Low-cost high-side over-current protection circuit and over-current protection method thereof

Abstract

The scheme discloses a low-cost high-side over-current protection circuit and an over-current protection method thereof, and the circuit comprises a sampling resistor which is connected in series with a positive wire of a bus; the light-emitting diode is connected in parallel with the sampling resistor; a photosensitive device coupled to the light emitting diode; the signal processing circuit is connected to the photosensitive device and is used for outputting a latch signal representing overcurrent based on the overcurrent signal; the PWM driving hardware circuit is connected to the photosensitive device; and the control circuit is connected to the signal processing circuit and the PWM driving hardware circuit and is used for controlling the PWM output to be turned off based on the latch signal. According to the scheme, a high-speed and reliable response effect is achieved, firstly, PWM is rapidly turned off on the hardware level based on an overcurrent signal, and high-speed hardware response is achieved; and secondly, the overcurrent signal is latched for a period of time through the latch logic, so that on one hand, the PWM turn-off time is prolonged, the current is prevented from instantly recovering work after rapid drop, and on the other hand, enough time is provided for the control circuit for logic processing, and the response reliability is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic product protection circuits, and in particular relates to a low-cost high-side overcurrent protection circuit and an overcurrent protection method thereof. Background Art

[0002] Servo drives and various electronic products can experience overcurrent and potentially halt operation during operation due to various issues, such as improper user application, component failure, environmental pollution, and other unexpected events. To prevent this, current electronic circuits are often designed with an overcurrent protection circuit that triggers protection actions by detecting an overcurrent signal source.

[0003] There are three types of overcurrent signal source acquisition points: phase current, busbar negative current, and busbar positive current. Using the busbar positive current as the overcurrent signal source requires the protection circuit's power supply to overcome high common-mode voltages, making it difficult to implement a low-cost detection circuit. Therefore, considering cost considerations, the phase current and busbar negative current are currently the most commonly used overcurrent signal sources.

[0004] However, when the phase current and the current on the negative pole of the busbar are used as the overcurrent signal source, the protection cannot fully cover the monitoring of various short circuit situations such as phase-to-phase, relative to PE (protective grounding wire), P (busbar positive pole) to phase, N (busbar negative pole) to phase, P to B (external braking resistor), etc. Figure 1 As shown in the figure, when the bus negative pole N is used as the overcurrent signal source, a sampling resistor (Rbus-) is designed on the bus negative pole. In this case, if a short circuit occurs between the phase line and the external braking resistor J4-J7, J5-J7, or J6-J7, the short circuit line shorts Rbus-, preventing the detection circuit from providing a current signal. Therefore, a short circuit between the phase line and PE cannot be detected. When the phase current is used as the overcurrent signal source, resistors R_U, R_V, and R_W are designed on the phase line. When a short circuit occurs between J1 and J3, the short-circuit current path is P (J1) - the positive pole of the braking circuit - the negative pole of the braking circuit - B (J3). The current does not flow through the R_U, R_V, and R_W paths, so a short circuit between PB cannot be protected. Summary of the Invention

[0005] The object of the present invention is to provide a low-cost high-side overcurrent protection circuit and an overcurrent protection method thereof in response to the above-mentioned problems.

[0006] A low-cost high-side overcurrent protection circuit, comprising: The sampling resistor is connected in series with the positive line of the busbar; A light emitting diode is connected in parallel to the sampling resistor and is turned on when the current flowing through the sampling resistor causes the voltage drop of the sampling resistor to be greater than the conduction voltage drop of the light emitting diode; A photosensor, coupled to the light emitting diode, for outputting an overcurrent signal; a signal processing circuit connected to the photosensor and configured to output a latch signal indicating overcurrent based on the overcurrent signal; A PWM drive hardware circuit, connected to the photosensitive device, for shutting down the PWM output based on the overcurrent signal; The control circuit is connected to the signal processing circuit and the PWM drive hardware circuit, and is used to control the PWM output to be turned off based on the latch signal.

[0007] In the above circuit, when a short circuit occurs, the hardware is first temporarily and quickly shut down, and then the software is continuously shut down.

[0008] In the above-mentioned low-cost high-side overcurrent protection circuit, the conduction voltage drop of the light-emitting diode is used as the current threshold judgment criterion. When the voltage drop of the sampling resistor exceeds the conduction voltage drop, the light-emitting diode is triggered to turn on and generate an overcurrent signal; The photosensitive device is used to convert the overcurrent signal in the form of an optical signal into the overcurrent signal in the form of an electrical signal.

[0009] In the above-mentioned low-cost high-side overcurrent protection circuit, the resistance Rx of the sampling resistor is based on the current threshold I 阈值 and the forward voltage drop of the light-emitting diode V F Set, meet ; In the above-mentioned low-cost high-side overcurrent protection circuit, the photosensor is a phototransistor, which forms an optical coupler with the light-emitting diode.

[0010] In the above-mentioned low-cost high-side overcurrent protection circuit, the signal processing circuit includes a latch circuit; The collector of the phototransistor is connected to a DC power supply through a current-limiting resistor, and the emitter is connected to the ground terminal, so as to output a low-level overcurrent signal when the circuit is short-circuited; The collector of the phototransistor is connected to the input end of the latch circuit; The collector of the phototransistor is also connected to the PWM drive hardware circuit so that the PWM drive hardware quickly shuts off the PWM output based on the overcurrent signal. The shutdown action does not involve the control circuit, and the shutdown will fail after the level is restored.

[0011] The output end of the latch circuit is connected to the control circuit to provide a latch signal to the control circuit; The control circuit outputs a shutdown instruction to the PWM drive hardware circuit according to the latch signal to shut down the PWM output at the application level. At this time, the control circuit is shut down for a long time or permanently, and additional measures or manual recovery are required.

[0012] In the above-mentioned low-cost high-side overcurrent protection circuit, the PWM drive hardware circuit includes a buffer circuit and a PWM drive circuit connected in sequence, the buffer circuit is high-level enabled, and the enable terminal of the buffer circuit is connected to the collector terminal of the phototransistor, the signal input terminal is connected to the control circuit, and the PWM drive circuit is connected to the power device; When the circuit is normal, the collector terminal of the phototransistor is at a high level, there is no overcurrent signal, and the buffer circuit is enabled; When short-circuited, the collector terminal of the phototransistor outputs a low-level overcurrent signal and the buffer circuit is disabled.

[0013] In the above-mentioned low-cost high-side overcurrent protection circuit, the signal processing circuit also includes a shaping circuit, the input end of the shaping circuit is connected to the collector of the phototransistor and the DC power supply, and the phototransistor is connected to the PWM drive hardware circuit and the latch circuit via the shaping circuit.

[0014] In the above-mentioned low-cost high-side overcurrent protection circuit, the shaping circuit is an inverter; The PWM drive hardware circuit includes a buffer circuit and a PWM drive circuit connected in sequence, the buffer circuit is low-level enabled, and the enable terminal of the buffer circuit is connected to the output terminal of the inverter, the signal input terminal is connected to the control circuit, and the PWM drive circuit is connected to the power device; When the circuit is normal, the phototransistor has no overcurrent signal output, the inverter output is low, and the buffer circuit is enabled; When short-circuited, the phototransistor outputs a low-level overcurrent signal, the inverter outputs a high-level signal, and the buffer circuit is disabled.

[0015] In the above low-cost high-side overcurrent protection circuit, the resistance of the current limiting resistor satisfies , where R3 is the resistance of the current limiting resistor, VCC is the DC power supply voltage, and IC is the saturation on-current of the photosensitive device.

[0016] An overcurrent protection method based on the low-cost high-side overcurrent protection circuit, the method comprising: When the circuit is normal, the voltage drop of the sampling resistor is less than the conduction voltage drop of the light-emitting diode, the phototransistor is disconnected, the collector remains in a high level state, there is no overcurrent signal, and no latch signal; When the circuit is short-circuited, the voltage drop of the sampling resistor increases until it is greater than the conduction voltage drop of the light-emitting diode, the phototransistor is turned on, the collector jumps to a low level state, and an overcurrent signal is generated; The overcurrent signal triggers the PWM drive hardware circuit to shut down the PWM output; Short circuit recovery, collector has no overcurrent signal output and returns to high level state; The latch circuit captures and latches the overcurrent signal and outputs a valid latch signal; The control circuit controls the PWM output to be turned off based on the latch signal.

[0017] The advantages of the present invention are: This solution proposes to collect the overcurrent signal source at the positive pole of the busbar, and also provides a power-free implementation circuit, without considering the common-mode voltage problem. It achieves a comprehensive protection effect covering various short-circuit situations such as phase-to-phase, phase-to-PE, P-to-phase, N-to-phase, and P-to-B at low cost. This solution achieves a high-speed and reliable response. First, it quickly shuts down the PWM at the hardware level based on the overcurrent signal, achieving a high-speed hardware response. Second, it uses latching logic to latch the overcurrent signal for a period of time. This not only prolongs the PWM off-time, preventing the PWM from resuming operation instantly after a rapid current drop, but also provides the control circuit with sufficient time for logic processing, ensuring a reliable response. This solution not only achieves full coverage response in terms of breadth, but also achieves zero missed triggering, and can accurately make a protection response even if the overcurrent signal disappears in a very short time. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a diagram of the current detection position of the protection circuit in the prior art; Figure 2 This is a circuit diagram of a low-cost high-side overcurrent protection circuit of the present invention; Figure 3 This is a circuit principle block diagram of the low-cost high-side overcurrent protection circuit of the present invention; Figure 4 This is a protection implementation flow chart of the low-cost high-side overcurrent protection circuit of the present invention; Figure 5 This is a test data curve diagram of the low-cost high-side overcurrent protection circuit of the present invention.

[0019] Reference numerals: latch circuit 1 ; control circuit 2 ; PWM drive hardware circuit 3 ; buffer circuit 31 ; PWM drive circuit 32 ; power device 4 . DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] As shown in the table below, using phase current as the overcurrent signal source, or using the current on the negative busbar as the overcurrent signal source, cannot fully protect against short-circuit conditions, such as between phases, relative to PE, P to phase, N to phase, and P to B. However, designing the sampling location at the positive busbar P allows for full protection against short-circuit conditions, such as between phases, relative to PE, P to phase, N to phase, and P to B, because short-circuit current at any location will pass through resistor R1.

[0022] The protection circuit of this solution sets the sampling position at the positive pole P of the busbar, which can achieve full coverage protection for various short circuit situations such as phase-to-phase, phase-to-PE, P-to-phase, N-to-phase, and P-to-B. At the same time, this solution proposes a corresponding processing circuit, which does not need to consider the common mode voltage problem and does not require high-cost components such as op amps and comparators, achieving low-cost full coverage protection and overcoming the high cost problem of setting a sampling point at the positive pole P of the busbar. Figure 2 As shown, the specific circuit is as follows: Various input power sources are supplied to the power system via rectified or non-rectified DC power. A sampling resistor R1 is connected in series at the high side of the power system, that is, the positive pole of the busbar. A light-emitting diode D1 is connected in parallel across the sampling resistor R1. When the current flowing through the sampling resistor R1 causes the voltage drop across the sampling resistor R1 to be greater than the conduction voltage drop of the light-emitting diode D1, the light-emitting diode D1 is turned on. A phototransistor Q1 is designed to be coupled to the light-emitting diode D1 to convert the optical signal into an electrical signal, ultimately outputting an overcurrent signal. The light-emitting diode D1 and the phototransistor Q1 form an optocoupler, which can be replaced by a high-speed optocoupler.

[0023] A signal processing circuit is connected to the output end of the phototransistor Q1 for latching the overcurrent signal and outputting a latch signal.

[0024] Specifically, the signal processing circuit includes a latch circuit 1 and a shaping circuit. The shaping circuit is used to shape the overcurrent signal in the form of an electrical signal. In this embodiment, the shaping circuit uses a buffer B1. The collector of the phototransistor Q1 is connected to a 3.3V DC power supply via a current-limiting resistor R3, and the emitter is connected to ground GND. This outputs a low-level overcurrent signal when the circuit is short-circuited and a high-level signal when the circuit is normal.

[0025] The collector of the phototransistor Q1 is also connected to the PWM drive hardware circuit 3 through the buffer B1 to provide an overcurrent signal to the PWM drive hardware circuit 3. The output end of the latch circuit 1 is connected to the control circuit 2 to provide a latch signal to the control circuit 2.

[0026] like Figure 3As shown, the PWM drive hardware circuit 3 includes a buffer circuit 31 and a PWM drive circuit 32 connected in sequence. In this embodiment, the buffer circuit 31 is enabled at a high level, and the enable end of the buffer circuit 31 is connected to the collector end of the phototransistor through the buffer B1. The signal input end of the buffer circuit 31 is connected to the control circuit 2, and the PWM drive circuit 32 is connected to the power device 4.

[0027] When the circuit is normal, the collector terminal of the phototransistor is at a high level, there is no overcurrent signal, the output of B1 is at a high level, the buffer circuit 31 is enabled, and the control circuit 2 inputs a control signal for normal operation to the buffer circuit 31 .

[0028] When short-circuited, the collector terminal of the phototransistor Q1 outputs a low-level overcurrent signal, B1 outputs a low-level signal, the buffer circuit 31 is disabled, and the PWM output is quickly cut off by hardware.

[0029] In addition, the collector of the phototransistor Q1 is also connected to the input end of the latch circuit 1 through the buffer B1. The latch circuit 1 is used to trigger the generation of a latch signal indicating overcurrent when an overcurrent signal occurs.

[0030] The duration of a momentary short circuit is very short, so the overcurrent signal is also very short, making it difficult for the control circuit 2 to capture this signal and initiate a protective action. This solution enables hardware-based rapid PWM output interruption by directly connecting the overcurrent signal to the enable terminal of the buffer circuit 31. Simultaneously, the control circuit's action is triggered by the latch circuit 1, which latches the overcurrent signal and maintains it for at least 1ms, providing the control circuit 2 with sufficient continuous signal for logic processing. This effectively avoids situations where the control circuit has difficulty accurately responding to protection due to the short duration of the overcurrent signal, achieving zero-missing triggering protection.

[0031] The above circuit uses the potential difference generated by the current flowing through the sampling resistor R1 to trigger the light-emitting diode D1. Since the light-emitting diode D1 has a diode voltage drop, the voltage across the sampling resistor R1 will trigger the light-emitting diode D1 to emit light only when it exceeds the diode voltage drop. The phototransistor Q1 changes linearly within the specific light-emitting range of the light-emitting diode D1. After exceeding the linear range, Q1 enters saturation conduction. The overcurrent signal, that is, the overcurrent voltage signal, is shaped by B1 and then latched to ensure that the voltage signal reflecting the instantaneous current is maintained for a sufficient period of time. This allows the hardware circuit to block the PWM signal for a sufficient period of time, while also providing sufficient time for the control circuit 2 to monitor and issue an alarm prompt and perform protection processing. The PWM is turned off at the software level through the signal input terminal of the buffer circuit 31. In this case, the user can manually clear the signal after the signal is turned off.

[0032] Specifically, the resistance Rx of the sampling resistor R1 is based on the current threshold I 阈值 and the forward voltage drop of the light-emitting diode VF Set, meet .

[0033] The current threshold I 阈值 Taking 100A as an example, it is necessary to trigger the light-emitting diode D1 to turn on when a current of 100A flows through the sampling resistor R1. If the voltage drop of the selected light-emitting diode D1 is 1.2V, then the sampling resistor R1 is Therefore, the resistance of the sampling resistor R1 is preferably 2 mΩ.

[0034] The resistance of the current limiting resistor R3 satisfies , where R3 is the resistance of the current limiting resistor, VCC is the DC power supply voltage, and IC is the saturation conduction current of the photosensitive device. Assuming that the transmission ratio CTR of the selected optocoupler is 100%, the forward operating current of the light-emitting diode D1 is 1mA, and the operating current of the phototransistor Q1 is also 1mA, therefore, the current limiting resistor In this embodiment, the current limiting resistor R3 is selected to be 5.1KΩ.

[0035] The working process of this circuit is: When the circuit is normal, the voltage drop of the sampling resistor R1 is less than the conduction voltage drop of the light-emitting diode D1, the phototransistor Q1 is disconnected, and the collector remains in a high level state due to the 3.3V DC power supply. There is no valid overcurrent signal and no valid latch signal. When the circuit is short-circuited, Figure 4 As shown, the voltage drop of the sampling resistor R1 increases until it is greater than the conduction voltage drop of the light-emitting diode D1, the phototransistor Q1 is turned on, the collector jumps to a low level state, and a low-level overcurrent signal is generated. Figure 2 The F0 terminal is low level; The overcurrent signal triggers the PWM drive hardware circuit 3 to turn off the PWM output; When the short circuit is restored instantaneously, the collector has no overcurrent signal output and returns to a high level state. At this time, the hardware shutdown fails. At the same time, the latch circuit 1 captures and latches the overcurrent signal and outputs a valid latch signal F1. Based on the latch signal F1, the control circuit 2 controls the PWM output to shut down at the software level and handles the overcurrent alarm event, including fault diagnosis and alarm issuance.

[0036] like Figure 5The test data for the circuit of this embodiment is shown. The blue curve at the bottom of the figure represents the actual short-circuit current, the green curve represents the F0 signal, and the yellow curve represents the F1 signal. As can be seen from the figure, after the current threshold is reached, F0 is the first to jump to a low level, promptly shutting down the hardware output (but not sustaining it). Approximately 5 to 20 μs later, the F0 signal returns to a high level. During this period, the overcurrent signal is captured by latch circuit 1, which then outputs a high-level F1 signal indicating overcurrent, latching the overcurrent signal for at least 1 μs. Control circuit 2 processes the overcurrent alarm event based on this long-lasting latch signal, achieving a fast and reliable response.

[0037] This solution balances cost and expands the short-circuit protection range, achieving comprehensive overcurrent protection at a low cost. When the current exceeds the designed threshold (e.g., due to a short circuit or abnormal load), this circuit quickly and reliably triggers protection, such as shutting off the circuit, to prevent damage to critical components such as wires, chips, and power supplies due to overheating or overload.

[0038] Example 2 This embodiment is similar to the first embodiment, except that in this embodiment, the shaping circuit uses an inverter, i.e. Figure 2 B1 in FIG. 1 is an inverter. The buffer circuit 31 of the PWM drive hardware circuit 3 uses a low-level enabled buffer circuit 31 . The enable terminal of the buffer circuit 31 is connected to the output terminal of the inverter. The signal input terminal is consistent with the embodiment and is connected to the control circuit 2 . The PWM drive circuit 32 is connected to the power device 4 .

[0039] When the circuit is normal, the phototransistor Q1 has no overcurrent signal output, and the collector is high. Accordingly, the inverter B1 outputs a low level, the F0 signal is low, the buffer circuit 31 is enabled, and the PWM output is normal.

[0040] When short-circuited, the phototransistor Q1 outputs a low-level overcurrent signal, the relay is low-level, and accordingly, the inverter outputs a high-level signal, the F0 signal is high-level, the buffer circuit 31 is disabled, and the PWM is temporarily cut off by hardware.

[0041] Explanation of terms: High Side: Any power supply has at least two polarities, and "high side" refers to the area of ​​the circuit where the potential is higher than the reference zero point.

[0042] Overcurrent: refers to the state where the current in the circuit exceeds the rated design range.

[0043] The connections mentioned herein include direct connections and indirect connections.

[0044] Although this document frequently uses terms such as latch circuit 1, control circuit 2, PWM drive hardware circuit 3, buffer circuit 31, PWM drive circuit 32, and power device 4, the use of other terms is not excluded. These terms are used solely to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitations would be contrary to the spirit of the present invention.

Claims

1. A low-cost high-side overcurrent protection circuit, characterized in that: include, The sampling resistor is connected in series with the positive line of the busbar; A light emitting diode is connected in parallel to the sampling resistor and is turned on when the current flowing through the sampling resistor causes the voltage drop of the sampling resistor to be greater than the conduction voltage drop of the light emitting diode; A photosensor, coupled to the light emitting diode, for outputting an overcurrent signal; a signal processing circuit connected to the photosensor and configured to output a latch signal indicating overcurrent based on the overcurrent signal; A PWM drive hardware circuit, connected to the photosensitive device, for shutting down the PWM output based on the overcurrent signal; The control circuit is connected to the signal processing circuit and the PWM drive hardware circuit, and is used to control the PWM output to be turned off based on the latch signal.

2. The low-cost high-side overcurrent protection circuit according to claim 1, characterized in that: The conduction voltage drop of the light emitting diode is used as a current threshold criterion, and when the voltage drop of the sampling resistor exceeds the conduction voltage drop, the light emitting diode is triggered to conduct and generate an overcurrent signal; The photosensitive device is used to convert the overcurrent signal in the form of an optical signal into the overcurrent signal in the form of an electrical signal.

3. The low-cost high-side overcurrent protection circuit according to claim 2, characterized in that: The resistance value Rx of the sampling resistor is based on the current threshold I 阈值 and the forward voltage drop of the light-emitting diode V F Set, meet .

4. The low-cost high-side overcurrent protection circuit according to claim 1, characterized in that: The photosensitive device is a phototransistor, which forms an optical coupler with the light emitting diode.

5. The low-cost high-side overcurrent protection circuit according to claim 4, characterized in that: The signal processing circuit includes a latch circuit; The collector of the phototransistor is connected to a DC power supply through a current-limiting resistor, and the emitter is connected to the ground terminal, so as to output a low-level overcurrent signal when the circuit is short-circuited; The collector of the phototransistor is connected to the input end of the latch circuit; The collector of the phototransistor is also connected to the PWM drive hardware circuit, so that the PWM drive hardware quickly shuts off the PWM output based on the overcurrent signal; The output end of the latch circuit is connected to the control circuit to provide a latch signal to the control circuit; The control circuit outputs a shutdown instruction to the PWM drive hardware circuit according to the latch signal to shut down the PWM output at the application level.

6. The low-cost high-side overcurrent protection circuit according to claim 5, characterized in that: The PWM drive hardware circuit includes a buffer circuit and a PWM drive circuit connected in sequence, the buffer circuit is enabled at a high level, and the enable terminal of the buffer circuit is connected to the collector terminal of the phototransistor, the signal input terminal is connected to the control circuit, and the PWM drive circuit is connected to the power device; When the circuit is normal, the collector terminal of the phototransistor is at a high level and the buffer circuit is enabled; When short-circuited, the collector terminal of the phototransistor outputs a low-level overcurrent signal and the buffer circuit is disabled.

7. The low-cost high-side overcurrent protection circuit according to claim 4, characterized in that: The signal processing circuit further includes a shaping circuit, the input end of which is connected to the collector of the phototransistor and a DC power supply, and the phototransistor is connected to the PWM drive hardware circuit and the latch circuit via the shaping circuit.

8. The low-cost high-side overcurrent protection circuit according to claim 7, characterized in that: The shaping circuit is an inverter; The PWM drive hardware circuit includes a buffer circuit and a PWM drive circuit connected in sequence, the buffer circuit is low-level enabled, and the enable terminal of the buffer circuit is connected to the output terminal of the inverter, the signal input terminal is connected to the control circuit, and the PWM drive circuit is connected to the power device; When the circuit is normal, the phototransistor has no overcurrent signal output, the inverter output is low, and the buffer circuit is enabled; When short-circuited, the phototransistor outputs a low-level overcurrent signal, the inverter outputs a high-level signal, and the buffer circuit is disabled.

9. The low-cost high-side overcurrent protection circuit according to claim 4, characterized in that: The resistance of the current limiting resistor satisfies , where R3 is the resistance of the current limiting resistor, VCC is the DC power supply voltage, and IC is the saturation on-current of the photosensitive device.

10. An overcurrent protection method based on the low-cost high-side overcurrent protection circuit according to any one of claims 1 to 9, characterized in that: The method includes: When the circuit is normal, the voltage drop of the sampling resistor is less than the conduction voltage drop of the light-emitting diode, the phototransistor is disconnected, the collector remains in a high level state, there is no overcurrent signal, and no latch signal; When the circuit is short-circuited, the voltage drop of the sampling resistor increases until it is greater than the conduction voltage drop of the light-emitting diode, the phototransistor is turned on, the collector jumps to a low level state, and an overcurrent signal is generated; The overcurrent signal triggers the PWM drive hardware circuit to shut down the PWM output; Short circuit recovery, collector has no overcurrent signal output and returns to high level state; The latch circuit captures and latches the overcurrent signal and outputs a valid latch signal; The control circuit controls the PWM output to be turned off based on the latch signal.

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