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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Three devices per OS. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur [an error occurred while processing this directive] The designs proposed in this article demonstrate options for constructing circuits with the active use of the ability to control the power consumption of the KR140UD1208 microcircuit. The KR140UD1208 microcircuit cannot but attract the attention of radio amateurs with its small size (case 2101.8-1), low current consumption (from 25 to 170 μA), large supply voltage range (from 2x1,5 to 2x18 V) and high gain (up to 2 105). There is protection of the output stage against overload [1]. The use of a microcircuit in an ultrasonic frequency converter, a microphone amplifier and a comparator is described in [2]. But this microcircuit has another unique property - the ability to regulate the current consumption through a special output. Most often, this feature is used passively. They simply select a quenching resistor from the condition Iupr = (Upit - 1.7 / Rupr, where Iupr is the current in the control circuit at a special output, mA; Upit is the supply voltage, V; Rupr is the resistance of the quenching resistor, kOhm, connected between the mentioned output and the supply minus microcircuits. By manipulating the current of the control circuit, it is possible to change the operating parameters of the microcircuit in a wide range. But we must immediately warn that according to the technical specifications, Iupr should be no more than 200 μA, which means that at a supply voltage of 9 V, the resistance Rupr should not be less than 41,5 kOhm. Low battery indicator This device (Fig. 1) contains a unit for comparing the pre-set voltage with the actual battery voltage and an indication unit (sound generator).
The sound generator is assembled on a DA1 KR140UD1208 chip. Resistors R1, R2 and R3 provide bias on the non-inverting input (pin 3) in our case of a single supply. Elements C1, R4, R5 are included in the feedback circuit, providing generation. From the output of the microcircuit (pin 6), the sound frequency oscillations are fed to the piezoceramic sound emitter BF1. But the sound generator starts working only when the gain, which depends on the current consumed by the microcircuit, exceeds the minimum threshold necessary for self-excitation. If the current consumption control input (pin 8) is shorted to negative power (pin 4) through resistors R6 and R7, the microcircuit generates sound vibrations. If pin 8 is connected to positive power through resistor R6 (pin 7), the microcircuit is inhibited and its current consumption is minimal. The voltage comparison unit is assembled on a transistor VT1, a zener diode VD1 and resistors R8 -R10. Resistor R8 is installed to securely close the transistor VT1. Resistor R10 prevents overload and failure of the transistor VT1 during the establishment. Capacitor C2 attenuates various pickups in the base circuit. The device works like this. At the nominal EMF of the battery, the voltage taken from the divider R9R10 is sufficient to breakdown the zener diode and the transistor VT1 is open. Its emitter-collector junction through resistor R6 closes the control output of the microcircuit to positive power. Emitter BF1 is silent. Despite the fact that in standby mode, the transistor VT1 is constantly open, the current consumption of the indicator is small due to the high resistance of the resistor R7. At a certain, pre-set resistor R9, battery voltage, the current through the zener diode VD1 noticeably decreases and the transistor VT1 closes. The current consumed by the microcircuit increases, and the sound generator turns on, signaling a decrease in battery voltage. Setting up the indicator is easy. Having set the slider of the resistor R9 to the upper (according to the diagram) position, the indicator is connected to the laboratory power supply, while the generator should work, and the BF1 emitter should sound. Then reduce the supply voltage to the required control level. For example, if the power battery consists of six TsNK-0,45 batteries and it is known that the discharge of each of the battery cells is permissible to a voltage of at least 1 V, then 6,5 V (with a margin) will be the maximum voltage level at which indicator will work. After that, the engine of the tuning resistor R9 is set to the position when the sound indication stops. Raising the voltage to 9 V and gradually reducing it to 6,5 V, make sure that the sound generator turns on in a timely manner. By repeating this procedure several times, the exact position of the resistor R9 slider is found, at which the indication is triggered at the planned undervoltage limit. By selecting capacitor C1, the sound generator is tuned to the resonant frequency of the piezoceramic emitter. Due to the small number of parts, the small size of the active elements, the indicator is easily placed inside any REA case. If the device is mounted in a pocket radio station of previous years of production (Laspi, VIS-R), then it is better to connect it not to the common terminal of the power switch "RX" and "TX", but to the terminal "RX", since a significant decrease in voltage during operation transmission may cause false positives of the indicator. If space permits, the indicator is turned on through a microswitch (MP-8, MP-9) directly on the plus of the battery to check its condition at any time. The comparison node uses an outdated miniature germanium transistor, which is associated with a lower voltage drop across it compared to silicon transistors. It is permissible to use other transistors. And further. In order to reduce the volume of the device, it is a good idea to replace the resistors R9 and R10 with two constants, experimentally selecting them during adjustment. If there is no need for a sound indication of the battery status, I suggest another option - with a light indication. In this case, the circuit is greatly simplified (Fig. 2). Here, the KR140UD1208 chip works as a switching (or switching off) voltage follower. In other words, its output voltage is equal to the input, but this condition is met only when the microcircuit is open for signal passage. Otherwise, the output voltage is small and corresponds to the low limit voltage. The node for comparing voltages (battery status) is similar to the node discussed above. To reduce the total number of parts, the key stage (transistor VT1) is connected to the same voltage divider as the non-inverting input of the microcircuit (pin 3). Its inverting input (pin 2) is directly connected to the output (pin 6).
The principle of operation of the device is as follows. With a normal supply voltage of the REA, the key stage on the transistor VT1 is open and closes the control output 8 through the resistor R2 to the power plus. The microcircuit is closed, and the output (pin 6) is set to a voltage close to zero. As soon as the battery voltage drops below the VD1 zener diode opening threshold, the VT1 transistor closes, the microcircuit goes into active mode and the LED lights up, signaling the battery is low. The threshold for the indicator is set by selecting the resistor R3. With the values of the elements indicated in the diagram and at the initial battery voltage of 9 V, the LED lights up when the voltage drops to 6,5 V. In standby mode, both described indicators consume current no more than 0,1 mA. This current depends mainly on the resistance of the resistor in the collector circuit of the transistor VT1 (Fig. 1 - R7, Fig. 2 - R1). In indication mode, the current rises to approximately 1 mA. Electric field indicator The electric field indicator was developed as an additional means of personal protection for locksmiths involved in the maintenance and repair of electrical equipment with an operating voltage of up to 6000 V. Its purpose is to warn the electrician in a timely manner about the inadmissible approach to live parts of an electrical installation that is energized. The small size and low power consumption in standby mode make the indicator convenient to carry around in the breast pocket of overalls. The scheme of the device is shown in fig. 3.
In this device, the KR140UD1208 chip works as a comparator. If we consider that the comparator is a kind of balance that compares the proposed load (voltage) with the reference one, and the unit of measurement is not a kilogram, but a volt, then the result of such a comparison will be expressed in two states: either the output voltage is minimal, i.e. Uout \u0d U1, or maximum, i.e. Uout = U1 [XNUMX]. For the KR140UD1208 microcircuit, the first state is formed when the voltage at the inverting input U2 is greater than the voltage at the non-inverting one: U2 > U3, and then Uout = U0. The second state is obtained when U2 < U3, in this case Uout = U1. According to this principle, the indicator of the electric field is built. Field effect transistor VT1 and resistor R1 form a voltage divider with controlled resistance. The signal taken from it further enhances the transistor VT2. Resistors R3 and R4 divide the supply voltage in half, forming a "reference weight" with which the "load" - the signal voltage - is compared. In the initial state, the resistance of the source-drain channel of the transistor VT1 is small, since there is no signal on its gate connected to the "antenna" WA1. Transistor VT2 is closed. The voltage at pin 2 of the DA1 chip is close to Upit, which means it is greater than at pin 3, where it is equal to Upit / 2. The condition U2 > U3 is observed, under which Uout = U0, transistors VT3 and VT4 are closed. When the indicator is introduced into an electric field of sufficient intensity, the resistance of the source-drain channel of the field-effect transistor VT1 increases, since it is closed by the induced voltage detected at the p-n gate junction. The transistor VT2 opens, reducing the voltage at pin 2 of DA1. At some point, the comparator switches and the voltage at its output becomes close to the supply voltage. The transistor VT3 opens, allowing the operation of the pulse generator (VT3, VT4). The pulse repetition rate depends on the values of the capacitor C3 and resistor R8. With the values indicated in the diagram, the pulse frequency is 2,5 ... 3 Hz. With the same frequency, the BF1 sound generator emits alarm signals, confirmed by flashes of the HL1 LED. In addition to the resistor R8, the capacitor C6 is included in the circuit for controlling the consumed current of the microcircuit (pin 2), and we can say that Rupr → ∞. In fact, Rupr has a finite value, which depends on the quality of the capacitor C2. But this is DC. And in terms of the variable - Rupr also depends on the capacitance of this capacitor. As soon as the generator (VT3, VT4) starts to work, the first pulse recharges the capacitor C2. The resulting current through the C2R6 circuit is much greater than the quiescent current and, as a result, the output power of the microcircuit increases. Since the time constant R8C3, which determines the frequency of turning on the generator, is much less than the time constant R6C2 and the capacitor C2 does not have time to discharge to its original state, then sound and light signals follow while the transistor VT2 is open. At the moment when the indicator is removed from the area of the electric field, the comparator switches. Capacitor C2 is discharged through the capsule BF1 and LED HL1. The device goes into standby mode. In this case, the consumption current decreases to 60...70 μA. The device is quite sensitive. With an "antenna" made of foiled fiberglass with dimensions of 55x33 mm (the front wall of the indicator case), it "recognizes" the consumer of electricity (a switched on lamp, an electric kettle) at a distance of more than 0,5 m. In motion, the indicator reacts to static electricity. Moving on synthetic pile carpeting triggers with almost every step. The indicator is assembled on a printed circuit board made of double-sided foil fiberglass with dimensions of 42x30 mm. Together with a V23GA battery (diameter 10 mm, length 27 mm), it is housed in a 55x33x14 mm case made of tinplate. The front wall of the housing is made of the same material as the circuit board. The foil on the outside is connected to the gate of the transistor VT1. Outside, for decorative purposes, the case is pasted over with a colored self-adhesive film. Transistor VT1 can be replaced with KP103L or KP103K. Transistors KT3102 and KT3107 can have any letter indices. In the case of using transistors KT315 and KT361 (which is also acceptable), it is necessary to modify the wiring of printed conductors. Capacitor C1 - ceramic, with a capacity of 0,068 to 0,68 microfarads. The remaining capacitors are oxide, small-sized. LED HL1 is better to use a red glow, any of the radio amateur's reserve. If the sound is too loud, so as not to overload the capsule and the built-in generator, it is useful to turn on a quenching resistor with a resistance of up to 300 ohms in series with the LED (not shown in the diagram). An indicator assembled without errors from serviceable parts does not need to be adjusted. If you set yourself the goal of minimizing the current in quiescent mode, then special attention should be paid to the selection of capacitor C2 (for the minimum leakage current). The indicator remains operational when the battery voltage drops to 6 V. Literature
Author: V.Markov, village of Tuloma, Murmansk region.
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