Self-powered switching device and method of operating such a device
阅读说明:本技术 自供电开关装置以及操作这种装置的方法 (Self-powered switching device and method of operating such a device ) 是由 G·奥古斯托尼 L·古洛特 T·萨托 于 2018-12-05 设计创作,主要内容包括:本发明涉及一种负载的开关装置(1),该开关装置包括:-两个开关端子(2a、2b);-串联设置在两个开关端子(2a、2b)之间并限定中点(M)的耗尽型高压晶体管(5)和增强型低压晶体管(6);-控制电路(4),其生成低压晶体管(5)的栅极的控制信号(IN),以选择性地将装置(1)置于导通状态或截止状态;-供电电路(7),其包括连接至中点(M)的输入端(7a)和向控制电路(4)提供供电电压(Va)的输出端(7b)。供电电路包括储能电容器(Cm),储能电容器连接至对储能电容器(Cm)充电的常通开关(7c),储能电容器在将开关装置(1)连接至负载时向控制电路(4)提供供电电压(Va)。(The invention relates to a switching device (1) for a load, comprising: -two switch terminals (2a, 2 b); -a depletion high voltage transistor (5) and an enhancement low voltage transistor (6) arranged in series between the two switch terminals (2a, 2b) and defining a mid-point (M); -a control circuit (4) generating a control signal (IN) for the gate of the low voltage transistor (5) to selectively place the device (1) IN a conducting state or IN a blocking state; -a supply circuit (7) comprising an input (7a) connected to the midpoint (M) and an output (7b) providing a supply voltage (Va) to the control circuit (4). The supply circuit comprises a storage capacitor (Cm) connected to an normally-on switch (7c) charging the storage capacitor (Cm), the storage capacitor providing a supply voltage (Va) to the control circuit (4) when connecting the switching device (1) to the load.)
1. A switching device (1) of a load, the switching device comprising:
-two switch terminals (2a, 2 b);
-a depletion high voltage transistor (5) and an enhancement low voltage transistor (6) arranged in series between the two switch terminals (2a, 2b) and defining a mid-point (M);
-a control circuit (4) generating a control signal (IN) of the gate of the low voltage transistor (6) so as to selectively place the device (1) IN a conducting state or IN a blocking state;
-a supply circuit (7) comprising an input (7a) connected to the midpoint (M) and an output (7b) providing a supply voltage (Va) to the control circuit (4);
the power supply circuit includes:
-a storage capacitor (Cm) which establishes the supply voltage (Va) provided to the control circuit (4) when the switching device (1) is connected to the load;
-an always-on switch (7c) arranged between said input (7a) and said storage capacitor (Cm) and adapted to electrically isolate said storage capacitor from said midpoint (M) when said switch is open.
2. The switching device (1) according to the preceding claim, wherein the gate of the high voltage transistor (5) is electrically connected to the source of the low voltage transistor (6).
3. The switching device (1) according to claim 1, wherein the control circuit generates a second control signal for the gate of the high voltage transistor (5).
4. The switching device (1) according to any of the preceding claims, wherein the switch (7c) comprises a depletion low voltage transistor and a diode electrically connected to the input (7a) of the circuit and arranged in series with the depletion low voltage transistor.
5. A switching device according to any one of claims 1 to 3, wherein the switch (7c) comprises a first depletion mode low voltage transistor and a second depletion mode low voltage transistor connected in series.
6. The switching device (1) according to any of the preceding claims, wherein the supply circuit (7) further comprises a circuit for regulating the supply voltage.
7. The switching device (1) according to any one of the preceding claims, wherein the control circuit (4) is configured to generate a deactivation signal (DIS) for the switch (7c) such that the first control signal is generated to place the device (1) in a conductive state.
8. The switching device (1) according to any one of the preceding claims, wherein the high voltage transistor (5) has a threshold voltage (Vt') greater in absolute value than the supply voltage (Va) sufficient to operate the control device (4).
9. The switching device (1) according to any one of the preceding claims, wherein the control circuit (4) is configured to generate a deactivation signal (DIS) for the switch (7c) when the supply voltage (Va) exceeds a threshold voltage (Vamax).
10. The switching device (1) according to any one of the preceding claims, wherein the control circuit (4) is configured to place the device in a protected configuration when the supply voltage (Va) falls below a minimum threshold voltage (Vamin).
11. A method of controlling a switching device (1) according to any one of the preceding claims, the method comprising:
-a cut-off phase, in which the control circuit (4) generates a control signal that turns on the low-voltage transistor (6);
-a conduction phase in which the control circuit (4) generates a control signal that closes the low voltage transistor (6);
the method comprises the following steps: the control circuit (4) generates a deactivation signal (DIS) for opening a switch (7c) of the supply circuit (7) at least during the on-phase of the switching device (1).
Technical Field
The present invention relates to a switching device for an electrical load. More specifically, the invention is directed to a switching device comprising a control circuit and a supply circuit for the control circuit.
Background
Load switching devices that combine a depletion mode high voltage transistor and an enhancement mode low voltage transistor in series are known in the art. The transistor is controlled to selectively place the device in a conducting, on state or in an off state depending on the value of an external switching signal applied to a pin of the device. The switching device is intended to be integrated into a system in which it is electrically connected to a load consisting of a power supply circuit and a generator and makes it possible to transfer electric power from the generator to the power supply circuit during a conduction period. The voltage provided by the generator is typically high, e.g., 400V, 600V or higher.
The two transistors may be mounted in a cascode fashion, in which case the source of the low voltage transistor is electrically connected to the gate of the high voltage transistor. The control circuit of the device may selectively place the device in an on state or an off state by a control signal applied to the gate of the low voltage transistor.
The two transistors may alternatively be mounted in a cascade, in which case the control circuit generates first and second control signals which are applied to the gates of the low and high voltage transistors, respectively, to selectively place the device in an on or off state.
In both cases, the switching device is normally open; in other words, the switching device is in an inactive mode, off-state, when the device is without power, in particular when the control circuit is without power. This avoids prematurely switching the device on to the load, potentially leading to serious safety issues.
In addition to the function of controlling the conduction state of the switching device, the control circuit ensures a good function of the device. If a fault or event that is likely to cause such a fault is detected, the control circuit generates a control signal to place the device in an inactive mode in which the device is switched off. This is particularly true if the operating temperature of the device is too high or if a particular voltage deviates from the associated set point voltage.
The control circuit is implemented in an integrated form, for example in the form of a programmable logic gate system, in the form of discrete components or in the form of a suitably programmed microcontroller. In all cases, the control circuit sequences the control signals appropriately according to the value of the external switching signal and the internal state of the device.
The control circuit must be supplied with power, and for this purpose the device is usually provided with a supply pin, so that a supply voltage from a dedicated circuit of the system is applied to the control circuit. The circuit implements high voltage components, such as diodes, inductors and/or capacitors, to draw power from the switched load of the system and process the power to provide a stable supply voltage with a relatively low magnitude (a few volts) to the device. This type of external power supply circuit is complex and expensive to implement.
EP0585788 discloses a switching device for an electrical load comprising a control circuit supplied at low voltage by the secondary winding of an external transformer. The starter circuit makes it possible to initiate the start-up of the control circuit and the power supply during operation of the switching device which requires a voltage provided by the secondary of the transformer.
Some prior art documents provide an auxiliary internal power supply for a switching device. This is particularly the case in US 9590507.
Disclosure of Invention
The present invention relates to an alternative solution to the prior art solutions presented. The invention relates in particular to a switching device for a load, comprising: two switch terminals; a depletion-mode high-voltage transistor and an enhancement-mode low-voltage transistor arranged in series between the two switch terminals and defining a midpoint; a control circuit that generates a control signal for the gate of the low-voltage transistor to selectively place the switching device in an on state or an off state; and a supply circuit including an input connected to the midpoint and an output providing a supply voltage to the control circuit.
According to the invention, the supply circuit comprises an energy storage capacitor which establishes the supply voltage to the control circuit when the switching device is connected to the load.
According to the invention, the supply circuit further comprises an always-on switch arranged between the input and the energy storage capacitor and adapted to electrically isolate the energy storage capacitor from the midpoint when the switch is open.
According to the invention, the energy storage capacitor establishes the supply voltage to the control circuit when the switching device is connected to the load, the energy storage capacitor being electrically isolated from the midpoint when the switch is open.
Thereby a self-powering circuit of the control circuit is provided and no power supply circuit external to the device has to be provided.
Other advantageous, non-limiting features according to the invention, taken alone or in any technically feasible combination:
-the gate of the high voltage transistor is electrically connected to the source of the low voltage transistor;
-the control circuit generates a second control signal for the gate of the low voltage transistor;
-the switch comprises a depletion low voltage transistor and a diode electrically connected to an input of the circuit and arranged in series with the depletion low voltage transistor;
-the switch comprises a first depletion mode low voltage transistor and a second depletion mode low voltage transistor connected in series;
-the supply circuit further comprises a circuit for regulating a supply voltage;
-the control circuit is configured to generate a deactivation signal of the switch such that the first control signal for placing the apparatus in a conductive state is generated;
-the high voltage transistor has a threshold voltage with an absolute value greater than the supply voltage, which is sufficient to make the control means active;
-the control circuit is configured to control the supply voltage (V) to be at a predetermined voltage levela) Generating a deactivation signal for the switch when a threshold voltage is exceeded;
-the control circuit is configured to place the apparatus in a protected configuration when the supply voltage falls below a minimum threshold voltage.
The invention also relates to a method for controlling such a switching device, comprising the following steps:
-a turn-off phase during which the control circuit generates a control signal to turn on the low voltage transistor;
-a conducting phase during which the control circuit generates a control signal to close the low voltage transistor.
According to the invention, the method comprises the following steps: the control circuit generates a deactivation signal to open the switch of the supply circuit at least during the on-phase of the switching device.
Drawings
Further features and advantages of the invention will become apparent from the following detailed description of the invention, made with reference to the accompanying drawings, in which:
figure 1 shows an exemplary embodiment of a switching device according to the present invention;
figure 2 is a timing diagram of the voltages that occur during operation of the device according to the invention;
figures 3a to 3d schematically show the state of the device according to the invention in different steps of its operation;
figure 4 shows a modified version of the switching device 1 according to the invention;
fig. 5 shows an example embodiment of a circuit for regulating a supply voltage;
fig. 6 shows a first embodiment of the supply circuit according to the invention;
fig. 7A to 7D show four further embodiments of the supply circuit according to the invention.
Detailed Description
Fig. 1 shows an exemplary embodiment of a switching device 1 according to the present invention.
The switching device comprises two switching terminals 2a, 2b which (as indicated by the dashed lines in the figure) can be connected to a load P and a generator G representing a power supply circuit connected to the switching device 1. Voltage V of generator GBusMay be quite large, e.g., 400V, 600V or higher, and the current that may flow in the power device may be high, e.g., greater than 1A.
As is known, the switching device 1 makes it possible to selectively apply the voltage of the generator G to the load P according to a switching signal COM, which can be applied to a pin of the device to be supplied to the
The switching device 1 comprises a depletion mode high voltage transistor 5.
A "high voltage transistor" refers to a transistor that includes a drain, a source, and a gate, and a low amplitude voltage (on the order of a few volts) applied to the gate can electrically turn on or off the connection between the drain and the source. In the off state, the voltage appearing between the drain and the source may be of high amplitude (e.g., 400V, 600V, or higher) without damaging the transistor.
Depletion transistors have a negative voltage threshold (typically between-8V and-5V in the context of the present invention). Therefore, the voltage between the gate and the source must be negative and lower than the threshold voltage to turn off the transistor.
The depletion high voltage transistor 5 may be, for example, a GaN or SiC based HEMT transistor. This type of transistor has an avalanche voltage of high amplitude (in other words, the maximum voltage that can be applied between the drain and the source of the transistor, which can be the breakdown voltage, without damaging the transistor) that is chosen to be greater than the voltage of the generator of the power supply circuit, for example greater than 400V or 600V.
The switching device 1 further comprises an enhancement mode low voltage transistor 6 having a drain, a source and a gate.
The enhancement transistor has a positive threshold voltage. Therefore, the voltage between the gate and the source must be positive and greater than the threshold voltage to turn on the transistor.
The low voltage transistor 6 may be a silicon based MOSFET transistor. The avalanche voltage of the low voltage transistor is lower than the avalanche voltage of the high voltage transistor. The avalanche voltage of the low voltage transistor may be about 30V, for example.
A low voltage transistor 6 and a high voltage transistor 5 are arranged in series between the two switch terminals 2a, 2 b. Thus, the drain of the high-voltage transistor is connected to one of the two terminals, and the source of the low-voltage transistor is connected to the other of the two terminals. The source of the high voltage transistor 5 is connected to the drain of the low voltage transistor 6 at a midpoint M. In the example shown, the first terminal 2a is connected to a load and the second terminal 2b is connected to the electrical ground of the system, but the invention is in no way limited to this particular configuration.
In the example shown, the low-voltage transistor 6 and the high-voltage transistor 5 are mounted in a cascode manner; in other words, the source of the low voltage transistor, here connected to the system ground, is also electrically connected to the gate of the high voltage transistor 5.
In this configuration, the on-state or off-state of the device 1 is determined by the voltage applied to the gate of the low voltage transistor 6. A voltage higher than the threshold voltage Vt of the transistor turns the transistor on, and a voltage lower than the threshold voltage Vt turns the transistor off.
The switching device 1 of fig. 1 is further described, which switching device also comprises a
As already seen, the
The
During operation of the device, the voltage Vm at the midpoint M varies between the electrical ground of the system when the device is on and the avalanche voltage of the low voltage transistor when the device is off.
The
The "normally on" function of the
The
As is well known, the
In the first embodiment of the present invention shown in fig. 6, the
The presence of this type of diode has the advantage of making it possible to avoid the storage capacitor Cm discharging into one of the high-voltage transistor 5 and the low-voltage transistor 6 and thus conserving the charge, if the voltage of the mid-point M has dropped below the supply voltage available at the terminals of the storage capacitor Cm.
In this case, the series connection of the diode and the depletion-mode low-voltage transistor makes it possible to electrically isolate the storage capacitor Cm from the midpoint.
The depletion mode low voltage transistor may be a P-channel transistor. In this case, the drain of the depletion type low-voltage transistor is connected to the terminal of the storage capacitor Cm, the source of the depletion type low-voltage transistor is connected to the diode, and the gate of the depletion type low-voltage transistor is connected to the
Alternatively, the depletion type low-voltage transistor may be an N-channel transistor. In this case, the source of the depletion type low-voltage transistor is connected to the terminal of the storage capacitor Cm, the drain of the depletion type low-voltage transistor is connected to the diode, and the gate of the depletion type low-voltage transistor is connected to the
Fig. 7A to 7D show four further embodiments according to the invention. In these four embodiments, the diode and the depletion type low-voltage transistor connected in series are replaced with the first depletion type low-voltage transistor and the second depletion type low-voltage transistor connected in series.
In one embodiment, the first depletion type low voltage transistor and the second depletion type low voltage transistor are two N-channel transistors or two P-channel transistors, and the drains of the respective transistors are interconnected or the sources of the respective transistors are interconnected.
As shown in fig. 7A, the first depletion type low voltage transistor and the second depletion type low voltage transistor may be two P-channel transistors. In this case, the body diode of each transistor may cause current to flow from the source to the drain, so that the two transistors should be placed back-to-back. Therefore, when the two depletion type low-voltage transistors are in a conducting state (in other words, in a default state of the two depletion type low-voltage transistors), a current flows from the midpoint M to the storage capacitor Cm. When the two depletion type low-voltage transistors are in an off state, the body diodes of the two depletion type low-voltage transistors are arranged in opposite directions, and current cannot flow in any direction, so that the storage capacitor Cm is isolated from the midpoint M.
Alternatively, as shown in fig. 7B, the first depletion type low-voltage transistor and the second depletion type low-voltage transistor may be two N-channel transistors. In this case, the body diode of each transistor may cause current to flow from the drain to the source, and the two transistors should likewise be placed back-to-back. Therefore, when the two depletion type low-voltage transistors are in the on state, a current flows from the midpoint M to the storage capacitor Cm. When the two depletion type low-voltage transistors are in an off state, the body diodes of the two depletion type low-voltage transistors are arranged in opposite directions, and current cannot flow in any direction, so that the energy storage capacitor Cm is isolated from the midpoint M.
The term "back-to-back" refers to either the drain interconnect of each transistor or the source interconnect of each transistor. Thus, in all these configurations, the drain of the first transistor is connected to the midpoint, the source of the first transistor is connected to the source of the second transistor, and the drain of the second transistor is connected to the terminal of the storage capacitor Cm.
Naturally, the terminal of the first transistor and the terminal of the second transistor may be reversed in the following manner: the source of the first transistor is connected to the midpoint, the drain of the first transistor is connected to the drain of the second transistor, and the source of the second transistor is connected to the terminal of the storage capacitor Cm.
In another embodiment, the first depletion type low voltage transistor and the second depletion type low voltage transistor are an N-channel transistor and a P-channel transistor or a P-channel transistor and an N-channel transistor, respectively, and the source of the first transistor is connected to the drain of the second transistor.
As shown in fig. 7C, the first transistor may be an N-channel transistor, and the second transistor may be a P-channel transistor. In this case, accordingly, the body diode of the N-channel transistor flows current from the source to the drain, and the body diode of the P-channel transistor flows current from the drain to the source, so that these two transistors should be arranged in series, meaning that the source of the first transistor is connected to the drain of the second transistor. Therefore, when the two depletion type low-voltage transistors are in the on state, a current flows from the midpoint M to the storage capacitor Cm. When the two depletion type low-voltage transistors are in an off state, the body diodes of the two depletion type low-voltage transistors are arranged in opposite directions, and current cannot flow in any direction, so that the energy storage capacitor Cm is isolated from the midpoint M.
Alternatively, as shown in fig. 7D, the first transistor may be a P-channel transistor and the second transistor may be an N-channel transistor. In this case, accordingly, the body diode of the P-channel transistor flows current from the drain to the source and the body diode of the N-channel transistor flows current from the source to the drain, so that these two transistors should be arranged in series, meaning that the source of the first transistor is connected to the drain of the second transistor. Therefore, when the two depletion type low-voltage transistors are in the on state, a current flows from the midpoint M to the storage capacitor Cm. When the two depletion type low-voltage transistors are in an off state, the body diodes of the two depletion type low-voltage transistors are arranged in opposite directions, and current cannot flow in any direction, so that the energy storage capacitor Cm is isolated from the midpoint M.
Naturally, the terminal of the first transistor and the terminal of the second transistor may be reversed in the following manner: the source of the first transistor is connected to the midpoint M, the drain of the first transistor is connected to the source of the second transistor, and the drain of the second transistor is connected to the terminal of the energy storage capacitor Cm.
Regardless of the embodiment chosen, it is particularly advantageous thermally that the two transistors forming the
Closing both transistors simultaneously makes it possible to force a current to flow through the channel of each of the two transistors, thereby short-circuiting the body diodes of the two transistors. This type of short circuit may avoid heat dissipation through the body diode.
Advantageously, in order to synchronize the on or off state of each of said transistors, the
Regardless of the configuration chosen, the
By way of illustration, fig. 2 is a chronogram of the voltages gradually obtained by the device 1 during its operation.
Very generally, the
a cut-off phase, IN which the
A conducting (or conducting) phase, in which the
Returning to the description of fig. 2, time t0 is defined as the time when the device 1 is physically connected to the load of the device. Therefore, at this time t0, the storage capacitor Cm is completely discharged and the supply voltage Va is zero. The
Fig. 3a schematically shows the state of the device at the start time t 0. The
When the supply voltage Va is sufficient, for example when it reaches the nominal supply voltage of the control circuit 4 (which may be 5V for example), the
Naturally, the threshold voltage Vt' of the high-voltage transistor is chosen (in absolute value) to be greater than the supply voltage Va sufficient to operate the control means 4.
The voltage Vm at the midpoint is equal to the supply voltage. Therefore, the voltage gradually increases with the supply voltage. t0 'indicates the moment at which the development of the midpoint voltage changes such that the control voltage Vgs (corresponding to the opposite midpoint voltage Vm) passes below the threshold voltage Vt' of the high-voltage transistor. From this time t0', the high-voltage transistor 5 is switched on and the voltage VDM applied between the terminals of this high-voltage transistor is approximately built up at the voltage of the generator VBus. However, the leakage current through this transistor causes the voltage to continue to increase from the midpoint up to the avalanche voltage VBR of the low voltage transistor 6. Fig. 3b shows a schematic state of the device 1 from this time t 0'.
In order to avoid continuing to charge the storage capacitor Vm up to the avalanche voltage VBR of the low voltage transistor 6, which may be too large, it can be set in such a way that the supply voltage Va is sufficient: the
For example, if the
If the
Alternatively and advantageously, the command DIS to open the switch may correspond to providing a signal to a control box CTRL configured to regulate the voltage level provided to the gate and at the same time to put the depletion type low voltage transistor in the off-state.
As already described above, this simultaneity makes it possible to avoid heat dissipation across the body diode of one transistor placed in the off-state when the other transistor is in the on-state.
At time t2,
The control means 4 generate a control signal IN for the gate of the low voltage transistor 6 to place the device 1 IN a conductive state for a period of time lasting t3, as shown IN fig. 2 and 3 c. Throughout this period between times t2 and t3, the
At time t3,
Shortly after this time t3, at a time t4 the control means 4 switch the deactivation signal DIS of the
At time t4, the device returns to a state similar to that at time t0 or t 0'. The on-phase and the off-phase of the device can therefore follow each other (according to the state of the switching signal COM) and reproduce the cycle that has just been elucidated.
In a supplementary explanation of the operation of the device 1 according to the invention, fig. 2 shows the following situation: at time t5, the deactivation signal DIS of the
It can thus be seen in fig. 2 that starting at time t5, opening
In a variant that is not shown, it is likewise possible to provide: the control circuit is configured to detect the supply voltage Va passing below a predetermined minimum threshold Vamin. Below this threshold supply voltage, the normal operation of the control circuit is no longer guaranteed. Further, the control circuit is configured in the following manner: this detection causes the device 1 to enter a protected configuration. This may involve, for example, keeping the control signal for the gate of the low-voltage transistor 6 in an open state or switching to an open state as soon as the supply voltage falls below this minimum threshold Vamin. The device 1 is thus placed in a protected off state.
Fig. 4 shows a modified form of the switching device 1 according to the invention, the high-voltage transistor 5 and the low-voltage transistor 6 being omitted for greater clarity.
In addition to the components already described in connection with the apparatus of fig. 1, the
It should be noted that the voltage appearing at the terminals of the storage capacitor Cm is still supplied to the
As is well known and as shown in fig. 5, the regulation circuit LDO generally comprises a transistor, the gate of which is connected to the output of a reference voltage comparator (such as a bandgap voltage) and has a voltage representative of the voltage appearing at the terminal of the regulation capacitor CR. The comparator turns the transistor on or off as required to transfer the charge of the storage capacitor Cm to the adjustment capacitor CR in the following manner: the voltage Va at the terminals of the regulating capacitor CR is substantially equal to a setpoint voltage sufficient to supply the
Instead of integrating this regulating function of the supply voltage Va into the
In general, the switching device according to the invention thus makes it possible to accumulate charges in the storage capacitor Cm of the
The present invention therefore describes a switching device comprising an internal power supply circuit which makes it possible to supply power to the device without any external power supply.
It should be noted that the supply circuit is not exposed to small voltages (corresponding to the avalanche voltage VBR of the low voltage transistor 6) and can thus be composed of components that are easy to manufacture or provide, and thus are inexpensive. Therefore, the power supply circuit can be replaced from the power supply outside the device at low cost.
Naturally, the invention is not limited to the described implementation and various variant embodiments can be applied to it without departing from the scope of the invention as defined by the claims.
Thus, although the low voltage transistor 6 and the low voltage transistor 5 have been shown connected in a cascode configuration, the switching device 1 according to the present invention may be implemented in a cascade configuration. IN this configuration, the gate of the low-voltage transistor 5 is not connected to the source of the low-voltage transistor 6, and therefore, the
The switching device according to the invention may be used in a power conversion system in a half-bridge configuration. As is known, this type of system comprises a high switch and a low switch (each of which may be according to the invention) connected to two connection terminals. One of these terminals is connected to a high continuous voltage source and the other terminal is connected to ground. The two switches define a midpoint of connection to the resonant load.
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