The considered continuous compensation voltage stabilizer reduces the maximum power dissipated by the control transistor in short-circuit mode. The electrical circuit diagram of the stabilizer is shown in Fig. 5.
Current limit mode
Resistor R 1 is a current sensor. In case of overcurrent R 1 a voltage arises, which through a resistor R 2 supplied to the base-emitter junction of the transistor VT3 , which opens slightly. As a result, base and collector currents appear VT3 , which reduce the base current of the transistor VT2 , the collector currents of the transistors decrease accordingly VT2 And VT1 , which leads to limiting the output current of the voltage regulator.
Short circuit protection
For protection, 2 resistors are used - R 2 And R 3 and during normal operation
transistor emitter voltage VT1 equals output. During a short circuit, the output voltage is zero, and accordingly the voltage at the emitter of the transistor VT1
is also zero and the entire input voltage is applied to the resistors R 2 And R 3 . Voltage at
R 2 increases and the voltage drop is added to it R 1 , which leads to the discovery
Rice. 5. Circuit diagram of the voltage stabilizer
on an op-amp with a varying current limit level
and with short circuit protection
transistor VT3 . Resistors R 2 And R 3 designed so that the collector current VT3 in short circuit mode was approximately 80% of the base current VT2 . Accordingly, the base current VT2 decreases by about 5 times, which leads to a decrease in the collector current VT1 also 5 times. Thus the transistor VT1 protected against overload in case of short circuit.
Output voltage stabilization
If in normal operation for some reason the output voltage of the stabilizer changes, then the voltage created by the divider also changes R 6 , R 7 , R 8 at point A. Operational amplifier DA1 amplifies the difference between the reference voltage () and the voltage at point A (), which can be calculated using the formula
If the voltage at the output of the stabilizer has decreased, then the difference will be positive and increases, which leads to a decrease in the current passing through the zener diode VD3 , which is part of the current passing through R 4 .The other part goes to the base of the transistor VT2 and to the output of the operational amplifier DA1 . Accordingly, if it decreases, then the currents increase, and, and, accordingly, increases. When increasing, the stabilization circuit works along a similar chain (reducing the deviation.
Zener diode VD3 turns on to enable the operational amplifier DA1 worked in active mode, in which it should be approximately half the operational amplifier supply voltage (+U). The output voltage of the stabilizer itself () can be significantly higher. Transistor based VT2 voltage is higher than 2. Accordingly, the difference between and the voltage at the base VT2 is a certain value, which is compensated using a zener diode VD3
POWER SUPPLIES
SIMPLIFIED VOLTAGE STABILIZER WITH DOUBLE OVERLOAD PROTECTION
A voltage stabilizer with double protection against short circuit in the load, described in, aroused considerable interest among radio amateurs. However, judging by the responses, it has a significant drawback: the engine
The output voltage regulator must be set to zero after eliminating the current overload before pressing the SB button! “Start* In connection with this, proposals appeared to eliminate this shortcoming. A constant voltage of 40...44 V is applied to the input of the stabilizer from the rectifier. The stabilized output voltage from 0.2 to 28 V is set with resistor R2 and controlled with a voltmeter PU1. Maximum load current - 2 A.
The appearance of the laboratory power supply, in which the described voltage stabilizer is installed, is shown in the title of the article. The stabilizer parts are mounted on a board made of foil fiberglass.
(Fig. 2) and on the front panel of the power supply housing. Regulating transistor VT2 is installed
flax on the heat sink - the back wall of the device.
Transistor KT608 (with letter index A or B) can be replaced with KT815 (B, C, D),
KT8I7 (V. G). KT801 (A B), and KT803A - on KT802A. KT805 (A. B), KT808A, KT819 (V. G). We will replace the KU202K thyristor with KU201V-KU201L, K U202 V-KU202N, the D816B zener diode with D816V or KS533A (you can connect in series the bottom of the D815 D816 zener diode for a total stable voltage of 28 ... 36 V) Instead of the D220A diode (VD2), D219 will be suitable, D220,
D223, KD102, KD YuZ with any letter indices, and instead of the KD105B (VD3) diode KD106A or any other silicon one with a forward current of up to 300 mA and a reverse voltage of at least 50 V.
Variable resistor R2 (6.8... 15 kOhm) of any type with characteristic A. Relay K1 - RES9 (passport RS4.524 200) or another with two groups of switching contacts, operating at a voltage of no more than 30 V.
Resistor R4 - several turns of a constant novo, pychrome or maiginin wire wound around the housing of the MLT-1 resistor. Its resistance is determined by the value of the current of the selected operating limit, which, in turn, depends on the voltage at the control electrode of the installed thyristor, at which this stabilizer key opens. for example, if the maximum operating current of the system is taken to be 2 A, and the transistor opens when the voltage on the control electrode is about 1 V, the resistance of resistor R4 should be (according to Ohm’s law) close to 0.5 Ohm.
More accurately, the resistor resistance is adjusted to the selected protection operation limit in this order. An ammeter and a wirewound variable resistor with a resistance of 25-30 Ohms connected in series are connected to the output of the stabilizer. The corresponding voltage is supplied to the input of the stabilizer from the rectifier and resistor R2 is set at the output voltage
10... 15 V. Then a variable resistor that performs the function of the equivalent of the installation load
This article will discuss the circuit of a simple but effective voltage stabilizer with output short circuit protection. The basis of the stabilizer is the K157HP2 integrated stabilizer; the KT808A n-p-n transistor is used as the control transistor. The stabilizer circuit is shown in Figure 1.
First, let's look at the internal structure of the K157HP2 microcircuit. Its diagram is presented in Figure 2.
In addition to the stabilizer itself, the microcircuit has two more separate transistor structures, these are transistors VT29 and VT30. We will use them, in parallel connection, as a preliminary amplification stage for the control transistor VT1 KT808A. The microcircuit has the function of smoothly switching on the stabilizer. The rise time of the output voltage depends on the capacitance of capacitor C5, Figure 1, connected to pin 8 of DA1. The presence of a smooth increase in voltage makes it possible to significantly reduce the amplitude of the charging current pulse when the stabilizer operates on a capacitive load. The microcircuit has internal protection against excess load current. The current sensor in this case is resistor R12. The limit threshold is 200mA. And one more very useful option for this microcircuit is On/Off. If a voltage of more than two volts is applied to pin 9 of DA1, the stabilizer will turn on; if the voltage is removed, the stabilizer will turn off almost completely. The output voltage of a closed stabilizer is only a few tens of millivolts.
Another plus is thermal protection. The crystal is protected from overheating by the VT18 transistor, the base of which is supplied with a part of the reference voltage, which is insufficient to open it at normal temperature. When the crystal temperature rises to +165...180°C, transistor VT18 opens and bypasses the base circuit of transistor VT22.
When voltage is applied to the stabilizer circuit, this voltage goes to the collector of transistors VT1, Figure 1, VT29 and VT30 pins 12 and 3 of the DA1 microcircuit. This voltage is also supplied to capacitor C4, which is located in the start circuit of the stabilizer circuit. At the moment voltage is applied to the circuit, the charging current of this capacitor turns on the stabilizer of the microcircuit. At the output of the microcircuit stabilizer, pin 11, an opening voltage appears, which is supplied through the limiting resistor R3 to the bases of transistors VT29 and VT30 of the DA1 microcircuit. From the emitters, pin 1 DA1, of these transistors, the signal is supplied to the base of the powerful transistor VT1, Figure 1. The voltage will appear at the output of the complete stabilizer circuit. Part of this voltage through resistor R3, a value of more than 2V, will go to pin 9 DA1- On/Off. Now the stabilizer in the on state will be held not by the charging current of capacitor C4, but by the current flowing through the feedback resistor R3. Based on the above, it becomes clear how the stabilizer protection circuits work against short circuit conditions. When the output terminals of the stabilizer are closed, the upper terminal of resistor R3 is shorted to the common wire of the device, the voltage at pin 9 of DA1 disappears, and the stabilizer turns off. The circuit can be returned to working condition by turning off and then turning on the stabilizer again. You can place the “Restart” button in parallel with the start capacitor C4.
The output voltage is adjusted using variable resistor R4. The minimum output voltage of the stabilizer is equal to the voltage of the internal ION and corresponds to 1.3 V. The maximum voltage naturally depends on the value of the input, but not more than 40 volts, the voltage drop on the stabilizer circuit and the value of resistor R5. If you do not need to limit the output voltage, then this resistor can be excluded from the circuit.
An n-p-n transistor of the KT808A structure is used as a powerful control transistor VT1
It can be replaced with any suitable transistors KT819, KT827, KT829, imported transistors from the TIR series, etc. and so on. It is better to use a tantalum capacitor for filter C3, such as ETO, but in the absence of this, you can also use a regular electrolyte. Any capacitor C1. It stands parallel to the input terminals of the circuit, but physically it must be located directly next to the DA1 chip. Like capacitor C2, according to the circuit it is parallel to the output, but it should also be located next to the microcircuit. The error amplifier of this microcircuit has a large gain; the greater the Kus, the greater the tendency to excitation. Therefore, how you install the stabilizer depends on the stability of its operation. Ultimately, the reliability of the devices that will be powered by this stabilizer depends on this.
The appearance of the experimental stabilizer module is shown in photo 1.
The photo shows an experimental board, but when you make your own, be sure to stick to the layout shown. Resistor R1 can be placed on the board, or it can be soldered directly to the terminals of transistor VT1. To reduce the output resistance of the stabilizer, the upper and lower terminals of the regulating chain R4 and R5 must be connected to the output terminal of the device in order to eliminate the influence of the voltage drop on the mounting wires, and do not forget about the cross-section of the wires for the corresponding load current.
Good luck, 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.
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