Surge protectors and surge protection methods

Abstract

This invention relates to surge protectors and surge protection methods. Exemplary surge protectors and surge protection methods provide precise clamping level control during voltage transients and surge events. An exemplary surge protector includes: a shunt transistor having a source coupled to ground and a drain coupled to a conductor at a supply voltage; and an operational amplifier having: an output coupled to the gate of the shunt transistor, an inverting input coupled to a reference voltage Vref, and a non-inverting input coupled to receive a sensed voltage, the sensed voltage being a fixed fraction f of the supply voltage, the operational amplifier being configured to drive the shunt transistor to shunt any overcurrent when the supply voltage reaches a clamping voltage Vc = Vref / f.

Description

Technical Field

[0001] This disclosure relates generally to surge protectors and transient voltage suppressors, and more specifically to surge protection methods and designs that provide such protection with minimal area and energy requirements while achieving accurate clamping level control. Background Technology

[0002] Many electronic devices are powered by direct current (DC) voltage from alternating current (AC) power sources, such as electrical outlets connected to the mains grid. The mains grid is large, complex, and susceptible to various events and faults that can cause voltage surges and transients, potentially damaging unprotected electronic components. Therefore, most electronic devices are equipped with surge and transient protection, most typically in the form of transient voltage suppression (TVS) diodes. Such diodes can impose undesirable large area requirements to adequately limit the maximum voltage induced by standard voltage surge tests, such as the maximum voltage specified by the current pulse in the International Electrotechnical Commission standard IEC 61000-4-5, which has an 8-microsecond wavefront time and a 20-microsecond duration, with a maximum value of 40 amps, often abbreviated as "(8μs / 20μs):40A".

[0003] Various attempts have been made to address this problem, including U.S. Patent Application Publication 2015 / 0303678 entitled "Precision Surge Clamp with Constant Clamping Voltage and Near-Zero Dynamic Resistance under various Thermal, Power, and Current Levels"; U.S. Patent Application Publication 2017 / 0373490 entitled "Surge Protection Circuit"; and U.S. Patent Application Publication 2018 / 0138696 entitled "Surge Protection Circuit with Feedback Control". These attempts have been evaluated and found to exhibit significant and undesirable variations in clamping voltage under different surge currents and temperatures. Summary of the Invention

[0004] Therefore, this paper discloses exemplary surge protectors and surge protection methods that achieve precise clamping level control during voltage transients and surge events.

[0005] According to one aspect of this disclosure, a surge protector is provided, characterized in that it comprises: a shunt transistor having a source coupled to ground and a drain coupled to a conductor at a supply voltage; and an operational amplifier having: an output coupled to the gate of the shunt transistor, an inverting input coupled to a reference voltage Vref, and a non-inverting input coupled to receive a sensed voltage f, the sensed voltage being a fixed fraction f of the supply voltage, the operational amplifier being configured to drive the shunt transistor to shunt any overcurrent when the supply voltage reaches a clamping voltage Vc = Vref / f.

[0006] In one embodiment, the surge protector is characterized in that the operational amplifier includes a differential amplifier, and the surge protector includes a power controller configured to disable the differential amplifier when the supply voltage is below a threshold voltage.

[0007] In one embodiment, the surge protector is characterized by further including a voltage divider configured to provide a sensing voltage to the non-inverting input.

[0008] In one embodiment, the surge protector is characterized in that the voltage divider includes a first impedance and a second impedance connected in series, the first impedance being formed by a first resistor connected in parallel with a first capacitor, and the second impedance being formed by a second resistor connected in parallel with a second capacitor.

[0009] In one embodiment, the surge protector is characterized in that it further includes a power controller configured to disable the voltage divider when the supply voltage is below a threshold voltage.

[0010] In one embodiment, the surge protector is characterized by further including a reference circuit comprising a reverse-biased Zener diode driven by a current source.

[0011] In one embodiment, the surge protector is characterized in that it further includes a power controller configured to disable the reference circuit when the supply voltage is below a threshold voltage.

[0012] In one implementation, the surge protector is characterized by a threshold voltage that matches the clamping voltage Vc.

[0013] According to another aspect, a surge protection method is provided, characterized by: deriving a sensed voltage as a fixed fraction f of the supply voltage; comparing the sensed voltage with a reference voltage Vref; and based on the comparison, driving a transistor to shunt any overcurrent when the supply voltage reaches a clamping voltage Vc = Vref / f.

[0014] In one embodiment, the surge protection method is characterized in that the comparison is performed by a differential amplifier, the derived sense voltage is performed using a voltage divider, and a reference voltage is provided by a reference circuit, and the surge protection method includes disabling at least one of the differential amplifier, the voltage divider, and the reference circuit when the supply voltage is below a threshold voltage. Attached Figure Description

[0015] Figure 1 A block diagram of an exemplary electronic device.

[0016] Figure 2 A block diagram of an exemplary surge protector.

[0017] Figure 3 This is a circuit diagram of an exemplary surge protector.

[0018] Figure 4 The graph shows the supply voltage and shunt current during an example surge event.

[0019] Figure 5 This is a flowchart of an exemplary surge protection method. Detailed Implementation

[0020] The following description and accompanying drawings are provided for illustrative purposes and not for limiting this disclosure. Rather, they provide a basis for those skilled in the art to understand all modifications, equivalents, and alternatives that fall within the scope of the claims.

[0021] Figure 1 As a block diagram of an exemplary electronic device, the device includes an integrated circuit 102 coupled via conductor 103 to a power supply 104 to receive a DC supply voltage Vin. Typical examples of Vin would include 3V, 5V, 6V, 9V, 12V, 15V, 16V, and 24V, but higher and lower values ​​are possible. A surge protector 106 is coupled between conductor 103 and ground to limit the supply voltage to its maximum value. The surge protector 106 is configured to suppress rapid voltage transients as well as voltage surges of longer durations, including at least standard IEC 61000-4-5 (8μs / 20μs): 40A current surges.

[0022] Surge protector 106 may be integrated onto the same substrate as integrated circuit 102 or into the same multi-chip module. Alternatively, surge protector 106 may be integrated into a power supply circuit responsible for converting AC voltage to DC supply voltage. As yet another alternative, surge protector 106 may be packaged as a discrete component to be mounted on a printed circuit board with integrated circuit 102, or otherwise routed between the power rails of the integrated circuit.

[0023] Figure 2A block diagram illustrating an exemplary embodiment of surge protector 106 is shown. The surge protector includes a shunt transistor 202 configured to shunt overcurrent from conductor 103 to ground when the supply voltage reaches the clamping voltage Vc, thereby preventing the supply voltage from exceeding the clamping voltage Vc during a surge event. "Overcurrent" is the portion of current that is not consumed by the load and, if not shunt to ground, would further increase the voltage of conductor 103. Figure 2 In this diagram, a shunt transistor is shown as a power metal-oxide-semiconductor field-effect transistor (power n-MOSFET) with an n-channel, its source connected to ground and its drain connected to a supply voltage conductor. Such transistors turn on when their gate-source voltage rises above a threshold voltage, which can be tailored to the application but is typically around 2 volts. MOSFETs may be particularly desirable for shunt transistors due to their fast response and negligible leakage current, but other transistor types may also be suitable, including bipolar junction transistors and junction-gate field-effect transistors.

[0024] The gate of the shunt transistor is coupled to the output of operational amplifier 204 to receive the drive signal Vdrv. Operational amplifier 204 has an inverting input coupled to reference circuit 206 to receive the reference voltage Vref, and a non-inverting input coupled to voltage divider 208 to receive the sensed voltage Vsen. When the sensed voltage Vsen is lower than the reference voltage Vref, the drive signal Vdrv is low, thereby keeping the shunt transistor in a non-conducting "OFF" state. When the sensed voltage Vsen reaches the reference voltage Vref, as long as the sensed voltage is at or above the reference voltage, operational amplifier 204 drives the shunt transistor 202 to a conducting "ON" state to shunt the overcurrent.

[0025] Reference circuit 206 can be any suitable type of reference voltage generator that provides a reference voltage that is largely independent of temperature, supply voltage, and process variations, including bandgap voltage references, Zener diode references, avalanche diode references, and V... BE Multiplier reference. As discussed further below, reference circuit 206 is disabled in the absence of surge events and therefore does not need to be designed to minimize power consumption, especially in a design that unnecessarily increases the complexity or physical area required to implement the circuit.

[0026] Voltage divider 208 derives the sensed voltage Vsen as a fixed fraction f of the supply voltage Vin. The term "fixed" is used herein to indicate that the fraction f is constant and independent of the supply voltage. Any dependence on temperature or process variations is also expected to be negligible. A voltage divider may typically incorporate capacitors and / or inductors to make the fraction f a complex number with a frequency-dependent amplitude; however, exemplary implementations employ a voltage divider that provides a real-valued fraction f without significant frequency dependence. An exemplary range for f will be from 0.1 to 0.8, and as will become apparent from the discussion below, the chosen precise value will balance various considerations, including the relationship between Vin (the source voltage of operational amplifier 204) and the desired clamping voltage, and the availability of a suitable reference voltage provided by reference circuit 206.

[0027] Since the sensed voltage Vsen is not allowed to exceed the reference voltage Vref, the clamping voltage Vc can be derived as:

[0028] V sen =fV in ≤V ref

[0029] V in ≤V ref / f=V c

[0030] The reference voltage Vref can be determined by the design of the reference circuit 206, and the voltage divider 208 can be designed to provide a fraction f that sets the clamping voltage Vc to the desired value.

[0031] An exemplary implementation also includes a power controller 210. When the supply voltage Vin is higher than a threshold voltage, the power controller 210 supplies the supply voltage Vin as the power supply voltage Vpwr to the operational amplifier 204, reference circuit 206, and voltage divider 208; otherwise, when the supply voltage Vin is lower than the threshold voltage, the power controller decouples the supply voltage Vin from these components. The threshold voltage is preferably matched to the clamping voltage Vc, meaning that the threshold voltage is lower than but almost equal to the clamping voltage Vc, such that components 204-208 are only enabled if necessary. The gap between the desired threshold voltage and the desired clamping voltage can be large enough to ensure that the threshold voltage is lower than the clamping voltage under expected process and parameter variations, for example, a 2-volt to 4-volt gap.

[0032] Although an n-channel transistor is shown in the exemplary embodiment, a p-channel transistor can also act as a shunt transistor with source and drain connections and corresponding adjustment of the gate signal voltage, which can be achieved by swapping the inverting and non-inverting inputs of an operational amplifier.

[0033] Figure 3This is a circuit diagram illustrating an exemplary implementation of surge protector 106. Figure 3 In this design, the power controller includes a set of reverse-biased Zener diodes 302 connected in series with a set of forward-biased Zener diodes 304. This series combination forms a diode arrangement such that current can only flow after the supply voltage reaches a threshold voltage level. The reverse-biased Zener diodes 302 have a breakdown voltage that increases with temperature, while the forward-biased Zener diodes 304 have a forward conduction voltage that decreases with temperature. This diode arrangement can be designed so that these temperature dependencies cancel each other out, allowing the series combination of Zener diodes to provide a consistent threshold voltage over a wide temperature range.

[0034] The diode arrangement couples the supply voltage Vin to the gate and drain of an n-type transistor 306, the source of which is coupled to ground. Transistor 306 converts the current flowing through the diode arrangement into a corresponding gate voltage. A matching transistor 308 acts as a current mirror transistor; that is, it is placed in the current mirror arrangement with transistor 306 to convert the gate voltage into a corresponding current flowing through a bias diode 310 (shown here as a reverse-biased Zener diode), thereby creating a voltage drop between the source and gate of the p-type power transistor 314, coupling the supply voltage Vin to the supply voltage Vpwr. When no current flows through the current mirror, a pull-up resistor 312 pulls the gate voltage of the power transistor 314 to the supply voltage, thereby decoupling the supply voltage Vpwr from the supply voltage Vin. The diode arrangement combined with transistor 306 provides a customizable threshold voltage, such as approximately 22 volts. As previously mentioned, when the supply voltage exceeds the threshold voltage, the power controller 210 couples the supply voltage Vin to other components 204 through 208.

[0035] Voltage divider 208 includes a first resistor 321 connected in parallel with a first capacitor 331 to generate a first impedance, and a second resistor 322 connected in parallel with a second capacitor 332 to form a second impedance. The first and second impedances are connected in series between the power supply voltage Vpwr and ground, with the intermediate node providing the sensed voltage Vsen.

[0036]

[0037] Z1 and Z2 are the first and second impedances, respectively, chosen to provide the real-valued fraction f. The impedance of the power transistor 314 is expected to be negligible, but if it is too large to be ignored, it may be included as part of the first impedance when the sensed voltage is represented according to the source voltage.

[0038]

[0039] In at least one intended specific embodiment, the first impedance and the second impedance are integer multiples of the base impedance Z, for example, Z1 = mZ and Z2 = nZ, where m and n are integers. (The base impedance Z can be the impedance of the power transistor 314 in the on state.) The sensed voltage can then be expressed as:

[0040]

[0041] Where f is a fixed fraction defined by voltage divider 208.

[0042] Reference circuit 206 includes a current source enabled by the supply voltage Vpwr. The current source provides current flowing through a reverse-biased Zener diode to generate a reference voltage Vref. This Zener diode (and Zener diode 310 of the power controller) can be a diode with a 5.6-volt breakdown voltage, where the temperature coefficient of the avalanche breakdown process cancels out the temperature coefficient of the Zener breakdown process, thereby minimizing any temperature dependence of the reference voltage.

[0043] Operational amplifier 204 includes a pair of differential transistors 341 and 342 driven by current source 343. Transistors 341 and 342 are shown as p-type MOSFETs with their sources connected to current source 343. The drain of transistor 341 is coupled to the drain and gate of n-type MOSFET 344, thereby converting the current flowing through transistor 341 into the gate voltage of current mirror transistor 345. The gate of transistor 341 receives a sensed voltage Vsen, and the gate of transistor 342 receives a reference voltage Vref. As long as the sensed voltage Vsen is less than the reference voltage Vref, the current from current source 343 is primarily directed through transistors 341 and 344. Transistor 342 carries less current than current mirror transistor 345, thereby discharging the gate of output transistor 346. When output transistor 346 is in a non-conducting state, pull-down resistor 348 pulls the drive voltage Vdrv low. In this case, shunt transistor 202 is turned off.

[0044] When the sensed voltage Vsen reaches or exceeds the reference voltage Vref, current from current source 343 is directed through transistor 342 because current mirror transistor 345 draws less current, thus charging the gate of output transistor 346. With output transistor 346 in the on state, pull-up resistor 347 pulls the drive voltage Vdrv high. In this state, shunt transistor 202 is on, allowing overcurrent to be drawn from supply voltage Vin, thereby providing accurate feedback control of the supply voltage.

[0045] Figure 4This is a graph showing the supply voltage Vin as a function of time during a surge event according to standard IEC 61000-4-5 (8μs / 20μs): 40A. The solid line represents the rapid voltage rise from zero volts to a clamping voltage of 26.5 volts, where it is capped by shunt of the overcurrent, as indicated by the dashed line. Once the overcurrent is shunted at approximately 32 microseconds, the voltage drops below the upper limit and the shunt transistor turns off, causing the voltage to gradually decay thereafter. The surge protector exhibits a dynamic resistance of 1 milliohm at 27°C and a maximum supply voltage of 26.8 volts when the shunt current peaks at 40A. The surge protector performs well across a range of temperature and parameter variations, limiting the supply voltage to a maximum of 27.99 volts with a dynamic resistance of 7.9 milliohms, representing a substantial improvement over previous methods. The measured current leakage is approximately 4 nA after the power controller disables the supply voltage Vpwr, and the measured input capacitance is 106 pF. The expected footprint (area requirement) of the surge protector shall not exceed approximately 1.1 mm × 1.1 mm.

[0046] Figure 5 This is a flowchart of a method that can be implemented by surge protector 106. In block 502, the surge protector (more precisely, power controller 210) cycles until it determines that the supply voltage is higher than a threshold. When the threshold is exceeded, in block 504, power controller 210 enables various circuit components of surge protector 106 (e.g., reference circuit 206, voltage divider 208, and operational amplifier 204). In block 506, operational amplifier 204 determines whether the supply voltage exceeds a clamping voltage. If the supply voltage exceeds the clamping voltage, a drive voltage is increased in block 508 to increase the shunt current through shunt transistor 202, and the method returns to block 506. If the supply voltage does not exceed the clamping voltage, power controller 210 determines in block 510 whether the supply voltage remains above the threshold. If the supply voltage remains above the threshold, i.e., if the supply voltage is between the threshold voltage and the clamping voltage, in block 512, operational amplifier 204 decreases the drive voltage to decrease the shunt current and cycles back to block 506. On the other hand, if the supply voltage has dropped below the threshold voltage, in block 514, the power controller 210 disables other circuit components of the surge protector 106 and returns to block 502.

[0047] Although the method is shown and described as a series of operations for clarity, in practice, various operations can be implemented simultaneously and asynchronously by different components of the surge protector. The method can be implemented as an application-specific integrated circuit or a component of discrete electronic parts. These and many other modifications, equivalents, and alternatives will become apparent to those skilled in the art once the foregoing disclosure is fully understood. It is intended that the following claims be construed as including all such modifications, equivalents, and alternatives where applicable.

[0048] In summary, various exemplary surge protectors and surge protection methods have been disclosed herein, enabling precise clamping level control during voltage transients and surge events. An exemplary surge protector includes: a shunt transistor having a source coupled to ground and a drain coupled to a conductor at a supply voltage; and an operational amplifier having: an output coupled to the gate of the shunt transistor, an inverting input coupled to receive a reference voltage Vref, and a non-inverting input coupled to receive a sensed voltage f, which is a fixed fraction f of the supply voltage. The operational amplifier is configured to drive the shunt transistor to shunt any overcurrent when the supply voltage reaches a clamping voltage Vc = Vref / f.

[0049] An exemplary surge protection method includes: (e.g., using a voltage divider 208) deriving a sensed voltage as a fixed fraction f of the supply voltage; comparing the sensed voltage with a reference voltage Vref (e.g., using an operational amplifier 204); and based on the comparison, driving a transistor to shunt any overcurrent when the supply voltage reaches a clamping voltage Vc = Vref / f (e.g., via the operational amplifier 204).

[0050] An exemplary method for providing surge protection includes: providing a shunt transistor configured to couple a conductor at the supply voltage to ground when the shunt transistor is enabled; coupling the output of an operational amplifier to the gate of the shunt transistor; coupling a reference voltage from a reference circuit to the inverting input of the operational amplifier; and coupling a sensed voltage from a voltage divider to the non-inverting input of the operational amplifier, the sensed voltage being a fixed fraction f of the supply voltage, the operational amplifier being configured to enable the shunt transistor to shunt any overcurrent when the supply voltage reaches a clamping voltage Vc = Vref / f.

[0051] Each of the aforementioned surge protectors and surge protection methods may be employed individually or in combination, and may include one or more of the following features in any suitable combination: 1. An operational amplifier comprising a differential amplifier. 2. A power controller configured to disable the differential amplifier when the supply voltage is below a threshold voltage. 3. A voltage divider configured to provide a sensed voltage to a non-inverting input. 4. The voltage divider comprising a first impedance and a second impedance in series, the first impedance being formed by a first resistor in parallel with a first capacitor, and the second impedance being formed by a second resistor in parallel with a second capacitor. 5. A power controller configured to disable the voltage divider when the supply voltage is below a threshold voltage. 6. A reference circuit comprising a reverse-biased Zener diode driven by a current source. 7. A power controller configured to disable the reference circuit when the supply voltage is below a threshold voltage. 8. A threshold voltage matched to a clamping voltage Vc. 9. The threshold voltage is set by a series combination of a Zener diode and a current mirror transistor.

Claims

1. A surge protector, characterized in that, include: A shunt transistor having a source coupled to ground and a drain coupled to a conductor at a supply voltage; A voltage divider configured to provide a sensing voltage that is a fixed fraction f of the supply voltage; A power controller configured to disable the voltage divider when the supply voltage is below a threshold voltage; as well as An operational amplifier, the operational amplifier having: The output terminal coupled to the gate of the shunt transistor, The inverting input is coupled to receive the reference voltage Vref provided by the reference circuit, and The non-inverting input terminal is coupled to receive the sensed voltage. The operational amplifier is configured to drive the shunt transistor to shunt any overcurrent when the supply voltage reaches the clamping voltage Vc = Vref / f. The power controller is configured to disable the reference circuit when the supply voltage is lower than the threshold voltage, wherein the threshold voltage is matched with the clamping voltage Vc.

2. The surge protector according to claim 1, characterized in that, The operational amplifier includes a differential amplifier, and the power controller is configured to disable the differential amplifier when the supply voltage is below the threshold voltage.

3. The surge protector according to claim 1, characterized in that, The voltage divider includes a first impedance and a second impedance connected in series. The first impedance is formed by a first resistor connected in parallel with a first capacitor, and the second impedance is formed by a second resistor connected in parallel with a second capacitor.

4. The surge protector according to claim 1, characterized in that, The surge protector also includes a reference circuit comprising a reverse-biased Zener diode driven by a current source.

5. The surge protector according to claim 1, characterized in that, The threshold voltage is set by a series combination of a Zener diode and a current mirror transistor.

6. A surge protection method, characterized in that, include: Use a voltage divider to derive a sensed voltage that is a fixed fraction f of the supply voltage; The sensed voltage is compared with the reference voltage Vref provided by the reference circuit; Based on the comparison, when the supply voltage reaches the clamping voltage Vc=Vref / f, the transistor is driven to shunt any overcurrent through the transistor; The voltage divider is disabled when the supply voltage is below a threshold voltage. as well as The reference circuit is disabled when the supply voltage is lower than the threshold voltage, wherein the threshold voltage is matched with the clamping voltage Vc.

7. The surge protection method according to claim 6, characterized in that, The comparison is performed by a differential amplifier, and the surge protection method further includes disabling the differential amplifier when the supply voltage is lower than the threshold voltage.

8. The surge protection method according to claim 6, characterized in that, The reference voltage is provided by the reference circuit, which has a reverse-biased Zener diode driven by a current source.

Images