A circuit for eliminating arcing produced by momentary opening of a circuit between a power source and a load

Abstract

The utility model discloses a kind of circuits for eliminating spark generated between power supply and load loop transient on-off, including loop current sampling circuit and loop current limiting circuit;The loop current sampling circuit includes loop current sampling resistance, voltage stabilizing element, reference voltage setting resistance group and differential amplifier tube group, for real-time acquisition loop current and conversion into voltage signal, after comparing with the set reference voltage threshold, output control signal;The loop current limiting circuit includes drive tube, main current-limiting tube and biasing element group, receive the control signal of the loop current sampling circuit, the loop current limiting circuit when loop current exceeds threshold value control the main current-limiting tube enters partial conduction state to limit loop current, when loop current returns normal, make the main current-limiting tube completely conductive.

Description

Technical Field

[0001] This utility model relates to the field of power supply and load connection protection technology, and in particular to a circuit for eliminating sparks generated by instantaneous switching of the circuit between the power supply and the load. Background Technology

[0002] During the connection process between a power supply (such as an AC / DC power adapter) and the adapted load, conductive connection is usually achieved through the contact of the conductive contacts between the plug and the socket. At the instant the plug is inserted into or removed from the socket, a huge instantaneous peak current (with an amplitude of tens or even hundreds of amperes) is generated due to the rapid discharge of the power supply output filter capacitor to the load terminal capacitor and the load itself; at the same time, the contact contacts may experience multiple rapid switching on and off, causing the air around the contacts to be ionized to form conductive plasma, producing a clearly visible spark.

[0003] Such sparks can cause contact carbonization and melting, increase contact resistance, affect the stability of switching operations, and even create high temperature risks. In situations where sparks are subject to strict requirements, this could lead to major safety issues.

[0004] In existing technologies, the traditional solution to eliminate sparks is to connect a large inductor in series in the current loop and use Lenz's law to limit peak current. However, in order to avoid magnetic flux saturation of the magnetic material and reduce the impact on efficiency, large cross-section magnetic materials and thick wire diameters are required for winding, resulting in a large inductor size, high cost, and increased overall size and weight, leading to low cost-effectiveness and limiting its application in miniaturized, low-cost devices. Utility Model Content

[0005] To address the shortcomings of existing series inductor solutions, such as large size, high cost, and significant impact on efficiency, this invention provides a circuit that eliminates sparks generated by instantaneous switching between the power supply and the load. This allows for limiting instantaneous peak current and eliminating sparks without the need for a large inductor, while simultaneously reducing cost, size, and impact on overall system efficiency.

[0006] To solve the above-mentioned technical problems, this utility model provides a circuit for eliminating sparks generated by instantaneous switching between the power supply and the load, including a loop current sampling circuit and a loop current limiting circuit.

[0007] The loop current sampling circuit includes a loop current sampling resistor, a voltage regulator, a reference voltage setting resistor group, and a differential amplifier transistor group. It is used to collect the loop current in real time and convert it into a voltage signal, and output a control signal after comparing it with the reference voltage threshold.

[0008] The loop current limiting circuit includes a driving transistor, a main current limiting transistor, and a bias element group. It receives the control signal from the loop current sampling circuit, controls the main current limiting transistor to enter a partially conducting state to limit the loop current when the loop current exceeds the threshold, and makes the main current limiting transistor fully conducting when the current returns to normal.

[0009] By combining the negative feedback of the loop current sampling circuit and the loop current limiting circuit, the current does not exceed the set threshold when the loop is instantaneously switched on and off, thus eliminating the peak current condition caused by sparks.

[0010] Preferably, one end of the loop current sampling resistor of the loop current sampling circuit is connected to the input positive terminal and the cathode of the voltage regulator element and the current inflow terminal of the second differential amplifier tube of the differential amplifier tube group, and the other end is connected to the output positive terminal and the current inflow terminal of the first differential amplifier tube of the differential amplifier tube group and one end of the bias resistor of the main current limiting tube of the loop current limiting circuit.

[0011] Preferably, the reference voltage setting resistor group includes an upper voltage divider resistor and a lower voltage divider resistor; the anode of the voltage regulator element is connected to one end of the voltage regulator bias resistor and one end of the upper voltage divider resistor, and the other end of the voltage regulator bias resistor is connected to the input negative terminal; the other end of the upper voltage divider resistor is connected to one end of the lower voltage divider resistor and the driving terminal of the first differential amplifier tube, the current output terminal of the first differential amplifier tube is connected to the other end of the lower voltage divider resistor and the driving terminal of the second differential amplifier tube, and the current output terminal of the second differential amplifier tube is connected to the loop current limiting circuit.

[0012] Preferably, the loop current limiting circuit includes a current limiting resistor, a differential output current sampling resistor, a positive feedback resistor, a driving transistor, a main current limiting transistor bias resistor, a main current limiting transistor drive bias voltage regulator element, and a main current limiting transistor. One end of the current limiting resistor is connected to the current output terminal of the second differential amplifier transistor, and the other end is connected to one end of the differential output current sampling resistor, one end of the positive feedback resistor, and the driving terminal of the driving transistor. The other end of the differential output current sampling resistor is connected to the negative input terminal, and the other end of the positive feedback resistor is connected to the negative output terminal.

[0013] Preferably, the biasing element group includes a main current limiting transistor bias resistor and a main current limiting transistor drive biasing regulator; one end of the main current limiting transistor bias resistor is connected to the output positive terminal, and the other end is connected to the current inflow terminal of the drive transistor, the cathode of the main current limiting transistor drive biasing regulator, and the drive terminal of the main current limiting transistor; the current outflow terminal of the drive transistor, the anode of the main current limiting transistor drive biasing regulator, and the current outflow terminal of the main current limiting transistor are all connected to the input negative terminal, and the current inflow terminal of the main current limiting transistor is connected to the output negative terminal.

[0014] Preferably, the first and second differential amplifier transistors of the differential amplifier transistor group are transistors in the same package or in separate packages, used to differentially amplify the sampled voltage and the reference voltage.

[0015] Preferably, the reference voltage threshold set by the loop current sampling circuit corresponds to 1.2-2 times the normal loop current, and the threshold value is adjusted by setting the resistance value of the reference voltage setting resistor group.

[0016] Preferably, the main current limiting transistor is a MOSFET or a transistor, which is in a fully conducting state (approximately short-circuited) during normal operation and in a partially conducting state (equivalent to a variable resistor) during current limiting to limit the current.

[0017] Compared with the prior art, the beneficial effects obtained by this utility model are:

[0018] By combining a loop current sampling circuit with a nanosecond-level response and a loop current limiting circuit with negative feedback, the peak current during instantaneous switching can be limited to a set threshold, such as 1.2-2 times the normal current, eliminating the conditions for spark generation at the source. Using surface-mount resistors, transistors, and voltage regulators, the number of components is reduced, eliminating the need for large inductors and significantly reducing space requirements. The overall cost is more than 50% lower than traditional series inductor solutions. During normal operation, the main current limiting transistor is fully conducting, meaning the saturation resistance is low, and the loop current sampling resistor has a small value, so its impact on power output efficiency is negligible. It can be built into the power supply or load, suitable for various switching connection methods such as plugs and sockets, switches, and relays, and compatible with different voltages, such as 12V, 24V, and current ratings in power supply and load systems. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0020] Figure 1 This is a schematic diagram of the circuit principle for eliminating sparks caused by instantaneous switching between the power supply and the load, according to this utility model.

[0021] Figure 2 This is a schematic diagram of the circuit principle of Embodiment 1 of this utility model.

[0022] Figure 3 This is a schematic diagram of the circuit principle of Embodiment 2 of this utility model.

[0023] Figure 4 This is a schematic diagram of the circuit principle of Embodiment 3 of this utility model.

[0024] Figure 5 This is a schematic diagram of the circuit principle of Embodiment 4 of this utility model.

[0025] Figure 6 This is a schematic diagram of the circuit principle of Embodiment 5 of this utility model.

[0026] Figure reference numerals: 1-Loop current sampling circuit; 2-Loop current limiting circuit; R1-Loop current sampling resistor; Z1-Voltage regulator; R2-Upper voltage divider resistor for reference voltage setting; R3-Lower voltage divider resistor for reference voltage setting; R4-Voltage regulator bias resistor; Q1-First differential amplifier transistor; Q2-Second differential amplifier transistor; R5-Current limiting resistor; R6-Differential output current sampling resistor; R7-Positive feedback resistor; R8-Main current limiting transistor bias resistor; Z2-Main current limiting transistor drive bias voltage regulator; Q3-Driver transistor; Q4-Main current limiting transistor; VIN+-Input positive; VIN--Input negative; VOUT+-Output positive; VOUT-Output negative. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] A circuit for eliminating sparks caused by momentary switching between power supply and load includes a loop current sampling circuit 1 and a loop current limiting circuit 2, such as... Figure 1 As shown.

[0029] Loop current sampling circuit 1 includes a loop current sampling resistor R1, a voltage regulator Z1 (such as a Zener diode), a voltage regulation bias resistor R4, a reference voltage setting upper voltage divider resistor R2, a reference voltage setting lower voltage divider resistor R3, a first differential amplifier transistor Q1, and a second differential amplifier transistor Q2. The first differential amplifier transistor Q1 and the second differential amplifier transistor Q2 are PNP transistors.

[0030] One end of the loop current sampling resistor R1 is connected to the input positive terminal VIN+, the cathode of Z1, and the emitter of the second differential amplifier Q2, i.e., the current inflow terminal. The other end of the loop current sampling resistor R1 is connected to the output positive terminal VOUT+, the emitter of the first differential amplifier Q1, and one end of the main current limiting transistor bias resistor R8. The anode of the voltage regulating element Z1 is connected to one end of the voltage regulating bias resistor R4 and one end of the reference voltage setting upper voltage divider resistor R2. The other end of the voltage regulating bias resistor R4 is connected to the input negative terminal VIN-. The other end of the reference voltage setting upper voltage divider resistor R2 is connected to one end of the reference voltage setting lower voltage divider resistor R3 and the base (driving terminal) of the first differential amplifier Q1. The collector (current outflow terminal) of the first differential amplifier Q1 is connected to the other end of the reference voltage setting lower voltage divider resistor R3 and the base of the second differential amplifier Q2. The collector of the second differential amplifier Q2 is connected to the loop current limiting circuit 2.

[0031] Loop current limiting circuit 2 includes current limiting resistor R5, differential output current sampling resistor R6, positive feedback resistor R7, drive transistor Q3 (NPN transistor), main current limiting transistor bias resistor R8, main current limiting transistor drive bias voltage regulator Z2 (such as Zener diode), and main current limiting transistor Q4 (N-channel MOSFET).

[0032] One end of the current-limiting resistor R5 is connected to the collector of the second differential amplifier transistor Q2, and the other end is connected to one end of the differential output current sampling resistor R6, one end of the positive feedback resistor R7, and the base (driving terminal) of the driving transistor Q3; the other end of the differential output current sampling resistor R6 is connected to the input negative terminal VIN-, and the other end of the positive feedback resistor R7 is connected to the output negative terminal VOUT-; one end of the main current-limiting transistor bias resistor R8 is connected to the output positive terminal VOUT+, and the other end is connected to the collector of the driving transistor Q3, the cathode of the main current-limiting transistor drive bias regulator Z2, and the gate (driving terminal) of the main current-limiting transistor Q4; the emitter of the driving transistor Q3, the anode of the main current-limiting transistor drive bias regulator Z2, and the source (current outflow terminal) of the main current-limiting transistor Q4 are all connected to the input negative terminal VIN-, and the drain (current inflow terminal) of the main current-limiting transistor Q4 is connected to the output negative terminal VOUT-.

[0033] Normal operating condition: When the power supply and load are stably connected and the loop current is within the normal range (e.g., 1A), the sampled voltage across R1 is lower than the reference voltage threshold (corresponding to a current of 1.7A). The output current of the differential amplifier circuit composed of Q1 and Q2 is close to zero, there is no voltage across R6, and Q3 is cut off. The gate-source voltage of Q4 is regulated by R8 and Z2 (e.g., 10V), Q4 is fully conducting (the resistance between D and S is extremely low), the circuit is approximately short-circuited, and it does not affect the normal output of the power supply.

[0034] Instantaneous on / off current limiting state: When the plug is inserted into the socket, the rapid charging of the load capacitor causes the loop current to rise sharply to exceed the 1.7A threshold. The sampled voltage on R1 exceeds the reference voltage, increasing the output current after differential amplification by Q1 and Q2. The voltage across R6 rises, turning on Q3. After Q3 turns on, it shunts the current from R8, causing the gate-source voltage of Q4 to drop, and Q4 enters a partial conduction state, limiting the loop current. Through negative feedback regulation, the loop current is stabilized at around 1.7A, preventing sparking.

[0035] Return to normal operation: As the load capacitor completes charging, the voltage gradually stabilizes, and the loop current drops to the normal range (<1.7A). The sampling voltage of R1 is lower than the threshold, the differential amplifier output current returns to zero, Q3 is cut off, the gate-source voltage of Q4 returns to the Z2 regulated value, Q4 is fully turned on, and the circuit returns to normal operating mode.

[0036] This circuit can be built into an AC / DC power adapter or load, and is suitable for scenarios such as electric water flossers and smart home devices that require frequent power plugging and unplugging. It effectively eliminates sparks during switching on and off, and improves device safety and lifespan.

[0037] Example 1: 24V / 1A AC / DC power adapter built-in solution (N-channel MOSFET main current limiting transistor + same package PNP differential transistor + with positive feedback resistor)

[0038] 1.1 Application Scenarios

[0039] Suitable for small household appliances such as electric water flossers and dental irrigators that require frequent plugging and unplugging. The power supply is an AC / DC adapter with a constant voltage of 24V and a rated output current of 1A. A 47μF / 35V filter electrolytic capacitor is connected in parallel at the load end. It is necessary to eliminate the sparks that occur when plugging and unplugging the plug and socket.

[0040] 1.2 Core Circuit Parameters

[0041] Rated operating voltage: 24VDC

[0042] Rated operating current: 1A

[0043] Reference current threshold: 1.67 times the normal current (1.67A), corresponding to a reference voltage threshold of 0.055V, determined by the voltage divider formed by Z1 (6.8V Zener diode), Q2_Veb (0.7V), R2 (100kΩ), and R3 (0.91kΩ).

[0044] Key component selection:

[0045] Loop current sampling resistor R1: 0.033Ω / 0.125W 0805 surface mount resistor (low resistance value ensures low loss during normal operation)

[0046] Differential amplifier transistor group Q1, Q2: Same package PNP transistor (model MMBT3906DT, dual transistors in the same package to offset temperature drift and reduce the impact of manufacturing tolerances)

[0047] Main current limiting transistor Q4: N-channel MOSFET (model PW2310, saturation on-resistance Rds_ON=70mΩ, low conduction loss, Vds=60V, Id=3A, SOT-23 ultra-small surface mount package)

[0048] The main current limiting diode drives the bias regulator Z2: a 12V Zener diode (to ensure that the gate-source voltage of Q4 is stable and does not exceed its maximum withstand voltage stress, thus achieving full conduction).

[0049] Differential output current sampling resistor R6: 10kΩ

[0050] Positive feedback resistor R7: 560kΩ (helps reduce power stress when Q4 is current-limited; it can be omitted if there is no risk of over-stress in Q4 power, and is an optional component)

[0051] Current-limiting resistor R5: 0.22kΩ (used to limit the maximum output current of Q2 and prevent Q2 output current from being overstressed. It can be omitted if there is no risk of Q2 output current being overstressed, and is an optional component).

[0052] 1.3 Installation Location

[0053] The circuit is built into the AC / DC power adapter between the output terminal and the output plug. The input terminal (VIN+ / -) is connected to the 24V output terminal of the adapter, and the output terminal (VOUT+ / -) is connected to the output plug via a cable.

[0054] 1.4 Detailed Work Process

[0055] (1) Standby state (plug not inserted into load)

[0056] With the loop current close to zero, the sampled voltage across R1 (U_R1=I_R1×R1) ≈ 0V, far below the reference voltage threshold (Vref_th=(Vz1-Veb_Q2)*R3 / (R3+R2)=(6.8V-0.7V)*0.91k / (0.91k+100k)=0.055V). At this time, the collector output current of Q2 is close to zero, there is no voltage across R6 (10kΩ), and Q3 is cut off; the gate and source of Q4 are regulated by R8 (100kΩ) and Z2 (12V), the gate and source voltage is 12V, Q4 is fully turned on (the resistance between D and S is 70mΩ), and the output plug voltage is equal to the adapter output voltage of 24V.

[0057] (2) Instantaneous on / off current limiting state (moment of plug insertion)

[0058] The 47μF capacitor at the load end charges rapidly, causing the loop current to rise sharply to over 1.67A. The sampling voltage of R1 exceeds the reference voltage threshold (0.055V). After differential amplification by Q1 and Q2, the collector output current of Q2 increases, flowing through R5 (0.22kΩ) and generating a voltage across R6 (U_R6=Ic_Q2×R6). When U_R6>=Q3_Vbe_th (0.7V), Q3 turns on. After Q3 turns on, it shunts the current of R8, and the gate-source voltage of Q4 drops rapidly from 12V to near its turn-on threshold voltage Vgs_th_Q4. Q4 enters a partially conducting state (equivalent to a resistor), and the loop current is limited to around 1.67A. The positive feedback resistor R7 further adjusts the base current of Q3 through "VOUT voltage change," avoiding frequent switching of Q4. At the same time, it can limit the loop current to a value lower than 1.67A, reducing the power loss of Q4.

[0059] (3) Return to normal state

[0060] Once the load capacitor is fully charged (voltage rises from 0V to 24V), the loop current drops from 1.67A to the normal load current (e.g., 1.0A, the operating current of the water flosser). The sampling voltage of R1 is less than the reference threshold, the output current of Q2 returns to zero, the voltage of R6 disappears, and Q3 is cut off. The gate-source voltage of Q4 is restored to 12V through charging via R8, Q4 is fully turned on, the circuit returns to normal mode, and the adapter provides stable power to the water flosser without any additional efficiency loss (the total loss during normal operation = I²×(R1+Rds_ON) = (1.0A)²×(0.033Ω+0.07Ω) = 1×0.103 = 0.103W, which is about 0.5% of its 24W rated output power and can be basically ignored).

[0061] Example 2: 12V / 2A Smart Lighting Fixture Load Built-in Solution (N-channel MOSFET main current limiting transistor + NPN independently packaged differential transistor + with positive feedback resistor)

[0062] 2.1 Application Scenarios

[0063] Suitable for smart home devices such as smart ceiling lights and ambient lights, the power supply is a 12V / 2A desktop adapter, the load is a 12V LED lamp (rated current 1.5A), a 100μF / 25V filter capacitor is connected in parallel at the lamp input terminal, and the circuit is built into the back of the lamp input socket to eliminate the sparks when plugging and unplugging the adapter.

[0064] 2.2 Core Circuit Parameters

[0065] Rated operating voltage: 12VDC

[0066] Rated operating current: 1.5A (lamp operating current)

[0067] Reference current threshold: 1.6 times the normal current (2.4A)

[0068] Key component selection:

[0069] Loop current sampling resistor R1: 0.022Ω / 0.25W 1206 surface mount resistor (compatible with 2.4A threshold, sampling voltage U=2.4A×0.022Ω=0.0528V)

[0070] Differential amplifier transistor groups Q1 and Q2: Independently packaged NPN transistors (model MMBT3904, low cost, suitable for low voltage applications, temperature drift is reduced through PCB layout optimization).

[0071] Main current limiting transistor Q4: N-channel MOSFET (model YJL2304B, Rds_ON=28mΩ, Vds=30V, Id=4A, SOT-23 ultra-small surface mount package, compatible with 12V low voltage)

[0072] Main current limiting transistor drives bias regulator Z2: Not used (because the maximum VIN+ voltage is only 12V, while the gate-source voltage of the selected Q4 is at most + / -20V).

[0073] R5, R6, Q3: Not used (the output of differential transistor Q2 directly controls the drive voltage of the main current limiting transistor Q4, without the need for logic level conversion)

[0074] Positive feedback resistor R7: 300kΩ (helps reduce power stress during Q4 current limiting)

[0075] 2.3 Installation Location

[0076] The circuit is built between the smart lighting input socket and the lighting main board. The input terminal (VIN+ / -) is connected to the socket, and the output terminal (VOUT+ / -) is connected to the LED driver circuit of the lighting fixture.

[0077] 2.4 Work Process

[0078] (1) Standby mode (adapter not plugged in)

[0079] The circuit is not powered and will not be analyzed.

[0080] (2) Instantaneous on / off current limiting state (the moment the adapter is inserted)

[0081] During rapid charging of the 100μF capacitor, the circuit current surged to over 2.4A. The sampling voltage of R1 exceeded the reference threshold (0.0528V), causing Q2 to conduct. The gate-source voltage of Q4 dropped to near its conduction threshold voltage Vgs_th_Q4, and Q4 entered a partially conducting state, with the current stabilizing at around 2.4A. Due to the large capacitance of the lamp (100μF), the current-limiting state lasted for approximately 0.5ms (capacitor charging time t = Cout*ΔV / I = 100*1e^-6*12 / 2.4 = 0.5ms), during which no sparks were generated.

[0082] (3) Return to normal state

[0083] When the capacitor is charged to 12V, the circuit current drops to 1.5A (LED operating current). The sampling voltage of R1 is less than the threshold, Q2 is cut off, and the gate-source voltage of Q4 recovers to about 12V, making it fully conductive. The LED driver circuit of the lamp works normally. The total circuit loss = I²×(R1+Rds_ON) = (1.5A)²×(0.022+0.028) = 2.25×0.05 = 0.113W, which hardly affects the brightness of the lamp.

[0084] Example 3: 48V / 0.5A Industrial Sensor Power Supply Built-in Solution (PNP Transistor Main Current Limiting Diode + NPN Same Package Differential Diode + Positive Feedback Resistor)

[0085] 3.1 Application Scenarios

[0086] Suitable for temperature and humidity sensors and pressure sensors in industrial automation scenarios. The power supply is a 48V / 0.5A rail-mounted power supply. The sensor's rated current is 0.3A. A 22μF / 63V high-frequency filter capacitor is connected in parallel at the input terminal. The circuit is built into the power supply output terminal to eliminate sparks when plugging and unplugging the sensor cable (industrial scenarios are sensitive to sparks and require higher reliability).

[0087] 3.2 Core Circuit Parameters

[0088] Rated operating voltage: 48VDC

[0089] Rated operating current: 0.3A (sensor current)

[0090] Reference current threshold: twice the normal current (0.6A)

[0091] Key component selection:

[0092] Loop current sampling resistor R1: 0.1Ω / 0.10W 0603 surface mount resistor (sampling voltage U=0.6A×0.1Ω=0.06V at 0.6A, facilitating differential detection)

[0093] Differential amplifier transistor group Q1, Q2: Same package NPN transistor (model BC546BDW, dual transistor co-package, strong anti-interference capability, suitable for industrial environment)

[0094] Main current limiting transistor Q4: PNP power transistor (model 2SB1260, MOSFET replacement, suitable for high voltage and low current applications, saturation voltage drop Vec(sat) <= 0.2V)

[0095] Main current limiting transistor drive bias regulator Z2: Not used (because Q4 uses a current-driven power transistor).

[0096] The bias resistor R8 of the main current-limiting transistor is 15kΩ, providing sufficient base current for Q4 to saturate.

[0097] Positive feedback resistor R7: 1.2MΩ (helps reduce power stress when Q4 is current-limited)

[0098] 3.3 Installation Location

[0099] The circuit is built into a 48V DIN rail power output module. The input terminal (VIN+ / -) is connected to the main power circuit, and the output terminal (VOUT+ / -) is connected to the sensor cable interface.

[0100] 3.4 Work Process

[0101] (1) Standby state (sensor not connected)

[0102] With zero loop current, R1 sampling voltage = 0V, Q2 output current is zero, R6 (10KΩ) has no voltage, and Q3 is cut off; the base of Q4 is biased by R8 (15kΩ), and the base current Ib = (48V - 0.7V) / 15kΩ = 3.15mA. Q4 is saturated and conducting (Vec <= 0.2V), and the output interface voltage = 48V - 0.2V ≈ 47.8V.

[0103] (2) Instantaneous on / off current limiting state (sensor cable inserted)

[0104] When the 22μF capacitor at the sensor end is charged, the loop current surges to over 0.6A. The sampling voltage of R1 is 0.06V, exceeding the reference threshold (obtained by voltage division of Z1 (12V Zener diode), Q2_Vbe (0.7V), R2 (200kΩ), and R3 (1.06kΩ), with a reference voltage difference of ≈0.06V). Q2 turns on, and the output current flows through R5 (0.47kΩ) and generates a voltage U=I×10kΩ across R6. When U>0.7V, Q3 turns on. After Q3 turns on, the base current of Q4 is shunt, and Ib drops below 1mA. Q4 switches from saturation conduction to amplification state, and the loop current is limited to 0.6A and stabilized through negative feedback.

[0105] (3) Return to normal state

[0106] When the capacitor is charged to 47.8V, the circuit current drops to 0.3A. The sampling voltage of R1 is 0.03V, which is less than the threshold. Q2 and Q3 are cut off. The base current of Q4 recovers to 3.15mA and is saturated and turned on again, allowing the sensor to collect data normally. When the circuit is working normally, the power loss is I×Vec(sat)_Q4+I²×R1=0.3A×0.2V+(0.3A)²×0.1Ω=0.06+0.009=0.069W, which meets the low power loss requirements of industrial power supplies.

[0107] Example 4: 5V / 3A Portable Power Bank with Built-in Input Solution (N-channel MOSFET main current limiting transistor + same package NPN differential transistor + no positive feedback resistor)

[0108] 4.1 Application Scenarios

[0109] Suitable for portable power banks (capacity 10000mAh), charged by a 5V / 3A charger. A 470μF / 10V solid capacitor (good high-frequency characteristics) is connected in parallel at the input end of the power bank. The circuit is built into the rear of the power bank's input interface to eliminate sparks when plugging and unplugging the charger (portable devices have extremely high requirements for size and weight).

[0110] 4.2 Core Circuit Parameters

[0111] Rated operating voltage: 5VDC

[0112] Rated operating current: 2A (power bank charging current)

[0113] Reference current threshold: 1.5 times the normal current (3A)

[0114] Key component selection:

[0115] Loop current sampling resistor R1: 0.01Ω / 0.125W 0805 surface mount resistor (sampling voltage U=3×0.01=0.03V at 3A, low loss)

[0116] Differential amplifier transistor groups Q1 and Q2: NPN differential transistors in the same package (model MMBT3904DW, small SOT-23-6 surface mount package).

[0117] Main current limiting transistor Q4: N-channel MOSFET (model YJS12N03A, Rds_ON=7mΩ, suitable for 5V low voltage drive, SOP-8 surface mount package)

[0118] Main current limiting transistor drives bias regulator Z2: Not used (because the maximum VIN+ voltage is only 5V, while the gate-source voltage of the selected Q4 is at most + / -20V, so Z2 is not needed for voltage limiting).

[0119] R5, R6, Q3: Not used (the output of differential transistor Q2 directly controls the drive voltage of the main current limiting transistor Q4, without the need for logic level conversion)

[0120] No positive feedback resistor R7 (considering the limited space in portable devices, the Q4 package is large enough and its PCB copper plating can dissipate heat).

[0121] 4.3 Installation Location

[0122] The circuit is built into the power bank PCB board between the input interface (Type C) and the charging management chip. The input terminal (VIN+ / -) is connected to the Type C interface, and the output terminal (VOUT+ / -) is connected to the charging management chip (such as TP4056).

[0123] 4.4 Work Process

[0124] (1) Standby mode (charger not plugged in)

[0125] With zero loop current, R1 sampling voltage = 0V, Q2 is off, Q4 gate is biased by R8 (22kΩ) to make Vgs_Q4 = 5V, Q4 is fully turned on (DS resistance 7mΩ), and the voltage at the input terminal of the charging management chip = Type C interface no-load voltage ≈ 5V.

[0126] (2) Instantaneous on / off current limiting state (the moment the charger is plugged in)

[0127] During fast charging of the 470μF solid capacitor, the circuit current surged to over 3A. The sampling voltage of R1 was 0.03V, exceeding the reference threshold (obtained by voltage division from Z1 (5.1V Zener diode), Q2_Vbe (0.7V), R2 (100kΩ), and R3 (0.68kΩ), with a reference voltage difference of ≈0.03V). After Q2 turned on, it pulled the gate-source voltage of Q4 to near its turn-on threshold voltage Vgs_th_Q4, and Q4 entered a partially conducting state. At this time, the gate-source voltage of Q4 was shunted and regulated by Q2 through R8, and the current was stabilized at 3A through negative feedback.

[0128] (3) Return to normal state

[0129] When the capacitor is charged to 5V, the circuit current drops to 2A (power bank charging current). The sampling voltage of R1 is 0.02V, which is less than the threshold. Q2 is cut off, and the gate-source voltage of Q4 returns to 5V, so Q4 is fully turned on. The charging management chip enters constant current charging mode. When the circuit is working normally, the power loss is I²×(R1+Rds_ON)=(2A)²×(0.01+0.007)=4×0.017=0.068W, which hardly affects the charging efficiency of the power bank. Moreover, the total PCB area occupied by the surface-mount components is less than 10mm×8mm, which meets the portability requirements.

[0130] Example 5: 36V / 1A Power Tool Power Supply Integrated Solution (P-type AC MOSFET main current limiting transistor + dual reference threshold transistors + same package PNP differential transistor + with positive feedback resistor)

[0131] 5.1 Application Scenarios

[0132] Suitable for power tools such as electric screwdrivers and drills. The power supply is a 36V / 1A lithium battery charger. The tool's rated current is 0.8A. A 10μF / 50V ceramic capacitor (vibration resistant, suitable for tool usage scenarios) is connected in parallel at the input terminal. The circuit is built into the charger output terminal to eliminate sparks when plugging and unplugging the tool (the current fluctuates greatly when the power tool starts, requiring dual threshold adaptation).

[0133] 5.2 Core Circuit Parameters

[0134] Rated operating voltage: 36VDC

[0135] Rated operating current: 0.8A (tool rated current)

[0136] Dual reference current thresholds: light load threshold 1.2A (1.5 times normal current, adapter tool standby plug-and-play), heavy load threshold 1.6A (2 times normal current, adapter tool under load plug-and-play).

[0137] Key component selection:

[0138] Loop current sampling resistor R1: 0.033Ω / 0.125W 0805 surface mount resistor

[0139] Differential amplifier transistors Q1 and Q2: Same package PNP transistor (model BC807DS, high current gain β=250, SOT-23-6 ultra-small package)

[0140] Reference voltage switching module: Single-pole double-throw switch S1 (surface mount micro switch), with selected lower voltage divider resistors R3a=0.91kΩ and R3b=0.68kΩ respectively.

[0141] Main current limiting transistor Q4: P-channel MOSFET (model YJL072P06AL, Rds_ON=55mΩ, suitable for 36V high voltage, SOT-23-3L ultra-small package)

[0142] R5, R6, Q3: Not used (the output of differential transistor Q2 directly controls the drive voltage of the main current limiting transistor Q4, without the need for logic level conversion)

[0143] Positive feedback resistor R7: 100kΩ (helps reduce power stress when Q4 is current-limited)

[0144] Main current limiting transistor drive bias regulator Z2: 12V Zener diode

[0145] 5.3 Installation Location

[0146] The circuit is built into the output interface of the 36V lithium battery charger. S1 is located on the side of the charger casing. Users can switch the threshold according to whether the tool is under load when plugging and unplugging.

[0147] 5.4 Work Process

[0148] (1) Threshold switching logic

[0149] Light load mode (S1 connected to R3b=0.68kΩ): The reference voltage is divided by Z1 (6.8V), Q2_Veb (0.7V), R2 (100kΩ), and R3b (0.68kΩ), corresponding to a reference current of 1.2A (U=1.2A×0.033Ω=0.0396V).

[0150] Heavy load mode (S1 connected to R3a=0.91kΩ): The reference voltage is divided by Z1 (6.8V), Q2_Veb (0.7V), R2 (100kΩ), and R3a (0.91kΩ), corresponding to a reference current of 1.6A (U=1.6A×0.033Ω=0.0528V).

[0151] (2) Light load insertion and removal (tool is unloaded, S1 is connected to R3b)

[0152] The moment the plug is inserted, the 10μF capacitor charges, and the current surges to nearly 1.2A. The sampling voltage of R1 triggers Q1 and Q2 to operate, and Q4 enters a partially conducting state, limiting the current to 1.2A. After the capacitor is fully charged, the current drops to 0.1A (tool standby current), and the circuit returns to normal.

[0153] (3) Heavy load plugging and unplugging (tool with load, S1 connected to R3a)

[0154] When the tool gets stuck and is plugged and unplugged under load, the current surges to nearly 1.6A. R1's sampling voltage triggers current limiting, and Q4 limits the current to 1.6A to prevent excessive current and sparking when the tool is stalled. After the tool returns to normal, the current drops to 0.8A, and the circuit returns to normal. At the same time, Z2's voltage regulation ensures the stability of Q4's source and gate voltage, preventing damage from overvoltage stress.

[0155] The above examples are merely specific embodiments of this utility model. Obviously, this utility model is not limited to the above embodiments, and many similar modifications are possible. All variations that can be directly derived or conceived by those skilled in the art from the content disclosed in this utility model should be considered within the scope of protection of this utility model.

Claims

1. A circuit for eliminating sparks generated by momentary switching between the power supply and the load, characterized in that, It includes a loop current sampling circuit and a loop current limiting circuit. The loop current sampling circuit includes a loop current sampling resistor, a voltage regulator, a reference voltage setting resistor group, and a differential amplifier transistor group. It is used to collect the loop current in real time and convert it into a voltage signal. After comparing it with the set reference voltage threshold, it outputs a control signal. The loop current limiting circuit includes a driver transistor, a main current limiting transistor, and a biasing element group. It receives the control signal from the loop current sampling circuit. When the loop current exceeds the threshold, the loop current limiting circuit controls the main current limiting transistor to enter a partially conducting state to limit the loop current. When the loop current returns to normal, it makes the main current limiting transistor fully conducting.

2. The circuit according to claim 1, characterized in that, One end of the loop current sampling resistor in the loop current sampling circuit is connected to the input positive terminal and the cathode of the voltage regulator element and the current inflow terminal of the second differential amplifier tube of the differential amplifier tube group. The other end of the loop current sampling resistor is connected to the output positive terminal and the current inflow terminal of the first differential amplifier tube of the differential amplifier tube group and one end of the bias resistor of the main current limiting tube of the loop current limiting circuit.

3. The circuit according to claim 2, characterized in that, The reference voltage setting resistor group includes an upper voltage divider resistor and a lower voltage divider resistor; the anode of the voltage regulator element is connected to one end of the voltage regulator bias resistor and one end of the upper voltage divider resistor, and the other end of the voltage regulator bias resistor is connected to the input negative terminal; the other end of the upper voltage divider resistor is connected to one end of the lower voltage divider resistor and the driving terminal of the first differential amplifier tube, the current output terminal of the first differential amplifier tube is connected to the other end of the lower voltage divider resistor and the driving terminal of the second differential amplifier tube, and the current output terminal of the second differential amplifier tube is connected to the loop current limiting circuit.

4. The circuit according to claim 3, characterized in that, The loop current limiting circuit includes a current limiting resistor, a differential output current sampling resistor, a positive feedback resistor, a driving transistor, a main current limiting transistor bias resistor, a main current limiting transistor drive bias voltage regulator element, and a main current limiting transistor. One end of the current limiting resistor is connected to the current output terminal of the second differential amplifier transistor, and the other end of the current limiting resistor is connected to one end of the differential output current sampling resistor, one end of the positive feedback resistor, and the driving terminal of the driving transistor. The other end of the differential output current sampling resistor is connected to the negative input terminal, and the other end of the positive feedback resistor is connected to the negative output terminal.

5. The circuit according to claim 4, characterized in that, The biasing element group includes the main current limiting transistor bias resistor and the main current limiting transistor drive bias regulating element; one end of the main current limiting transistor bias resistor is connected to the output positive terminal, and the other end of the main current limiting transistor bias resistor is connected to the current inflow terminal of the drive transistor, the cathode of the main current limiting transistor drive bias regulating element, and the drive terminal of the main current limiting transistor; the current outflow terminal of the drive transistor, the anode of the main current limiting transistor drive bias regulating element, and the current outflow terminal of the main current limiting transistor are all connected to the input negative terminal, and the current inflow terminal of the main current limiting transistor is connected to the output negative terminal.

6. The circuit according to claim 1, characterized in that, The first and second differential amplifier transistors in the differential amplifier transistor group are transistors in the same package or in separate packages, used to differentially amplify the sampled voltage and the reference voltage.

7. The circuit according to claim 1, characterized in that, The reference voltage threshold set by the loop current sampling circuit corresponds to 1.5-2 times the normal loop current, and the threshold value is adjusted by setting the resistance value of the reference voltage set resistor group.

8. The circuit according to claim 1, characterized in that, The main current limiting transistor is a MOSFET or a transistor. It is fully on during normal operation and partially on during current limiting to restrict the current.

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