Voltage stabilizer for lm317
After the failure of an old SN, similar to the one described in, made during my student years, it became a little difficult to work. Having visited his favorite radio market, Karavaev Dacha, in the hope of something inexpensive, uncomplicated with decent parameters and a minimum of parts, the author settled on KR142EN12A, an imported analogue of LM317. Since the voltage stabilizer on the KR142EN12A IC does not have short-circuit protection, we had to modify it a little.
The diagram of the modernized CH is shown in the figure, the appearance is presented on the website. In the standard KR142EN12A switching circuit, with the adjusting resistor R5 slider in the upper position (low potential), the microcircuit has a minimum output voltage of 1.2 V. At a high potential, the maximum is 37V. Maximum stabilization current 1.5 A.
Short circuit protection works as follows: when a load current flows (in the author's version, more than 1.1 A), the voltage drop across resistor R6 increases, and the current of the optocoupler LED U1 increases accordingly, which leads to the opening of the optocoupler thyristor and transistor VT1. When the transistor opens at pin 1 of the DA1 stabilizer, the potential is low, the CH goes into the minimum output voltage mode. The current flowing through the optocoupler thyristor U1 is sufficient to maintain it in the open state.
LEDs VD1 (green color) and VD2 (red color) serve to indicate the activation of the voltage stabilizer and the short-circuit protection mode, respectively. Button SA1 is used to return the CH to operating mode. The disadvantage of the design is the incomplete shutdown of the output voltage of the stabilizer. By saving on the dissipation area of the DA1 radiator by installing a small cooler from a PC processor on the radiator, the author received a worthy replacement for the failed design.
Details. The stabilizer uses resistors MLT-0.25, resistor R6 - C5-16V. Imported capacitors. Small-sized imported LEDs. Optocoupler U1 – AOU103 with any letter index.
Setup. After checking the correct installation, turn on the device. (The transformer and diode bridge are not shown in Fig. 1.) Check the output voltage regulation range, then, by connecting a load resistor (about 20 Ohms), gradually increase the output voltage from 1.2V to the maximum. An ammeter is used to monitor the protection operation current. It may be necessary to change the resistance of resistor R6, and resistor R7 may be excluded from the circuit. Depending on the types of LEDs VD1 and VD2, you may have to select the resistance of resistors R1, R2.
We offer to order in our online store popular stabilizing devices with an energy-saving control mode and a fully automatic system for eliminating emergency situations in the electrical network. The main objectives of these Energia and Voltron brands are: fail-safe protection against short circuits, high-speed equalization of high and low power supplies in household and industrial consumer networks and solving problems associated with unpredictable short-term overloads. The official manufacturer of Russian recommended equipment for 220V, 380V electrical networks is the ETK Energy company. The stabilization accuracy of some household rulers is only ±3% and ±5%, thanks to which they will ideally work even with high-precision medical devices. You can buy a voltage stabilizer with short circuit protection in Moscow, St. Petersburg and the region. Many domestic single-phase and three-phase brands Energia and Voltron offered for purchase are excellent for simple and highly sensitive modern electrical equipment also because they have smooth automatic adjustment of dangerous input surges and sags. The best Russian-made electrical appliances at the moment are considered to be new, improved models with a pure sinusoidal waveform, namely: Energy Hybrid, Classic and Ultra. It is also worth noting that during the operation of these lines there is absolutely no flickering of light bulbs. The universal housing of automatic devices Energia Classic, Ultra, Hybrid U and Voltron RSN provides, in addition to standard floor operation, compact wall installation.
Single-phase and three-phase voltage stabilizers with short-circuit protection, widely presented on our website today, are in great consumer demand for highly efficient and durable protection of various individual low-power equipment and the entire home, apartment, office, country house, educational, entertainment and medical institutions, industrial and other facilities where problems often arise in a 1-phase or 3-phase network. The model range consists of mid- and premium-class devices with maximum capacities provided by the manufacturer for 1, 2, 3, 5, 8, 10, 15, 20 and 30 kW (kVA). Therefore, with us you can choose such electrical equipment even for the safety of the largest cottage or industrial premises with a large number of consumers in use. You can buy a voltage stabilizer with short-circuit protection in Moscow, St. Petersburg from us at an affordable price. According to the type of equalization of low-quality power supply in the household electrical network, there are relay, electronic (thyristor) and electromechanical Russian network devices. Almost all series have high technical characteristics and are additionally equipped with a self-diagnostic system for carefully monitoring the state of the power supply at the input and output. For continuous use in conditions of negative external temperatures (up to -20, -30 degrees Celsius) there are special frost-resistant models. A digital display allows you to monitor important parameters on the network. With us you can choose high-quality and very reliable low-noise and absolutely silent network equipment with multi-level protection against emergency failures. Warranty 1-3 years. The manufacturer's stated service life for most of our certified electrical appliances is at least 10 years. All devices can be used 24 hours a day.
Current stabilizer with short circuit protection
Current stabilizer overload protection
Current stabilizers are widely used in various devices. Their schemes are simple and not very simple. But in any case, it will be better if it has overload protection. The problem that we will consider is the following, we have a voltage stabilizer with load current limitation. That is, such a stabilizer is not afraid of short circuits at its output.
But in short-circuit mode, a large amount of power will be released on the regulating transistor of such a stabilizer; this will require the use of an appropriate heat sink, which will entail an increase in the size of the device and, well, its price. Otherwise - thermal breakdown of the structure of a powerful transistor.
For example, let's take a simple current stabilizer circuit on a microcircuit, shown in Figure 1.
Everything is in general terms. The stabilization current, in accordance with formula 1, is 1A. Let's say the normal load resistance is 6 ohms. Then, at a current of 1A, the voltage on the microcircuit will drop equal to: U = IxR - IxRн = 12-1.25-6 = 4.75V. Accordingly, the power P = UxI = 4.75 W will be released on the microcircuit. If you close the output of the current stabilizer, then the voltage on the microcircuit will already drop 10.75V and, accordingly, the power released on the microcircuit will be equal to 10.75W. It is this power that the radiator must be designed for, then the reliability of your device will be at its best. But what to do if it is not possible to install a larger radiator? Right! It is also necessary to limit the power allocated to the chip. It is possible to install a tracking stabilizer in front of this circuit, which in the event of a short circuit would take on part of the released thermal power, but this is a bit complicated. It would be better to completely turn off the stabilizer in the event of a short circuit at its input. Knowing that power is equal to the product of current, and we set the current ourselves and it is stabilized, then we will monitor the voltage drop on the current regulator.
The circuit of an adjustable current stabilizer is taken from the article. You can read more about the operation of this adjustable current stabilizer in the article.
Operation of the over-power protection circuit
To ensure protection of the current stabilizer, we introduce only five parts into the circuit. Transistor VT1, which acts as a key and completely turns off the stabilizer during short circuit mode. A MOSFET transistor with channel P is used here. For small currents, on the order of one or two amperes, the IRFR5505 is suitable
At high currents, it is better to use a transistor with a large operating drain current and lower open channel resistance. For example - IRF4905
Thyristor optocoupler, you can use a domestic one - AOU103 with any letter, you can choose an imported one, for example - TLP747GF
Zener diode, any low-power one, read the article to the end and, if necessary, choose the one you need. R1 is a resistor through which a negative opening voltage is supplied to the key gate. R2 is a resistor that limits the current of the thyristor optocoupler LED. Yes, if the input voltage is more than 20V, then in parallel with the optocoupler thyristor it is necessary to install another 12V zener diode, which will protect the gate-source transition of the key transistor. Since most MOSFET transistors have a maximum allowable voltage of this junction of 20V.
For example, let's take the case of charging a twelve-volt battery with a stable current of 3A. When supply voltage is applied to the circuit, transistor VT1 will be open, since a negative voltage is supplied to its gate and the circuit operates in normal mode. We will not take into account the voltage drop across the switch due to its small value. Under such conditions, the power P = (20 - 12) ∙ I = 8 ∙ 3 = 24 W will drop on the current stabilizer itself. During a short circuit, the power will increase to 60W, if without protection. This is too much, and it is not safe for the VT2 transistor, so after 30W we will turn off the stabilizer by placing a zener diode with a stabilization voltage of 10V in the protection circuit. Thus, we get a circuit with protection not only from short circuits, but also from exceeding the permissible power dissipation on the current stabilizer. Let's say that for some reason, completely unnecessary to us, the load resistance begins to drop. This will cause an increase in the voltage drop across the stabilizer and, accordingly, the power dissipation on it. But as soon as the voltage between the input and output exceeds 10 volts, the zener diode VD1 will “break through” and current will flow through the LED of the optocoupler U1. The emission of the LED will open the photothyristor, which will bypass the gate-source transition of the key transistor. It will, in turn, close and turn off the stabilizer circuit. It will be possible to return the circuit to working condition either by turning off the power and reconnecting it, or by short-circuiting the photothyristor, for example with a button. Thus, by monitoring the voltage between the input and output of the current stabilizer, you can set the power limit threshold you need using zener diodes for different stabilization voltages.
This circuit is applicable to almost all stabilizers, whether for current or voltage. It can be built into a ready-made stabilizer that does not have short-circuit protection.
Good luck and good luck. K.V.Yu.
In transistor stabilizers, three types of protection are most often used: from increasing the output voltage, from decreasing the output voltage, from overcurrent or short circuit in the load.
Overcurrent protection in stabilizers can be limited to a constant level of I K.Z. exceeding the value of I NOM or with a sharp decrease in current consumption to I K.Z.0 in short circuit mode. In the first case, the overcurrent mode is characterized by greater power allocated to the control transistor. Therefore, in such cases, the supply voltage at the stabilizer input is usually turned off. In the second case, the power dissipated by the transistor during a short circuit is significantly less than the power at the rated load current. Therefore, turning off the power in such a circuit is not necessary.
Traditional transistor stabilizers often have unreliable overload protection. Inertia-free protection systems falsely trigger even from short-term overloads when connecting a capacitive load. Inertial protection means do not have time to operate in the event of a strong current pulse, for example, in the event of a short circuit leading to breakdown of transistors. Devices with an output current limiter are inertia-free; they do not have a trigger effect, but in the event of a short circuit, a large amount of power is dissipated on the control transistor, which requires the use of an appropriate heat sink .
The only way out in this situation is the simultaneous use of means for limiting the output current and inertial protection of the control transistor from overload, which will provide it with two to three times less power and heat sink dimensions. But this leads to an increase in the number of elements, design dimensions and complicates the repeatability of the device in amateur conditions.
A schematic diagram of a stabilizer, the number of elements in which is minimal, is shown in Fig. 1. The source of the reference voltage is a thermally stabilized zener diode VD1.
To eliminate the influence of the input voltage of the stabilizer on the mode of the zener diode, its current is set by a stable current generator (GCT), built on a field-effect transistor VT1. Thermal stabilization and stabilization of the Zener diode current increase the output voltage stabilization coefficient.
The reference voltage is supplied to the left (according to the circuit) input of the differential amplifier on transistors VT2.2 and VT2.3 of the K125NT1 microassembly and resistor R7, where it is compared with the feedback voltage taken from the output voltage divider R8R9. The voltage difference at the inputs of a differential amplifier changes the balance of the collector currents of its transistors.
The regulating transistor VT4, controlled by the collector current of the transistor VT2.2, has a large base current transfer coefficient. This increases the depth of feedback and increases the stabilization coefficient of the device, and also reduces the power dissipated by the differential amplifier transistors.
Let's look at the operation of the device in more detail.
Let us assume that in steady state, with an increase in the load current, the output voltage will decrease slightly, which will also cause a decrease in the voltage at the emitter junction of transistor VT3.2. At the same time, the collector current will also decrease. This will lead to an increase in the current of transistor VT2.2, since the sum of the output currents of the differential amplifier transistors is equal to the current flowing through resistor R7, and practically does not depend on the operating mode of its transistors.
In turn, the growing current of transistor VT2.2 causes an increase in the collector current of the control transistor VT4, proportional to its base current transfer coefficient, increasing the output voltage to the original level and allows it to be maintained unchanged regardless of the load current.
For short-term protection of the device with its return to its original state, a collector current limiter of the regulating transistor is introduced, made on transistor VT3 and resistors R1, R2.
Resistor P1 performs the function of a current sensor flowing through the regulating transistor VT4. If the current of this transistor exceeds the maximum value (about 0.5 A), the voltage drop across resistor R1 will reach 0.6 V, i.e. the threshold voltage for opening transistor VT3. Opening, it shunts the emitter junction of the control transistor, thereby limiting its current to approximately up to 0.5 A.
Thus, when the load current briefly exceeds the maximum value, transistors VT3 and VT4 operate in the GTS mode, which causes a drop in the output voltage without tripping the overcurrent protection. After some time, proportional to the time constant of circuit R5C1, this leads to the opening of transistor VT2.1 and the further opening of transistor VT3, which closes transistor VT4. This state of the transistors is stable, therefore, after eliminating the short circuit or de-energizing the load, it is necessary to disconnect the device from the network and turn it on again after discharging capacitor C1.