Power regulator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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Using relatively cheap powerful field-effect transistors with an insulated gate (MIS - transistors), you can make a good device for controlling the power of incandescent lamps, soldering irons and other equipment. The main difference between the design proposed in this article and those previously described on the pages of the Radio magazine is the low current consumption in the control circuits, smoother power control, especially in the initial section of the control characteristic.

The schematic diagram of the device is shown in fig. one.

(click to enlarge)

On the element DD1.1, a shaper of rectangular pulses is assembled, the shape of which is close to the "meander". The fronts and falls of these pulses coincide in time with the moments when the mains voltage passes through zero. The pulses are fed to the differentiating circuit C3R3 and inverter DD1.2. After passing through the inverter, they go further to the C4R4 chain. Diodes VD4, VD5 form an OR element for differentiated pulses coming through the R7R8 divider to the input (pin 8) of the DD1.3 element, which works as a comparator. Capacitor C5 provides smooth voltage regulation, which is especially important for incandescent lamps.

When moving the slider of the resistor R5 (Fig. 2), the voltage at point A changes, and hence the duty cycle of the pulses at the output (pin 10) of the DD1.3 element. Moreover, with an increase in this voltage, the duty cycle increases until the complete disappearance of the pulses and the establishment of a log level at the output of the DD1.3 element. 0 in the upper position of the resistor R5 slider according to the diagram, which corresponds to the off load. When the voltage at point A decreases, the duty cycle of the pulses decreases until they merge completely and establish a log level at the output of the DD1.3 element. 1. This happens in the lower position of the resistor R5 slider and corresponds to a fully turned on load.

The input capacitance of powerful field-effect transistors is significant. Large currents are required to quickly recharge this capacitance, and hence the fast switching of the transistor. For this reason, the signal is fed to the gate of the transistor VT3 through a current amplifier made on transistors VT1, VT2. Transistor VT3 opens when the mains voltage is close to zero, and closes at a voltage determined by the position of the resistor R5 slider.

The power regulator uses fixed resistors MLT-0D25, variable SP-1; oxide capacitors - K50-35, the rest - KM-6. Diodes KD226D (VD1, VD2 and VD6-VD9) can be replaced with any with a reverse voltage of at least 400 V and a maximum direct current of at least 1 A. We will replace the Zener diode D814B (\/D3) with another one with a stabilization voltage of 9V. Replacing the K176DE5 (DD1) chip with others, such as the K561 series, is undesirable. The fact is that at input voltages different from levels 0 and 1, through currents arise in CMOS microcircuits [1] and, as measurements have shown, even in a static mode at input voltages close to the threshold, they can consume current from hundreds of microamperes (for microcircuits of the K176 series) and up to tens of milliamps (for microcircuits of the K561 series). With an increase in the supply voltage, the consumed current increases sharply. It also turned out that if at one of the inputs of the microcircuit the voltage corresponds to the threshold, and at the others - 0 or 1, the current consumed is about 20% less, if there were a threshold voltage at all inputs. With this in mind, unused inputs must be connected to a common wire.

Instead of the K176LE5 microcircuit, you can use M76LA7, but its inputs (pins 2,5,9) must be connected to pin 10 through 14 kΩ resistors. A powerful field-effect transistor with an insulated gate and an n-type channel KP3102A107 can be replaced with the KP1V2 used in television power supplies [707, 1]. Good results are obtained with BUZ707 transistors, since their input capacitance is almost an order of magnitude lower than that of KP2A2.

The design of the regulator can be any. It is only necessary that the length of the connecting conductors be as short as possible. The VT3 transistor is mounted on a duralumin heat sink with an area of ​​24 cm2. The free inputs of the element DD1.4 (pins 12 and 13) are connected to pin 14 DD1.

To set up the regulator, you will need an oscilloscope with an input impedance of at least 1 mΩ. It starts by turning on the device without load. When moving the slider of the resistor R5, a change in the duty cycle of the pulses should be observed at pin 10 of the DD1.3 element. Then check the voltage at the zener diode VD3 in all positions of the R5 engine and, if it falls below 7 V, reduce the resistance of the resistor R1. Next, instead of the load, the MLT-1 resistor with a resistance of 100 ... 300 kOhm is connected and the power adjustment limits are specified. To do this, the engine of the resistor R5 is set to the upper position according to the diagram and by selecting the resistor R7, its minimum value is found, at which there are no pulses at pin 10 of the DD1.3 element, and the voltage will correspond to the log level. 0. Then the slider of the resistor R5 is moved to the lower position and the maximum possible resistance of the resistor R6 is selected. at which, at pin 10 of the DD1.3 element, the voltage will correspond to the log level. 1.

After that, the operation of the device is checked in different positions of the resistor R5 engine, controlling the waveform at the load. In the case of self-excitation of the device, it is eliminated by selecting the capacitance of capacitor C2. It should be noted that in the extreme positions of the engine of the resistor R5, a slight asymmetry of the voltage across the load is possible. You can reduce it by selecting capacitors C3, C4 and resistors R3, R4.

If it is necessary to connect a more powerful load, the VD6 - VD9 diodes are replaced with more powerful ones and increase the heat sink area of ​​the VT3 transistor. It is also possible to connect several field-effect transistors in parallel.

On the basis of the considered regulator, it is possible to make a device for smoothly turning on and off incandescent lamps. To do this, remove the resistors R5. R6, between points A and B, two resistors connected in series with a resistance of 47 kOhm are installed. A switch is installed between the connection point of these resistors and point B. Capacitor C5 is replaced with another one with a capacity of 47 microfarads and an operating voltage of 25 V. It is permissible to exclude the current amplifier (VT1, VT2 and R10), and reduce the resistance of resistor R9 to 12 kOhm.

It is convenient to install the device near the junction box. Parallel to the switch, you can install the executive circuit of the optocoupler, the LED part of which receives signals from an external programming device, for example, described in [4]. It. in the absence of the owners of the apartment, it will turn on the light for some time at night, thereby scaring away uninvited "guests".

When setting up the regulator, special care must be taken, since the device does not have a galvanic isolation from the network.

Literature

1. Zeldin EA Digital integrated circuits in information-measuring equipment. - L.: Energoatomizdat. Leningrad branch, 1986.
2. Petukhov V, M. Field and high-frequency bipolar transistors of medium and high power and their foreign analogues. Directory. T. 3 - M .: KubK-a, 1997.
3. Perelman B. L. Semiconductor devices. Directory. - Solon. Micro-tech, 1996.
4. Vinogradov Yu. Automatic "evening light". - Radio, 1994, No. 11, p. 28 - 30.

Author: S. Zorin, Znamensk, Astrakhan Region

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