CN216901463U

CN216901463U - Linear voltage stabilizer with low voltage drop and short-circuit protection characteristics

Info

Publication number: CN216901463U
Application number: CN202122900093.1U
Authority: CN
Inventors: 崔建国; 宁永香; 崔燚
Original assignee: Shanxi Institute of Technology
Current assignee: Shanxi Institute of Technology
Priority date: 2021-11-24
Filing date: 2021-11-24
Publication date: 2022-07-05
Anticipated expiration: 2031-11-24

Abstract

The utility model discloses a linear voltage regulator with low voltage drop and short-circuit protection characteristics, unstable input voltage Ui is simultaneously connected with a collector of a transistor T1 and an emitter of a transistor T3, Ui is simultaneously connected with a cathode of a diode D1 through a resistor R1, a collector of a transistor T3 sequentially passes through a forward diode D1 and a resistor R3, the reverse voltage stabilizing diode D2 is connected to work, the collector of the transistor T3 is connected to work sequentially through the resistor R4 and the resistor R5, the base of the transistor T3 is connected to the collector of the transistor T2, the collector of the transistor T2 is connected to the base of the transistor T2 through the capacitor C1, the base of the transistor T2 is connected to the negative electrode of the voltage stabilizing diode D2, the emitter of the transistor T1 is connected to the emitter of the transistor T2, the emitter of the transistor T1 is connected to work sequentially through the resistor R2, the base of the transistor T1 is connected to the connection point of the resistor R4 and the resistor R5, and the upper end of the resistor R4 outputs the stable voltage Uo.

Description

Linear voltage stabilizer with low voltage drop and short-circuit protection characteristics

Technical Field

The utility model relates to a design technology of a linear voltage stabilizer, in particular to a linear voltage stabilizer with low voltage drop and short-circuit protection characteristics, the unstable input voltage of the voltage stabilizer is only 0.35V higher than the required output voltage, and the voltage stabilizer can provide foldback current limiting or short-circuit protection, and the power supply has higher conversion efficiency.

Background

The process of stabilizing the output voltage by using the regulation action of the circuit is called voltage stabilization, and the process is divided into a linear voltage-stabilized power supply and a switching voltage-stabilized power supply according to the working state of a regulating tube, wherein the linear voltage-stabilized power supply is generally a series-type voltage-stabilized power supply.

The switch voltage-stabilized power supply adjusts the duty ratio or frequency of high-frequency alternating current pulse to adjust output voltage through an energy storage element inductor or capacitor, has the advantages of high voltage conversion efficiency and large output ripple waves and can generate high-frequency interference to a circuit sometimes.

When the input voltage and the output voltage in the system are close, the linear voltage regulator is the best choice, and high efficiency can be achieved. Linear regulators are most often used in applications where the lithium ion battery voltage is converted to 3V, and although ten percent of the battery's final discharge energy may not be used, linear regulators can still provide longer battery life in a low noise configuration.

The linear series type voltage-stabilized power supply adjusts the output voltage by adjusting the dynamic resistance of the adjusting tube, and has the advantage of small output ripple.

However, the conventional linear voltage regulator has the serious disadvantages that the voltage drop between the input and the output is too large, and the voltage regulator has very low conversion efficiency and serious heat generation under the condition of large input-output voltage difference.

The current-limiting protection is generally of a current-limiting type and a foldback current-limiting type 2, the former means that the output current is limited to the maximum value, the greatest disadvantage of the method is that the power consumption of the internal loss of the voltage stabilizer is large, and the latter means that the output current is reduced while the output voltage is reduced, and the greatest advantage is that when an overcurrent condition occurs, the energy consumed in a power tube is relatively small.

Low dropout linear regulators typically use discrete component designs but are difficult to provide short circuit protection as integrated regulators.

The linear voltage-stabilized power supply with low voltage drop between input and output is designed, and the saturation voltage drop of the PNP transistor with lower power can be as low as 0.3V, so that the unstable input voltage of the linear voltage-stabilized power supply is only 0.35V higher than the required output voltage, and the linear voltage-stabilized power supply can provide foldback current limiting or short-circuit protection and has higher conversion efficiency.

Disclosure of Invention

The utility model aims to solve the technical problem of providing a technology for designing a linear voltage stabilizer, which has the advantages of simple structure, low manufacturing cost and reliable use.

In order to achieve the above object, the present invention provides a linear regulator with low voltage drop and short circuit protection characteristics, wherein an unstable input voltage Ui is connected to a collector of a transistor T1 and an emitter of a transistor T3, an unstable power source Ui is connected to a cathode of a diode D1 through a resistor R1, a collector of a transistor T3 is connected to an operating ground through a forward diode D1, a resistor R3 and a reverse zener diode D2 in sequence, a collector of a transistor T3 is connected to an operating ground through a resistor R4 and a resistor R5 in sequence, a base of a transistor T3 is connected to a collector of a transistor T2, a collector of a transistor T2 is connected to a base of a transistor T2 through a capacitor C1, a base of a transistor T2 is connected to a cathode of a zener diode D2, an emitter of a transistor T1 is connected to an emitter of a transistor T2, an emitter of a transistor T1 is connected to an operating ground through a resistor R2, the base of the transistor T1 is connected to the connection point of the resistor R4 and the resistor R5, and the upper end of the resistor R4 outputs a stable voltage Uo.

Drawings

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are provided to provide a further understanding of the present invention and form a part of the present application, and FIG. 1 is a schematic diagram of a conventional linear series regulator; FIG. 2 shows the maximum efficiency and U of a conventional linear regulator_OA plot of the ratio/Uin; FIG. 3 is a schematic diagram of a linear regulator with low dropout and short circuit protection features; fig. 4 is a folded-back characteristic of the voltage regulator short-circuit protection.

Detailed Description

Since the regulated power supply designed herein is also a linear regulated power supply, it is necessary to first introduce the structure of a conventional linear series regulated power supply, as a comparison, so as to embody the novelty of the technical features of the present design, and the circuit structure of the conventional linear regulated power supply is shown in fig. 1.

FIG. 1 is a very mature conventional linear regulator circuit, whose operation principle is not described in detail, and whose maximum efficiency and U are the same as those of the conventional linear regulator_O/U_INThe ratio is proportional, as shown in fig. 2.

As can be seen from fig. 2, the efficiency of the conventional linear regulator is only 27.5% when the input is 12V and the output is 3.3V, in which case 82.5% of the input power is completely wasted and heat is generated in the regulator. This means that the transistor must be provided in the worst case (maximum U)_inAnd full load) the thermal capability to handle its power/heat dissipation. Therefore, the size of the conventional linear regulator and its heat sink may be large, especially in U_OFar below U_inWhen the user wants to use the device.

Alternatively, the linear regulator may be in U_OIs close to U_inHas very high efficiency, as in fig. 2, U_OAt a ratio of 0.8/Uin, the power efficiency is 80%.

Yet another limitation of conventional linear regulators is that U_inAnd U_OThe minimum voltage difference between them requires that the transistor T must operate in its linear mode.

Thus, it requires a certain minimum voltage drop across the collector to emitter of a bipolar transistor or the drain to source of a FET, when U is_OToo close to U_inConventional linear regulators may no longer be able to regulate the output voltage.

It is also apparent that linear regulators, including the regulated power supply designed herein, can only provide step-down DC/DC conversion. In those requiring U_OThe voltage is higher than U_inVoltage, or need to be derived from a positive U_inVoltage generating negative U_OIn voltage applications, linear regulators are obviously inoperative.

The linear voltage regulator with low voltage drop and short circuit protection features is described in detail as follows:

the integrated three-pin voltage stabilizer is not suitable for occasions where input voltage and output voltage are almost the same, for example, chips of a three-terminal voltage-stabilizing 78XX series require that the input voltage is at least 2V-3V higher than the output voltage, otherwise, the integrated three-pin voltage stabilizer cannot work normally. However, in some cases, such conditions are obviously too harsh, e.g. 5V to 3.3V, and the voltage difference between the input and the output is only 1.7V, which obviously does not satisfy the operating conditions of the conventional linear regulator.

In practice most linear regulated power supplies, typically with an input voltage 3V greater than the output voltage, must use discrete components to accommodate the requirement that the two voltages be nearly identical, as shown in figure 3.

As can be seen from fig. 3, the linear regulator includes an unstable input voltage circuit, a differential amplifier circuit, a reference voltage circuit, a soft start circuit, a sampling voltage generation circuit, and a stable output voltage circuit.

It can be seen that the conventional linear regulator shown in fig. 3 is similar to that shown in fig. 1 in structure, and the regulating transistors are operated in common emitter state, but they are still different (e.g. T in fig. 3)₃) The selection and connection structure of the voltage regulator is different from that of fig. 1, fig. 1 is a linear voltage regulator using an integrated circuit, a regulating tube is an NPN-type transistor, fig. 3 is a linear voltage regulator of a discrete component, and the regulating tube is a PNP-type transistor.

For a given supply voltage, the bipolar transistor can provide the maximum output current, wherein the PNP transistor is better than the NPN transistor, because the base of the PNP transistor can be connected with the ground, the transistor can be fully saturated when necessary, and the saturation voltage drop of the transistor with lower power can be as low as 0.3V; the base of the NPN transistor can only be connected with the highest possible power voltage, so that the minimum voltage drop is limited to one U_BEJunction voltage drop (in this case U)_CB= 0). Therefore, the NPN transistor and the composite tuning tube cannot provide a voltage difference of less than 1 v.

The PMOS transistor and the PNP transistor can quickly reach saturation, thereby minimizing the voltage loss and power consumption of the regulator tube, and allowing the regulator tube to be used as a low dropout, low power consumption voltage regulator. The main disadvantage of PMOS transistors, which provide the lowest possible voltage drop and allow the lowest possible quiescent current, is that MOS transistors are often used as external devices, especially when large currents are controlled, so that the error amplifier IC constitutes a controller and cannot constitute a complete regulator itself.

The ordinary voltage stabilizer generally uses an NPN tube or an NPN composite adjusting tube as an adjusting tube, and the low dropout voltage stabilizer designed in the text uses a PMOS transistor or a PNP transistor as the adjusting tube.

The series PNP transistor T in FIG. 3₃Connected in common emitter circuit mode, so that the output voltage is lower than the input voltage by only transistor T₃The saturation voltage drop of the regulator of fig. 3 is a problem that the regulator of the discrete component design is difficult to provide short-circuit protection like the integrated regulator.

FIG. 3 shows a series-connected adjusting tube T₃Slave transistor T₂To obtain a base drive current, a transistor T₁And T₂Forming a differential amplifier, a resistor R₂A DC degeneration resistor of the common emitter of the differential amplifier circuit; resistance R₃A voltage stabilizing diode D₂Constituting a reference voltage stabilizing circuit, D₂The stable regulated voltage value is T of the differential amplifier₂The base electrode of the power supply provides a reference voltage and outputs a voltage U_OThrough a resistance R₄、R₅Obtaining T of sampling voltage as differential amplifier₁Provides the operating voltage.

The above circuit structure can ensure the voltage divider R₄、R₅And a Zener voltage regulator diode D₂The negative poles of the differential amplifier have almost the same potential, that is, the voltages at the two input ends of the differential amplifier are almost the same, and the regulating tube is in a stable state.

If the output voltage of the regulator changes for some reason, the voltage divider R₄、R₅The obtained sampling voltage changes, the potential balance of two input ends of the differential amplifier is broken, the output of the differential amplifier changes, and the adjusting tube T₃Is just differencedOutput drive of amplifier, T₃The current amplification capability of the voltage stabilizer is changed, and the output voltage of the voltage stabilizer is reversely changed.

For example, if the voltage regulator outputs a voltage U_OIncrease, increase of sampling voltage, T of differential amplifier₁The on-state of the resistor is increased, and the DC negative feedback resistor R is increased₂Increase in pressure drop over T₂The base voltage is the reference voltage U_D2，T₂Reducing the amount of conduction of the adjusting tube T₃The working current of the voltage stabilizer is reduced, the output voltage of the voltage stabilizer is reduced, and the original stable state is recovered, otherwise, if the output voltage U is reduced_OAnd the output voltage is increased and the original stable state is restored again.

Another innovation of the regulator with the structure of the circuit in FIG. 3 is that the differential amplifier can only be used for the regulating tube T₃Certain current amplification capability is provided to provide technical support for the circuit protection function of the voltage regulator of fig. 2.

According to the circuit configuration of FIG. 3, the transistor T is adjusted₃In a linear operating state, which requires current amplification for normal operation, but the transistor T₂To which only a dc feedback resistor R can be supplied₂Allowed base current, R₂The voltage drop across is equal to the zener diode D₂Maximum voltage and T of₂The difference of the emitter junction voltage of R in practical application₂Is about 4V, and therefore flows through R₂Is about 11mA, then, assuming T₃Has a current amplification factor of 50, T₃The maximum collector output current is 0.55A.

The output voltage U continues to increase if the collector current exceeds the maximum current_OWill fall if U_ODown to D₂Below the stable voltage, a negative feedback resistor R₂The pressure drop across the two ends is also reduced, flowing through R₂Will decrease, T₃The operating current (i.e., the regulator output current) of (a) is reduced, which indicates that the regulator output current has a foldback characteristic shown in fig. 4, where I_KThe lowest output current of the voltage stabilizer is indicated, and the voltage stabilizer is equivalent to a constant current source; i is_maxRefers to the maximum output current of the regulator.

It is thus clearly seen that the series transistor T shown in FIG. 3₃Has the function of resisting large current (short-circuit current).

Diode D₁And a resistance R₁For starting, if there is no starting resistor R₁The voltage-stabilized power supply cannot start because of the diode D₁The output of the voltage stabilizer is connected, at the moment of switching on the power switch, the voltage at two ends of the diode is zero, and after the power supply is normally started, the output voltage U of the voltage stabilizer is_OBy D₁、R₃、D₂Generating a reference voltage supply T₂The base of (1).

Due to the high amplification factor of the circuit, the oscillation is possible, and a capacitor C is connected₁Stability is provided.

Output voltage U_OCan be composed of D₂、R₄、R₅In series connection with the adjusting tube T₃Is arbitrarily adjusted within the limits of (a) and can be determined by the following formula:

the following notes are taken in the actual production: resistance R₂The maximum power of the BD140, which has good cooling, must be matched to the current gain of the tuning tube for the specific application, which is 5W.

If a noiseless output is required, a 10uF electrolytic capacitor is used with D₂And the circuit has a real soft start function at the moment, namely, the voltage stabilizer has no voltage output about 0.2 second after the power supply is switched on, and then the stable voltage is normally output.

The linear voltage stabilizer with low voltage drop and short circuit protection characteristics skillfully utilizes the characteristic that the base electrode of a PNP transistor can be grounded and can completely saturate the transistor when necessary, and the requirement of low voltage drop between the input and the output of the voltage stabilizer is met; when the output voltage drops to the voltage regulator tube D due to output short circuit₂When the voltage is lower than the stable voltage, the current of the adjusting tube is folded back to realize short-circuit protectionThe function of (c).

Claims

1. A linear regulator having low dropout and short circuit protection characteristics, comprising: in the linear voltage regulator, an unstable input voltage Ui is simultaneously connected with a collector of a transistor T1 and an emitter of a transistor T3, the unstable input voltage Ui is simultaneously connected with a cathode of a diode D1 through a resistor R1, a collector of a transistor T3 sequentially passes through a forward diode D1 and a resistor R3, the reverse voltage stabilizing diode D2 is connected to work, the collector of the transistor T3 is connected to work sequentially through the resistor R4 and the resistor R5, the base of the transistor T3 is connected to the collector of the transistor T2, the collector of the transistor T2 is connected to the base of the transistor T2 through the capacitor C1, the base of the transistor T2 is connected to the negative electrode of the voltage stabilizing diode D2, the emitter of the transistor T1 is connected to the emitter of the transistor T2, the emitter of the transistor T1 is connected to work through the resistor R2, the base of the transistor T1 is connected to the connection point of the resistor R4 and the resistor R5, and the upper end of the resistor R4 outputs the stable voltage Uo.