CN216387887U

CN216387887U - USB device comprising low-cost voltage stabilizing circuit

Info

Publication number: CN216387887U
Application number: CN202123199722.9U
Authority: CN
Inventors: 彭增金
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-12-20
Filing date: 2021-12-20
Publication date: 2022-04-26
Anticipated expiration: 2031-12-20

Abstract

The utility model discloses a USB device comprising a low-cost voltage stabilizing circuit, wherein the USB device comprises a universal integrated operational amplifier LM324 or LM358 and a load voltage adjusting tube (PNP triode or P-channel MOS tube), one unit of the integrated operational amplifier is used as a voltage adjusting operational amplifier unit, the output of the voltage adjusting operational amplifier unit is pulled up to the input voltage of the USB device through a pull-up resistor network and is connected to the control electrode of the load voltage adjusting tube, and the reference voltage can be changed, and the resistance ratio of a feedback resistor can be changed to adjust the voltage stabilizing value of the output voltage.

Description

USB device comprising low-cost voltage stabilizing circuit

Technical Field

The utility model belongs to the field of microelectronic circuits, and particularly relates to a low-cost voltage stabilizing circuit which is particularly suitable for USB equipment.

Background

USB equipment is more and more widely applied in daily production and life. The USB interface provides a 5V power voltage, and usually requires a voltage reduction circuit to reduce the voltage to a lower voltage such as 3.3V, 3V, or 1.8V, which is supplied to a chip in the USB device, such as an MCU (micro controller unit). Since the voltage difference between 5V and 3.3V is not large, it is generally necessary to use ldo (low Drop regulator) low-dropout regulator chip for voltage reduction.

In some USB devices requiring low cost and large current, the LDO voltage stabilization chip cannot meet the requirements of price and performance at the same time.

In some USB devices, the output voltage of the LDO needs to be regulated. The adjustable LDO voltage stabilization chip has higher price.

In some USB devices, it is also necessary that the output of the LDO does not output excessive current even in the event of load abnormality such as a short circuit, which may cause damage to the device.

In some USB devices, the regulated output voltage needs to be output to an external circuit for use, and the output load current needs to be measured.

Disclosure of Invention

The utility model aims to realize an LDO circuit which has low cost, large current and easy output voltage regulation, and provides a circuit scheme for detecting load current.

In order to achieve the purpose, the utility model adopts the following technical scheme:

the USB device for use after the USB input voltage is reduced comprises an LM 324-class general integrated operational amplifier chip, the USB device comprises a load voltage adjusting tube which is a PNP triode or a P-channel MOS tube, the load voltage adjusting tube comprises a control electrode, an input electrode and an output electrode, the USB device comprises a pull-up resistor network, one unit of the LM 324-class general integrated operational amplifier chip is used as a voltage adjusting operational amplifier unit, an output pin of the voltage adjusting operational amplifier unit is pulled up to the input voltage of the USB device through the pull-up resistor network and is connected to a control electrode of the load voltage adjusting tube, the pull-up resistor network comprises a pull-up resistor, or the pull-up resistor network comprises a pull-up resistor and a current-limiting resistor, or the pull-up resistor network comprises two pull-up resistors and a current-limiting resistor.

Furthermore, the input electrode of the load voltage adjusting tube is connected with the input voltage of the USB device, the output electrode of the load voltage adjusting tube outputs voltage for a load, and the output electrode can be connected with an output filter capacitor.

Furthermore, the input electrode of the load voltage adjusting tube is connected with the input voltage of the USB device, the output electrode of the load voltage adjusting tube is connected with a current sampling resistor, the output voltage is supplied for a load, a unit of the LM 324-type general integrated operational amplifier chip is used as a current detection operational amplifier unit, voltages at two ends of the current sampling resistor are respectively connected with an in-phase input pin and an opposite-phase input pin of the current detection operational amplifier unit after being reduced by a divider resistor, the other end of the divider resistor is connected with a bias voltage node instead of being grounded, the output pin of the current detection operational amplifier unit is connected with the opposite-phase input pin through a feedback resistor, and the output pin of the current detection operational amplifier unit is used as a measured value of the load current.

Furthermore, an input electrode of the load voltage adjusting tube is connected with an input voltage of the USB device through a current sampling resistor, an output electrode of the load voltage adjusting tube outputs a voltage for a load, a unit of an LM 324-class general integrated operational amplifier chip is used as a current detection operational amplifier unit, voltages at two ends of the current sampling resistor are respectively reduced by a divider resistor and then connected to an in-phase input pin and an opposite-phase input pin of the current detection operational amplifier unit, the other end of the divider resistor is directly grounded, an output pin of the current detection operational amplifier unit is connected to the opposite-phase input pin through a feedback resistor, and an output pin of the current detection operational amplifier unit is used as a measured value of a load current;

furthermore, when the current sampling resistor is connected to the input electrode of the load voltage adjusting tube, the other end of the voltage dividing resistor is connected to a bias voltage node instead of being grounded;

furthermore, a feedback resistor of the current detection operational amplifier unit is connected in parallel with a filter capacitor.

Compared with the prior art, the embodiment of the utility model has the following beneficial effects:

1. the universal operational amplifier LM324(4 operational amplifier units) or LM358(2 operational amplifier units) which is the cheapest, most commonly used and easy to purchase is adopted, and a pull-up resistor is added to be matched with a PNP triode or a PMOS (P-channel metal oxide semiconductor) tube, so that low-dropout voltage stabilization output is realized, and the universal operational amplifier is cheaper than an LDO (low dropout regulator) chip, especially on occasions needing multi-path voltage stabilization output and large-current output; the voltage endured by the universal operational amplifier LM324/LM358 reaches 20-30V, and compared with the withstand voltage below 7V of most LDO chips, the universal operational amplifier LM324/LM358 has higher reliability.

2. The output voltage is conveniently adjusted, the reference voltage can be controlled, and the resistance ratio of the feedback end divider resistor can be controlled like a common adjustable LDO.

3. Tong (Chinese character of 'tong')The over-voltage resistor reduces the input voltage to satisfyThe input voltage range of the general operational amplifier LM324/LM358 is used for realizing current detection; at the same time provideThe circuit structure is convenient for the resistance value matching of the divider resistor and the calibration of the integrated operational amplifier offset voltage.

4. In embodiment 3, the current sampling resistor is placed at the USB input voltage end, so that the influence of the variation of the common mode voltage on the load current detection is greatly reduced, the requirement on the matching accuracy of the resistance values of the voltage dividing resistors is reduced, and the cost is reduced.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

FIG. 1 is a schematic diagram of a USB device including a low-cost voltage regulator circuit according to embodiment 1;

FIG. 2 is a schematic diagram of a current detection circuit in which a current sampling resistor is connected to an output terminal in embodiment 2;

FIG. 3 is a schematic diagram of a current detection circuit in which a current detection resistor is connected to an input terminal according to embodiment 3;

FIG. 4 shows the simulation result of circuit simulation software Tina for example 1, which is inconsistent with the actual circuit result;

FIG. 5 is a schematic diagram of the internal principles of LM324/LM358 for reference in understanding the above embodiments.

Detailed Description

In order to make the objects, features and advantages of the present invention more apparent and understandable, the embodiments of the present invention will be described in detail and completely with reference to the accompanying drawings, and it is to be understood that the embodiments described below are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The technical scheme of the utility model is further explained by the specific implementation mode in combination with the attached drawings.

Example 1

Referring to fig. 1, the present embodiment provides a USB device 190 for use after stepping down a USB input voltage;

the general operational amplifier LM324 (including 4 operational amplifier units) or LM358 (including 2 operational amplifier units) is the most common, cheapest and most easily purchased integrated operational amplifier chip in the market, has a power voltage range of about 3-32V, and has a power current of about 300uA, and may be called as an LM 324-like general integrated operational amplifier chip or simply LM324, and actually there are many other models such as LM124, LM224, LM2904, LM2902, and the like, or some manufacturers are called as KA358, KA324, KM358, EG358, XL358, HT358, and the like, although they are different, they all belong to such chips, and a unit may be provided as the operational amplifier unit 101 in this embodiment, and fig. 5 shows an internal principle schematic diagram provided by the manufacturer of such chips, and different versions have differences, but input and output structure principles are all consistent.

However, LM324 has 2 limitations: 1. the output voltage range can not reach the full swing of 0-power voltage, the low voltage outputs dozens of mV to 1V, and the high voltage output is about 1.3V-2V lower than the power voltage; 2. the input voltage range can be as low as 0, but the high range is 1.5V-2V lower than the power voltage, that is to say, if the input voltage is close to the power voltage, the operational amplifier can not work normally.

Therefore, in general, to use the operational amplifier unit 101 to drive the control electrode of the load voltage adjusting transistor 102(PNP transistor or PMOS transistor) to form a low dropout voltage regulator circuit, an additional transistor is required to match the voltage level. If the operational amplifier unit 101 directly outputs the driving load voltage adjusting tube 102, the load voltage adjusting tube 102 cannot be turned off and the load voltage adjusting function cannot be realized because the high voltage output of the operational amplifier unit 101 is about 1.3V-2V lower than the power voltage.

In embodiment 1, a pull-

up resistor network

103, 104, and 105 is added, so that when the output high level of the operational amplifier unit 101 cannot reach the power voltage, the control voltage of the load voltage regulating tube 102 is pulled up to achieve the purpose of turning off.

This improvement is based on the fact that the operational amplifier unit 101 is not an ideal operational amplifier, and it can be seen from the schematic diagram that the output high level is formed by 2 NPN transistors to form a darlington structure, so that the output current flows from the power supply terminal to the output terminal. Although the highest high voltage output by the operational amplifier unit 101 is still 1.5-2V lower than the power voltage (almost Vbe of 2 NPN transistors), when the operational amplifier unit 101 wants to output a high voltage and cannot output the high voltage, the operational amplifier unit 101 will not compete with the high voltage by boosting the voltage at the output terminal in another way. Therefore, the addition of a pull-up resistor network is equivalent to the ability of the operational amplifier unit 101 to output a high level to the power supply voltage, so that the control electrode of the load voltage adjusting transistor 102 can be directly driven.

It should be noted that, after the pull-up resistor network is added, the lowest voltage that the operational amplifier unit 101 can output is significantly increased to more than 1V and less than 0V, but in this embodiment, the driving load voltage adjusting tube 102 is not affected.

The load voltage adjusting tube 102 may be a PNP triode, and the control electrode is a Base electrode; the input electrode is an Emitter, and is connected with the input voltage 111 of the USB equipment; the output electrode is a Collector, and the output voltage 110 is used by an electric load 150 and can be connected with an output filter capacitor 109.

The load voltage adjusting tube 102 can be a P-channel MOS tube, and the control electrode is a Gate electrode; the input electrode is a Source electrode Source and is connected with the input voltage 111 of the USB equipment; the output terminal is a Drain Drain, and the output voltage 110 is used by an electrical load 150, which may be connected to an output filter capacitor 109.

The reference voltage 108 is connected to the inverting input terminal of the operational amplifier unit 101, and the

feedback resistors

106 and 107 divide the output voltage 110, and then the divided output voltage is connected to the non-inverting input terminal of the operational amplifier unit 101 and compared with the reference voltage 108, so that the output terminal of the operational amplifier unit 101 is controlled, and the regulated output voltage 110 is realized.

The feedback resistor 107 may be omitted such that the operational amplifier unit 101 forms a voltage follower, and the output voltage 110 is equal to the reference voltage 108. Although theoretically, the feedback resistor 106 could be replaced by a short circuit, it is preferable to use a resistor of 1k or more for the purpose of protecting the integrated op-amp.

By changing the reference voltage 108, the regulated value of the output voltage 110 can be changed; the same as a general adjustable LDO chip, the resistance ratio of the

feedback resistors

106 and 107 can be changed, so as to change the regulated value of the output voltage 110.

The pull-

up resistor networks

103, 104, 105 may have various combinations, and their resistance values are selected according to the characteristics of the operational amplifier unit 101 and the load voltage adjusting tube 102.

The output end of the operational amplifier unit 101 LM324 has a constant current source to ground, the typical value of the constant current source is 12uA to 120uA, which depends on different manufacturers and versions of LM324 chip, and the maximum value of the constant current source, the manual of the chip is not marked, we must consider some margin, for example, 500uA as the basis.

When the load voltage adjusting tube 102 uses a PNP triode, its characteristics are relatively consistent, that is, the base voltage Vbe of the triode is generally 0.4 to 0.6V, and the turn-on voltage is generally 0.6 to 1.2V.

When the load voltage adjusting tube 102 uses a PMOS transistor, the gate threshold voltage can be as low as 0.3V, that is, when the control voltage is lower than the power voltage by 0.3V, the PMOS transistor starts to conduct (generally, the conduction current flowing through the load voltage adjusting tube 102 is 250uA, which is the basis for determining the threshold voltage); the gate threshold voltage of some PMOS transistors is higher, and can reach 0.6V-2V.

The simplest combination is that only one pull-

up resistor

103 or 105 and the current-limiting resistor 104 are directly shorted (the resistance value is 0), and this combination is also the most preferred choice because the innovation purpose of this embodiment is to reduce one transistor for level matching, thereby achieving the purpose of reducing cost.

For a threshold voltage of 0.3V, a pull-up resistor of 600 ohms is selected, and an LM324 constant current source of 500uA is considered, so that the output voltage can be just pulled up to 0.3V; at this time, the low voltage output by the operational amplifier unit 101 can only be as low as about 1.3V, which is equivalent to a gate control voltage of 3.7V for a USB input voltage of 5V, and the required on-state voltage is also low enough for a PMOS transistor with a low threshold voltage.

When the load voltage adjusting tube 102 uses a PNP triode, the pull-up resistance of 600 ohms and the control electrode turn-off voltage of 0.3V can also meet the voltage requirement of the triode Vbe turn-off.

If 103 is 1k, 104 is 5k, and 105 is 5k, the off state 103 can be pulled up to 0.5V, and after voltage division by 104 and 105, the gate voltage is 0.25V; in the conducting state, the low voltage output by the operational amplifier unit 101 is as low as about 1.3V, and after the voltage is divided by 104 and 105, the grid voltage is 1.85V, so that the operational amplifier unit is suitable for PMOS transistors with low conducting voltage.

The current-limiting resistor 104 can be connected in series with a diode with voltage-stabilizing characteristics, such as a 2V voltage-stabilizing diode, the forward voltage-stabilizing characteristic of a red light-emitting diode is about 1.4V, and the forward voltage drop of a general silicon switch diode is about 0.6V, so that the grid voltage in a turn-off state is reduced, the grid voltage in a turn-on state is improved, the cost is correspondingly improved, and level matching is almost realized by adding an additional triode.

The innovation of the technical scheme of the embodiment 1 does not conform to general engineering thinking, simulation is performed by using circuit simulation software such as MultiSim and Tina, even if a pull-up resistor is added according to the technical scheme, the voltage of a control electrode of the load voltage adjusting tube 102 cannot approach to an input voltage, so that the output voltage is higher than a required regulated voltage, and referring to fig. 4, the simulation result of Tina simulation software on the technical scheme can refer to 4.94V instead of the required 3V regulated voltage. And the verification is carried out in an actual circuit, and the load voltage adjusting tube 102 can meet the expectation of the technical scheme and output correct regulated voltage.

Example 2

As shown in fig. 2, the input electrode of the load voltage adjusting tube 222 is connected to the input voltage 221, and the output electrode of the load voltage adjusting tube 222 passes through a current sampling resistor 224 and then is connected to the output voltage 226 to be output to the electrical load.

Filter capacitors

223 and 225 may be optionally installed.

The voltage at one end of the current sampling resistor 224 is divided by the voltage dividing resistors RH 1206 and RL 1207 and then is connected to an input pin of an operational amplifier unit 201 of the LM324/LM 358; the voltage at the other end of the current sampling resistor 224 is divided by the voltage dividing resistors RH 2204 and RL 2205 and then is connected to the other input pin of the operational amplifier unit 201 of the LM324/LM 358; the output voltage V _ i 202 of the operational amplifier unit 201 is connected to the inverting input pin of the operational amplifier unit 201 through the feedback resistor RF-203.

The output voltage V _ i 202 of the operational amplifier unit 201, which is the measured value of the load current, may be connected to an ADC of the microcontroller, or may be connected to a comparison circuit, so as to implement load overcurrent protection.

The innovation of this embodiment is that the low ends of the voltage dividing resistors RL 1207 and RL 2205 are not directly grounded, but are connected to a bias voltage 211; the other resistor RF + 208 is connected to the bias voltage 211 from the non-inverting input pin of the op-amp unit 201 instead of ground.

This is because the voltage dividing resistors RH 1206, RL 1207, RH 2204, and RL 2205 have errors in resistance values, the divided voltage values on both sides are not uniform, the variation of the output voltage 226, the equivalent variation value generated after voltage division, and the differential pressure value of the current sampling resistor 224 are input to the operational amplifier unit 201 and amplified, which seriously affects the accuracy of current measurement.

For example, if the resistance is 1% accurate, the voltage dividing resistances on both sides may generate a voltage dividing error of + -1%, the output voltage 226 may vary by 5V, and after voltage division, the equivalent variation value may reach 5V × 0.01+0.01) =100mV (+ -50mV), assuming that the current sampling resistance is 0.1 ohm, which corresponds to a load current measurement error of 100mV/0.1 ohm =1000mA (+ -500 mA).

Therefore, the divider resistors RH 1206, RL 1207, RH 2204, RL 2205 must be resistance-matched to reduce the error of the divider voltage to an acceptable range.

In addition, the operational amplifier unit 201 also has an offset voltage Vos, that is, two voltages of the in-phase input pin and the anti-phase input pin caused by the manufacturing process always have a difference, and the operational amplifier such as the LM324 is generally in the level of several mV.

The introduction of the bias voltage 211 facilitates calibration by a microcontroller in the device, measures and eliminates the influence of the offset voltage Vos of the op-amp unit 201, and performs resistance matching on the voltage dividing resistors RH 1206, RL 1207, RH 2204 and RL 2205.

When the voltage of the output voltage 226 is equal to the bias voltage 211, no current flows through the voltage dividing resistors RH 1206, RL 1207, RH 2204, RL 2205, and the resistance thereof does not affect the input voltage of the operational amplifier unit 201, and at this time, the difference between the output voltage of the operational amplifier unit 201 and the bias voltage 211 is equal to the voltage value of the offset voltage Vos amplified by the feedback resistor 203 and the voltage dividing resistors, so that the offset voltage Vos can be measured and recorded in the memory for correcting the current measurement value and eliminating the influence of the offset voltage Vos of the operational amplifier unit 201. After the device leaves the factory, the offset voltage Vos of the operational amplifier unit 201 may drift, and this calibration may be performed each time the device is turned on.

Then, under the condition that the electric load is not used, the differential pressure value of the current sampling resistor 224 is 0, the voltage of the output voltage 226 is adjusted, the resistance value matching unbalance degree of the voltage dividing resistors RH 1206, RL 1207, RH 2204 and RL 2205 can be quantitatively measured, and therefore a correction resistor is added to the voltage dividing resistors according to the unbalance degree, and the voltage dividing error is made to be within an acceptable error. For example, a voltage dividing resistor with 1% accuracy is used, the maximum voltage dividing error can reach 2%, the voltage dividing error can reach 100mV (+ -50mV) through conversion to 5V variation, after the voltage dividing error is measured, 100 steps are performed, one correcting resistor in 100 resistor resistance values is added, and the voltage dividing error can be reduced to 1 mV. Because the unbalance degree has + -50mV, according to the unbalance degree, one correction resistor in 50 resistor resistance values is added to one side of the voltage dividing resistors on the two sides, and the voltage dividing error can be reduced to 1 mV.

Because the divider resistor is the same type of resistor, the characteristics are consistent, the increase of the voltage division error can not be caused by general temperature drift, and the resistance value of the correcting resistor only needs to be matched once when leaving a factory.

The adoption of the high-precision divider resistor can reduce the unbalance degree of the resistance matching, but the cost is increased, and the cost is possibly lower than that of the adoption of an integrated operational amplifier which allows the input voltage to reach the power supply voltage to replace a low-cost integrated operational amplifier such as LM324/LM 358.

The bias voltage 211 is preferably 0.5V to 1.5V.

The bias voltage 211 can be obtained by dividing the voltage from a stable voltage 214 by 2 dividing resistors RZ 1212, RZ 2213, as long as the resistances of 212, 213 are much smaller than the dividing

resistors

204, 205, 206, 207, for example, 15k is selected for the dividing resistors RH 1206, RL 1207, RH 2204, RL 2205, and RZ 2213 is 150 ohms, the voltage varies from 5V to 0, the bias voltage 211 also varies by 1%, i.e. 50mV, and the voltage is not amplified but 1: the ratio of 1 is reflected to the output voltage of the operational amplifier unit 201, and has little influence on the current measurement accuracy. Of course, it is more cost effective to have the appropriate regulated voltage 214 directly as the bias voltage 211.

The resistor RF + 208 and the voltage dividing resistor of the non-inverting input pin are actually connected in parallel, and in actual manufacturing, a resistor with the same resistance as the parallel resistor can be used instead.

Due to the existence of the bias voltage 211, the high voltage terminal and the low voltage terminal of the current sampling resistor can be inverted and connected to the non-inverting and inverting input pins of the operational amplifier unit 201, and reflected in the output voltage V _ i 202, which is different in polarity with respect to the difference of the bias voltage 211. In the figure, the high voltage end is divided and then connected to the non-inverting input pin, and the output voltage V _ i 202 becomes higher as the load current becomes larger.

Example 3

Referring to fig. 3, the input voltage 321 is connected to the input terminal of the load voltage adjusting tube 322 through a current sampling resistor 324, and the output terminal of the load voltage adjusting tube 322 is connected to the output voltage 326 for outputting to the electrical load. The filter capacitor 323 may be selectively installed, and may not be installed when a capacitor is included in the load.

The voltage at one end of the current sampling resistor 324 is divided by the voltage dividing resistors RH 1306 and RL 1307 and then is connected to an input pin of an operational amplifier unit 301 of the LM324/LM 358; the voltage at the other end of the current sampling resistor 324 is divided by the voltage dividing resistors RH 2304 and RL 2305 and then is connected to the other input pin of one operational amplifier unit 301 of LM324/LM 358; the output voltage V _ i 302 of the operational amplifier unit 301 is connected to the inverting input pin of the operational amplifier unit 301 through the feedback resistor RF-303.

The output voltage V _ i 302 of the operational amplifier unit 301, which is the measured value of the load current, may be connected to an ADC of the microcontroller, or may be connected to a comparison circuit, so as to implement load overcurrent and constant current protection.

Unlike embodiment 2, the low ends of the voltage dividing resistors RL 1307 and RL 2305 are directly grounded; the other resistor RF + 308 is connected to ground from the non-inverting input pin of the op-amp unit 301.

Since one end of the current sampling resistor 324 is connected to the input voltage 321, and the input voltage 321 is basically stable after the USB device is connected to the USB interface, and is approximately about 5V, the voltage dividing resistors RH 1306, RL 1307, RH 2304, and RL 2305 generate voltage dividing errors due to the resistance value errors, but the voltage dividing deviation caused by the voltage dividing errors is also fixed. The voltage division deviation and the offset voltage Vos of the operational amplifier unit 301 will cause the output voltage V _ i 302 of the operational amplifier unit 301 to generate an initial bias voltage, but after the load voltage adjusting tube 322 is turned off, the initial error bias voltage can be measured, so that the initial error bias voltage can be eliminated by calculation in the subsequent measurement and control.

The resistor RF + 308 and the voltage dividing resistor of the non-inverting input pin are actually connected in parallel, and in practice, a resistor may be used instead, and the resistance value of this resistor is intentionally selected, and a fixed voltage dividing deviation is preset, so that the output value of the output voltage V _ i 302 of the operational amplifier unit 301 is always higher than 0V after the load voltage adjusting tube 322 is turned off, and thus, it is not necessary to set a bias voltage as in embodiment 2 to achieve this purpose.

For example, considering that + -10mV is applied to the offset voltage Vos of the operational amplifier unit 301, 10k 1 is applied to RH 1306, RL 1307, RH 2304 and RL 2305, 200k 1 is applied to the feedback resistor RF-303, and + -50mV is applied to the voltage division error generated by RH 1306, RL 1307, RH 2304 and RL 2305, and we select the resistor RF + 308 to be 130k 1%, so that a positive offset of about 61mV is generated at the non-inverting input terminal of the operational amplifier unit 301 compared with a resistor of 200k 1%, and the offset of the whole system is always within the range of the positive offset. Since the resistors RF + 308 and RL 1307 are actually connected in parallel, a resistor of 130k and 10k, i.e., about 9.285k, may be used instead, or a standard resistor sequence of 9.1k may be used instead.

Of course, presetting a fixed voltage-dividing deviation will cause the imbalance degree of the resistance matching to be further increased, and is not suitable for the case where the divided input voltage 321 is unstable, and for the case where the input voltage 321 is unstable, the low ends of the voltage-dividing resistors RL 1307 and RL 2305 and the low end of the resistor RF + 308 in embodiment 3 may also be connected to a bias voltage without being grounded, like embodiment 2. Therefore, a fixed voltage division deviation does not need to be preset, and the current measurement value is influenced when the input voltage 321 is unstable.

When the input voltage 321 is unstable, similarly to embodiment 2, in factory production, the degrees of imbalance in resistance matching among RH 1306, RL 1307, RH 2304, and RL 2305 may be measured, and a correction resistor may be added to the voltage dividing resistor. Since the input voltage 321 is still unstable, the typical ripple amplitude is below 10% of the USB input voltage, which is at least an order of magnitude lower than the matching requirement of example 2 in example 3.

In embodiment 3, a feedback capacitor CF 309 may also be connected in parallel to the feedback resistor RF-303 to implement low-pass filtering of the current measurement value, thereby eliminating the task of software filtering performed by the microcontroller after ADC sampling. Because the current sampling resistor of embodiment 3 is placed before the load voltage adjusting tube 322, and there is no filter capacitor, the current flowing may fluctuate more than the load current fluctuation of the electric load.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. The USB device with the low-cost voltage stabilizing circuit is characterized in that the USB device comprises an LM 324-class general integrated operational amplifier chip, the USB device comprises a load voltage adjusting tube which is a PNP triode or a P-channel MOS tube, the load voltage adjusting tube comprises a control electrode, an input electrode and an output electrode, the USB device comprises a pull-up resistor network, one unit of the LM 324-class general integrated operational amplifier chip is used as a voltage adjusting operational amplifier unit, an output pin of the voltage adjusting operational amplifier unit is pulled up to the input voltage of the USB device through the pull-up resistor network and is connected to a control electrode of the load voltage adjusting tube, the pull-up resistor network comprises a pull-up resistor, or the pull-up resistor network comprises a pull-up resistor and a current-limiting resistor, or the pull-up resistor network comprises two pull-up resistors and a current-limiting resistor.

2. The USB device of claim 1, wherein the input terminal of the load voltage regulator is connected to the input voltage of the USB device, and the output terminal of the load voltage regulator outputs the voltage for the load.

3. The USB device of claim 1, wherein the input terminal of the load voltage regulator is connected to the input voltage of the USB device, the output terminal of the load voltage regulator is connected to a current sampling resistor, and the output voltage is supplied to the load, a unit of the LM 324-like general integrated operational amplifier chip is used as a current detection operational amplifier unit, voltages at two ends of the current sampling resistor are respectively reduced by a voltage divider resistor and then connected to the non-inverting input terminal and the inverting input terminal of the current detection operational amplifier unit, the other end of the voltage divider resistor is connected to a bias voltage node, the output terminal of the current detection operational amplifier unit is connected to the inverting input terminal of the current detection operational amplifier unit through a feedback resistor, and the output terminal of the current detection operational amplifier unit is used as a measured value of the load current.

4. The USB device of claim 1, wherein the input terminal of the load voltage regulator is connected to the input voltage of the USB device through a current sampling resistor, the output terminal of the load voltage regulator outputs a voltage for the load, a unit of the LM 324-like general integrated operational amplifier chip is used as a current detecting operational amplifier unit, voltages at two ends of the current sampling resistor are respectively reduced by a voltage dividing resistor and then connected to the non-inverting input terminal and the inverting input terminal of the current detecting operational amplifier unit, the other end of the voltage dividing resistor is directly grounded, the output terminal of the current detecting operational amplifier unit is connected to the inverting input terminal of the current detecting operational amplifier unit through a feedback resistor, and the output terminal of the current detecting operational amplifier unit is used as a measured value of the load current.

5. The USB device of claim 1, wherein the input terminal of the load voltage regulator is connected to the input voltage of the USB device through a current sampling resistor, the output terminal of the load voltage regulator outputs a voltage for the load, a unit of the LM 324-like general integrated operational amplifier chip is used as a current detecting operational amplifier unit, voltages at two ends of the current sampling resistor are respectively reduced by a voltage dividing resistor and then connected to the non-inverting input terminal and the inverting input terminal of the current detecting operational amplifier unit, the other end of the voltage dividing resistor is connected to a bias voltage node, the output terminal of the current detecting operational amplifier unit is connected to the inverting input terminal of the current detecting operational amplifier unit through a feedback resistor, and the output terminal of the current detecting operational amplifier unit is used as a measured value of the load current.

6. The USB device of claim 3, 4 or 5, wherein a filter capacitor is connected in parallel to the feedback resistor connected to the inverting input pin of the current sense op-amp unit.