|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Voltage stabilizer on the KR142EN19 chip with protection 27 volts / 7-25 volts 2 amperes. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Surge Protectors The article describes a voltage stabilizer with reliable impulse protection. If the output current of the stabilizer exceeds the protection threshold for some time, the stabilizer turns off for a few seconds to cool the regulating transistor, then turns on and off again until the accident in the load is eliminated. Since the control transistor is closed most of the time in this mode, the average power dissipated by it, even with a short circuit of the output, is no more than in normal mode. In the proposed stabilizer, an impulse protection unit is used on a reed relay included in a high-current circuit. Such an assembly contains few additional parts, almost does not reduce the efficiency of the stabilizer, and most importantly, the operation current of the reed protection depends very little on temperature. The stabilization coefficient of the device exceeds 400. The minimum voltage drop between the input and output is 0,5 V. The regulator circuit is shown in fig. 1.
The main element of the stabilizer is the KR142EN19 (DA1) chip. If the voltage at the control input (pin 1) of the microcircuit relative to the cathode (pin 2) exceeds its opening threshold (2,5 V), the anode current increases with a slope of about 2 mA / mV. The voltage at the anode of an open microcircuit, determined by its internal device, is at least 2,5 V. This microcircuit has a feature: if the input voltage is greater than necessary for its full opening, it may turn off. At the same time, it ceases to control the stabilizer, as a result of which an input voltage may appear at its output. Overloading the input of the microcircuit can occur due to an output voltage surge that occurs when the load is disconnected from the operating stabilizer. In this case, the current supplied to the load before it was turned off begins to charge the capacitor installed at the output of the stabilizer. This leads to an increase in the output voltage until the control transistor is closed by the error signal passed through the stabilizer. Obviously, the voltage surge will be the smaller, the larger the capacitance of the capacitor at the output of the device and the faster the error signal passes through the stabilizer. Experiments with load disconnection showed that a capacitance of at least 1000 microfarads for each ampere of the output current is enough to prevent the microcircuit from turning off in the described stabilizer. When repeating the device, one should refrain from changes that lead to a decrease in performance, for example, from the use of low-frequency transistors. It is especially dangerous to artificially reduce the performance by adding integrating RC links to the error signal path in order to combat generation. Since part of the output voltage is supplied from the slider of the output voltage adjustment resistor R12 to the control input of the microcircuit, an increase in voltage between the output terminals of the stabilizer leads to an increase in the voltage between the control input of the microcircuit and its cathode, which leads to the opening of the microcircuit. Its output signal closes the transistor VT3, connected according to the common gate circuit, and then the composite regulating transistor VT2VT1, included in the negative wire of the stabilizer, which leads to a decrease in current through it. If the microcircuit is closed, the transistor VT3 must be open, the current of its channel must be within 4 ... 10 mA. This mode is obtained if a voltage of about 5 V is applied to the gate relative to the common positive wire. It turned out that applying a part of the input voltage with ripples to the gate leads to the appearance of ripples at the output of the stabilizer with an amplitude of about 1 mV. Therefore, the voltage at the gate of the transistor VT3 is stabilized relative to the common wire by the zener diode VD1, and then also filtered by the circuits R2C3, R5C4. The use of a field-effect transistor made it possible to significantly reduce the current through the filters, and, consequently, their dimensions. Resistor R7 prevents self-excitation. Without it, the stage on the VT3 transistor can self-excite at a frequency of about 20 MHz. The described stabilizer has three degrees of protection against accidents both in the load and in the stabilizer itself. Fast protection against short-term overloads is provided by resistor R8. With a significant, approximately two times, excess of the load current of a given maximum of 2 A, the voltage drop across the resistor R8 increases to the level of the input voltage, the transistor VT2 saturates as a result and stops amplifying the current, which leads to limiting the load current. From longer failures, the stabilizer is protected by impulse protection on the K1 reed relay. If the load current exceeds the relay actuation current (2 A), the reed switch closes and the capacitor C3 quickly discharges through the resistor R1. This also begins the discharge of the capacitor C4 through the resistor R5. But this process is much slower due to the relatively large resistance of the resistor R5. When the voltage drop across the capacitor C4 decreases to about 1 V, the transistor VT3 will close, thereby turning off the stabilizer. The delay for turning off the stabilizer by the R5C4 circuit is introduced so that the capacitor C3 has time to discharge almost completely before the opening of the reed switch K1.1. After opening the reed switch, the slow charging of the capacitor C3 through the resistor R2 begins. This leads to the gradual opening of the transistor VT3 and the launch of the stabilizer. Similarly, the stabilizer starts when the power is turned on. If the UMZCH is powered from this stabilizer, when it is turned on, there will be no click in the acoustic systems. The described stabilizer, like any device with deep feedback, can be prone to generation. When prototyping the device, generation was observed in the form of pulses at the output of the stabilizer with an amplitude of about 5 mV and a frequency of about 100 kHz. It turned out that the quality of the capacitor C5 most of all affects the tendency of the stabilizer to generate. To understand why this happens, the following reasoning helps. Let's say the voltage at the output of the stabilizer accidentally changed by 1 mV. The IC converts this voltage into a 2mA output current change. Regulating transistors will amplify it by about 500 times, which will result in a change in current through the stabilizer and capacitor C5 by 1 A. This change in current will cause a voltage drop across the equivalent series resistance (ERS) of the capacitor, which will go through the feedback loop "in the second circle ". If this voltage drop exceeds 1 mV, oscillation may occur. Obviously, the stability of the stabilizer can be provided by capacitor C5 with an ESR of less than 0,001 Ohm. To make a choice, measurements of the ESR of capacitors of various series were carried out. A unipolar voltage with a frequency of 100 kHz and a current swing of 1 A was applied to the capacitor through a resistor. The ESR was calculated from the voltage across the capacitor measured by an oscilloscope. It turned out that for capacitors with a capacitance of more than 500 μF, the ESR at a frequency of 100 kHz depends mainly on the design of the capacitor, and weakly depends on its capacitance and rated voltage. According to the measurement results, the capacitor C5 is composed of ten capacitors of the K50-24 series of 470 microfarads connected in parallel, as a result of which self-excitation is suppressed without the use of other means. To fully use the low resistance of the capacitor bank C5, it is necessary that the length of the connecting wires from the terminals of the capacitor C5 to the right terminal of the resistor R13 according to the output circuit and to the connection point of the resistors R10 and R14 be as short as possible, as shown in the diagram. The tendency of the stabilizer to generate, as follows from the above, increases with an increase in the maximum possible amplitude of the current pulse that the stabilizer can supply to capacitor C5. This can be a major problem when trying to increase the maximum output current. You can improve the stability of the stabilizer by selecting a resistor R10, which creates a local negative feedback in the cathode circuit of the microcircuit. When establishing a stabilizer, this resistor is closed with a jumper, then generation is eliminated by increasing the number of capacitors in the C5 battery, after which the jumper is removed. The stabilizer acquires a stability margin sufficient for its normal operation even after a partial loss of C5 battery capacity. Capacitor C2 eliminates the influence of the inductance of the reed relay winding on the stability of the stabilizer. Another degree of protection can be added to the stabilizer - from overheating of the regulating transistor VT1. To do this, it is enough to press a thermal relay with a bimetallic plate to the body of this transistor, which operates at a temperature of 60 ... 70 ° C. The closed contacts of the thermal relay are included in the open circuit of the drain of the transistor VT3. Overheating of the transistor VT1 will cause the thermal relay contacts to open, as a result of which the transistor VT1 will be closed until it cools down. Transistor KP507A (VT3) will be replaced by close parameters KP508A. It is permissible to replace the KR142EN19 (DA1) microcircuit with KR142EN19A or a foreign analogue TL431. Capacitors C3, C4, used in the protection node as timing, must be with low leakage, for example, from the FT, K78, K71-4 series. The capacitance of the capacitor C3 determines the period of operation of the impulse protection, as well as the duration of the launch of the stabilizer. With the resistance of the resistor R2 and the capacitance of the capacitor C3 indicated on the diagram, this period is approximately equal to 3 s. It should not be significantly reduced by reducing the capacitance of the capacitor C3, since if the start is too fast, the charging current of the capacitors that may be part of the load may exceed 2 A, which will cause the protection to trip. Reed relay K1 - homemade. On the reed switch KEM1 (or another similar one), 15 turns of winding wire with a diameter of 0,4-0,7 mm are wound. Then the number of turns is specified by the operation of the reed switch at a load current of 2 A. The transistor VT1 must be installed on a heat sink with a cooling surface area of at least 200 sq. cm. When adjusting, voltage is applied to the input from the output of the laboratory power source. Its maximum value should not exceed 30 V (the limiting voltage of the anode-cathode of the DA1 microcircuit). By selecting the resistor R14, the upper limit of the output voltage adjustment is set to 0,5 ... 1 V less than the input voltage. Resistor R8 is selected so that the voltage drop across it at a load current of about 2 A is equal to half the input voltage. The stabilizer should be used with caution in bipolar sources due to its slow start-up. Since the reed switch of the impulse protection can close due to strong shaking, it is not recommended to use the proposed stabilizer in on-board systems. Author: S. Kanygin, Kharkov; Publication: cxem.net
Artificial leather for touch emulation
15.04.2024 Petgugu Global cat litter
15.04.2024 The attractiveness of caring men
14.04.2024
▪ A well-fed woman becomes more romantic ▪ Women remember words better than men ▪ MIPI CSI-2 specification v1.3
▪ site section Frequency synthesizers. Selection of articles ▪ article I am strange, but who is not strange? Popular expression ▪ article How do oysters make pearls? Detailed answer ▪ Article Blue-green algae. Legends, cultivation, methods of application ▪ article Block effects for solo guitar. Encyclopedia of radio electronics and electrical engineering ▪ article I knew you would choose this card! Focus secret. Focus Secret
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page