Tri-state power amplifier. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

 Comments on the article

The article describes a non-reversible power amplifier operating on direct current in the mode of switching to an active-inductive load. In order to reduce power consumption after actuation of the actuator, the load is transferred from the rated DC voltage to the third state - a pulsed power supply mode with an unregulated duty cycle.

Active-inductive loads (solenoids, clutches, electromagnets, relays, etc.) operating on direct current are widely used both in production and in everyday life. Most of these loads operate in an on-off mode, they are connected through amplifiers, and they do not require reverse (change the sign of the output voltage). Typically, such an amplifier operates in relay mode, when the control signal takes only two extreme values, corresponding either to the absence of current in the load, or to the rated current. The value of the traction force of the actuator is provided by the rated load current. After the actuator has worked, the conductivity of its magnetic circuit increases, and in order to maintain it in working condition, the load current must be reduced, just twice as compared to the rated current, which will save electricity.

The relay mode of operation of the amplifier, as it were, excludes the third state of the load circuit without an additional ballast resistor, which extinguishes part of the load voltage, or without an additional power source with a voltage equal to half of the nominal one. Such amplifiers are described, for example, in [1], and are known under different names. The presence of a ballast or an additional power source is the main disadvantage of such circuits.

The devices described below, after switching to the rated current mode, after a certain specified time, pass into the third state, in which a part of the rated voltage is set on the load, and the unregulated value of the latter is obtained as a result of a change in the relative duration of the pulse voltage on the load, i.e. by pulse-width modulation (PWM) amplifier. The amplifier is controlled by a PWM modulator operating at a certain frequency, depending on the load time constant.

(click to enlarge)

The main technical characteristics of the device:

• Rated load current, A, no more.......2
• Rated load voltage, V.......24...27
• Control voltage, V, not less than ....... 9
• Control current, mA, not less.......2
• Operating load current after device actuation, not less than.......0,5Inom
• Holding time of the rated load current, s, not more than....... 8

The device (Fig. 1) consists of a power amplifier (PA) based on transistors VT1 and VT2, operating in the switching mode, and a DD1 logic circuit that controls it, made on the same package of the K561LN2 microcircuit. The microcircuit is powered from the input signal, and there must be no bounce of the input signal for reliable operation of the device. On inverters DD1.1 and DD1.4, an input signal delay circuit is made, on inverters DD1.2, DD1.3 and DD1.5, a rectangular pulse generator circuit that can provide both the required frequency (capacitor C2) and the relative pulse duration (resistors R3, R4). The VD4 diode acts as an anti-coincidence circuit, and the DD1.6 inverter is used to obtain the required magnitude and phase of the signal that controls the PA. Diodes VD5, VD6 protect the amplifier in the event of a short circuit of the load, which is shunted by the reverse diode VD7.

The device works as follows. In the initial state, the input voltage is not applied, the microcircuit is not powered, the control voltage is not supplied to the PA input, the load is de-energized. When the control voltage is applied to the input of the device, the supply voltage is supplied to DD1, the charge of the capacitor C1 begins, and until the voltage equal to the inverter switching threshold voltage appears on the capacitor (ton = 0,7R1C1), the voltage at output 12 is log. "0". At the same time, a rectangular voltage appears at the output 6 of the generator with a duty cycle equal to 2, but until the delay circuit is triggered, the voltage log "10" is maintained at the output 1.6 of the inverter DD1. The PA turns on, the load is powered by the rated voltage. This voltage is held on the load until the end of transients and can vary from tenths of a second to several seconds by choosing capacitor C1. After the delay circuit is triggered at log "1" at the output 6 of the generator, a log "1" appears at the input 11 of the inverter DD1.6 and, accordingly, log "0" at its output 10. The PA closes, the voltage is removed from the load.

The appearance of a log. "0" at the output of the generator will again turn on the PA, the load Y1 will again be energized, etc. If the generator output has rectangular pulses with a duty cycle of 2, then the load will have a voltage equal to 0,5 Unom. The load is powered by pulsed voltage modulated in duration with a constant repetition rate.

As is known [2], in an active-inductive load, the current can flow continuously through the transistor from the power source, and when the transistor is closed, under the action of self-induction EMF, it can flow through the diode shunting the load. The average voltage at the load is not

 depending on the value of the inductance Un = kUp, where k is the pulse duration in relation to the pulse repetition period (the reciprocal of the duty cycle); Up - load power supply voltage. With an increase in the ratio of the load time constant τ = Ln/Rn to the pulse repetition period, the mode of continuous load currents begins. Taking into account the minimum current ripple in the load, the pulse duration should be

ti = τ/(5...7). (one)

The pulse frequency is selected in the range from several tens to several hundreds (and even thousands) Hz, depending on the time constant τ.

The main technical characteristics of the device according to Fig. 2:

• Rated load current, A, no more.......2
• Rated load voltage, V.......24...27
• Control voltage, V, not less than ....... 9
• Control current, mA, not less.......2
• Operating load current after device actuation, not less than.......0,5Inom
• Holding time of the rated load current, s, no more ....... 8
• Voltage between input and output, V, not more than.......100

In the devices shown in Fig. 1 and Fig. 2, the pulse frequency is 50 Hz, which is suitable for a large class of active-inductive loads, for which condition (1) is met.

In the circuit of Fig.2 in module A1 in relation to the circuit of Fig.1 it is necessary to: 1) remove the jumper 4-5; 2) install jumper 4-6; 3) install a jumper in place of the VD4 diode; 4) set R5 = R6 = 9,1 kOhm.

This device works similarly to the one described above in Fig.1.

The circuits shown in Fig.3,4,5 are variants of the main circuit of Fig.1, but with the following changes in module A1:

For Fig.3 in module A1 it is necessary to: 1) remove jumper 4-5; 2) install jumper 4-6; 3) install a jumper in place of the VD4 diode; 4) set R5 = R6 = 3,9 kOhm; C1 \u0,47d 2 uF; C0,01 = XNUMX uF.

For Fig.4 in module A1 it is necessary to: 1) remove jumper 4-5; 2) install jumper 4-6; 3) install a jumper instead of the VD4 diode, instead of the resistors R5, R6, install the diodes with the cathode to the output of the microcircuit; 4) set C1 = 0,47 uF; C2 = 0,01 uF.

For Fig.5 in module A1 it is necessary to: 1) remove jumper 4-5; 2) install jumper 4-6; 3) install a jumper in place of the VD4 diode; 4) set C1 = 10 uF; C2 = 0,1 uF; R5 \u6d R3,9 \uXNUMXd XNUMX kOhm.

The circuit in Fig. 3 was tested with a load in the form of a REN34 relay (passport KhP4.500.030-01) with a nominal voltage of 12 V, a winding resistance of 75 Ω, and a trip current of 160 mA. When a capacitor C1 = 1 μF was installed in the circuit of module A0,1, a rectangular voltage with a frequency of 50 Hz was set at the generator output. At the same time, the relay vibrated. When, instead of resistors R3, R4, a variable resistor with a resistance of 220 kOhm was soldered, a voltage was established on the relay winding with a pulse duration of 15 ms, pauses of 25 ms, and the relay bounce stopped, the current in the relay winding became continuous (140 mA), the average value of the voltage on the winding was 10,4 .2 V (economical mode is not achieved). If you set the ratings: R82 \u3d 200 kOhm; R2 = 0,01 kOhm; C400 \u6d 80 μF, then a rectangular voltage follows with a frequency of XNUMX Hz, there is no contact bounce. The average value of the voltage on the winding is XNUMX V, the current in the winding is continuous and equal to XNUMX mA. In this case, the efficiency of the regime has been achieved.

The circuit in Fig. 4 can be used to control a low-power active-inductive load, the operating current of which corresponds to the input current at log "0" at the output of the microcircuit.

The circuit in Fig. 5 can be used to control an incandescent lamp. First, part of the voltage is supplied to the load, and after the filament has warmed up, the voltage becomes nominal.

Details. All resistors in MLT type circuits. The 0,25 W resistors in the A1 module can be replaced with 0,125 W resistors, but this will not reduce the dimensions of the module. Low-power diodes can be replaced with KD102, KD103, KD226 diode - with KD213A. Capacitors type K739, K73-17, MBM. Electrolytic capacitor C1 type K52, K53, K50-16, K50-24. It is convenient to choose the oscillator frequency with capacitor C2.

The devices described above can be used in production for various types of actuators, but the reliability of their operation in non-rated modes must be verified in practice. In particular, their use depends on the intermittent mode of operation of the actuator.

References:

1. Arnoldov S. Electronic switch of electromagnets with low power consumption // Radioamator. -1995. -#11. - P.11.
2. Kossov O. Power amplifiers on transistors in the switching mode. Moscow: Energy, 1971.

Author: V.A. Ermolov

See other articles Section Power Supplies.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive Internet addiction is hidden in the genes 13.09.2012 A group of German researchers from the University of Bonn says that the Internet addiction of many users of the World Wide Web is often due to the mutation of certain genes. Scientists reported this in the September issue of the Journal of Addiction Medicine. Researchers interviewed 843 people and found that 132 of them exhibit "problem behavior" associated with the Web - such users admitted that their thoughts constantly revolve around the Internet, and they show extreme anxiety when they do not have access to it. DNA samples were taken from all interviewees. After analyzing the samples, the scientists found that in the genomes of those "addicted" to the Internet very often there is a mutation of the CHRNA4 gene, which is characteristic of people with nicotine addiction. Researchers explain the connection between nicotine and network addiction simply. University of Bonn psychologist Christian Montag, lead author of the article, says that nicotine acts on a so-called acetylcholine receptor, which is formed by this gene, and in the case of the mutant gene, this receptor activates the reward center of the brain in response. The Internet, Montag believes, acts on the acetylcholine receptor in exactly the same way. The mechanism of this effect is not yet clear, and it remains to be studied before adequate treatments can be proposed. Dr. Montag acknowledges that much more research is needed to further analyze the link between genetic mutations and internet addiction, but he says, "The findings point unequivocally to the genetic roots of online addiction."

Other interesting news:

▪ How to water gardens

▪ Graphene Coated Aircraft

▪ In the newborn brain, neurons travel from place to place.

▪ Geranium Gold

▪ Accountants - low ceilings

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Aphorisms of famous people. Article selection

▪ Article Much Ado About Nothing. Popular expression

▪ article What languages ​​do most people speak? Detailed answer

▪ article Catamaran on mattresses. Personal transport

▪ article Temperature controller on a microcontroller. Encyclopedia of radio electronics and electrical engineering

▪ article Adder and phase shifter for subwoofer channel on field-effect transistors and op-amp. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024