Low voltage dropout regulator. Voltage stabilizer on a field-effect transistor. Rostec is “fencing itself” and encroaching on the laurels of Samsung and General Electric

Extend the life of a set of batteries or battery charge by simply adding linear voltage regulators to the circuit? Increase voltage stability and reduce ripple after a pulse converter with virtually no decrease in power supply efficiency? This is real if you use modern micro-power LDO stabilizers from STMicroelectronics with a low production voltage drop.

For a long time, developers of electronic equipment had access to only classic stabilizers (for example, or stabilizers of the 78xx/79xx series) with a minimum drop on the control element of 0.8 V and above. This was due to the fact that an n-p-n transistor was used as a regulating element, connected in a circuit with a common collector. In order to open such a transistor to saturation, an additional power source is required, the voltage of which exceeds the input voltage. However, the development of technology does not stand still, and with the advent of powerful and compact p-channel field-effect transistors, they also began to be used in voltage stabilizers, including in a common-source circuit. This circuit allows, if necessary, to completely open the transistor, and the voltage drop across its junction will actually depend only on the channel resistance and load current. This is how the LDO (Low DropOut) stabilizer appeared.

It should be taken into account that the minimum drop on the channel of an LDO stabilizer transistor depends almost linearly on the current flowing through it, since the channel is actually an electrically adjustable resistor with some minimum resistance. Therefore, when the output current decreases, this voltage also decreases proportionally to a certain limit, usually equal to 10...50 mV. The leaders should be recognized as microcircuits and, whose minimum voltage drop is only 0.4 mV. If voltage drop is one of the key requirements for a stabilizer, then you should take a closer look at stabilizers with a large current reserve, since due to the lower resistance of the control transistor channel they may have a much lower voltage drop at the same load current.

The unique feature of LDO is its ability to stabilize voltage, smooth out surges and reduce noise on the power bus for highly sensitive devices such as radios, GPS modules, audio devices, high-resolution ADCs, VCO generators, with virtually no deterioration in the overall efficiency of the power supply. For example, to power a 3.3V circuit, we chose an LDO with a minimum dropout of 150mV and a buck regulator with a ripple output of 50mV (top curve in Figure 1). The output voltage of a switching regulator can be approximately estimated using the formula:

U Imp ≥ U Load + U Drop + 1/2∆U Pulse + 100…200 mV,

where U Imp is the output voltage of the pulse stabilizer, U Load. – output voltage of the linear stabilizer (load supply voltage), ∆U Imp – amplitude of voltage ripple at the output of the pulse stabilizer. Therefore, we choose it equal to 3.6 V. As a result, the efficiency will deteriorate by only 8%, however, the voltage ripple will significantly decrease. The supply voltage ripple suppression ratio (SVR) is determined by the formula:

SVR = 20Log*(∆U IN /∆U OUT)

With a typical coefficient of about 50 dB, ripple is attenuated by approximately 330 times. That is, the ripple amplitude at the output of our power supply will decrease to hundreds of microvolts (we also need to take into account the noise of the LDO itself, usually it is tens of μV/V) - this result is practically unattainable for most pulse converters without an additional stabilizer or multi-stage LC filters at the output. The best stabilization characteristics are provided by microcircuits and microcircuits of the LD39xxx series - the noise does not exceed 10 µV/V, and the SVR coefficient reaches 90 dB.

However, LDOs also have disadvantages, one of which is their tendency to self-excite, not only when the ESR of the output capacitor is too large (or its capacitance is too small), but also when the ESR is too low. This feature is due to the fact that a cascade with a common emitter (common source) has a high output impedance, so an additional low-frequency pole appears on the frequency response of the stabilizer (its frequency depends on the load resistance and the capacitance of the output capacitor). As a result, already at frequencies of tens of kilohertz, the phase shift can exceed 180° and negative feedback turns into positive. To solve this problem, you need to add a zero to the frequency response, and the easiest way to do this is to increase the series resistance (ESR) of the output capacitor: this practically does not increase the output voltage ripple, but is key to the stability of the entire circuit. Moreover, the capacitance and ESR of the capacitor must be within strictly defined limits. They are specified individually for each LDO stabilizer. Alas, the standard approach “the larger the capacitance and the lower the ESR of the output capacitors, the better”, applicable to classic linear and switching stabilizers, does not work here.

Depending on the components of the internal correction circuit, LDO stabilizers can be divided into three groups:

• stabilizers designed to work with tantalum or electrolytic capacitors - they require a capacitor with an ESR of 0.5...10 Ohms or more;
• stabilizers designed to work with tantalum capacitors (ESR 0.3...5 Ohm);
• stabilizers designed to work with ceramic capacitors - they maintain stability when the ESR of the output capacitor is from 0.005 to 1 Ohm.

For high-frequency and/or high-current digital circuits, it is recommended to install filtering ceramic capacitors with a capacity of 0.1 ... 1 μF near each chip, and they can also disrupt the stability of the LDO stabilizer. To prevent this from happening, it is recommended to increase the length and reduce the thickness of the tracks from the stabilizer to the load (thereby increasing the inductance of the tracks), install chokes or resistors in the power supply circuit, and also choose LDO stabilizers compensated for low ESR loads.

There is another way to increase the stability of the converter - to use an n-channel transistor connected in a circuit with a common drain as a regulator. This circuit is stable with almost any characteristics of the output capacitor, and even without a capacitor at all (so-called capless stabilizers). However, for its correct operation, an internal voltage multiplier is required, which will increase the input voltage to enable the control transistor to turn on until saturation. It was manufactured according to this scheme - thanks to the lower channel resistance of n-channel transistors of the same area, it was possible to significantly reduce the voltage drop, however, due to the constantly operating multiplier, the current consumed by the microcircuit in active mode increased sharply. But, according to the author, such stabilizers are the future of LDO, so the problem of increased power consumption will probably be solved soon.

Due to the significant gate capacitance, the transistor's ability to quickly respond to sudden changes in load current deteriorates. As a result, when the load current decreases, the output voltage of the stabilizer increases by inertia (until the built-in operational amplifier can slightly turn off the transistor), and when the current increases, the output voltage sags slightly (lower curve in Figure 1). The load capacity of the stabilizer can be increased by increasing the output power of the built-in operational amplifier, but this will subsequently increase the current consumed by the stabilizer. Therefore, the designer has to choose: either use ultra-low-power stabilizers in the circuit (for example, series or with a current consumption of units of microamps, but with very high inertia and large voltage drops with sudden changes in load current), or medium- and high-speed stabilizers, but with a consumption of up to hundreds of microamps. As an alternative, there are stabilizers with energy saving modes (for example), which, when the load current decreases, automatically switch to micro-power mode. Many modern microcontrollers work similarly (for example, the STM8 and STM32 families) - the latter have two built-in LDO stabilizers, one of which operates in micropower mode and the second in active mode, which ensures high energy efficiency in all operating modes and over the entire voltage range nutrition.

All stabilizers discussed in this article require a minimum of external components for their operation - only two capacitors, and an input capacitor with a capacity of at least 1 μF is required for most microcircuits, and only for adjustable versions a divider of two resistors is also required (Figure 2). All microcircuits are protected against overload and overheating and are capable of operating in the temperature range of -40...125°C. Many microcircuits have an Enable input: the current consumption in the “Off” mode usually does not exceed a few...hundreds of nanoamps. The main electrical characteristics of stabilizers are shown in Table 1.

Table 1. Basic electrical characteristics of ST LDO stabilizers

Name	Input voltage, V	Day off voltage, V	Out. current, mA	A fall voltage¹, mV	Required current (min), µA	SVR², dB	Output noise³, μVRMS/V	Enable/Power Good	Recommended Specifications exit capacitor		Frame
									Capacity, uF	ESR, Ohm
	2,5…6	1,22; 1,8; 2,5; 2,6; 2,7; 2,8; 2,9; 3,0; 3,3; 4,7	150	0,4…60	85	50	30	+/-	1…22	0,005…5	SOT23-5L, TSOT23-5L, CSP (1.57×1.22 mm)
	2,5…6	1,5; 1,8; 2,5; 2,8; 3,0; 3,3; 5,0	300	0,4…150	85	50	30	+/-	2,2…22	0,005…5	SOT23-5L, DFN6 (3×3 mm)
	1,5…5,5	0,8; 1,0; 1,2; 1,25; 1,5; 1,8; 2,5; 3,3	150	up to 80	18	62	29	+/-	0,33…22	0,15…2	SOT23-5L, SOT666, CSP (1.1×1.1 mm)
	2,4…5,5	0,8; 1,2; 1,5; 1,8; 2,5; 3,0; 3,3	150	up to 150	31	76	20	+/-	0,33…22	0,05…8	SOT323-5L
	1,5…5,5	0,8…5,0	200	up to 200	20	65	45	+/-	0,22…22	0,05…0,9	DFN4 (1×1 mm)
	1,5…5,5	1,0; 1,2; 1,4; 1,5; 1,8; 2,5; 2,8; 3,0; 3,3	150	80 (100 mA)	20	67	30	+/-	1…22	0,1…1,8	CSP4 (0.8×0.8 mm)
	1,5…5,5	1.0; 1.2; 1.8; 2.5; 2.9; 3.0; 3.3; 4.1; Adj	300	up to 300	55 (1)	65 (48)	38 (100)	+/-	0,33…22	0,1…4	CSP4 (0.69x0.69 mm)/DFN6 (1.2x1.3 mm)
	1,5…5,5	2.5; 3.3; Adj	500	up to 200	20	62	30	+/+	1…22	0,05…0,8	DFN6 (3×3 mm)
	1,5…5,5	1.2; 2.5; 3.3; Adj	1000	up to 200	20	65	85	+/+	1…22	0,05…0,15	DFN6 (3×3 mm)
	1,25…6,0	3.3; Adj	2000	up to 135	100	50	24	+/+	1…22	0,05…1,2	DFN6 (3×3 mm), DFN8 (4×4 mm)
	1,9…5,5	0.8; 1.0; 1.1; 1.2; 1.5; 1.8; 2.5; 2.8; 2.9; 3.0; 3.1; 3.2; 3.3; 3.5; Adj	200	up to 150	30	55	51	+/-	1…22	0…10
	1,9…5,5	0.8; 1.1; 1.2; 1.5; 1.8; 2.5; 2.9; 3.0; 3.2; 3.3; Adj	300	up to 200	30	55	51	+/-	1…22	0…10	SOT23-5L, SOT323-5L, DFN6 (1.2×1.3 mm)
	2,5…13,2	1.2…1.8; 2.5…3.3; 3.6; 4.0; 4.2; 5.0; 6.0; 8.5; 9.0; Adj	200	up to 200	40	45	20	+/-	1…22	0,05…0,9	SOT23-5L, SOT323-5L, DFN6 (1.2×1.3 mm)
	2,1…5,5	1,0; 1,2; 1,5; 1,8; 2,5; 2,8; 3,0; 3,3	150	up to 86	17	89	6,3…9,9	+/-	0,33…10	0,05…0,6	DFN6 (2×2 mm)
	1,8…5,5	3.3; Adj	150	up to 70	120	51	40	+/-	Any	Any	SOT23-5L
	2,3…12	1.8; 2.5; 3.3; 5.0; Adj	50	up to 350	3	30	560	-/-	0,22…4,7	0…10	SOT323-5L
	1,5…5,5	1,2; 1,5; 1,8; 2,5; 2,8; 3,0; 3,1; 3,3	150	up to 112	1	30	75	+/-	0,47…10	0,056…6	SOT666
	2,5…24	2.5; 3.3; Adj	85	up to 500	4,15	45	95	-/-	0,47…1	0…1,5	SOT23-5L, SOT323-5L, DFN8 (3×3 mm)

Notes:

1. at maximum output current;
2. at a frequency of 10 kHz;
3. in the frequency range from 10 Hz to 100 kHz;
4. Values ​​for Green mode are shown in parentheses.

Micropower LDO stabilizers

As is known, in many circuits with a wide range of supply voltages, as the voltage increases, the current consumption increases, therefore, to increase the service life of the battery set, the voltage should be stabilized at the minimum acceptable level, at which the operation of the circuit is not disrupted. However, we need to take into account the current consumption of the LDO itself - it should be much lower than the difference that we are trying to save. We also need to take into account the minimum voltage drop on the stabilizer, since the higher it is, the sooner our batteries will run out. And if 20 years ago developers only had access to microcircuits of the KREN family with a typical current consumption of more than 3 mA, now the choice is much wider.

For operation in micro-power mode, a unique stabilizer with a consumption of about 1 µA (up to 2.4 µA at maximum load current) and a voltage drop of less than 112 mV is best suited. At the same time, its output voltage over the entire operating range changes by no more than 3...5%. The stabilizer circuit is the simplest (Figure 3), without any additional options. Slightly higher power consumption. This microcircuit is capable of operating at input voltages up to 12 V. A, with a current consumption of 4.5 μA and a relatively low cost, it can withstand input voltages up to 26 V. The microcircuits are manufactured in medium-sized packages and are ideal for battery-powered devices - at current load no more than a few microamps, even a small CR2032 battery in a device with will work for decades!

Continuous Series Voltage Regulator - Adjustable, Low Dropout

Adjustable series regulator

To adjust the output voltage in the previous circuit, an integral element with an adjustable stabilization voltage (controlled zener diode) can be used as a zener diode. There is another option.

Here is a selection of materials for your attention: Low Dropout Voltage Stabilizer Both previous circuits work well if the difference between the input and output voltage allows the desired bias to be generated at the base of transistor VT1. This requires at least a few volts. Sometimes it is not practical to maintain such a voltage, for example, because the losses and heating of the power transistor are proportional to this voltage. Then the following scheme applies. It can work even if the difference between the input and output voltages is only a few tenths of a volt, since this voltage does not participate in the formation of the bias. The bias is supplied through transistor VT2 from the common wire. If the voltage on the trimmer resistor motor is less than the stabilization voltage of the zener diode plus the saturation voltage of the base-emitter junction VT3, then transistor VT3 is closed, transistor VT2 is open, transistor VT1 is open. When the voltage on the resistor motor exceeds the sum of the stabilization voltage of the zener diode and the saturation of the base-emitter junction VT3, transistor VT3 opens and drains current from the base of VT2. VT2 and VT3 are closed. [Zener diode stabilization voltage, V] = - [Base-emitter saturation voltage VT3, V] = ([Minimum possible input voltage, V] - [Base-emitter saturation voltage VT2, V]) * * [Minimum possible current transfer coefficient of transistor VT2] / [Resistor R2 resistance, Ohm] = [Minimum output voltage, V] * [Resistor R1 resistance, Ohm] * [Minimum possible current transfer coefficient of transistor VT3] / / 3 [Transistor power VT1, W] = ([Maximum possible input voltage, V] - [Minimum output voltage, V]) * [Maximum possible output current, A] [Transistor power VT2, W] = [Maximum possible input voltage, V] * [Maximum possible output current, A] / [Minimum possible current transfer coefficient of transistor VT1] There is practically no power dissipation on the VT3 transistor and the zener diode.

All modern radio-electronic equipment is built on elements that are sensitive to the supply electricity. Not only the correct functioning, but also the performance of the circuits as a whole depends on it. Therefore, first of all, electronic devices are equipped with fixed stabilizers with a low voltage drop. They are made in the form of integrated circuits, which are produced by many manufacturers around the world.

What is a low dropout voltage stabilizer?

A voltage stabilizer (SV) is understood as a device whose main task is to maintain the load voltage at a certain constant level. 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 SN looks like a closed system, where in automatic mode the output voltage is adjusted in proportion to the reference (reference) voltage, which is generated by a special source. This type of stabilizer is called compensatory. The regulating element (RE) in this case is a transistor - a bipolar or field-effect transistor.

The voltage regulation element can operate in two different modes (determined by the design diagram):

• active;
• key.

The first mode implies continuous operation of the RE, the second - operation in a pulsed mode.

Where is a fixed stabilizer used?

Electronic equipment of the modern generation is characterized by mobility on a global scale. Device power systems 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 least possible loss of electricity on them.

Modern SVs are used in the following systems:

• mobile communications;
• portable computers;
• microcontroller power supplies;
• autonomously operating security cameras;
• autonomous security systems and sensors.

To solve power supply issues for stationary electronics, voltage stabilizers with a low voltage drop in a housing with three terminals of the KT type (KT-26, KT-28-2, etc.) are used. They are used to create simple circuits:

• chargers;
• power supplies for household electrical equipment;
• measuring equipment;
• communication systems;
• special equipment.

What are the types of fixed type SN?

All integral stabilizers (which also include fixed ones) are divided into two main groups:

• Stabilizers with a minimum low voltage drop of a hybrid design (GISN).
• Semiconductor microcircuits (SIC).

SN of the first group is made on integrated circuits and semiconductor elements of the unpackaged type. All components of the circuit are placed on a dielectric substrate, where connecting conductors and resistors, as well as discrete elements - variable resistances, capacitors, etc., are added by applying thick or thin films.

Structurally, microcircuits are complete devices whose output voltage is fixed. These are usually stabilizers with a low voltage drop of 5 volts and up to 15 V. More powerful systems are built on powerful unpackaged transistors and a (low-power) film-based control circuit. The circuit can carry currents up to 5 amperes.

ISN microcircuits are made on a single chip, which is why they are small in size and weight. Compared to previous microcircuits, they are more reliable and cheaper to manufacture, although they are inferior in parameters to GISN.

Linear SN with three terminals are referred to as ISN. If we take the L78 or L79 series (for positive and negative voltages), then they are divided into microcircuits with:

• 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).

Operating principle of a low voltage drop linear regulator

A typical stabilizer structure consists of:

• Reference voltage source.
• Error signal converter (amplifier).
• A signal divider and a regulating element, assembled on two resistors.

Since 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 low dropout voltage regulator is based on the process of comparing the reference voltage with the one that is supplied to the output. Depending on the level of discrepancy between these two indicators, the error amplifier acts on the gate of the power transistor at the output, covering or opening its junction. Thus, the actual level of electricity at the output of the stabilizer will differ little from the declared nominal one.

The circuit also contains sensors for protection against overheating and overload currents. Under the influence of these sensors, the output transistor's channel is completely blocked and it stops passing current. In shutdown mode, the microcircuit consumes only 50 microamps.

Low voltage drop stabilizer connection circuits

An integrated stabilizer chip is convenient because it has all the necessary elements inside. Installing it on the board requires only the inclusion of filter capacitors. The latter are designed to remove 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 input and output bypass capacitors, the capacitance of the latter should be within the range of up to 2 µF (input) and 1 µF (output) at any permissible voltage and current values. If you use aluminum capacitors, their rating should not be lower than 10 μF. The elements should be connected as close as possible to the pins of the microcircuit.

In the case where a voltage stabilizer with a low voltage drop of the required rating is not available, you can increase the rating of the MV from a smaller one to a larger one. By raising the electricity level at the common terminal, it is achieved to increase it by the same amount at the load, as shown in the diagram.

Advantages and disadvantages of linear and switching stabilizers

Continuous Continuous Circuits (CIs) have the following advantages:

1. Implemented in one small package, which allows them to be effectively placed on the working space of the printed circuit board.
2. Does not require installation of additional regulatory elements.
3. Provide good stabilization of the output parameter.

The disadvantages include low efficiency, not exceeding 60%, associated with the voltage drop across the built-in control element. If the power of the microcircuit is high, it is necessary to use a chip cooling radiator.

Those with a low voltage drop across the field, the efficiency of which is approximately 85%, are considered more productive. This is achieved thanks to the operating mode of the control element, in which current passes through it in pulses.

The disadvantages of the pulsed MV circuit include:

1. Complexity of schematic execution.
2. Presence of pulsed interference.
3. Low stability of the output parameter.

Some circuits using a linear voltage regulator

In addition to the intended use of microcircuits as SN, it is possible to expand the scope of their application. Some variants of such circuits are based on the L7805 integrated circuit.

Switching on stabilizers in parallel mode

To increase the load current, the MVs are connected in parallel to each other. To ensure the functionality of such a circuit, a small nominal resistor is additionally installed in it between the load and the output of the stabilizer.

Current stabilizer based on MV

There are loads that must be powered by direct (stable) current, for example, an LED string.

Circuit diagram for regulating fan speed in a computer

This type of regulator is designed in such a way that when initially turned on, all 12 V is supplied to the cooler (for its spin-up). Then, after charging of capacitor C1 is complete, variable resistor R2 can be used to regulate the voltage value.

Conclusion

When assembling a circuit using a voltage stabilizer with a low 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 an electronic element!

Sometimes in amateur radio practice there is a need to stabilizer with low voltage drop on the regulating element (1.5-2V). This may be caused by insufficient voltage on the secondary winding of the transformer, dimensional restrictions when the case does not accommodate a radiator of the required size, considerations of device efficiency, etc.

And if the choice of microcircuits for building “conventional” stabilizers is wide enough (such as LM317, 78XX etc.), then microcircuits for building Low-Drop stabilizers are usually not available to everyone. Therefore, a simple scheme on available components may be very relevant.

I present a scheme that I myself have used for many years. During this time, the circuit showed reliable, stable operation. Available components and ease of setup will allow even novice radio amateurs to repeat the design without difficulty.

click to zoom

The circuit resembles a fairly standard parametric stabilizer, which is supplemented with a GST (stable current generator) to control the base current of the regulating transistor, due to which it was possible to obtain low voltage drop.

The circuit is designed for an output voltage of 5V (set by resistor R4) and a load current of 200mA. If you need to get more current, then instead of T3 you should use composite transistor.

If you need to get a higher output voltage, you will have to recalculate the resistor values.

When lack of transistor assemblies discrete transistors can be used. In my version, instead of assembling KR198NT5, two selected KT361 transistors were used. The KR159NT1 assembly can be replaced with two KT315 transistors, the selection of which is not required.

Since there is practically no information on the Internet on domestic components, I provide the pinout of transistor assemblies for reference.

Voltage stabilizer with low minimum voltage drop

One of the important parameters of series voltage stabilizers (including microcircuit ones) is the minimum permissible voltage between the input and output of the stabilizer (ΔUmin) at maximum load current. It shows at what minimum difference between the input (Uin) and output (Uout) voltages all parameters of the stabilizer are within normal limits. Unfortunately, not all radio amateurs pay attention to it; usually they are only interested in the output voltage and maximum output current. Meanwhile, this parameter has a significant impact on both the quality of the output voltage and the efficiency of the stabilizer.

For example, for widespread microcircuit stabilizers of the 1_M78xx series (xx is a number equal to the stabilization voltage in volts), the minimum permissible voltage dUmin = 2 V at a current of 1 A. In practice, this means that for a stabilizer on the LM7805 chip (Uout = 5 V) the voltage Uinmin must be at least 7 V. If the ripple amplitude at the rectifier output reaches 1 V, then the value of Uinmin increases to 8 V, and taking into account the instability of the mains voltage within ±10%, it increases to 8.8 V. As a result, the efficiency of the stabilizer will not exceed 57%, and with a high output current the microcircuit will become very hot.

A possible way out of the situation is the use of so-called Low Dropout (low voltage drop) microcircuit stabilizers, for example, the KR1158ENxx series (ΔUmin = 0.6 V at a current of 0.5 A) or LM1084 (Umin = 1.3 V at a current of 5 A ). But even lower values ​​of Umin can be achieved if a powerful field-effect transistor is used as a regulating element. It is this device that will be discussed further.

The diagram of the proposed stabilizer is shown in Fig. 1. Field-effect transistor VT1 is connected to the positive power line. The use of a device with an n-channel is due to the results of tests carried out by the author: it turned out that such transistors are less prone to self-excitation and, moreover, as a rule, their open channel resistance is less than that of p-channel ones. Transistor VT1 is controlled by parallel voltage regulator DA1. In order for a field-effect transistor to open, the voltage at its gate must be at least 2.5 V greater than at the source. Therefore, an additional source is needed with an output voltage that exceeds the voltage at the drain of the field-effect transistor by exactly this amount.

Such a source - a step-up voltage converter - is assembled on the DD1 chip. Logic elements DD1.1, DD1.2 are used in a pulse generator with a repetition rate of about 30 kHz, DD1.3, DD1.4 are buffer elements; diodes VD1, VD2 and capacitors SZ, C4 form a rectifier with doubling the voltage, resistor R2 and capacitor C5 form a smoothing filter.

Capacitors C6, C7 ensure stable operation of the device. The output voltage (its minimum value is 2.5 V) is set with trimming resistor R4.

Laboratory tests of the device prototype showed that with a load current of 3 A and a decrease in the input voltage from 7 to 5.05 V, the output decreases from 5 to 4.95 V. In other words, at the specified current, the minimum voltage drop ΔUmin does not exceed 0.1 V. This allows you to more fully use the capabilities of the primary power source (rectifier) ​​and increase the efficiency of the voltage stabilizer.

The device parts are mounted on a printed circuit board (Fig. 2) made of one-sided foil-coated fiberglass laminate with a thickness of 1.5...2 mm. Fixed resistors - R1-4, MLT, trimmer - SPZ-19a, capacitors C2, C6, C7 - ceramic K10-17, the rest are imported oxide, for example, TK series from Jamicon. In a stabilizer with an output voltage of 3...6 V, a field-effect transistor with an opening voltage of no more than 2.5 V should be used. Such transistors from International Rectifier are usually marked with the letter L (see the fact sheet "Power field-effect switching transistors company International Rectifier" in "Radio", 2001, No. 5, p. 45). When the load current is more than 1.5...2 A, it is necessary to use a transistor with an open channel resistance of no more than 0.02...0.03 Ohm.

To avoid overheating, the field-effect transistor is fixed to the heat sink, and a board can be glued to it through an insulating gasket. The appearance of the mounted board is shown in Fig. 3.

The output voltage of the stabilizer can be increased, but we should not forget that the maximum supply voltage of the K561LA7 microcircuit is 15 V, and the limit value of the gate-source voltage of the field-effect transistor in most cases does not exceed 20 V.

Therefore, in such a case, you should use a boost converter assembled according to a different circuit (on an element base that allows a higher supply voltage), and limit the voltage at the gate of the field-effect transistor by connecting a zener diode with the corresponding stabilization voltage in parallel with capacitor C5. If the stabilizer is supposed to be built into a power source with a step-down transformer, then the voltage converter (microcircuit DD1, diodes VD1, VD2, resistor R1 and capacitors C2, SZ) can be excluded, and the “main” rectifier on the diode bridge VD5 (Fig. 4) can be supplemented with a doubler voltage on diodes VD3, VD4 and capacitor C9 (the numbering of elements continues what was started in Fig. 1).

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