A high-side ideal diode based on current sensing

Abstract

The utility model discloses a high -end ideal diode based on current detection, including voltage comparator, MOS pipe and resistance, voltage comparator, MOS pipe and resistance constitute circuit, the MOS pipe is NMOS pipe or PMOS pipe, the MOS pipe source or drain series into a current detection resistance. This circuit has the function of preventing the backflow, can protect the preceding stage circuit, has the advantages such as small static current loss, reference level is 0V, no backflow current, is applicable to the occasion of small current, and the circuit is simple, and the cost is very low, and the practicality is strong.

Description

Technical Field

[0001] This utility model relates to the field of diode technology, specifically to a high-end ideal diode based on current detection. Background Technology

[0002] In electronic circuits, diodes, due to their unidirectional conduction characteristics, are widely used in various circuits and are as important as resistors and capacitors, making them indispensable components. Although diodes are widely used, they have an inherent physical defect: their forward voltage (forward and forward bias voltages) is not 0V. Generally, the forward voltage of a diode is V... F =Approximately 0.6V to 0.7V (turn-on voltage U) ON =0.5V), this is an inherent physical characteristic of PN junctions and cannot be eliminated. Although Schottky diodes with lower on-state voltages have been fabricated using improved semiconductor processes, the on-state voltage V of a Schottky diode is still... F With a turn-on voltage of 0.3V to 0.4V, the power loss of Schottky diodes is still unsatisfactory for applications requiring unidirectional conduction characteristics and low turn-on voltage. Therefore, it is necessary to design unidirectional conduction devices with low turn-on voltages to reduce conduction losses and improve power supply efficiency.

[0003] When a metal-oxide-semiconductor field-effect transistor (MOSFET) is turned on, the on-resistance between the drain and source is small, and the on-voltage drop is small. If the unidirectional conduction characteristic of the MOSFET can be utilized, it can replace the diode as a good unidirectional conduction device.

[0004] An ideal diode device typically includes a MOSFET and its driving circuit. The source and drain of the MOSFET can correspond to the cathode and anode (or anode and cathode) of the diode, respectively. The driving circuit generally uses modules such as voltage comparators or amplifiers to detect the potential difference between the drain and source of the MOSFET. When the anode (drain) potential is higher than the cathode (source) potential, the driving circuit outputs a driving signal to the gate of the MOSFET to turn it on. After the MOSFET is turned on, the current can flow from the anode to the cathode through the drain-source channel of the MOSFET. Conversely, if the anode potential is lower than the cathode potential, the driving circuit outputs the driving signal required to turn off the MOSFET. Therefore, the anode and cathode are in an open circuit state, and the unidirectional conduction device is in a cut-off (closed) state.

[0005] The existing technical solutions for realizing an ideal diode device based on current detection are as follows.

[0006] Low-side current sensing (current sensing resistor) technology solution 1: This solution primarily uses the forward voltage drop generated by the sensing resistor to control the conduction and cutoff of the MOSFET. For example, a high-side active diode consists of a voltage comparator (operational amplifier) ​​and a MOSFET. The main transistor of the high-side ideal diode can be a PMOS or NMOS (requiring an additional bias power supply). A current sensing resistor is connected in series at the low end (between the negative terminal of the power supply and the load). During normal operation, current flowing through the current sensing resistor generates a certain forward voltage drop. The voltage comparator compares the voltage difference across the current sensing resistor, determines the current direction based on the magnitude of the voltage difference, and outputs a signal to the gate of the MOSFET to control its conduction and cutoff. This can achieve reverse current protection for the low-side ideal diode. However, this solution has drawbacks: the current sensing resistor has a certain forward voltage drop (not 0V), the magnitude of which is the reference level of the load. For the ADC module, this introduces an error in the conversion result. Since the current is constantly changing, and the load reference level is constantly changing, the ADC module cannot predict the magnitude of the operating current. Therefore, this reference level error cannot be eliminated by eliminating a fixed error. This solution is unsuitable for modules such as ADCs that require a stable reference level.

[0007] Low-side current detection (MOSFET drain-source impedance) technical solution 2: This solution primarily uses the on-state voltage drop generated by the MOSFET drain-source resistance to control the MOSFET's on / off state. For example, a low-side active diode consists of a voltage comparator and an NMOS transistor. The NMOS transistor acts as the main conductor of the low-side ideal diode, located between the negative terminal of the power supply and the load. The voltage comparator compares the voltage difference between the drain and source of the NMOS transistor, determines the current direction based on the magnitude of the voltage difference, and outputs a signal to the gate of the NMOS transistor to control its on / off state. This can achieve the reverse-current protection function of the low-side ideal diode. However, it has shortcomings: the on-resistance of a power-type NMOS transistor is very small, lower than that of a power-type PMOS transistor with the same parameters. If the current flowing through the NMOS transistor is small, the voltage difference between the drain and source is also small, which may not reach the threshold voltage of the hysteresis voltage comparator or hover near the threshold voltage, easily causing misjudgment and incorrect output results. Furthermore, since the current is constantly changing, the voltage difference between the drain and source of the NMOS transistor is also changing. Although the voltage difference is small, it means that the reference level of the load is not 0V. This solution has a reference level that is not 0V, making it unsuitable for low-current loads, ADC modules, etc.

[0008] High-side current sensing (MOSFET drain-source impedance) technology solution 3: This solution primarily uses the on-state voltage drop generated by the MOSFET's drain-source resistance to control the MOSFET's on / off state. For example, a high-side active diode consists of a voltage comparator and a MOSFET. The main transistor of the high-side ideal diode can be a PMOS or NMOS transistor (requiring an additional bias power supply). The voltage comparator compares the voltage difference between the MOSFET's drain and source, determines the current direction based on the magnitude of the voltage difference, and outputs a signal to the MOSFET's gate to control its on / off state. This can achieve reverse current protection for the high-side ideal diode. However, it has drawbacks: the on-resistance of power MOSFETs is relatively small. If the current flowing through the MOSFET is small, the voltage difference between the MOSFET's drain and source will be small, potentially failing to reach the threshold voltage of the hysteresis voltage comparator or hovering near the threshold voltage, easily leading to misjudgments and incorrect output results. This solution uses a 0V reference level and is suitable for high-current, stable reference-level ADC modules, but is unsuitable for low-current loads.

[0009] The comparator offset voltage, also known as the input offset voltage (VIO, sometimes abbreviated as VOS), is the voltage at which the output voltage of an ideal voltage comparator should also be zero when the input voltage is zero (without a zero-adjustment device). However, in reality, it is difficult to achieve perfect symmetry in the parameters of the differential input stage. Typically, when the input voltage is zero, there is a certain output voltage that is not zero; this voltage is called the offset voltage. The magnitude of VIO reflects the degree of symmetry and potential matching of the circuit in the comparator manufacturing process. The larger the VIO value, the worse the symmetry of the circuit; it is generally approximately ±(1~10)mV.

[0010] Overdrive voltage (VOD) is the differential voltage generated between the positive and negative inputs of a voltage comparator at the offset voltage (VIO). It is the absolute value of the voltage difference between the two inputs of the voltage comparator. For accurate comparison, the overdrive voltage (VOD) should be higher than the offset voltage (VIO).

[0011] The input offset voltage (VIO) of TI's LM393B voltage comparator chip is VIO = ±0.37mV (typical value), |VIO| ≤ 2.5mV; the input offset voltage of the LMC7211AIM5 voltage comparator chip is VIO = 3mV (typical value), |VIO| ≤ 8mV. When selecting a voltage comparator, a chip with a lower offset voltage should be chosen. The input offset voltage reflects the symmetry of the circuit, and its value is typically ±(1~10)mV.

[0012] When the NMOS transistor is turned on, the drain-source channel on-resistance R DS(ON) It is relatively small, assuming R is small. DS(ON) =10mΩ, I D >VIO / R DS(ON) =2mV / 10mΩ =0.2A means that the voltage comparator can only work normally if the current is greater than 0.2A. Obviously, NMOS transistors are suitable for high current applications.

[0013] For applications with an operating current less than 0.2A, one solution is to choose R. DS(ON) NMOS transistors with an impedance greater than 100mΩ, meeting R... DS(ON) ×I D >VIO, i.e., R DS(ON) >VIO / I D Secondly, a current sensing resistor R can be connected in series with the drain or source of the NMOS transistor to satisfy (R+R). DS(ON) )×I D >VIO, that is, R>VIO / I D -R DS(ON) .

[0014] PMOS transistor drain-source channel on-resistance R DS(ON) It's relatively large, let's assume R is large. DS(ON) =100mΩ, I D >VIO / R DS(ON) =2mV / 100mΩ =0.02A, meaning that the voltage comparator can operate normally when the current is greater than 0.02A. Obviously, the PMOS transistor is suitable for low-current applications. For low-current applications, a current sensing resistor can be connected in series with the drain or source of the PMOS transistor.

[0015] For applications with an operating current less than 0.2A, one solution is to choose R. DS(ON) PMOS transistors with a resistance greater than 100mΩ, meeting R... DS(ON) ×I D >VIO, i.e., R DS(ON) >VIO / I D Secondly, a current sensing resistor R can be connected in series with the drain or source of the PMOS transistor to satisfy (R+R). DS(ON) )×I D >VIO, that is, R>VIO / I D -R DS(ON) .

[0016] Therefore, combining the advantages of the above schemes to achieve complementary advantages, based on the high-end current sensing (drain-source impedance) technology scheme 3, we design a high-end ideal diode based on current sensing: a current sensing resistor is connected in series with the drain or source of the MOS main tube, which is suitable for low current applications and meets the application requirements of a reference level of 0V. It overcomes the disadvantage of hysteresis voltage comparators being prone to misjudgment. To this end, we propose a high-end ideal diode based on current sensing to solve the above problems. Utility Model Content

[0017] The purpose of this invention is to provide a high-end ideal diode based on current sensing to solve the problems mentioned in the background art.

[0018] To achieve the above objectives, this utility model provides the following technical solution: a high-end ideal diode based on current detection, comprising a voltage comparator, a MOSFET, and a resistor, wherein the voltage comparator, MOSFET, and resistor form a circuit, the MOSFET being an NMOS or PMOS transistor, and a current detection resistor is connected in series with the source or drain of the MOSFET.

[0019] Preferably, the voltage comparator is used to compare the magnitude of the voltage drop to determine the direction of the current.

[0020] Preferably, the voltage drop is the sum of the MOSFET turn-on voltage drop and the current sensing resistor voltage drop.

[0021] Compared with the prior art, the beneficial effects of this utility model are: this circuit has the function of preventing backflow, which can protect the preceding circuit; it has the advantages of low static current loss, reference level of 0V, and no backflow current, and is suitable for low current applications. The circuit is simple, the cost is very low, and it is highly practical. Attached Figure Description

[0022] Figure 1 This is a block diagram of a high-end ideal diode based on current sensing, constructed using an NMOS transistor according to this invention.

[0023] Figure 2 This is a block diagram of a high-end ideal diode based on current sensing, constructed using a PMOS transistor of this invention.

[0024] Figure 3 This utility model Figure 1 Forward conduction simulation test diagram;

[0025] Figure 4 This utility model Figure 1 Reverse cutoff simulation test diagram;

[0026] Figure 5 This utility model Figure 2 Forward conduction simulation test diagram;

[0027] Figure 6 This utility model Figure 2 Reverse cutoff simulation test diagram. Detailed Implementation

[0028] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model. Example 1

[0029] Reference Figure 1 This is the first embodiment of the present invention. This embodiment provides a high-side ideal diode based on current sensing, including a voltage comparator, an NMOS transistor, and a resistor. The voltage comparator, NMOS transistor, and resistor form a circuit. Since the NMOS transistor has a low on-resistance, its on-state voltage drop is very small in low-current applications. When the on-state current is small, the on-state voltage drop between the drain and source of the NMOS transistor is generally on the order of millivolts. The on-state voltage drop is so small that it is difficult to meet the requirement that the overdrive voltage (VOD) should be higher than the offset voltage (VIO). Therefore, a current sensing resistor (the resistance value depends on the specific situation) needs to be connected in series. The sensing voltage drop (the sum of the on-state voltage drop of the NMOS transistor and the voltage drop of the current sensing resistor) serves as the overdrive voltage (VOD) of the two input terminals of the comparator. Only when the sensing voltage drop is greater than the offset voltage can the comparator work normally.

[0030] When the main transistor is an NMOS transistor: a bias power supply VBIAS is required. A current sensing resistor is connected in series between the positive terminal of the power supply and the drain (or source, load RL high end) of the NMOS main transistor. A voltage comparator compares the voltage difference between the positive terminal of the power supply and the source (or drain, load RL high end). The output of the voltage comparator is an open-drain output and requires an external pull-up resistor R2.

[0031] A voltage comparator is used to compare and detect the voltage drop, and then determine whether the NMOS main conductor is on or off. This prevents external power supply from flowing back into the input power supply, protecting the input power supply's pre-amplifier circuit. Specifically, when the detected voltage drop is greater than the voltage comparator's positive threshold VT2, the voltage comparator output level is VBIAS (VBIAS > VCC + V). TN V TN The NMOS transistor turns on (the threshold voltage for NMOS transistor conduction), and the NMOS transistor V1 turns on. Conversely, when the detected voltage drop is less than the voltage comparator threshold VT1, the voltage comparator output level is low, and the NMOS transistor V1 turns off, preventing the Vout current from flowing back to VCC and protecting the VCC power supply front-end circuit.

[0032] Bias power supply VBIAS: Since the drain of the NMOS transistor is connected to the positive terminal of the power supply, the control circuit system requires a bias power supply VBIAS referenced to ground to be higher than the gate voltage (turn-on threshold voltage) of the source voltage, satisfying the condition VBIAS > VCC + V. TN V TN This is the turn-on threshold voltage of the NMOS transistor; otherwise, the NMOS transistor cannot be turned on.

[0033] Voltage comparators with a priority hysteresis loop propagation characteristic (also known as a Schmitt trigger) have threshold voltages that change rapidly with the output voltage, improving their noise immunity. Hysteresis voltage comparators exhibit hysteresis, or inertia, thus providing some noise immunity; however, stronger noise immunity comes at the cost of lower sensitivity. A hysteresis voltage comparator circuit has two threshold voltages: VT1, which causes a jump in the output voltage Vout as the input voltage VCC gradually increases; and VT2, which causes a jump in the output voltage Vout as the input voltage VCC gradually decreases. VT1 ≠ VT2, hence the hysteresis characteristic. Similar to a single-threshold voltage comparator, when the input voltage changes in one direction, the output voltage Vout jumps only once. Example 2

[0034] The difference from Implementation Method 1 is that in the circuit of Implementation Method 1... Figure 1 Based on this, a PMOS transistor can be used to replace or an NMOS transistor can be used to control V1. The connections of the non-inverting and inverting input terminals of the voltage comparator will differ, such as... Figure 2 As shown, the rest remain unchanged.

[0035] When the main transistor is a PMOS transistor: A current sensing resistor R1 is connected in series between the positive terminal of the power supply and the drain (or source, load RL high end) of the PMOS main transistor. The voltage comparator compares the voltage difference between the positive terminal of the power supply and the source (or drain, load RL high end). The output of the voltage comparator is an open-drain output and requires an external pull-up resistor R2.

[0036] The voltage comparator compares the magnitude and direction of the detected voltage drop (the sum of the PMOS transistor's on-state voltage drop and the current sensing resistor's voltage drop) to determine whether the PMOS transistor is on or off. This prevents backflow from external power into the input power supply and protects the input power supply's pre-amplifier circuitry. Specifically: when the detected voltage drop is greater than the comparator's positive threshold VT2, the comparator outputs a low level VB, approximately 0V, and the PMOS transistor V1 is on; conversely, when the detected voltage drop is less than the comparator's threshold VT1, the comparator outputs a level VB approximately equal to VCC (>-V). TP V TPTo prevent the turn-on threshold voltage, PMOS transistor V1 is turned off to prevent Vout current from flowing back into VCC, thus protecting the VCC power supply's preceding circuitry. The power supply voltage must satisfy: VCC > -V TP V TP This is the turn-on threshold voltage of the PMOS transistor; otherwise, the PMOS transistor cannot be turned on. Example 3

[0037] Reference Figure 1-6 This is the third embodiment of the present invention, which is based on the above two embodiments.

[0038] according to Figure 1 , Figure 2 The circuit schematic was simulated and tested using National Instruments' Multisim simulation software (version V14.0). The voltage comparator selected was the LMC7211AIM5, a rail-to-rail operational amplifier, with a push-pull amplification in the output stage to achieve approximately full swing. The PMOS transistor was selected from ON Semiconductor, model NVTFS5124PLTAG, with a minimum turn-on threshold voltage of V. TP(MIN) =-1.5V, maximum value V TP(MAX) =-2.5V, typical value V not given. TP The conduction current can reach -6A, and the conduction resistance R DS(ON) =0.26Ω(V GS =-10V), R DS(ON) =0.38Ω (V GS =-4.5V). The NMOS transistor used is an NXP device, model BSP030, with a minimum turn-on threshold voltage of V. TN(MIN) =1V, maximum value V TN(MAX) =2.8V, typical value V not given. TN The conduction current reaches 10A, and the conduction resistance R DS(ON) =30mΩ (V) GS =10V), R DS(ON) =50mΩ (V) GS =4.5V). Load resistance RL=1000Ω, current sensing resistor R1=1Ω.

[0039] The specific simulation test is as follows:

[0040] Implementation Method 1: Simulation test, using an NMOS transistor as the main control for simulation of a high-side ideal diode based on current sensing.

[0041] Simulation test of a high-end ideal diode based on current sensing, constructed from an NMOS transistor, DC power supply forward conduction simulation test: VBIAS=20.0V, VCC=VCC1=12.0V (switch J1 closed), pull-up resistor R2=100kΩ. For different current applications, the value of the load resistor RL is changed. The simulation test results are shown in Table 1.

[0042]

[0043] According to the simulation test results of different load currents in Table 1, the load RL=100kΩ, the main conduction voltage drop is 2.619μV, the detection voltage drop is 122.616μV, the comparator output voltage VB≈VCC=20.0V (approximately the bias power supply voltage), the NMOS main conduction V1 is turned on, and the conduction current is 120μA.

[0044] DC power supply forward conduction simulation test: Load RL=1kΩ, VCC (VCC1)=12V (switch J1 closed). During forward conduction, the NMOS main conductor V1 output voltage Vout=12.0V (measured by a digital multimeter as 11.988V), the voltage difference between the two input ports of the voltage comparator is VP-VN=12.249mV (measured by a digital multimeter), the voltage comparator output level is VB=20V (probe PR4), and the NMOS main conductor V1 forward voltage drop is VCC-Vout=12V-11.988V =0.012V=12mV, which is much lower than the diode forward voltage drop V. F =0.6V, the positive output current of the power supply is 11.988V / 1000Ω = 11.988mA ≈ 12mA, corresponding to the on-resistance R DS(ON) =12.249mV / 11.988mA - R1 = 1.0218Ω - 1Ω = 21.8mΩ, which conforms to the datasheet parameters. Specific simulation results are as follows... Figure 3 As shown.

[0045] DC power supply reverse cutoff simulation test: After switch J1 is closed, switch J2 is also closed, i.e., Vout(VCC2) = 13V > VCC(VCC1) = 12V. The voltage comparator output level is VB = 144mV (probe PR4). The NMOS main conductor V1 is cut off, and the reverse current flowing into VCC1 is approximately -178nA (probe PR1), which can be ignored. It can be considered that no reverse current occurs. The specific simulation is as follows: Figure 4 As shown.

[0046] Implementation Method 2: Simulation test, which simulates the forward conduction of a high-side ideal diode based on current sensing, with the main component being a PMOS transistor.

[0047] VCC1=12.0V (switch J1 closed), pull-up resistor R2=100kΩ. For different current applications, the value of the load resistor RL is changed. The simulation test results are shown in Table 2.

[0048]

[0049] According to the simulation test results of different load currents in Table 2, the load RL=100kΩ, the main conduction voltage drop is 6.574mV, the detection voltage drop is 6.727mV (the sum of the PMOS tube conduction voltage drop and the current sensing resistor voltage drop), the comparator output voltage VB≈VCC=9.71V, the PMOS main conduction V1 is turned on, and the conduction current is 120μA.

[0050] DC power supply forward conduction simulation test: Load RL = 1000Ω, VCC (VCC1) = 12V (switch J1 closed). During forward conduction, the output voltage Vout of PMOS transistor V1 is 12.0V (measured as 11.985V with a digital multimeter). The voltage difference between the two input ports of the voltage comparator is VP - VN = 15.247mV (measured with a digital multimeter). The output level of the voltage comparator is VB = 128mV (probe PR4). The forward voltage drop of PMOS transistor V1 is VCC - Vout = 12V - 11.985V = 0.015V, which is lower than the forward voltage drop of the diode V. F =0.6V, the positive output current of the power supply is 11.985V / 1000Ω = 11.985mA, corresponding to the on-resistance R DS(ON) =15.247mV / 11.985mA - R1 = 1.2722Ω - 1Ω = 272.2mΩ, which conforms to the datasheet parameters. Specific simulation results are as follows: Figure 5 As shown.

[0051] DC power supply reverse cutoff simulation test: Load RL = 1000Ω, switches J1 and J2 are both closed, i.e., Vout(VCC2) = 13V > VCC(VCC1) = 12V, voltage comparator output level is VB = 13.0V (probe PR4), VB - Vout ≈ 0V > V TP With PMOS transistor V1 cut off, the reverse current flowing into VCC1 is approximately 0A (probe PR1), which can be ignored. Therefore, it can be assumed that no reverse current occurs. The specific simulation is as follows: Figure 6 As shown.

[0052] Compared with the high-side current sensing (drain-source impedance) technology solution 3 based on current sensing in the background technology, this solution has advantages such as low static current loss, a reference level of 0V, and no reverse current, making it suitable for low-current applications. The circuit has reverse current prevention function, which can protect the upstream circuit; it has low loss and low static current loss; the circuit is simple, the cost is very low, and it is highly practical.

[0053] In Implementation Method 1, the current sensing resistor R1 is located between the power supply VCC and the drain of the NMOS transistor; in Implementation Method 2, the current sensing resistor R1 is located between the power supply VCC and the drain of the PMOS transistor. Furthermore, referring to the above implementation methods, the current sensing resistor can be inserted between the drain of the NMOS transistor and the load RL, or between the source of the PMOS transistor and the load RL, with the rest remaining unchanged. The schematic diagram is omitted. The voltage comparator can also compare the voltage drop across the current sensing resistor independently, with the rest remaining unchanged. The schematic diagram is omitted, and the working principle is the same as described in the above implementation methods, and will not be repeated here.

[0054] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-side ideal diode based on current sensing, comprising a voltage comparator, a MOSFET, and a resistor, characterized in that: The circuit consists of a voltage comparator, a MOSFET, and a resistor. The MOSFET is either an NMOS or a PMOS transistor. A current sensing resistor is connected in series with the source or drain of the MOSFET, and the current sensing resistor is electrically connected to the positive terminal of the power supply.

2. The high-side ideal diode based on current sensing according to claim 1, characterized in that: The voltage comparator is used to compare the magnitude of the voltage drop to determine the direction of the current.

3. The high-side ideal diode based on current sensing according to claim 2, characterized in that: The voltage drop is the sum of the MOSFET's on-state voltage drop and the current sensing resistor's voltage drop.

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