of wide application. - Radio. 1999. No. 2, p. 69-71.
2. Biryukov S. Network adapters. - Radio. 1998. No. 6. p. 66. 67.

Author: I.Nechaev

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