I needed to make a speed controller for the propeller. To blow away the smoke from the soldering iron and ventilate the face. Well, just for fun, pack everything into a minimum price. The easiest way is a low-power engine DC, of course, to regulate with a variable resistor, but to find a reduction for such a small value, and even the required power, it takes a lot of effort, and it will obviously not cost ten rubles. Therefore, our choice is PWM + MOSFET.
I took the key IRF630. Why this one MOSFET? Yes, I just got about ten of them from somewhere. So I use it, so I can install something smaller and low-power. Because the current here is unlikely to be more than an ampere, but IRF630 capable of pulling through itself under 9A. But it will be possible to make a whole cascade of fans by connecting them to one fan - enough power :)
Now it's time to think about what we will do PWM. The thought immediately suggests itself - a microcontroller. Take some Tiny12 and do it on it. I threw this thought away instantly.
- I feel bad about spending such a valuable and expensive part on some kind of fan. I'll find a more interesting task for the microcontroller
- Writing more software for this is doubly frustrating.
- The supply voltage there is 12 volts, lowering it to power the MK to 5 volts is generally lazy
- IRF630 will not open from 5 volts, so you would also have to install a transistor here so that it supplies a high potential to the field gate. Fuck it.
Op amps can be discarded outright. The fact is that for general-purpose op-amps, already after 8-10 kHz, as a rule, output voltage limit it begins to collapse sharply, and we need to jerk the fieldman. Moreover, at a supersonic frequency, so as not to squeak.
Op-amps without such a drawback cost so much that with this money you can buy a dozen of the coolest microcontrollers. Into the furnace!
Comparators remain; they do not have the ability of an op-amp to smoothly change the output voltage; they can only compare two voltages and close the output transistor based on the results of the comparison, but they do it quickly and without blocking the characteristics. I rummaged through the bottom of the barrel and couldn’t find any comparators. Ambush! More precisely it was LM339, but it was in a large case, and religion does not allow me to solder a microcircuit for more than 8 legs for such a simple task. It was also a shame to drag myself to the storehouse. What to do?
And then I remembered such a wonderful thing as analog timer - NE555. It is a kind of generator where you can set the frequency, as well as the pulse and pause duration, using a combination of resistors and a capacitor. How much different crap has been done on this timer over its more than thirty-year history... Until now, this microcircuit, despite its venerable age, is printed in millions of copies and is available in almost every warehouse for a price of a few rubles. For example, in our country it costs about 5 rubles. I rummaged through the bottom of the barrel and found a couple of pieces. ABOUT! Let's stir things up right now.
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How does this work
If you don’t delve deeply into the structure of the 555 timer, it’s not difficult. Roughly speaking, the timer monitors the voltage on capacitor C1, which it removes from the output THR(THRESHOLD - threshold). As soon as it reaches the maximum (the capacitor is charged), the internal transistor opens. Which closes the output DIS(DISCHARGE - discharge) to ground. At the same time, at the exit OUT a logical zero appears. The capacitor begins to discharge through DIS and when the voltage on it becomes zero (full discharge), the system will switch to the opposite state - at output 1, the transistor is closed. The capacitor begins to charge again and everything repeats again.
The charge of capacitor C1 follows the path: “ R4->upper shoulder R1 ->D2", and the discharge along the way: D1 -> lower arm R1 -> DIS. When we turn the variable resistor R1, we change the ratio of the resistances of the upper and lower arms. Which, accordingly, changes the ratio of the pulse length to the pause.
The frequency is set mainly by capacitor C1 and also depends slightly on the value of resistance R1.
Resistor R3 ensures that the output is pulled to a high level - so there is an open-collector output. Which is not capable of independently exhibiting high level.
You can install any diodes, the conductors are approximately the same value, deviations within one order of magnitude do not particularly affect the quality of work. At 4.7 nanofarads set in C1, for example, the frequency drops to 18 kHz, but it is almost inaudible, apparently my hearing is no longer perfect :(
I dug into the bins, which itself calculates the operating parameters of the NE555 timer and assembled a circuit from there, for astable mode with a fill factor of less than 50%, and screwed in a variable resistor instead of R1 and R2, with which I changed the duty cycle of the output signal. You just need to pay attention to the fact that the DIS output (DISCHARGE) is via the internal timer key connected to ground, so it could not be connected directly to the potentiometer, because when twisting the regulator to its extreme position, this pin would land on Vcc. And when the transistor opens, there will be a natural short circuit and the timer with a beautiful zilch will emit magic smoke, on which, as you know, all electronics work. As soon as the smoke leaves the chip, it stops working. That's it. Therefore, we take and add another resistor for one kilo-ohm. It won’t make a difference in regulation, but it will protect against burnout.
No sooner said than done. I etched the board and soldered the components:
Everything is simple from below.
Here I am attaching a signet, in the native Sprint Layout -
And this is the voltage on the engine. A small transition process is visible. You need to put the conduit in parallel at half a microfarad and it will smooth it out.
As you can see, the frequency floats - this is understandable, since our operating frequency depends on the resistors and capacitor, and since they change, the frequency floats away, but this does not matter. Throughout the entire control range, it never enters the audible range. And the entire structure cost 35 rubles, not counting the body. So - Profit!
Adjusting the speed of electric motors in modern electronic technology is achieved not by changing the supply voltage, as was done before, but by applying current pulses to the electric motor, of different durations. PWM, which has recently become very popular, is used for these purposes ( pulse width modulated) regulators. The circuit is universal - it also controls the engine speed, the brightness of the lamps, and the current in the charger.
PWM regulator circuit
The above diagram works great, attached.
Without altering the circuit, the voltage can be raised to 16 volts. Place the transistor depending on the load power.
Can be assembled PWM regulator and according to this electrical diagram, with a conventional bipolar transistor:
And if necessary, instead of the composite transistor KT827, install a field-effect IRFZ44N, with resistor R1 - 47k. The polevik without a radiator does not heat up at a load of up to 7 amperes.
PWM controller operation
The timer on the NE555 chip monitors the voltage on capacitor C1, which is removed from the THR pin. As soon as it reaches the maximum, the internal transistor opens. Which shorts the DIS pin to ground. In this case, a logical zero appears at the OUT output. The capacitor begins to discharge through DIS and when the voltage on it becomes zero, the system will switch to the opposite state - at output 1, the transistor is closed. The capacitor begins to charge again and everything repeats again.
The charge of capacitor C1 follows the path: “R2->upper arm R1 ->D2”, and the discharge along the path: D1 -> lower arm R1 -> DIS. When we rotate the variable resistor R1, we change the ratio of the resistances of the upper and lower arms. Which, accordingly, changes the ratio of the pulse length to the pause. The frequency is set mainly by capacitor C1 and also depends slightly on the value of resistance R1. By changing the charge/discharge resistance ratio, we change the duty cycle. Resistor R3 ensures that the output is pulled to a high level - so there is an open-collector output. Which is not able to independently set a high level.
You can use any diodes, capacitors of approximately the same value as in the diagram. Deviations within one order of magnitude do not significantly affect the operation of the device. At 4.7 nanofarads set in C1, for example, the frequency drops to 18 kHz, but it is almost inaudible.
If after assembling the circuit the key control transistor gets hot, then most likely it does not open completely. That is, there is a large voltage drop across the transistor (it is partially open) and current flows through it. As a result, a lot of power is dissipated for heating. It is advisable to parallel the circuit at the output with high-capacity capacitors, otherwise it will sing and be poorly regulated. To avoid whistling, select C1, the whistling often comes from it. IN general area applications are very wide, its use as a brightness regulator for powerful LED lamps, LED strips and spotlights, but more about that next time. This article was written with the support of ear, ur5rnp, stalker68.
In this article you will learn about:
Each of us uses a large number of different electrical appliances in our lives. A very large number of them require low-voltage power. In other words, they consume electricity, which is not characterized by a voltage of 220 volts, but should have from one to 25 volts.
Of course, special devices are used to supply electricity with such a number of volts. However, the problem does not arise in lowering the voltage, but in maintaining its stable level.
To do this, you can use linear stabilization devices. However, such a solution will be a very cumbersome pleasure. This task will be ideally performed by any switching voltage stabilizer.
Disassembled pulse stabilizer
If we compare pulse and linear stabilization devices, their main difference lies in the operation of the control element. In the first type of devices, this element works like a key. In other words, it is either in a closed or open state.
The main elements of pulse stabilization devices are regulating and integrating elements. The first ensures the supply and interruption of electrical current. The task of the second is to accumulate electricity and gradually release it to the load. 
Operating principle of pulse converters
Operating principle of a pulse stabilizer
The main principle of operation is that when the regulating element is closed, electrical energy is accumulated in the integrating element. This accumulation is observed by increasing voltage. After the control element is switched off, i.e. opens the electricity supply line, the integrating component releases electricity, gradually reducing the voltage. Thanks to this method of operation, the pulse stabilization device does not waste large quantity energy and may have small dimensions.
The regulating element can be a thyristor, a bipolar transient or field effect transistor. Chokes, batteries or capacitors can be used as integrating elements.
Note that pulse stabilization devices can operate in two in various ways. The first involves the use of pulse width modulation (PWM). The second is a Schmitt trigger. Both PWM and Schmitt trigger are used to control the switches of the stabilization device.
Stabilizer using PWM
A switching DC voltage stabilizer, which operates on the basis of PWM, in addition to the switch and integrator, contains:
- generator;
- operational amplifier;
- modulator
The operation of the switch directly depends on the input voltage level and the duty cycle of the pulses. The last characteristic is influenced by the frequency of the generator and the capacitance of the integrator. When the switch opens, the process of transferring electricity from the integrator to the load begins.
Schematic diagram of a PWM stabilizer
In this case, the operational amplifier compares the levels of the output voltage and the reference voltage, determines the difference and transmits the required gain to the modulator. This modulator converts the pulses produced by the generator into rectangular pulses.
The final pulses are characterized by the same duty cycle deviation, which is proportional to the difference between the output voltage and the comparison voltage. It is these impulses that determine the behavior of the key.
That is, at a certain duty cycle, the switch can close or open. It turns out that impulses play the main role in these stabilizers. This is actually where the name of these devices comes from.
Schmitt trigger converter
Those pulse stabilization devices that use a Schmitt trigger no longer have such a large number of components as in the previous type of device. Here the main element is the Schmitt trigger, which includes a comparator. The task of the comparator is to compare the voltage level at the output and its maximum permissible level.
Stabilizer with Schmitt trigger
When the output voltage has exceeded its maximum level, the trigger switches to the zero position and opens the switch. At this time, the inductor or capacitor is discharged. Of course, the characteristics of the electric current are constantly monitored by the aforementioned comparator.
And then, when the voltage drops below the required level, phase “0” changes to phase “1”. Next, the key closes and electric current flows into the integrator.
The advantage of such a pulse voltage stabilizer is that its circuit and design are quite simple. However, it cannot be applied in all cases.
It is worth noting that pulse stabilization devices can only work in certain directions. What we mean here is that they can be either purely downward or purely upward. There are also two more types of such devices, namely inverting and devices that can arbitrarily change the voltage.
Scheme of a reducing pulse stabilization device
In the future, we will consider the circuit of a reducing pulse stabilization device. It consists of:
- Regulating transistor or any other type of switch.
- Inductors.
- Capacitor.
- Diode.
- Loads.
- Control devices.
The unit in which the supply of electricity will be accumulated consists of the coil itself (inductor) and a capacitor.
While the switch (in our case, the transistor) is connected, current flows to the coil and capacitor. The diode is in the closed state. That is, it cannot pass current.
The initial energy is monitored by a control device, which at the right moment turns off the key, that is, puts it in the cut-off state. When the switch is in this state, there is a decrease in the current that passes through the inductor.
Buck pulse stabilizer
In this case, the direction of voltage in the inductor changes and as a result the current receives a voltage, the value of which is the difference between electromotive force self-inductance of the coil and the number of volts at the input. At this time, the diode opens and the inductor supplies current to the load through it.
When the supply of electricity is exhausted, the key is connected, the diode is closed and the inductor is charged. That is, everything repeats itself.
A step-up switching voltage stabilizer works in the same way as a step-down voltage regulator. An inverting stabilization device is characterized by a similar operating algorithm. Of course, his work has its differences.
The main difference between a pulse boost device is that its input voltage and coil voltage have the same direction. As a result, they are summed up. The switching stabilizer first places a choke, then a transistor and a diode.
In an inverting stabilization device, the direction of the EMF of the self-induction of the coil is the same as in a step-down device. While the switch is connected and the diode closes, the capacitor provides power. Any of these devices can be assembled with your own hands.
Helpful advice: instead of diodes, you can use switches (thyristor or transistor). However, they must perform operations that are the opposite of the primary key. In other words, when the main key closes, the key should open instead of the diode. And vice versa.
Based on the above-defined structure of voltage stabilizers with pulse regulation, it is possible to determine those features that are considered advantages and which are disadvantages.
Advantages
The advantages of these devices are:
- It is quite easy to achieve such stabilization, which is characterized by a very high coefficient.
- High level efficiency. Due to the fact that the transistor operates in a switch algorithm, low power dissipation occurs. This dissipation is significantly less than in linear stabilization devices.
- The ability to equalize voltage, which at the input can fluctuate over a very wide range. If the current is constant, then this range can be from one to 75 volts. If the current is alternating, then this range can fluctuate between 90-260 volts.
- Lack of sensitivity to input voltage frequency and power supply quality.
- The final output parameters are quite stable even if very large changes in current occur.
- The voltage ripple that comes out of a pulse device is always within the millivolt range and does not depend on the power of the connected electrical appliances or their elements.
- The stabilizer always turns on softly. This means that the output current is not characterized by jumps. Although it should be noted that when turned on for the first time, the current surge is high. However, to level out this phenomenon, thermistors are used that have a negative TCR.
- Small values of mass and size.
Flaws
- If we talk about the disadvantages of these stabilization devices, they lie in the complexity of the device. Due to the large number of different components that can fail quite quickly, and the specific method of operation, the device cannot boast of a high level of reliability.
- He constantly faces high voltage. During operation, switching occurs frequently and difficult temperature conditions for the diode crystal are observed. This clearly affects the suitability for current rectification.
- Frequent switching of switches creates frequency interference. Their number is very large and this is a negative factor.
Helpful advice: to eliminate this shortcoming you need to use special filters.
- They are installed both at the entrance and at the exit. In the case when repairs need to be made, they are also accompanied by difficulties. It is worth noting here that a non-specialist will not be able to fix the breakdown.
- Repair work can be carried out by someone who is well versed in such current converters and has required quantity skills. In other words, if such a device burns out and its user does not have any knowledge about the features of the device, then it is better to take it to specialized companies for repair.
- It is also difficult for non-specialists to configure switching voltage stabilizers, which may include 12 volts or another number of volts.
- If a thyristor or any other switch fails, very complex consequences may arise at the output.
- The disadvantages also include the need to use devices that will compensate for the power factor. Also, some experts note that such stabilization devices are expensive and cannot boast of a large number of models.
Areas of application
But despite this, such stabilizers can be used in many areas. However, they are most used in radio navigation equipment and electronics.
In addition, they are often used for LCD TVs and LCD monitors, power supplies for digital systems, as well as for industrial equipment, which needs a current with a low number of volts.
Helpful advice: pulse stabilization devices are often used in networks with alternating current. The devices themselves convert such current into direct current, and if you need to connect users who need alternating current, then you need to connect a smoothing filter and a rectifier at the input.
It is worth noting that any low-voltage device requires the use of such stabilizers. They can also be used to directly charge various batteries and power high-power LEDs.
Appearance
As noted above, pulse-type current converters are characterized by small sizes. Depending on the range of input volts they are designed for, their size and appearance depend.
If they are designed to operate with very low input voltages, they may consist of a small plastic box from which a certain number of wires extend.
Stabilizers, designed for a large number of input volts, are a microcircuit in which all the wires are located and to which all components are connected. You have already learned about them.
The appearance of these stabilization devices also depends on functional purpose. If they provide a regulated (alternating) voltage output, then the resistor divider is placed outside the integrated circuit. In the event that a fixed number of volts comes out of the device, then this divider is already located in the microcircuit itself.
Important Features
When selecting a switching voltage stabilizer that can produce constant 5V or another number of volts, pay attention to a number of characteristics.
The first and most important characteristic is the minimum and maximum voltage that will be included in the stabilizer itself. The upper and lower limits of this characteristic have already been noted.
Second important parameter is the highest current level at the output.
The third important characteristic is the nominal output voltage level. In other words, the spectrum of quantities within which it can be found. It is worth noting that many experts claim that the maximum input and output voltages are equal.
However, in reality this is not the case. The reason for this is that the input volts are reduced at the switch transistor. The result is a slightly smaller number of volts at the output. Equality can only occur when the load current is very small. The same applies to minimum values.
An important characteristic of any pulse converter is the accuracy of the output voltage.
Helpful advice: you should pay attention to this indicator when the stabilization device provides an output of a fixed number of volts.
The reason for this is that the resistor is located in the middle of the converter and its exact operation is determined in production. When the number of output volts is adjusted by the user, the accuracy is also adjusted.
Linear stabilizers have a common disadvantage - low efficiency and high heat generation. Powerful devices that create load current over a wide range have significant dimensions and weight. To compensate for these shortcomings, pulse stabilizers have been developed and used.
A device that maintains a constant voltage at a current consumer by adjusting an electronic element operating in key mode. A switching voltage stabilizer, just like a linear one, exists in series and parallel types. The role of the key in such models is played by transistors.
Since the effective point of the stabilizing device is almost constantly located in the cutoff or saturation region, passing through the active region, a little heat is generated in the transistor, therefore, the pulse stabilizer has a high efficiency.
Stabilization is carried out by changing the duration of the pulses, as well as controlling their frequency. As a result, a distinction is made between pulse-frequency and, in other words, width-width regulation. Pulse stabilizers operate in a combined pulse mode.
In stabilization devices with pulse-width control, the pulse frequency has a constant value, and the duration of the pulses is a variable value. In devices with pulse-frequency control, the duration of the pulses does not change, only the frequency is changed.
At the output of the device, the voltage is presented in the form of ripples; accordingly, it is not suitable for powering the consumer. Before supplying power to the consumer load, it must be equalized. To do this, leveling capacitive filters are mounted at the output of pulse stabilizers. They come in multi-link, L-shaped and others.
The average voltage applied to the load is calculated by the formula:
- Ti is the duration of the period.
- ti – pulse duration.
- Rн – value of consumer resistance, Ohm.
- I(t) – value of the current passing through the load, amperes.
Current may stop flowing through the filter by the start of the next pulse, depending on the inductance. In this case we are talking about the operating mode with alternating current. The current can also continue to flow, which means operation with direct current.
With increased sensitivity of the load to power pulses, the DC mode is performed, despite significant losses in the inductor winding and wires. If the size of the pulses at the output of the device is insignificant, then operation with alternating current is recommended.
Operating principle
In general, a pulse stabilizer includes a pulse converter with an adjustment device, a generator, an equalizing filter that reduces voltage pulses at the output, and a comparing device that supplies a signal of the difference between the input and output voltages.
A diagram of the main parts of the voltage stabilizer is shown in the figure.
The voltage at the output of the device is supplied to a comparing device with the base voltage. The result is a proportional signal. It is supplied to the generator, having previously amplified it.
When controlled in a generator, the difference analog signal is modified into a ripple with a constant frequency and variable duration. With pulse-frequency control, the duration of the pulses has a constant value. It changes the frequency of the generator pulses depending on the properties of the signal.
The control pulses generated by the generator pass to the elements of the converter. The control transistor operates in key mode. By changing the frequency or interval of the generator pulses, it is possible to change the load voltage. The converter modifies the output voltage value depending on the properties of the control pulses. According to theory, in devices with frequency and width adjustment, voltage pulses at the consumer may be absent.
With the relay operating principle, the signal controlled by the stabilizer is generated using a trigger. When constant voltage enters the device, the transistor, which acts as a switch, is open and increases the output voltage. the comparing device determines the difference signal, which, having reached a certain upper limit, changes the state of the trigger, and the control transistor switches to cutoff.
The output voltage will begin to decrease. When the voltage drops to the lower limit, the comparing device determines the difference signal, switching the trigger again, and the transistor will again go into saturation. The potential difference across the device load will increase. Consequently, with a relay type of stabilization, the output voltage increases, thereby equalizing it. The trigger limit is adjusted by adjusting the amplitude of the voltage value on the comparing device.
Relay type stabilizers have increased speed reactions, in contrast to devices with frequency and latitude regulation. This is their advantage. In theory, with a relay type of stabilization, there will always be pulses at the output of the device. This is their disadvantage.
Boost stabilizer
Switching boost regulators are used together with loads whose potential difference is higher than the voltage at the input of the devices. The stabilizer does not have galvanic isolation between the power supply and the load. Imported boost stabilizers are called boost converters. The main parts of such a device:
The transistor enters saturation, and current flows through the circuit from the positive pole through the storage inductor, the transistor. In this case, energy accumulates in the magnetic field of the inductor. The load current can only be created by a discharge of capacitance C1.
Let's turn off the switching voltage from the transistor. At the same time, it will enter the cut-off position, and therefore a self-induction EMF will appear on the throttle. It will be switched in series with the input voltage, and connected via a diode to the consumer. The current will flow through the circuit from the positive pole to the inductor, through the diode and the load.
At this moment, the magnetic field of the inductive choke supplies energy, and capacitance C1 reserves energy to maintain the voltage at the consumer after the transistor enters saturation mode. The choke is for energy reserve and does not work in the power filter. When voltage is applied again to the transistor, it will open and the whole process will begin again.
Stabilizers with Schmitt trigger
This type of pulse device has its own characteristics with the smallest set of components. The trigger plays a major role in the design. It includes a comparator. The main task of the comparator is to compare the value of the output potential difference with the highest permissible value.
The principle of operation of the device with a Schmitt trigger is that when the highest voltage increases, the trigger is switched to the zero position with the electronic key opening. At one time the throttle discharges. When the voltage reaches its lowest value, switching by one is performed. This ensures the switch closes and current flows to the integrator.
Such devices are distinguished by their simplified circuit, but they can be used in special cases, since pulse stabilizers are only step-up and step-down.
Buck stabilizer
Pulse-type stabilizers operating with voltage reduction are compact and powerful power devices electric shock. At the same time, they have low sensitivity to consumer interference with a constant voltage of the same value. There is no galvanic isolation of the output and input in step-down devices. Imported devices are called chopper. The output power in such devices is always less than the input voltage. The circuit of a buck-type pulse stabilizer is shown in the figure.
Let's connect the voltage to control the source and gate of the transistor, which will enter the saturation position. It will carry current through the circuit from the positive pole through the equalizing choke and the load. No current flows through the diode in the forward direction.
Let's turn off the control voltage, which turns off the key transistor. After this, it will be in the cut-off position. The inductive emf of the equalizing choke will block the path for changing the current, which will flow through the circuit through the load from the choke, along the common conductor, diode, and again come to the choke. Capacitance C1 will discharge and will maintain the voltage at the output.
When an unlocking potential difference is applied between the source and gate of the transistor, it will go into saturation mode and the entire chain will repeat again.
Inverting stabilizer
Inverting-type switching stabilizers are used to connect consumers with constant voltage, the polarity of which has the opposite polarity direction to the potential difference at the output of the device. Its value can be above the power supply network, and below the network, depending on the settings of the stabilizer. There is no galvanic isolation between the power supply and the load. Imported inverting type devices are called buck-boost converters. The output voltage of such devices is always lower.
Let's connect a control potential difference, which will open the transistor between the source and the gate. It will open, and the current will flow through the circuit from the plus through the transistor, the inductor, to the minus. In this process, the inductor reserves energy using its magnetic field. Let's turn off the control potential difference from the switch on the transistor, it will close. The current will flow from the inductor through the load, diode, and return to its original position. The reserve energy on the capacitor and magnetic field will be consumed by the load. Let's apply power to the transistor again to the source and gate. The transistor will again become saturated and the process will repeat.
Advantages and Disadvantages
Like all devices, a modular switching stabilizer is not ideal. Therefore, it has its own pros and cons. Let's look at the main advantages:
- Easily achieve alignment.
- Smooth connection.
- Compact sizes.
- Output voltage stability.
- Wide stabilization interval.
- Increased efficiency.
Disadvantages of the device:
- Complex design.
- There are many specific components that reduce the reliability of the device.
- The need to use power compensating devices.
- Difficulty of repair work.
- Formation of a large amount of frequency interference.
Allowable frequency
The operation of a pulse stabilizer is possible at a significant conversion frequency. This is the main distinctive feature from devices with a network transformer. Increasing this parameter makes it possible to obtain the smallest dimensions.
For most devices, the frequency range will be 20-80 kilohertz. But when choosing PWM and key devices, it is necessary to take into account high current harmonics. The upper limit of the parameter is limited by certain requirements that apply to radio frequency devices.
This circuit is a step-down regulator with the ability to regulate and protect or limit the current. A special feature of the device is the use of a static induction bipolar transistor (BSIT) and a TL494 microcircuit with two operational amplifiers in the power section. Op-amps are used in the negative feedback circuit of the regulator, ensuring optimal operation.
Operating parameters of the regulator:
- rated supply voltage – 40…45V;
- adjustable output voltage range – 1…30V;
- PWM controller frequency – 40 kHz;
- regulator output circuit resistance – 0.01 Ohm;
- long-term maximum output current is 8A.
The stabilizer circuit is shown in Figure 1. A smoothing filter made of capacitors C16-18, storage inductance L1, spark gap diode VD6, switch VT1 make up the power circuit of the device. The construction of the power circuit is classic, the difference is the additional elements C5, VDD1, R7, VT2, designed to ensure safe operation of the power switch (VT1). Transformer T2 allows you to reduce the rate of current increase when opening the VT1 switch. The energy accumulated when the key is closed goes to the input of the circuit through the right side of the diode assembly VD1. Capacitance C5 is designed to reduce the rate of voltage rise across the switch. Installation of OBR circuit elements optimizes the operating mode of the key transistor, reducing heat losses and shock loads. The protection of the VT1 key from the effects of reverse current through the C5T2 circuit is provided by the VD1 diode located on the left.
Figure 1
The control signal to the switch gate is supplied through the isolation transformer T1, the primary winding of which is connected to the collector circuit of transistor T2. Elements R1, VD2, VD3 are designed to limit surges in the reverse voltage of the switch gate. The VT2 emitter is connected through a limiting resistor R8 to pins 8 and 10 of the DA1 microcircuit (collectors of the output transistors). The limiting resistor allows you to select the optimal value of the gate current of the VT1 switch.
The operation of the circuit is controlled on a specially designed TL494 chip. The connection principle is classic, pins 7 and 13 are connected, single-ended mode. To be able to work with a minimum voltage, a reference voltage of approximately 0.9V is set at pin 2 by a divider. The voltage on the 4th leg determines the maximum duty cycle of the generated pulses. The amplitude-frequency response of the circuit is time-corrected by the master chains C12R14, C11R13. The generation frequency is set by the C14R21 chain. Negative feedback voltage is set by elements VD8, R20, R25, R24. The voltage at the output of the stabilizer is set by variable resistance R24. Current control is performed by the voltage drop across resistors R5, R4 installed in parallel. The signal from them goes to the 2nd operational amplifier of the control chip (contacts 16,15). The maximum current limitation at the device output is adjusted by resistance R19.
The op-amp of the DA2 chip is designed to protect the device when the output current exceeds the maximum permissible. The inputs of op-amp DA1 and op-amp DA2 are connected to a current sensor using resistors R5, R4. When the voltage drop across the sensor increases, the output of the comparator will appear high voltage. Through the closed contact SA1, a positive feedback chain is formed; the high voltage will maintain op-amp DA2 in this state and block the operation of DA1 through input 16.
Switch SA1 in the open state ensures operation of the device with maximum current limitation. The HL1 LED lights up when the load is disconnected or when the current is limited.
The power supply for the control part of the circuit is provided by a stabilizing chain of elements C6-10, C4, C3, R3, R2, VD5, VD4, VT2.
The device is assembled on a fiberglass board with foil on one side. Remote parts:
- switch SA1;
- LED HL1;
- voltage regulator
All tracks intended for the power part of the circuit should be additionally reinforced with copper wire with a cross-section of at least 1 mm 2. Parts can be used Russian production or their foreign analogues. The heat sink area for the key transistor and diode assembly VD1 is at least 370 cm 2, for VD6 - at least 130 cm 2.