Air ionizer automation. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Home, household, hobby

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In most home-made power sources for air ionizers, the emphasis is on the simplicity and cheapness of manufacturing a device from improvised materials. We are not talking about any operational conveniences. The authors of the proposed article decided to supplement the traditional source with a microcontroller, which made it possible to diversify its operating modes.

Under the control of the microcontroller, the air ionizer will be able to work not only in the usual continuous mode, although it also provides the ability to regulate the voltage supplied to it. It will turn on and off with a set period and automatically stop working after the set time has elapsed. The parameters of all modes can be changed from the keypad, observing their values ​​on the LED digital indicator.

The main part of the source circuit (without the input/output board connected to the XP1 plug) is shown in fig. 1.

There are three main functional units here.

The power supply unit is transformerless. This is fully justified when the total current consumed from the network is not more than 15 mA. The diode bridge VD1 rectifies the AC mains voltage. Resistor R1 limits the amplitude of the pulses of the charging current of the capacitor C1. The rectified voltage through the quenching resistors R14 and R15 feeds the final stage of the high-voltage inverter on the field-effect transistor VT4, and through the resistors R2-R4 (approximately 70 V falls on them) - a +12 V voltage regulator on the transistor VT1 for the preliminary stages of the inverter. From the +12 V voltage, using the DA1 integral stabilizer, +5 V is obtained to power the device microcircuits.

The control unit is built on the basis of the PIC16F628 microcontroller, which must be pre-programmed in accordance with the table. The microcontroller stores data on the source operation mode set by the user in the internal non-volatile memory. Therefore, there is no need, turning on the ionizer, each time to set up its power source again - the work will be automatically resumed in the mode that was in effect at the time of shutdown.

(click to enlarge)

To recognize this moment in advance, two comparators built into the microcontroller are used. Their inputs (pins 1 and 18 DD1) receive voltage from the diagonal of the resistor bridge R18-R21, and during the operation of the device, the voltage at pin 18 DD1 is higher than at pin 1. After disconnecting from the mains, the voltage at pin 18 DD1 drops rapidly, and in the +5 BII circuit and at pin 1 DD1 remains almost unchanged for some time thanks to the VD3C7 circuit. Having found that the potential difference between terminals 18 and 1 has changed sign, the microcontroller manages to write data on the operating mode to the non-volatile memory before its supply voltage drops to a value insufficient to continue operation.

Pins 10-13 of the microcontroller receive signals from four buttons installed on the I / O board, which control the source. The control signals generated by the microcontroller in serial form by two digital LED indicators located on the same board are converted by the shift register DD2 into a parallel form. The indication is dynamic: depending on the voltage levels at pins 6 and 9 of DD1, only one of the indicators works at a time.

The high-voltage inverter is built on transistors VT2-VT4 and a pulse transformer T1 - line from a small-sized black and white TV. Rectangular pulses with a frequency of 150 ... 350 Hz, generated by the microcontroller DD1 at pin 8, amplify the transistors VT2 and VT3 to an amplitude of 10..-12V. After shortening by the differentiating circuit C8R13, these pulses open a powerful CMOS transistor VT4, in the drain circuit of which the winding 5-7 of the transformer T1 is included. Diode VD4 - damper.

Pulses from the step-up winding (9-11) of the transformer are fed to the rectifier with voltage multiplication on the diode columns VD6-VD11. The scheme and design of such a rectifier is well known. When making it, you can use the recommendations of the article by V. Utin "Options for the power supply unit" Chandeliers Chizhevsky "(" Radio ", 1997, No. 10, p. 42, 43).

Depending on the pulse repetition frequency, the voltage supplied to the ionizer varies in the range of 15 ... 35 kV, if necessary, it can be increased by adding a few more steps of voltage multiplication

The main printed circuit board of the source, on which almost all the elements shown in the diagram (see Fig. 1) are located, is shown in fig. 2. The board is double-sided, and the parts are installed on both sides. Capacitors C2 and C9 - K73-17, and oxide - K50-35 or their analogues. The remaining capacitors (except C10-C15) are ceramic of any type.

(click to enlarge)

Transformer T1 with high-voltage rectifier and socket XS1 for connecting the ionizer are located in a separate unit. Capacitors C10-C15 - K73-13 or others for a voltage of at least 10 kV. The protective resistor R17 must withstand the full output voltage of the source without breakdown between the terminals. Resistors MLT-2 and the like are designed for only 1200 V and are not suitable here. Suitable, for example, KEV-2. You can make a resistor R17 from several less high-voltage ones by connecting them in series.

The input / output board is assembled according to the diagram shown in fig. 3 Pressing any of the buttons SB1-SB4 not only sends a command to the microcontroller, but also turns on the corresponding LED HL1-HL4, giving the user the opportunity to visually verify that the command has been given. Resistors R1 - R8 limit the current of LED elements with common cathodes HG1 and HG2. When replacing indicators of the type indicated in the diagram with others, it may be necessary to increase the brightness of their glow by reducing the value of the mentioned resistors.

Like the main one, the I/O board is double-sided. Drawings of printed conductors and layouts of elements on both sides are shown in fig. 4. The board is attached to the front panel of the low voltage unit housing so that the decimal points on the HG1 and HG2 LED indicators are on top (and not on the bottom, as usual). It is in this position that the numbers on the indicators look correct (this is provided for by the microcontroller program). The XP1 plug is connected to the 16-wire cable of the same name on the main board.

The source starts working three seconds after being connected to the network and closing the SA1 switch (see Fig. 1). The two-digit number displayed on the digital indicators is the value of the high voltage supplied to the air ionizer in kilovolts. It can be changed in steps of 1 kV using the buttons SB2 "Up" (up) and SB3 "Dw" (down). The status of the decimal points on the indicators shows which of the possible operating modes is set. There are six in total:

The decimal point on the HG1 indicator is lit. High voltage is generated continuously.

The decimal point on the HG2 indicator is lit. Cyclic mode with a period of 1...10 min. In the first half of the cycle, there is high voltage, in the second it is not.

The decimal points are lit on both indicators. Similar to mode 1, but after a set time (1...99 min) the high voltage is automatically turned off.

The decimal point on the HG1 indicator flashes. High voltage is on for 1 s, off for N s. The number N is set in the range from 3 to 10.

The decimal point on the HG2 indicator flashes. The device operates as in mode 4 for a specified time (1...99 min), after which the high voltage is automatically turned off.

The decimal points are flashing on both indicators. The high voltage smoothly rises to the maximum (35 kV), then smoothly decreases to the minimum (15 kV). The cycle repetition period is 5 minutes.

In modes 3 and 5, after the specified time has elapsed, the device "falls asleep" - the high voltage is turned off, the indicators are extinguished. It is removed from this state by pressing any button, after which the exposure will be repeated.

Switch modes by briefly pressing the button SB1 "Set" (setting). The first of them turns off the high voltage, and the numbers on the indicator start flashing, showing the current value of the set mode parameter, for example, the time during which the high voltage will be turned on. The value can be changed using the "Up" and "Dw" buttons. Subsequent clicks on the "Set" button switch modes with a corresponding change in the state of decimal points. The numbers on the indicators stop flashing, and the new mode takes effect if you hold down the "Set" button for more than a second.

Button SB4 "Adj" (tuning) is intended for calibration - bringing the output voltage in accordance with the indicator readings. The voltage is measured with a kilovoltmeter connected between the XS1 socket and the common wire. You can use, for example, a microammeter with a total deflection current of 50 μA, connecting it in series with a set of resistors with a total resistance of 1000 MΩ.

Before starting the calibration, it is recommended to set the minimum voltage value (15 kV) on the source indicators, although the procedure can be started from any. After pressing the "Adj" button, the numbers on the indicators will flash alternately, signaling that the calibration mode is enabled. Using the "Up" and "Dw" buttons, adjust the kilovoltmeter readings to the value displayed on the indicators. Press the "Set" button. At this moment, the microcontroller stores in the non-volatile memory the value of the pulse frequency necessary to obtain the specified voltage and increases the number on the indicators by 1. Use the "Up" and "Dw" buttons to adjust the output voltage again and press the "Set" button. This procedure is repeated as many times as necessary. Exit the calibration mode by holding the "Set" button pressed for more than a second.

You should not turn on the source again earlier than a minute after turning it off.

Authors: V.Sekrieru, E.Munteanu, Chisinau, Moldova

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