Low-end ideal diode based on current detection

Abstract

The utility model discloses a low-end ideal diode based on current detection, which comprises a voltage comparator, an NMOS (N-channel metal oxide semiconductor) tube and a resistor, the voltage comparator, the NMOS tube and the resistor form a circuit, the NMOS tube is a main tube, a current detection resistor is serially connected to a source electrode or a drain electrode of the NMOS main tube, and the voltage comparator is a Schmitt trigger. The circuit has an anti-backflow function and can protect a pre-stage circuit; the circuit has the advantages of low quiescent current loss, 0V reference level, no reverse current and the like, is suitable for low-current occasions, and is simple, low in cost and high in practicability.

Description

Technical Field

[0001] This utility model relates to the field of diode technology, specifically to a low-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 V) 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 are as follows.

[0006] Low-side current sensing (resistor) technology solution 1: The 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 transistor (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 flows through the current sensing resistor, generating a certain 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 voltage drop (not 0V), the magnitude of which is the load's reference level. For the ADC module, this introduces an error in the conversion result. Since the current is constantly changing, and the load's 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 (drain-source impedance) technical solution 2: The 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 conduction and cutoff. This can achieve reverse current protection for 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, with a non-0V reference level, is unsuitable for low-current loads, ADC modules, etc.

[0008] High-side current detection (drain-source impedance) technical solution 3: The high-side active diode consists of a voltage comparator and a MOSFET. The main conductor of the high-side ideal diode can be a PMOS or NMOS (requiring an additional bias power supply). The voltage comparator compares the voltage difference between the drain and source of the MOSFET, determines the current direction based on the magnitude of the voltage difference, and outputs a signal to the MOSFET gate to control the MOSFET's on / off state. This can achieve reverse current protection for the high-side ideal diode. However, it has drawbacks: the on-resistance of the power MOSFET is relatively small. If the current flowing through the MOSFET is small, the voltage difference between the drain and source of the MOSFET 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] Therefore, combining the advantages of the above schemes to achieve complementary advantages, based on the low-end current sensing (drain-source impedance) technology scheme 2, we design a low-end ideal diode based on current sensing: a current sensing resistor is connected in series with the drain or source of the NMOS 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 low-end ideal diode based on current sensing to solve the above problems. Utility Model Content

[0015] The purpose of this invention is to provide a low-end ideal diode based on current detection to solve the problems mentioned in the background art.

[0016] To achieve the above objectives, this utility model provides the following technical solution: a low-end ideal diode based on current detection, comprising a voltage comparator, an NMOS transistor, and a resistor, wherein the voltage comparator, NMOS transistor, and resistor form a circuit, the NMOS transistor is the main transistor, and a current detection resistor is connected in series with the source or drain of the NMOS main transistor, and the voltage comparator is a Schmitt trigger.

[0017] Preferably, the voltage comparator compares the magnitude of the detected voltage drop and determines the direction of the current.

[0018] Preferably, the detection voltage drop is the sum of the NMOS transistor's on-state voltage drop and the current sensing resistor's voltage drop.

[0019] 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

[0020] Figure 1 This is a block diagram of a low-end ideal diode based on current sensing, constructed from an NMOS transistor according to this invention.

[0021] Figure 2 This utility model Figure 1 Forward conduction simulation test diagram;

[0022] Figure 3 This utility model Figure 1 Reverse conduction simulation test diagram. Detailed Implementation

[0023] 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

[0024] Reference Figure 1 This is the first embodiment of the present invention. This embodiment provides a low-end ideal diode based on current detection, including a voltage comparator, an NMOS transistor and a resistor. The voltage comparator, NMOS transistor and resistor form a circuit. The NMOS transistor is the main control. A current detection resistor is connected in series with the source or drain of the NMOS main control. The voltage comparator is a Schmitt trigger.

[0025] Because NMOS transistors have low on-resistance, their on-voltage drop is very small in low-current applications. When the on-current is small, the on-voltage drop between the source and drain of the NMOS transistor is generally on the order of microvolts. The on-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 value depends on the specific situation) needs to be connected in series. The sense voltage drop is used as the overdrive voltage (VOD) of the two input terminals of the comparator. Only when the sense voltage drop is greater than the offset voltage can the comparator work normally.

[0026] When the main transistor is an NMOS transistor: A current sensing resistor is inserted between the source of the NMOS transistor and the load. A voltage comparator compares the voltage difference between the source of the NMOS transistor and the load to detect the voltage drop and then determines whether the NMOS transistor is turned on or off. This prevents the external power supply from flowing back into the input power supply and protects the front-end circuit of the input power supply. Example 2

[0027] Reference Figure 1 This is the second embodiment of the present invention, based on the previous embodiment. Specifically, the voltage comparator compares the magnitude of the detected voltage drop and determines the direction of the current. The detected voltage drop is the sum of the NMOS transistor's on-state voltage drop and the current sensing resistor's voltage drop. By comparing the magnitude of the detected voltage drop with the voltage comparator, the on / off state of the NMOS transistor is determined, preventing external power supply from flowing back into the input power supply and 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's output level is VCC (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.

[0028] The voltage comparator outputs a signal to the gate of the NMOS transistor, thereby controlling the NMOS transistor's conduction and cutoff. This achieves the reverse current protection function of the low-side ideal diode, preventing external power from flowing back into the input power and protecting the input power supply's pre-amplifier circuit.

[0029] Furthermore, voltage comparators possess a priority hysteresis loop-through characteristic (also known as a Schmitt trigger). The threshold voltage of this type of comparator changes rapidly with the output voltage, improving its anti-interference capability. Hysteresis voltage comparators exhibit hysteresis, or inertia, thus providing a certain degree of anti-interference capability; however, the stronger the anti-interference capability, the lower the 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, and the circuit exhibits hysteresis. Similar to a single-threshold voltage comparator, when the input voltage changes in a single direction, the output voltage Vout jumps only once. Example 3

[0030] Reference Figure 1-3 This is the third embodiment of the present invention, which is based on the above two embodiments and according to... Figure 1The 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 NMOS transistor was selected from NXP, 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). Current sensing resistor R1 = 1Ω (resistance value depends on the specific requirements);

[0031] The specific simulation test is as follows:

[0032] Simulation test of a low-side ideal diode based on current sensing, constructed from an NMOS transistor, DC power supply forward conduction simulation test: VCC=VCC1=12V (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.

[0033]

[0034] Based on the simulation test results for different load currents in Table 1, with a load RL = 100kΩ and a mains voltage drop V1... SD =V1S=2.27μV, detection voltage drop VP=122μV, comparator output voltage VB≈VCC=12.0V (approximately the power supply voltage), NMOS transistor V1 is turned on, and the conduction current is approximately 120μA. The source-drain voltage drop V1S=2.27μV generated by transistor V1 is very small (measured with a multimeter, corresponding to the on-resistance V1R). DS(ON) =2.27μV / 120μA=18.9mΩ (compliant with datasheet parameters), which is insufficient to meet the requirement that the overdrive voltage (VOD) should be higher than the offset voltage (VIO). Therefore, a current sensing resistor needs to be connected in series, resulting in a sensing voltage drop of 122μV, which is equivalent to further amplifying the sensing voltage. Appropriately increasing the sensing voltage can serve as the overdrive voltage (VOD) for the two input terminals of the comparator. Only when the sensing voltage drop is greater than the offset voltage can the comparator function normally. A specific simulation is shown below. Figure 2 As shown in the figure, simulation tests for other different load resistance values ​​are shown in Table 1.

[0035] DC power supply reverse bias simulation test: Load RL = 100kΩ, drain V1D of main pipe V1 is changed to VCC2, switches J1 and J2 are both closed. When VCC2 = 12.001V > VCC = 12V, V1S = VP = 12.0V, comparator output voltage VB = 12.0V (probe PR4), VB - V1S = 12.0V - 12.0V ≈ 0V < V TN With the NMOS main transistor V1 off, the output current of VCC1 is approximately 10.1 μA (probe PR1). There is no reverse current flowing to VCC. The required quiescent current for U1 is 10.1 μA (PR1), which is the current required for the voltage comparator to operate. A detailed simulation is shown below. Figure 3 As shown.

[0036] DC power supply reverse bias simulation test: Load RL = 100kΩ, drain V1D of main pipe V1 is changed to VCC2, switches J1 and J2 are both closed. When VCC2 = 30.0V > VCC = 12V, V1S = VP = 12.0V, comparator output voltage VB = 12.0V (probe PR4), VB - V1S = 12.0V - 12.0V ≈ 0V < V TN When the NMOS main controller V1 is turned off, the output current of VCC1 is approximately 10.1μA (probe PR1). There is no backflow current to VCC. The quiescent current required by U1 is 10.1μA (PR1), which is the current required for the voltage comparator to operate. Simulation diagram omitted.

[0037] Similarly, referring to the above implementation method, the current sensing resistor can be inserted between the drain of the NMOS main tube and the negative power supply (GND), with the rest remaining unchanged. The schematic diagram is omitted, and the working principle is the same as described in the above implementation method, so it will not be repeated here.

[0038] 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 low-end ideal diode based on current sensing, comprising a voltage comparator, an NMOS transistor, and a resistor, characterized in that: The circuit consists of a voltage comparator, an NMOS transistor, and a resistor. The NMOS transistor is the main transistor, and a current sensing resistor is connected in series with the source or drain of the NMOS main transistor. The voltage comparator is a Schmitt trigger.

2. The low-end ideal diode based on current sensing according to claim 1, characterized in that: The voltage comparator compares the magnitude of the detected voltage drop and determines the direction of the current.

3. The low-end ideal diode based on current sensing according to claim 2, characterized in that: The detection voltage drop is the sum of the NMOS transistor's on-state voltage drop and the current sensing resistor's voltage drop.

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