TOTEM POLE PFC WITH A SURGE PROTECTION CIRCUIT AND SURGE PROTECTION METHOD FOR A TOTEM POLE PFC

The disclosure concerns a totem pole PFC with a surge protection circuit, wherein the totem pole PFC comprises at least one bypass-diode branch with at least two bypass-diodes, at least one switch branch with at least two switches, at least one polarity changer branch with at least two switches, an input bridge connecting the switch branch(es) with an input voltage source, and at least one bypass branch connecting the input bridge in parallel with the bypass-diodes of the bypass-diode branch(es). The surge protection circuit comprises at least one current sensor configured to detect a current flowing through at least one of the bypass-diodes of the bypass-diode branch(es), and a control unit configured to receive a detected current value from the current sensor(s) and to switch at least one switch of the totem pole PFC at least in dependence on the detected current value.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to European Patent Application No. 22183677.8, filed on Jul. 7, 2022, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure concerns a totem pole PFC (power factor correction circuit) with a surge protection circuit and a surge protection method for a totem pole PFC.

BACKGROUND

Conventional PFC power converters, known from for example US 2012/0294053A1 or US 2020/0161962A1, are generally used for reducing interference of an electric grid caused by power harmonic waves and decreasing the noise of the electric grid. Especially during initial product testing of the PFC, as well as during use thereof, a voltage supplied from an input voltage source, for instance the electric grid, can be prone to producing surge voltages. For such cases, surge protection circuits are commonly employed to protect the device from breakdown resulting from these surge voltages as well as their induced current. However, none of the conventional surge protection circuits suitably and reliably protect a totem pole PFC. In particular, conventional surge protection circuits provide no suitable surge protection for a totem pole PFC comprising a polarity changer.

SUMMARY

It is an object of the present disclosure to provide a totem pole PFC with a surge protection circuit which can suitably, reliably, and quickly react to surge voltages and protect the totem pole PFC. Further, it is an object of the present disclosure to provide a corresponding surge protection method for a totem pole PFC which can suitably, reliably, and quickly protect the totem pole PFC from surge voltages.

The solution of this object is solved by the features of the independent claims. The dependent claims contain advantageous embodiments of the present disclosure.

The present disclosure concerns a totem pole PFC with a surge protection circuit. Therein, the totem pole PFC comprises at least one bypass-diode branch with at least two bypass-diodes, at least one switch branch with at least two switches, at least one polarity changer branch with a least two switches, and an input bridge connecting the switch branch(es) with an input voltage source. Further, the totem pole PFC comprises at least one bypass branch connecting the input bridge in parallel with the bypass-diodes of the bypass-diode branch(es). The surge protection circuit comprises at least one current sensor configured to detect a current flowing through at least one of the bypass-diodes of the bypass-diode branch(es). The surge protection circuit also comprises a control unit configured to receive a detected current value from the current sensor(s) and to switch at least one switch of the totem pole PFC at least in dependence on the detected current value.

The totem pole PFC with a surge protection circuit has the advantage that the current sensor(s) can suitably detect a surge voltage by detecting the current flowing through at least one of the bypass-diodes of the bypass-diode branch(es).

In an embodiment, the at least one current sensor is a current transformer, a Hall-effect sensor, further a magneto resistive (AMR) sensor. In addition or alternatively thereto, the at least one current sensor is a shunt resistor (current sensing resistor).

In an embodiment, a current only flows through the bypass-diode branch(es) during and shortly following an initial start-up of the PFC device and when the input voltage source inputs a surge voltage. Therefore, by detecting a current flowing through the bypass-diode branch(es), the present disclosure quickly and reliably detects the occurrence of a surge voltage.

In an embodiment, the term “initial start-up” refers to a state of turning on the device, especially for the first time and/or after having been shut off entirely.

In addition to advantageously detecting and protecting from surge voltages, the surge protection circuit can detect PLDs (power line disturbances) and protect from these accordingly.

In an embodiment, the totem pole PFC comprises, especially at its output, a capacitor which is charged during the start-up process of the totem pole PFC. In an embodiment, a current only flows through the bypass-diode branch(es) during the charging process of the capacitor, when no surge voltage is present. In other words, once the capacitor is fully charged, no current will flow through the bypass-diodes without the presence of a surge voltage during operation of the totem pole PFC.

In an embodiment, the term “no current” means “substantially no current”. In other words, small, induced currents, for instance due to electromagnetic interference, are not necessarily excluded by the term “no current”. Further, in an embodiment, for example, “no current” means “no intentional current”, i.e. the totem pole PFC and surge protection circuit are designed in such a way that no intentional current, for instance via explicit switching of the device to deliver current, flows at the time and/or location to which “no current” refers to.

In an embodiment, the current sensor(s) is/are arranged on the bypass branch. Further, in an embodiment, the current sensor(s) is/are especially arranged on a node of the bypass branch between a connection point of the bypass branch with the input bridge and a connection point of the bypass branch with the bypass-diode branch(es).

In an embodiment, the surge protection circuit comprises a plurality of current sensors. Therein, each bypass-diode of the bypass-diode branch(es) is connected in series with at least one of these current sensors. In an embodiment, each bypass-diode of one or more bypass-diode branches is connected with at least one current sensor of the plurality of current sensors.

Advantageously, at least one bypass-diode branch is connected in parallel with the at least one switch branch. Therein, the one or more current sensors are respectively arranged on nodes between a connection point of the bypass-diode branch(es) with the bypass branch and connection points of the bypass-diode branch(es) with the switch branch(es).

Further, in an embodiment, one first current sensor is arranged on a node between a connection point of the bypass-diode branch with the bypass branch and a connection point of the bypass-diode branch with a high-side switch of at least one of the switch branch(es). Further, in an embodiment, a second current sensor is arranged on a node between a connection point of the bypass-diode branch with the bypass branch and a connection point of the bypass-diode branch with a low-side switch of the switch branch(es).

Advantageously, the totem pole PFC comprises one or more of the aforementioned switch branch(es) and one polarity changer branch. In the case of multiple switch branches, the switch branch closest to the bypass-diode branch(es) may be referred to as a first switch branch, which has direct connection points with the bypass-diode branch(es). The one or more further switch branches may be referred to as second or more switch branches, which have a direct connection point with the first switch branch, and not a direct connection point with one or more or any of the bypass-diode branch(es).

In an embodiment, when the totem pole PFC comprises a plurality of current sensors, at least one current sensor is arranged on each node connecting the connection point of the bypass-diode branch with the bypass-branch with the connection point of the first switch branch, i.e. at least one on the high-side node and the low-side node between the bypass-diode branch and the first switch branch. These current sensors are in addition or alternatively to the at least one current sensor arranged on the bypass branch.

In one advantageous embodiment, the totem pole PFC comprises exactly one bypass-diode branch.

In an embodiment, the totem pole PFC comprises one or more, or two or more, or three or more, or four or more switch branches. In an embodiment, the totem pole PFC comprises exactly one or exactly two or exactly three switch branches. Further, in an embodiment, each switch branch comprises exactly two switches.

Further, in an embodiment, the totem pole PFC comprises exactly one polarity changer branch. Advantageously, the polarity changer branch comprises exactly two switches.

In an embodiment, any or all switches of the totem pole PFC are, especially each, connected to antiparallel diodes. In the exemplary case of MOSFET switches, these are antiparallel body diodes.

In an embodiment, the bypass-diode branch is coupled in parallel with the two switch branches. Further, in an embodiment, the polarity changer branch is coupled in parallel with the switch branches and the bypass-diode branch.

Advantageously, the polarity changer branch is additionally coupled in parallel with the input voltage source, especially via the bypass branch. Further, in an embodiment, the totem pole PFC comprises a polarity changer bridge connecting the polarity changer branch with the input voltage source.

In one embodiment, the control unit comprises a latch for switching off the at least one switch of the totem pole PFC and a latch reset input for resetting the latch. Therein, the latch reset input is especially configured to receive a latch reset signal from a digital signal processor. The digital signal processor is included in the totem pole PFC, particularly in the surge protection circuit of the totem pole PFC.

In an embodiment, the latch is an integrated logic latch. Further, in an embodiment, the latch is a discrete transistor/MOSFET circuit, especially realized with diode feedback. Further, in an embodiment, the latch is an integrated driver, especially wherein self holding is realized with diode feedback.

In an embodiment, the latch is of an edge triggered flip-flop type.

In an embodiment, depending especially on whether the respective switches are normally-on or normally-off switches, the latch actively (via an OFF-signal) switches off the respective switches or passively (via no ON-signal) switches off the switches.

Further, in an embodiment, the control unit comprises a comparator for comparing the detected current with a predetermined protection current value.

In an embodiment, the comparator is an integrated operation amplifier (OPV). Further, in an embodiment, the comparator is an integrated comparator (IC). Further, in an embodiment, the comparator is an integrated driver, especially using a constant input level of a driver.

In an embodiment, the predetermined protection current value is a predetermined value that is higher than a start-up current value of the PFC. For instance, during start-up of the totem pole PFC, a current of for example 30 A may be generated in one or more of the bypass-diodes of the bypass-diode branch. In an embodiment, the predetermined protection current value is set to above 30 A, for example, between 30 A and 100 A. Further, in an embodiment, the predetermined protection current value is below 300 A.

In one advantageous embodiment, the comparator outputs a latch input signal for the latch of the control unit. Thereby, in an embodiment, when the comparator determines that the detected current is equal to or higher than the predetermined protection current value, the comparator outputs the latch input signal, which controls the latch to switch at least one switch of the totem pole PFC.

In an embodiment, the comparator is a Schmitt-trigger or an analog comparator. In the case of the comparator being a Schmitt-trigger, a lower threshold thereof is set to within a predetermined range of the start-up current flowing through the bypass-diode branch. Further, in an embodiment, an upper threshold thereof is set to the predetermined protection current value. Thereby, the comparator does not output the latch input signal during start-up of the totem pole PFC. If the protection circuit is triggered during start-up or PLD (power line disturbances), the control unit recognizes this and resets the latch. The PFC can continue then continue the normal operation.

In an embodiment, the control unit is configured to switch the at least one switch of the totem pole PFC in dependence of the detected current and in dependence on a predetermined time duration after switching on the totem pole PFC. In an embodiment thereby, the surge protection circuit does not switch the at least one switch of the totem pole PFC in reaction to a current flowing through the at least one of the diodes due to the start-up of the device.

In an embodiment, the control unit, especially the latch of the control unit, is configured to switch off all switches of the totem pole PFC. In particular, the control unit is configured to switch off all switches of all switch branches and of all polarity changer branches.

In an embodiment, the aforementioned OFF-switching of the respective switches is achieved by the control unit outputting an active OFF-signal, especially in the preferable case of one or more switches being of the normally-ON type. Alternatively, or in addition thereto, in the preferable case that one or more switches is of the normally-OFF type, the control unit is configured to switch off the respective switch by not supplying an ON-signal and/or ceasing to output an ON-signal.

The present disclosure also concerns a surge protection method for a totem pole PFC. Therein, the totem pole PFC comprises at least one bypass-diode branch with at least two bypass-diodes, at least one switch branch with at least two switches, at least one polarity changer branch with at least two switches, an input bridge connecting the switch branch(es) with an input voltage source, and at least one bypass branch connecting the input bridge in parallel with the bypass-diodes of the bypass-diode branch(es). Therein, the surge protection method comprises the following steps. A current flowing through at least one of the bypass-diodes of the bypass-diode branch(es) is detected and/or measured by at least one current sensor. The detected current value is compared with a predetermined protection current value. If the detected current value is equal to or larger than the protection current value, at least one switch of the totem pole PFC is switched to a switched state, especially to an off state.

In an embodiment, the surge protection method is carried out by the totem pole PFC with the surge protection circuit according to any one of the foregoing embodiments. In particular, the surge protection method is carried out by the control unit of the totem pole PFC with the surge protection circuit according to any one of the foregoing embodiments.

In an embodiment, the surge protection method comprises a step of holding the switched state, for example, the off state, with a latch for a predetermined latch time duration. Therein, the surge protection method comprises the step of resetting the latch after the predetermined latch time duration.

In an embodiment, the surge protection method resets the latch once the detected current value is equal to or less than the protection current value and the latch time duration has passed.

Further, in an embodiment, all switches of the totem pole PFC are switched to an off state if the detected current value is equal to or larger than the protection current value.

In one preferable embodiment, the method comprises a step of waiting for a predetermined time duration after the totem pole PFC has been shut on before carrying out the switching of the at least one switch to an off state. In an embodiment, the step of waiting is carried out by disconnecting at least one of the comparator and the latch of the surge protection circuit from the totem pole PFC.

In an embodiment, the step of holding the off state for a predetermined latch time duration and the comparing of the detected current value with the predetermined protection current value are alternatingly repeated. In other words, in the surge protection method, once the predetermined latch time duration has passed, the surge protection method (again) compares the detected current value with the predetermined protection current value and, if the detected current value is equal to or less than the protection current value, resets the latch. If in this case the detected current value is (still) not equal to or less than the protection current value, the surge protection method does not reset the latch after the predetermined latch time duration. In an embodiment, in the case of the detected current value not being equal to or less than the protection current value, the surge protection method resets the predetermined latch time and holds the off state (again) for the predetermined latch time duration.

In an embodiment, especially alternatively to the aforementioned re-measuring and comparing of the current value, the surge protection method resets the latch after the predetermined latch duration without re-measuring and comparing the current value. Therein, if the current value is (still) equal to or higher than the protection current value, the surge protection method re-latches the switches to the off state.

In an embodiment, resetting the latch enables the normal operation of the totem pole PFC.

DESCRIPTION OF EMBODIMENTS

In particular,FIGS.1-4show a first embodiment of a totem pole PFC1with a surge protection circuit2. InFIGS.1-3, as shown in the inlet diagram thereof, a surge voltage is introduced by an input voltage source10. InFIG.4, the inlet shows an incorrect polarity changer7switching operation, which also introduces a surge current in the totem pole PFC1.

As can be taken in detail from the circuit diagram ofFIG.1, the totem pole PFC1of this embodiment comprises one bypass-diode branch3with two bypass-diodes4. For the sake of simplicity, the two bypass diodes4shown in the figures will be referred to as elements of a single bypass-diode branch3, with additional coupling or connection points therein (explanation of for example a bypass branch11below) not affecting this wording. The same or similar wording will also be used in reference to switch branches5and the polarity changer branch7.

The totem pole PFC1comprises one or more switch branches5. In the present embodiment, the totem pole PFC1comprises two switch branches5. Each of the switch branches5comprises two switches6.

In addition, the totem pole PFC1comprises a polarity changer branch7, which comprises two switches8(polarity changer switches8). The polarity changer branch7functions to change the polarity of the signal output by the switch branches5to the appropriate DC voltage at a capacity branch12with capacity13and outputs14of the totem pole PFC1.

Furthermore, the totem pole PFC1comprises an input bridge9, which connects the switch branches5respectively with an input voltage source10. The input bridge9includes one inductance branch15per switch branch5, connecting the respective switch branch5with the input voltage source10.

In addition, the totem pole PFC1includes an electromagnetic interference filter16(EMI-filter16).

The totem pole PFC1further includes a bypass branch11, which connects the input bridge9in parallel with the bypass-diodes4of the bypass-diode branch3. As will be explained in detail below, a current flows through the bypass branch11only during startup of the totem pole PFC1, in particular during a charging operation of a capacitor13, and when a surge voltage is introduced by the input voltage source10.

For the following explanation of surge input voltages, it is assumed that the capacitor13has already been charged, especially fully charged. In other words, a predetermined startup time has already elapsed.

As shown by the inlet inFIG.1, the voltage source10, for instance an electrical grid, introduces an AC voltage. In the case shown inFIG.1, the voltage source10introduces a high surge voltage during a positive phase of the (otherwise regular) AC voltage.

In this case, as shown inFIG.1, the polarity changer branch7, via its polarity changer switches8, is in an intended, or correct state, namely the high-side polarity changer switch8being OFF and the low-side polarity changer switch8being ON. In this case, “high-side” and “low-side” refer to the polarity of an output signal voltage at the outputs14of the totem pole PFC1.

In the case of the high surge voltage ofFIG.1, a current, namely a surge current, flows through the bypass branch11. As can be seen in bold inFIG.1, as well as the indication “isurge” therein, the surge current produced by the high surge voltage flows from the voltage source10, through the bypass branch11, the high-side bypass-diode4, the capacitor13, the low-side polarity changer switch8, which is in an ON-state, and via a polarity changer bridge17to the EMI filter16and the voltage source10.

Thereby, a high surge current flows especially through the low-side switch8of the polarity changer branch7, which can cause a breakdown of the device.

To mitigate this, the totem pole PFC1includes a surge protection circuit2, which is shown inFIG.1andFIG.5.

FIG.5shows a detail functional circuitry diagram of a control unit21of the surge protection circuit2of the present embodiment. InFIG.1, a current sensor18of the surge protection circuit2is shown. In the present embodiment, the current sensor18is arranged on the bypass branch11.

In an embodiment, the current sensor18is arranged on a node of the bypass branch11between a first connection point24of the bypass branch11with the input bridge9and a second connection point25of the bypass branch11with the bypass-diode branch3.

The control unit21comprises a comparator19, especially a hardware-based comparator, which compares a current measured by the current sensor18(see alsoFIG.1), with a predetermined protection current value27. The current measured by the current sensor18is shown inFIG.5as “isurge_measure”.

The predetermined protection current value27is a current value, especially an absolute value, with which (and/or above which) damage to and/or breakdown of the totem pole PFC1may be caused by the surge current. This protection current value27is input to the comparator19via a signal processing unit23, and is especially set to a constant value.

In an embodiment, the signal processing unit23is an element of the totem pole PFC1and/or of the surge protection circuit2. In an embodiment, the signal processing unit23is further configured to control the totem pole PFC1, especially during normal operation. Further, in an embodiment, the signal processing unit23is a part of the control unit21or is a unit which is separate from the control unit21. In an embodiment, the signal processing unit23is a digital signal processor.

Further, the control unit21of the surge protection circuit2comprises a latch20, wherein the comparator19inputs a latch signal into the latch20when the current measured by the current sensor18, i.e. when the detected “isurge_measure” current, is equal to or higher than the predetermined protection current value27.

The latch20is further configured to output an OFF signal to, in this embodiment, all switches6,8of the totem pole PFC1. Thereby, all switches6,8, including those of the switch branches5and those of the polarity changer branch7, are switched to an OFF state. In this regard, depending on whether the respective switches are normally-on or normally-off switches, the latch20can actively (via an OFF-signal) switch off the switches or passively (via no ON-signal) switch off the switches6,8.

Thereby, the surge protection circuit2reliably and quickly switches off all switches6,8so as to protect the totem pole PFC1from breakdown during occurrence of a surge voltage.

Further, the signal processing unit23is configured to output a latch reset signal22into the latch20so as to reset the latch20and thereby revert to a normal operation of the totem pole PFC1.

The signal processing unit23is especially configured to output the latch reset signal22after a predetermined latch time duration. After this latch time duration, the signal processing unit23outputs the latch reset signal22. Then, if the current detected by the current sensor18is below the protection current value27, normal operation of the totem pole PFC1resumes. On the other hand, if the current detected by the current sensor18is (still or again) equal to or higher than the protection current value27, the latch20will again latch and switch off all switches6,8.

As explained above, during normal startup operation of the totem pole PFC1, when the capacitor13is being charged, a current will flow through the bypass-diodes4and the current sensor18.

In an embodiment, in order to prevent the latch20from switching off the switches6,8during normal startup operations (i.e. no surge voltage input via the input voltage source), the control unit21and/or the signal processing unit23are configured to set the protection current value27to an appropriate level equal to or above a startup current surge value flowing during the normal startup operation.

In addition or alternatively thereto, the control unit21and/or the signal processing unit23are configured to switch, especially via the latch20, the switches6,8in dependence on a predetermined time duration after switching on the totem pole PFC1. In an embodiment, the predetermined time duration is the time necessary for at least partially, especially fully, charging the capacitor13after initial startup of the totem pole PFC1.

To achieve this, the control unit21and/or the signal processing unit23are configured to disconnect at least one of the comparator19and the latch20for the predetermined time duration. In an embodiment, the signal processing unit23is configured to output a constant latch reset signal to the latch20during the predetermined startup time duration, so as to prevent the latch20from latching.

In an embodiment, the comparator19is a Schmitt-trigger with a lower threshold and a higher threshold. In this case, the lower threshold is set to at least the startup surge current flowing through the bypass-diodes4during startup operation of the totem pole PFC1. For example, this current is roughly 30 A, but may be higher or lower depending on the device characteristics and use-case. Further, the upper threshold is set to the predetermined protection current value. Thereby, the Schmitt-trigger only outputs the latch signal (for instance, a high signal, i.e. “1”) once the upper threshold, i.e. the protection current value, has been reached, and outputs no latch signal (for instance, a low signal, i.e. “0”) once the detected current is below the startup surge current.

In an embodiment, an output of the comparator19is input to the signal processing unit23, which in turn outputs the latch signal to the latch20. In this case, the signal processing unit23outputs the latch signal to the latch20when the comparator19outputs a high signal, and outputs the latch reset signal to the latch20when the comparator19outputs a low signal.

Thereby, the surge protection circuit2suitably and reliably protects the totem pole PFC1from overcurrent caused by the surge voltage input by the input voltage source10. Due to the charged capacitor13, an interruption of output of the totem pole PFC1can be prevented during the surge protection.

FIG.2shows a schematic circuit diagram of the totem pole PFC1with the surge protection circuit2according to the first embodiment of the present disclosure as well as a schematic diagram of an input surge voltage.

As can be taken from the inlet ofFIG.2, in this example, the input voltage source10inputs a negative or low surge voltage during a (normally) positive phase of the input AC voltage. In this case, due to the phase of the input AC voltage being positive before the low surge, the polarity changer branch7is switched as in the case ofFIG.1. Therein, the high-side polarity switch8is OFF, whereas the low-side polarity switch8is ON.

In this case, the generated surge current “isurge” flows from the voltage source10, through the polarity changer bridge17, through the low-side polarity switch8, which is ON, through the low-side bypass-diode4and through the bypass branch11back to the voltage source10. Thereby, especially the low-side polarity switch8can be damaged due to the high surge current flowing therethrough. This is prevented via the surge protection circuit2described above, since the surge current flows through the bypass branch11on which a current sensor18is arranged.

FIG.3shows a further example of a surge voltage. In this case, the input voltage source10inputs a negative or low surge voltage during a (normally) positive phase of the input AC voltage, wherein it abruptly switches to the negative phase of the AC voltage, such that the AC voltage is in the negative phase after the surge voltage.

In this case, due to the initial positive phase of the input AC voltage, the polarity changer branch7is switched as inFIG.1andFIG.2. However, due to the abrupt switch to the negative phase of the input AC voltage, the polarity changer branch7is thereby essentially in a faulty switching configuration. In contrast to the case shown inFIG.3, under normal operation, during the negative phase, the low-side polarity changer switch8should be OFF, whereas the high-side polarity changer switch8should be ON.

Therefore, a surge or short current flows, from the voltage source10through the polarity changer bridge17, through the low-side polarity changer switch8, which is ON, through the low-side bypass-diode4, and through the bypass branch11back to the voltage source10. Thereby, especially the low-side polarity switch8can be damaged due to the high surge current flowing therethrough. This is prevented via the surge protection circuit2described above, since the surge current flows through the bypass branch11on which a current sensor18is arranged.

FIG.4shows a schematic circuit diagram of the totem pole PFC1with the surge protection circuit2according to the first embodiment of the present disclosure as well as a schematic diagram of an input surge voltage and of an input signal for a polarity changer7of the totem pole PFC1.

In the example shown inFIG.4, instead of the input voltage source10inputting a surge voltage, a switching operation of the polarity changer branch7is erroneous.

In the inlet ofFIG.4, the input voltage (bottom of inlet) is shown as well as a control signal for the polarity changer branch7(top of inlet). Therein, a positive signal corresponds to the low-side polarity changer switch8being ON, and a negative signal corresponds to the low-side polarity changer switch8being OFF, with the high-side polarity changer switch8being respectively switched in the opposite manner.

Under normal operation, as also explained above with respect toFIG.1toFIG.3, the high-side polarity changer switch8switches from OFF to ON when the AC input voltage switches from positive to negative, and the low-side polarity changer switch8switches from ON to OFF. In other words, during positive phase of the AC input voltage, the high-side polarity changer switch8should be in the OFF state (as shown inFIG.1toFIG.3, wherein switching is carried out correctly), and the low-side polarity changer switch8should be in the ON state.

Therefore, in this case ofFIG.4, the high-side polarity changer switch8should be in the ON state, due to the negative phase of the input AC voltage being reached. The low-side polarity changer switch8should correspondingly be in the OFF state. Herein, however, the low-side polarity changer switch8switches erroneously back to the ON state. This is shown in the horizontal middle of the top inlet ofFIG.4, in which the switch signal for the low-side polarity changer switch8switches first from the positive signal (corresponding to ON) to the negative signal (corresponding to OFF), which is correct, but subsequently erroneously switches back to the positive signal (corresponding to ON), as shown in the circuit diagram ofFIG.4.

In this case, a surge current flows in the same manner as shown inFIG.3. This is due to the fact that the erroneous switching ofFIG.4is essentially equal to correct switching in the case of a reverse surge voltage being introduced by the AC voltage, which is shown inFIG.3. Thereby, especially the low-side polarity switch8can be damaged due to the high surge current flowing therethrough. This is prevented via the surge protection circuit2described above, since the surge current flows through and is detected on the bypass branch11on which a current sensor18is arranged.

Thus, in any one of the cases described above, as well as corresponding cases of surge voltages and/or faulty switching of the polarity changer7, the surge protection circuit2can protect the switches6,8of the totem pole PFC1from overcurrent and potential breakdown thereof.

FIG.6shows a second preferable embodiment of the totem pole PFC1with the surge protection circuit2.

In particular,FIG.6shows an alternative or additional arrangement of current sensors18as compared withFIG.1toFIG.4. In an embodiment, the second embodiment includes the control unit21and/or the digital signal processor23of the surge protection circuit2described above, especially with reference toFIG.1andFIG.5.

Herein, the surge protection circuit2comprises two additional current sensors18, each detecting a current flowing through one of the high-side and the low-side bypass-diodes4. In the preferable case that the surge protection circuit2comprises only these two additional current sensors18, especially without the current sensor18on the bypass branch11, the surge protection circuit2can further reliably detect and protect from all cases of surge voltage, since the surge current always flows through one of the bypass-diodes4.

In an embodiment, these current sensors18are each connected in series with one bypass-diode4.

As can be taken fromFIG.1toFIG.4andFIG.6, the bypass-diode branch3is connected in parallel with the at least one (in this case exactly two) switch branch(es)5. Thereby, third connection points26of the bypass-diode branch3with the switch branches5are formed. In an embodiment, the current sensors18are arranged on nodes between the second connection point25of the bypass branch11with the bypass-diode branch3and the respective third connection points26. In an embodiment, a first current sensor18is provided on the node between the second connection point25and a low-side third connection point26. Further, a second current sensor18is provided on the node between the second connection point25and a high-side third connection point26.

Furthermore, the control unit21comprises two or more comparators19and/or two or more latches20to account for the plurality of current sensors18.

In addition or alternatively thereto, the control unit21comprises at least one combiner circuit which combines the current value outputs from the different current sensors18, especially to a common signal for the comparator19. In addition or alternatively thereto, the control unit21comprises at least one combiner circuit which combines the comparator19output signals corresponding to multiple comparators19for the latch20, especially to a common signal for the latch20.

The foregoing described configuration of the two current sensors18is to be understood as in addition or alternatively to the current sensor18arranged on the bypass bridge11.

FIG.7shows a schematic block diagram of a surge protection method for a totem pole PFC1according to one embodiment of the present disclosure. In an embodiment, the surge protection method is carried out on/with the totem pole PFC1described above with respect toFIG.1toFIG.6, the case of which will be described below. Therein, any of the foregoing embodiments and examples explaining functional configurations of the totem pole PFC1and/or the surge protection circuit2and/or the control unit21and/or the digital signal processor23are also to be understood as preferable embodiments and examples of the surge protection method for the totem pole PFC1.

In an embodiment, the surge protection method is separate from, especially in addition to, a normal operating method of the PFC1, i.e. a power factor correction method of driving the switches6,8in reaction to a (normal, non surged) input voltage.

The surge protection method comprises a step100of measuring, via at least one current sensor18, a current flowing through at least one of the bypass-diodes4of the bypass-diode branch3.

Further, the surge protection method comprises a step200of comparing the current value detected100by the current sensor(s)18with a predetermined protection current value27. The step200is especially carried out using the comparator19.

The surge protection method additionally comprises a step300, in which, if the detected current is equal to or larger than the protection current value27, at least one switch6,8of the totem pole PFC1is switched to an OFF state. In particular, this switching operation300is carried out only if the detected current is equal to or larger than the protection current value. In an embodiment, this switching operation does not correspond to a (normal) switching operation of the switches6,8for the usual operation, i.e. the power factor correction by the PFC1.

In an embodiment, the switching operation300switches off all switches6,8.

The surge protection method according to the present embodiment further comprises a step400of holding the off state, especially with a latch20, for a predetermined latch time duration.

In an embodiment, the latch time duration is between and including 50 μs and 100 μs.

Additionally, the surge protection method comprises a step500of resetting the latch20, especially after the predetermined latch time duration has passed and when the detected current value is equal to or less than the protection current value27.

For the possible case that the detected current value is not equal to or less than the protection current value27after the predetermined latch duration, i.e. when the latch20has been reset in step500, the surge protection method comprises an additional preferable loop back to step100. Therein, during and/or after resetting500the latch20, the surge protection method again detects or measures (step100) a current via the current sensor(s)18and repeats steps200-500.

In addition, the surge protection method comprises an optional, preferable step600. The step600comprises waiting for a predetermined time duration after the totem pole PFC1has been shut on before carrying out the switching off of any or all switches6,8in reaction to a surge current. This optional step600may be carried out before step100, such that the surge protection method with steps100-500is started only after the predetermined time duration. In addition or alternatively thereto, the optional step600is carried out before the switching step300, after the detection step100and/or after the comparing step200.

As elucidated above with respect toFIG.1, in addition or alternatively to the optional step600, the surge protection method sets the predetermined protection current value27as higher than a (typical) surge current (startup surge current), for example higher than 30 A, so as to only switch off the switch(es)6,8when the surge current is higher than the startup surge-current.

The aforementioned surge protection method is carried out by the surge protection circuit2, in particular by the control unit21and/or preferably by the signal processing unit23.

With the surge protection method of the present embodiment, it is possible to reliably and quickly protect the totem pole PFC1from damages or breakdown resulting from surge voltages and/or surge currents and/or PLDs (power line disturbances).

In addition to the foregoing written explanation of the disclosure, it is explicitly referred toFIGS.1to7, which in detail show features of the disclosure. The figures in detail show especially technical details on the circuitry configuration, particularly parallel and series connections, of the branches and elements described in the foregoing. It should, however, be emphasized that the circuitry configurations shown in the figures, in the technical sense, also encompass their equivalents via so-called “redrawing” or “simplifying” of these circuit schematics.