Temperature-compensated overcurrent detection system

Abstract

An overcurrent detection circuit for a semiconductor switch (10), such as an IGBT or MOSFET, the detection circuit comprising a compensation circuit configured to at least partially compensate for the temperature dependence of an output of a built-in current mirror (12) of the power semiconductor switch (10), the current mirror output (12) being connected to a measurement resistor Rs (20, 20') connected between the current mirror output and a low voltage level of a driver voltage source (40), and an offset V ofst (32) is connected to a first summer input having a second summer input receiving a reference current i to provide a mirror voltage Vs that mirrors the current Ic flowing through the collector-emitter or drain-source junction of the power switch. R a current source (31) configured to provide a reference current i R a current source (31) that provides a reference voltage Ve through the temperature sensitive element (13, 14) at least during a dedicated measurement period, and a comparator (34, 34') that compares the reference voltage Ve or an amplified reference voltage βVd with the mirrored voltage, and the compensation circuit is configured to provide at the output of the comparator a detection signal Ocd that changes state when the mirrored voltage exceeds the reference voltage Ve or the amplified reference voltage βVd.

Description

[Technical Field]

[0001] The present disclosure relates to the field of protection of power semiconductor switches, such as IGBTs or MOSFETs, against overcurrents and damage caused by such overcurrents. Priority is claimed to European Patent Application No. 23305830.4, filed May 25, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] It is known to measure the collector-emitter or drain-source current of a power semiconductor switch in order to detect the occurrence of an overcurrent.

[0003] Monitoring the current through a power semiconductor switch, such as an IGBT or MOSFET, is important to protect the power semiconductor switch from overcurrent or short-circuit (e.g., shoot-through) current. Several means for measuring this current can be found in the literature. Monolithic current mirrors integrated into the power die or chip can provide a scaled value of the collector (or drain) current in a compact and reliable manner and have been implemented in several commercial products. Figure 1 shows an example of a current measurement device for an IGBT 10, with a current mirror output 12 that provides a current signal proportional to the IGBT's output current, e.g., 1 / 100 of the IGBT's output current. The current measurement device includes a sense resistor Rs, a low-pass filter 21, and a reference voltage V corresponding to a current level that should not be exceeded in the IGBT. Ref and a comparator 22 having a

[0004] One of the limitations of built-in current sensors such as the current mirror output 12 is the dependency of the current ratio on the junction temperature Tj, which can reach a sensitivity of around 1% / K. Unless countermeasures are taken, the chip temperature margin, which reduces the ability to precisely detect overcurrents and measure the correct current value, must be taken into account in the product design.

[0005] Compensation circuits are sometimes implemented in such power semiconductor switches or in power modules built with such switches, but such compensation circuits and temperature sensors add cost and complexity to such power semiconductors and power modules. Summary of the Invention

[0006] The present disclosure improves the situation and in particular addresses the problem of finding alternative ways to correct the current sensor sensitivity to the junction temperature Tj.

[0007] The principle used in this disclosure is to combine an integrated temperature-dependent current sensor with a die temperature-sensitive element that has a temperature curve similar to that of the current sensor of the semiconductor switch, in order to compensate for the temperature dependence of the current sensor and obtain a temperature-independent overcurrent detection circuit.

[0008] More precisely, the present disclosure provides an overcurrent detection circuit for a semiconductor switch, such as an IGBT or a MOSFET, the detection circuit comprising a compensation circuit configured to at least partially compensate for the temperature dependence of an integrated current mirror output of the power semiconductor switch, the current mirror output being connected to a measuring resistor Rs and a low voltage level of a driver voltage source to generate a voltage V Rs =i s · Provides Rs and offset V ofst The mirror voltage Vs=V mirrors the current Ic flowing through the collector-emitter or drain-source junction of the power switch. Rs +V ofst a compensation circuit connected to the first adder input and a second adder input providing a reference current i R a current source connected to the temperature sensitive element of the power semiconductor switch, configured to provide a reference current i Rcomprises a current source which flows through the temperature sensitive element during at least a dedicated measurement period to provide a reference voltage Ve, and a comparator which compares the reference voltage Ve or an amplified reference voltage βVd with the mirrored voltage, and a compensation circuit which is configured to provide at the output of the comparator a detection signal Ocd which changes its state when the mirrored voltage exceeds the reference voltage Ve or the amplified reference voltage βVd.

[0009] The following features may optionally be implemented separately or in combination with other features.

[0010] The temperature sensor is the gate resistor Rg of the semiconductor switch, and the reference current i R A current source may be connected to the gate resistor Rg of the power semiconductor switch via the emitter or source of the semiconductor switch so that a current flows through the gate resistor Rg at least during a dedicated measurement period to provide a reference voltage Ve, and a comparator may compare the reference voltage Ve with the mirror voltage Vs.

[0011] The current source generates a reference current i R The command signal V to suppress the flow SI A dedicated period is configured in parallel with the switch to shunt the current source (31) using a command signal line (41) providing a driver voltage V driver The pulse may be comprised of a pulse during the on period of a semiconductor switch driven by the

[0012] The measuring resistor Rs may be connected to a low voltage level of the driver voltage source via a capacitor Cs forming a charging circuit arranged to generate a mirror voltage Vs having a trapezoidal voltage shape with a positive voltage ramp lower than the gate voltage Vg, the charging circuit comprising a reset switch connected to the charging circuit for discharging the capacitor Cs and connected to the command signal line.

[0013] The temperature sensitive element may be a series of diodes Di disposed on the die of the semiconductor switch, and a current source may provide a reference current i to the series of diodes Di. R which provides a reference current iR flows through a series of diodes Di permanently or at least during a dedicated measurement period to provide a reference voltage Vd, and amplifies the reference voltage Vd via an amplifier to provide an amplified reference voltage βVd that is compared with the amplified reference voltage βVd and the mirror voltage in a comparator.

[0014] The detection circuit may comprise a logic gate receiving the detection signal Ocd and a measurement inhibit signal line providing an inhibit signal for inhibiting false detections outside of a dedicated measurement period, the logic gate providing an overcurrent detection logic signal TI-OCD.

[0015] The measurement inhibit signal line may be a command signal line.

[0016] The overcurrent detection circuit may be connected to an overcurrent detection input of the command circuit, the command circuit being configured to switch off the semiconductor switch in the event of an overcurrent.

[0017] The signal line may come from the switching controller for the power switch. [Brief explanation of the drawings]

[0018] Other features, details and advantages are set forth in the following detailed description and drawings.

[0019] [Figure 1] FIG. 1 illustrates an example of a semiconductor power switch incorporating a current sensor and current measurement circuit.

[0020] [Figure 2] 1 is a schematic diagram of a first example implementation of an over-current detection circuit according to the present disclosure;

[0021] [Figure 3] FIG. 10 is a schematic diagram of a second example implementation of an over-current detection circuit according to the present disclosure.

[0022] [Figure 4] FIG. 10 is a schematic diagram of a third example implementation of an over-current detection circuit according to the present disclosure.

[0023] [Figure 5A] FIG. 2 is a schematic diagram of the signals of a first example of realization.

[0024] [Figure 5B] FIG. 10 is a schematic diagram of the signals of a second example of realization.

[0025] [Figure 6] FIG. 10 is a diagram of the resulting curves of the first example of realization. DETAILED DESCRIPTION OF THE INVENTION

[0026] In a power switch like the one shown in Figure 1, the current sensor output i s is a function of the collector current ic and the junction temperature Tj. For some commercially available components, this relationship is well expressed, for example, by the following equation: i s =A·i c +B·Tj·i c , Vs=Rs·i s

[0027] A and B are two parameter characteristics of the built-in current source for a given sense resistor Rs value. Furthermore, the internal gate resistance of the switch is known to vary, for example, according to: Rg=R0+α·Tj where R0 and α are parameter characteristics, and their values ​​may be changed depending on the design.

[0028] FIG. 2 shows a semiconductor switch 10, such as an IGBT, provided with a first example of an overcurrent detection circuit.

[0029] In this example, it is shown that the IGBT may be replaced by a MOSFET, shown at the top of the diagram, with the emitter E of the IGBT replaced by the source of the MOSFET, the collector of the IGBT replaced by the drain of the MOSFET, and the current mirror output linked to the source of the MOSFET instead of the emitter of the IGBT.

[0030] The detection circuit comprises a compensation circuit configured to compensate for the temperature dependence of the built-in current mirror of the power semiconductor switch 10, the current mirror output 12 being connected to a measuring resistor Rs20, which is connected between the current mirror output and the low voltage level of the driver voltage source 40 to generate a voltage V Rs =i s ·Providing Rs.

[0031] Note that for the half-bridge case, the schematic diagram in Figure 2 corresponds to the upper branch switches, and for the lower branch switches, the low voltage level is the low voltage of the lower branch switches.

[0032] The current mirror output and resistor offset V ofst 32 is connected integrally to a summer 33 having a second summer input receiving the mirror voltage Vs=V Rs +V ofst to provide.

[0033] The summer provides a mirror voltage Vs that mirrors the current Ic flowing through the collector-emitter or drain-source junction of the power switch.

[0034] The compensation circuit uses the reference current i R such current source is connected to a temperature sensitive element, which in this example is the gate resistor Rg14 of the power semiconductor switch, and provides a reference current i R flows at least during the dedicated measurement period, as can be seen in correspondence with FIG. 5A.

[0035] The current i flowing through the thermosensitive element 14 in FIG. R provides a reference voltage Ve that is input to a comparator 34 having a voltage Vs at its other input for comparing the reference voltage Ve with the mirrored voltage Vs. In this configuration, the compensation circuit is configured to provide at the output of the comparator 34 a detection signal Ocd that changes state when the mirrored voltage exceeds the reference voltage Ve.

[0036] In this example, the temperature sensitive element is the internal gate resistor Rg14 of the semiconductor switch, and the reference current i R A current source is connected to such gate resistor Rg14 via a power emitter E, or in the case of the illustrated IGBT via a Kelvin emitter output, or via the source of a MOSFET switch as shown above the IGBT in the figure, in such a way that V flows through the gate resistor Rg14 to provide a reference voltage Ve, which is compared to a mirror voltage Vs in comparator 34.

[0037] Reference current i R The measurement period during which is injected into the gate resistor is defined by a switch 37 in parallel with the current source. When switch 37 is open, the current i generated by the current generator 31 R is allowed to flow through the gate resistor. When switch 37 is closed, it shunts current source 31, stopping the current through the resistor outside of the measurement period.

[0038] Switch 37 operates in response to a command signal V shown as curve 150 in FIG. SI 5A, the dedicated period is gated by a command signal line 41 providing a driver voltage V driver V during the on-period of the semiconductor switch driven by SI It consists of pulses.

[0039] current I R is injected through the gate-emitter of the die. It intersects with the internal gate resistor Rg and the input capacitance Ciss. In Figure 5A, the result is V GE This causes a drop 110a in the curve 110, R , and provides a voltage Ve at curve 120 which is fed to comparator 34.

[0040] Current sensor output i S is shown by the solid curve 130 for the emitter-collector current of the switch under overcurrent limit, and by the dotted curve 135 for the emitter-collector current above the overcurrent limit. Such current flows through the voltage VRs across the sense resistor Rs to provide

[0041] The voltage across Rs is the offset voltage V ofst The result of this addition is the voltage Vs in Figure 5A, where the sensed voltage is an image of the sensed current without overcurrent, curve 140, and with overcurrent, curve 145.

[0042] The voltages Ve and Vs are compared in comparator 34, shown as Vs-Ve in FIG. 5A, and an overcurrent is detected if Vs exceeds Vs during the detection period, even if only for a short duration, as shown in curve 175. Such an overcurrent corresponds to the dashed square signal TI-OCD 160 corresponding to the detection period Vsi curve 150. If no overcurrent is present, the detection period curve Vs-Ve remains below zero, as shown in curve 170.

[0043] The circuit described above generates a current i R This allows monitoring for overcurrents only at specific moments when a current is injected through the gate. Before that moment, if no current is injected, the value at the output of the comparator is positive. This can be easily reversed by a combination of the logical AND gate 36. For example, if the output of the comparator is high and the signal in the line 41 controlling the injection is high, an overcurrent is detected. Depending on the type of logic available, other possibilities for logic gate design become possible.

[0044] Starting from the above formula, we can say:

[0045] Below is the first moment of current injection. Ve=Rg·i R

[0046] Assuming that Vs is complemented by an additional offset voltage, we obtain: Vs-Ve=Rs·A·i c +V ofst -R0·i R +Rs·B·Tj·i c -α·Tj i R

[0047] Overcurrent threshold i c =i cMAX The formula to obtain the temperature dependence of is:

number

[0048] i c =i cMAX In this case, Vs-Vg=0 is obtained.

number

[0049] Typical values ​​and results are as follows: [Table 1]

[0050] In the above figures, the intersection of Vs and V occurs at 100 A regardless of junction temperature, as shown by point 180 on the curve (Vs-Ve) plotted against Ic for different temperatures in Figure 6. In such an example, the overcurrent detector detects i C =i cMAX = 100A and is temperature insensitive. The sensitivity of the comparison is > 10mV with an error of 6A, which increases at high temperatures.

[0051] As can be seen, the compensation provided by the disclosed design is very good at the specified currents and is accurate for currents near those specified currents.

[0052] Figure 3 is based on the example of Figure 2, but with the addition of capacitor C S 23 is added between resistor Rs20' and the low voltage level of the circuit to create a trapezoidal voltage shape V with a positive voltage ramp but lower than that of Vg. STherefore, in the case of an overcurrent, the output of the comparator will be high for a longer time. In such a case, the capacitor C S must be discharged, which means V SI This is done by a further switch 38 which can also be triggered by a signal 41 .

[0053] The resulting curves are shown in FIG. 5B, and it can be seen that the Vs of curve 140a and curve 145a without overcurrent ramped during the detection period causes a higher Vs-Ve curve 175a, and when overcurrent is present causes a longer detection 160a in the detection period Vsi 150.

[0054] Figure 4 shows an alternative design in which the temperature is estimated from small diodes Di13 integrated into the die of the semiconductor switch as in Figure 1. A DC current i R When injected, the voltage drop becomes temperature sensitive.

[0055] For a given constant current, the voltage drop across the sensing diode may be expressed as a linear relationship with temperature. VT=V0-α·Tj

[0056] Assuming that this voltage drop can be scaled by a parameter β using a multiplier circuit 39, for example using a voltage divider or an operational amplifier, the following relationship can be obtained: Vs+VT=Rs·A·ic+Vofst+V0·β+Rs·B·Tj·ic-α·Tj·β

[0057] The formula for obtaining the temperature dependence of the overcurrent threshold is:

number

[0058] In such a design, the current source is not connected to an IGBT or MOSFET, but to a diode 13, the voltage Vd at the pin of the diode is amplified in an amplifier 39, and the result βVd is compared with the output Vs as in the design of FIG.

[0059] This design, depending on the presence of the diode Di, simplifies the circuit since the current source 31 does not need to be shunted.

[0060] For the first and second examples, during injection, the presence of Ciss15 increases Ve, pulling down the TI-OCD signal. Thus, if the signal TI-OCD goes high, even for a brief moment, an overcurrent is detected. Low-cost components may be advantageously used to latch this signal and increase the robustness and detectability of the detection.

[0061] In practice, too small a moment can be filtered by the electronic circuit, and V is set to trigger at the overcurrent threshold value. ofst It is necessary to define the value of i. For this purpose, a calibration method can be used. In the ON state, the value i cMAX A current pulse having a voltage V can be applied to the die. The duration of this pulse is typically short (i.e., less than 1 second) to prevent excessive self-heating. An offset voltage V ofst is increased until TI-OCD is detected. ofst The corresponding values ​​of are defined and applied. The results of this calibration mostly depend on the electronic circuit implementation of the TI-OCD. After being performed once, it can be applied to other circuits, even when used with other power modules.

[0062] Therefore, the parameter V ofst Identification is practical and low cost.

[0063] i R The value of is not very sensitive to the circuit implementation. Prior knowledge of the temperature sensitivity of the built-in current sensor and the internal gate resistor is required, which can be easily performed using conventional measurement setups.

[0064] In some cases, continuous monitoring of overcurrent is required. In this case, the temperature dependent overcurrent is monitored by R S 20, 20' directly, i.e., without temperature correction, or at the output of summer 33. If an overcurrent is detected, a temperature-independent overcurrent estimation can be instantly triggered to verify whether the detection is a temperature artifact or a real overcurrent detection.

[0065] Therefore, both continuous overcurrent detection and temperature overcurrent detection can be achieved.

[0066] The present disclosure is not limited to the examples described herein, and by way of example, other temperature dependent components may be used in place of diode 13 if present on the die of the semiconductor switch.

Claims

1. An overcurrent detection circuit for a semiconductor switch (10), such as an IGBT or MOSFET, the detection circuit comprising a compensation circuit configured to at least partially compensate for the temperature dependency of an output of a built-in current mirror (12) of the power semiconductor switch (10), the current mirror output (12) being connected to a measuring resistor Rs (20, 20') and connected between the current mirror output and a low voltage level of a driver voltage source (40) to generate a voltage V Ｒｓ = i ｓ Provides Rs and offset V ｏｆｓｔ (32) and mirrors the current Ic flowing through the collector-emitter or drain-source junction of the power switch, Ｒｓ +V ｏｆｓｔ and a second adder input providing a reference current i Ｒ a current source (31) configured to provide a reference current i Ｒ a current source (31) flowing through the temperature sensitive element (13, 14) at least during a dedicated measurement period to provide a reference voltage Ve; and a comparator (34, 34') comparing the reference voltage Ve or an amplified reference voltage βVd with the mirrored voltage, wherein the compensation circuit is configured to provide at an output of the comparator a detection signal Ocd that changes its state when the mirrored voltage exceeds the reference voltage Ve or the amplified reference voltage βVd.

2. The temperature sensitive element is the gate resistor Rg(14) of the semiconductor switch, and the reference current i Ｒ 2. The overcurrent detection circuit of claim 1, wherein the current source is connected to the gate resistor Rg (14) of the power semiconductor switch via an emitter or a source of the semiconductor switch such that current flows through the gate resistor Rg (14) during at least the dedicated measurement period to provide the reference voltage Ve, and the comparator (34) compares the reference voltage Ve with the mirror voltage Vs.

3. The current source generates the reference current i Ｒ A command signal V ＳＩ and configured in parallel with a switch to shunt the current source (31) using a command signal line (41) providing a driver voltage V ｄｒｉｖｅｒ 3. The overcurrent detection circuit according to claim 2, wherein the overcurrent detection signal is a pulse during an on-period of the semiconductor switch driven by the

4. 4. The overcurrent detection circuit of claim 3, wherein the measuring resistor Rs (20') is connected to the low voltage level of the driver voltage source (40) through a capacitor Cs (23) forming a charging circuit arranged to generate the mirror voltage Vs having a trapezoidal voltage shape with a positive voltage ramp lower than the gate voltage Vg, the charging circuit comprising a reset switch (38) connected to the charging circuit for discharging the capacitor Cs (23) and connected to the command signal line (41).

5. The temperature sensitive element is a series of diodes Di (13) arranged on the die of the semiconductor switch, and the current source (31) supplies the reference current i to the series of diodes Di (13). Ｒ and providing the reference current i Ｒ flows through the series of diodes Di (13) permanently or at least during the dedicated measurement period to provide the reference voltage Vd, and amplifies the reference voltage Vd via the amplifier (39) to provide the amplified reference voltage βVd for comparing the amplified reference voltage βVd with the mirror voltage in the comparator (34').

6. 6. The overcurrent detection circuit of claim 1, further comprising: a logic gate (36) receiving the detection signal Ocd; and a measurement inhibit signal line providing an inhibit signal for inhibiting false detections outside the dedicated measurement period, the logic gate providing an overcurrent detection logic signal TI-OCD.

7. 7. An overcurrent detection circuit according to claim 3, 4 or 5 and claim 6, wherein the measurement inhibit signal line is the command signal line (41).

8. 8. A command circuit for a semiconductor switch comprising the overcurrent detection circuit according to claim 1, wherein the overcurrent detection circuit is connected to an overcurrent detection input of the command circuit, and the command circuit is configured to turn off the semiconductor switch when an overcurrent occurs.

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