All modern electronic equipment is built on elements that are sensitive to supply electricity. Not only the proper functioning, but also the operability of the circuits as a whole depends on it. Therefore, first of all, electronic devices are equipped with fixed stabilizers with a small voltage drop. They are made in the form of integrated circuits, which are produced by many manufacturers around the world.
What is a low voltage drop voltage regulator?
Under the voltage stabilizer (CH) understand such a device, the main task of which is to maintain at a certain constant level of voltage at the load. Any stabilizer has a certain accuracy of parameter output, which is determined by the type of circuit and the components included in it.
Internally, the CH looks like a closed system, where in automatic mode the output voltage is adjusted in proportion to the reference (reference), which generates a special source. This type of stabilizer is called compensatory. The regulating element (RE) in this case is a transistor - a bipolar or a polevik.
The voltage control element can operate in two different modes (determined by the construction scheme):
The first mode implies the continuous operation of the RE, the second - work in a pulsed mode.
Where is a fixed stabilizer used?
The electronic equipment of the modern generation is characterized by mobility on a global scale. The power supply systems of devices are based on the use of mainly chemical current sources. The task of the developers in this case is to obtain stabilizers with small overall parameters and the lowest possible loss of electricity to them.
Modern HF are used in the following systems:
- means of mobile communication;
- laptop computers;
- microcontroller batteries;
- autonomous security cameras;
- autonomous security systems and sensors.
To solve the issues of supplying stationary electronics, voltage stabilizers with a small voltage drop are used in a housing with three terminals of the CT type (KT-26, KT-28-2, etc.). They are used to create simple circuits:
- Chargers
- power supplies for household electrical equipment;
- measuring equipment;
- communication systems;
- special equipment.
What are fixed-type CHs?
All integral stabilizers (which include fixed ones) are divided into two main groups:
- Stabilizers with minimally low voltage drop hybrid performance (GISN).
- Semiconductor integrated circuits (ISN).
CH of the first group is performed on integrated circuits and semiconductor elements of the open-type type. All components of the circuit are placed on a dielectric substrate, where connecting conductors and resistors are added by applying thick or thin films, as well as discrete elements - variable resistors, capacitors, etc.
Structurally, microcircuits represent complete devices whose output voltage is fixed. These are usually stabilizers with a small voltage drop of 5 volts and up to 15 V. More powerful systems are built on high-power transistors unpacked and a control circuit (low-power) based on films. The circuit can pass currents up to 5 amperes.
ICN microcircuits perform on a single chip, because they have small sizes and mass. Compared to previous microcircuits, they are more reliable and cheaper to manufacture, although they are inferior to GISN in parameters.
Linear SNs with three leads belong to the ISN. If we take the L78 or L79 series (for positive and negative voltages), then they are divided into microcircuits with:
- A low output current of about 0.1 A (L78L **).
- The average current value is around 0.5 A (L78M **).
- High current up to 1.5 A (L78).
Principle of operation of a linear regulator with a low voltage drop
A typical stabilizer structure consists of:
- Voltage reference source.
- The converter (amplifier) โโof the error signal.
- Signal divider and regulating element, assembled on two resistors.
Since the magnitude of the output voltage directly depends on the resistances R1 and R2, the latter are built into the microcircuit and a CH with a fixed output voltage is obtained.
The operation of a voltage stabilizer with a small voltage drop is based on the process of comparing the reference voltage with that which is output. Depending on the level of mismatch between these two indicators, the error amplifier acts on the gate of the power transistor at the output, covering or opening its transition. Thus, the actual level of electricity at the output of the stabilizer will differ little from the declared nominal.
Also in the circuit there are sensors for protection against overheating and overload currents. Under the influence of these sensors, the channel is completely blocked at the output transistor, and it ceases to pass current. In shutdown mode, the chip consumes only 50 microamps.
Low voltage drop stabilizer switching circuits
The integrated stabilizer chip is convenient in that it has all the necessary elements inside. Installing it on a board requires only filter capacitors. The latter are designed to remove the interference coming from the current source and load, as can be seen in the figure.
Regarding the 78xx series SN and the use of tantalum or ceramic capacitors for shunting the input and output, the capacitance of the latter should be up to 2 ฮผF (input) and 1 ฮผF (output) for any acceptable voltage and current. If aluminum capacitors are used, then their value should not be lower than 10 microfarads. Connect elements should be as close to the terminals of the chip.
In the case when there is no voltage stabilizer with a small voltage drop of the desired rating, it is possible to increase the nominal value of CH from smaller to larger. By raising the level of electricity at the general output, it is increased by the same value at the load, as shown in the diagram.
Advantages and disadvantages of linear and pulse stabilizers
Continuous Integrated Circuits (CH) have the following advantages:
- They are implemented in one small-sized case, which allows you to effectively place them on the working space of the printed circuit board.
- Do not require the installation of additional regulatory elements.
- Provide good stabilization of the output parameter.
The disadvantages include low efficiency, not exceeding 60%, associated with a voltage drop on the built-in regulating element. With a high power microcircuit, it is necessary to use a crystal cooling radiator.
More productive are considered pulse voltage regulators with a small voltage drop across the field, the efficiency of which is approximately at the level of 85%. This is achieved thanks to the operating mode of the regulating element, in which the current passes through it with pulses.
The disadvantages of the pulsed SN circuit include:
- The complexity of the schematic.
- The presence of pulsed interference.
- Low stability of the output parameter.
Some circuits using a linear voltage regulator
In addition to the intended use of microcircuits as CH, it is possible to expand the scope of their application. Some variants of such circuits are based on the integrated circuit L7805.
Turn on stabilizers in parallel
To increase the load current, SNs are connected in parallel to each other. To ensure the operability of such a circuit, a small-value resistor is additionally installed in it between the load and the output of the stabilizer.
MV-based current stabilizer
There are loads whose power must be supplied with a constant (stable) current, for example, an LED circuit.
Computer fan speed control circuit
A regulator of this type is constructed in such a way that upon initial switching on the cooler receives all 12 V (for its promotion). Further, at the end of the charge of the capacitor C1, the variable resistor R2 will be able to adjust the voltage value.
Conclusion
When assembling a circuit using a voltage stabilizer with a small voltage drop with your own hands, it is important to consider that some types of microcircuits (built on field-effect transistors) cannot be soldered with a conventional soldering iron directly from a 220 V network without grounding the case. Their static electricity can damage the electronic element!