JP2020120418A - Switching circuit - Google Patents

Abstract

To provide a switching circuit capable of solving at least one problem generated in the switching circuit.SOLUTION: In a switching circuit 200, a low-side transistor Mis provided between a switching line 204 and a reference line 206. A low side driver 222 drives the low-side transistor M. A first charge pump 230 performs charge pump operation synchronously with the low side driver 222 and supplies a first voltage less than a reference voltage of the reference line 206 to a lower-side power supply terminal 224 of the low side driver 222 during a period in which at least the low side driver 222 should be turned off.SELECTED DRAWING: Figure 2

Description

The present invention relates to switching circuits.

The DC/DC converter, AC/DC converter, motor driver, and inverter circuit include a switching circuit that receives a DC voltage and generates a rectangular voltage. FIG. 1 is a circuit diagram of a switching circuit. The switching circuit 2R includes a high-side transistor M _H and a low-side transistor M _L which are power transistors, a high-side driver 12 and a low-side driver 14, and a controller 16. The high-side driver 12 and the low-side driver 14 drive the high-side transistor M _H and the low-side transistor M _L according to the pulse signals S _H and S _L from the controller 16.

In recent years, as a power transistor, development of a compound semiconductor device such as SiC (silicon carbide) or GaN (gallium nitride), which has higher power, higher efficiency, and smaller size than a conventional silicon MOSFET (Metal Oxide Semiconductor Field Effect Transistor), has been developed. It is being advanced.

A normally-on type (also called a depletion type) is the mainstream of a compound semiconductor (especially GaN) power transistor because it is difficult to manufacture a normally-off type because of its device structure. Although normally-off type (enhancement type) devices are under development, the threshold voltage V _GS(th) between the gate and the source remains at 2 V or less, and it is practical in a system where the input voltage exceeds 100 V. It can be regarded as a normally-on device.

(First issue)
In order to reliably turn off the normally-on type power transistor, it is necessary to apply a voltage lower than its source potential to its gate.

Consider a state in which the switching circuit 2R outputs a low level, that is, 0 V (low output state). The low output state, the gate of the high side transistor M _H, a negative gate voltage V _GH below its source voltage (i.e. the switching voltage V _{SW =} 0V) is applied, it is necessary to turn off the high-side transistor M _H.

Therefore, it is necessary to supply the lower power supply terminal 13 of the high-side driver 12 with a power supply voltage that is lower than the source voltage V _SW by a predetermined voltage, and therefore the insulating power supply 20 is required. The insulated power supply 20 has a complicated circuit configuration, which causes a cost increase.

(Second task)
Regardless of whether the high-side transistor M _H or the low-side transistor M _L is normally on, a parasitic gate drain capacitance Cgd exists between the gate drains thereof. Switching circuit 2R is high level, i.e. the state (high output state) that outputs the V _IN, the low-side transistor M capacitive load current to flow through the gate-drain capacitance Cgd of the _L, the gate of the low side transistor M _L to be off When the capacitance is charged and its potential rises, the low-side transistor M _L may turn on unintentionally and cause a shoot-through current. The same problem may occur in the high side transistor M _H.

As a measure against the second problem, an approach of inserting a gate resistor to reduce the slew rate (slope of the gate voltage) or reducing the on-resistance of the power transistor to suppress the rise of the gate voltage can be considered. , It is necessary to sacrifice some characteristics of the switching circuit.

Note that the problems described here should not be recognized as general technical recognition by those skilled in the art.

The present invention has been made in such a situation, and one of the exemplary objects of an aspect thereof is to provide a switching circuit capable of solving at least one of the problems described above.

One aspect of the present invention relates to a switching circuit. The switching circuit includes a low-side transistor provided between the switching line and the reference line, a low-side driver that drives the low-side transistor, a charge pump operation in synchronization with the low-side driver, and at least in a period when the low-side driver should be turned off, A first charge pump that supplies a first voltage lower than the reference voltage of the reference line to a lower power supply terminal of the low-side driver.

The output voltage of the first charge pump may have a voltage level higher than the first voltage during the period when the low-side transistor should be turned on.

The first charge pump has a first capacitor whose one end is connected to the lower power supply terminal of the low-side driver, and a positive power supply voltage at a high level and a reference voltage at the other end of the first capacitor in synchronization with the low-side driver. It may include a first sub-driver that applies a first charge pump signal that is at a low level, and a first rectifying element that is provided between one end of the first capacitor and the reference line.

The positive power supply voltage may be common to the voltage of the upper power supply terminal of the low side driver. The positive power supply voltage may be a voltage different from the voltage of the upper power supply terminal of the low side driver.

The low side transistor may be a normally-on type device.

The switching circuit has a high side transistor provided between the input line and the switching line, a high side driver for driving the high side transistor, and a charge pump operation in synchronization with the high side driver, and at least the high side transistor is turned off. Power supply, a second charge pump that supplies a second voltage lower than the switching voltage of the switching line to the lower power supply terminal of the high side driver, and a third voltage higher than the switching voltage to the upper power supply terminal of the high side driver. The bootstrap circuit for supplying may further be provided.

The output voltage of the second charge pump may have a voltage level higher than the second voltage during the period when the high side transistor should be turned on.

The second charge pump has a second capacitor, one end of which is connected to the lower power supply terminal of the high side driver, and the other end of the second capacitor, the third voltage being at a high level and the second capacitor being synchronized with the high side driver. A second sub-driver that applies a second charge pump signal that sets the voltage to a low level and a second rectifying element that is provided between one end of the second capacitor and the switching line may be included.

The high side transistor may be a normally-on type device.

The switching circuit may be integrated on one semiconductor substrate. "Integrated integration" includes the case where all the components of the circuit are formed on the semiconductor substrate and the case where the main components of the circuit are integrally integrated. A resistor or a capacitor may be provided outside the semiconductor substrate. By integrating the circuit on one chip, the circuit area can be reduced and the characteristics of the circuit element can be kept uniform.

Parts of the switching circuit other than the high-side transistor and the low-side transistor may be integrated on one semiconductor substrate, and the high-side transistor and the low-side transistor may be discrete parts or power modules.

It should be noted that any combination of the above constituent elements and those in which the constituent elements and expressions of the present invention are mutually replaced among methods, devices, systems, etc. are also effective as an aspect of the present invention.

According to an aspect of the present invention, at least one of the above problems can be solved.

It is a circuit diagram of a switching circuit. It is a circuit diagram of a switching circuit according to the first embodiment. FIG. 3 is an operation waveform diagram of the switching circuit of FIG. 2. It is a circuit diagram of a switching circuit according to a second embodiment. FIG. 5 is an operation waveform diagram of the switching circuit of FIG. 4. It is a circuit diagram of a switching circuit according to a third embodiment. FIG. 7 is an operation waveform diagram of the switching circuit of FIG. 6. FIG. 8A to FIG. 8D are diagrams showing applications of the switching circuit.

Hereinafter, the present invention will be described based on preferred embodiments with reference to the drawings. The same or equivalent constituent elements, members, and processes shown in each drawing are denoted by the same reference numerals, and duplicated description will be omitted as appropriate. Further, the embodiments are merely examples and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In the present specification, the “state in which the member A is connected to the member B” means that the members A and B are electrically connected to each other in addition to the case where the members A and B are physically directly connected. It also includes a case where they are indirectly connected through other members that do not substantially affect the general connection state or do not impair the functions and effects achieved by their connection.

Similarly, "the state in which the member C is provided between the member A and the member B" means that the members A and C or the members B and C are directly connected and their electrical It also includes a case where they are indirectly connected through other members that do not substantially affect the general connection state or do not impair the functions and effects achieved by their connection.

(First embodiment)
FIG. 2 is a circuit diagram of the switching circuit 200 according to the first embodiment. The switching circuit 200 is configured to switch the electrical state of the switching line 204 in two states.

In one embodiment, the switching circuit 200 may be a part of a circuit including a high side transistor and a low side transistor, like the switching circuit 2R in FIG. In this case, the high side transistor M _H may be connected to the switching line 204.

In one embodiment, the switching circuit 200 may be an open drain output circuit. In this case, a load (not shown) is connected instead of the high side transistor.

The switching circuit 200 includes an output stage 210 and a drive stage 220. The output stage 210 includes a low side transistor M _L provided between the switching line 204 and the reference line 206. In this embodiment, the reference line 206 is grounded and the reference voltage is the ground voltage V _GND .

The switching circuit 200 may be a functional IC integrated on one semiconductor substrate. The low side transistor M _L may be a discrete component or a power module, in which case the output stage 210 is an IC and the low side transistor M _L is externally attached to the IC chip. The capacitor used for the charge pump may be integrated in the IC chip or may be an external chip component.

The positive power supply voltage V _CC is supplied to the power supply line 208 of the driving stage 220. The driving stage 220 includes a low side driver 222, a first charge pump 230 and a first level shifter 228. The low side driver 222 drives the low side transistor M _L. The positive power supply voltage V _CC is supplied to the upper power supply terminal 226 of the low side driver 222.

The first charge pump 230 performs a charge pump operation (switching) in synchronization with the low-side driver 222, and at least during a period when the low-side driver 222 should be turned off, the lower-side power supply terminal 224 of the low-side driver 222 is supplied with the reference voltage of the reference line 206. The first voltage V _CPOUTL lower than V _GND (0V) is supplied.

The first charge pump 230 includes a first capacitor C ₁₁ , a first sub driver 232, and a first rectifying element D ₁₁ . One end of the first capacitor C ₁₁ is connected to the lower power supply terminal 224 of the low side driver 222. The first sub-driver 232 synchronizes with the low-side driver 222, and at the other end of the first capacitor C ₁₁ , the first charge pump signal V that sets the positive power supply voltage V _CC to high level and the reference voltage V _GND to low level. _{Apply CPL} . The first rectifying element D ₁₁ is a diode provided such that the cathode is on the reference line 206 side and the anode is on the lower power supply terminal 224 side of the low-side driver 222. A Zener diode may be used as the first rectifying element D ₁₁ .

The first level shifter 228 receives the low side pulse S _L generated by a controller (not shown). The first level shifter 228 outputs a low side pulse S _L that sets the power supply voltage V _CC to a high level and a reference voltage V _GND to a low level, and a low side pulse S _L ′ that _{sets the} power supply voltage V _CC to a high level and a voltage V _CPOUTL to a low level. Level shift to.

The above is the configuration of the switching circuit 200. Next, the operation will be described. FIG. 3 is an operation waveform diagram of the switching circuit 200 of FIG.

First, the operation of the first charge pump 230 will be described.

When the low-side pulse S _L becomes high level in the low output period T _L , the first sub-driver 232 applies V _CPL =V _CC to one end of the first capacitor C ₁₁ . When the forward voltage of the first rectifying element _{D 11} to Vf, is across the first capacitor _{C 11,} V CC -Vf is applied, the first capacitor _{C 11} is charged.

When the low-side pulse S _L becomes low level during the high output period T _H , the output V _CPL of the first sub-driver 232, that is, one end of the first capacitor C ₁₁ becomes low level V _GND . Since the electric charge of the first capacitor C ₁₁ is stored, in other words, the voltage across the first capacitor C ₁₁ (V _CC −Vf) is maintained, the voltage V _{CPOUTL at} the other end of the first capacitor C ₁₁ is V _CPOUTL =−(V _CC -Vf).

Thus, by the first charge pump 230, the low side transistor _{M L} period shall be deactivated, the lower the power supply terminal 224 of the low-side driver 222, a low voltage _-V CC + Vf than the voltage _{V GND} reference line 206 is supplied To be done.

Next, operations of the low side driver 222 and the low side transistor M _L will be described. In low output period _{T L,} the low-side driver 222, a _V GL _{= V CC} is applied to the gate of the low side transistor _{M L,} turns on the low side transistor _{M L.} As a result, the switching voltage V _SW becomes the low level V _GND .

In the high-output period _{T H,} the low-side driver 222, the low-side transistor _{M L} gate in _V GL _{= V} CPOUTL _{= -} applying a _(V CC -Vf). As a result, the low side transistor M _L is turned off and the switching voltage V _SW becomes a predetermined high level voltage (or high impedance state).

The above is the operation of the switching circuit 200.
According to this switching circuit 200, the normally-on low-side transistor M _L can be reliably turned off without using an insulated power supply or the like. As a result, the number of parts and the circuit area can be reduced, and the cost can be reduced.

The switching circuit 200 according to the first embodiment is also effective when the low-side transistor M _L is a normally-off type device. That is, since a gate voltage lower than the source voltage can be applied to the gate of the low-side transistor M _L , the intention of the transistor M _L due to the rise of the gate voltage via the parasitic capacitance Cgd at the steep rise of the output V _SW. It becomes possible to suppress turn-on (self-turn-on) that does not occur, and high-speed switching operation becomes possible.

Also, note that the output voltage of the first charge pump 230 is not constant in the first embodiment. The output of a general charge pump is a DC voltage, but the output voltage V _CPOUTL of the first charge pump 230 in FIG. 2 is a pulse voltage as shown in FIG. This is because it is not necessary to supply a negative voltage to the lower power supply terminal 224 of the low side driver 222 during the period when the low side transistor M _L should be turned on. A general DC output charge pump requires another rectifying element and an output capacitor (smoothing capacitor) in addition to the configuration of the first charge pump 230, whereas the first charge pump of FIG. In the pump 230, those elements can be omitted, and an increase in circuit area and cost is suppressed.

(Second embodiment)
FIG. 4 is a circuit diagram of the switching circuit 300 according to the second embodiment. The switching circuit 300 includes a high side transistor _MH and a driving stage 320 in addition to the switching circuit 200 of FIG. The switching circuit 300 is in a high output period _{T H,} and outputs an input voltage _{V IN} supplied to the input line 302.

The high side transistor M _H is provided between the input line 302 and the switching line 204. Driver stage 320 drives the high-side transistor _{M H} on the basis of the high-side pulse _{S H.}

The driving stage 320 includes a high side driver 322, a second level shifter 328, a second charge pump 330, and a bootstrap circuit 340.

The bootstrap circuit 340 generates a bootstrap voltage V _BST on the power supply line 342, which is higher than the voltage V _SW of the switching line 204 by a predetermined voltage (V _CC ). The high side driver 322 drives the high side transistor _MH . The bootstrap voltage (third voltage) V _BST is supplied to the upper power supply terminal 326 of the high side driver 322. The bootstrap circuit 340 includes a diode D ₃₁ and a capacitor C ₃₁ . A transistor may be used instead of the diode D ₃₁ .

The second charge pump 330 performs charge pump operation (switching) in synchronization with the high side driver 322, operates as a charge pump, and at least during a period when the high side transistor _MH should be turned off, a lower power supply terminal of the high side driver 322. The second voltage V _CPOUTH lower than the switching voltage V _SW of the switching line 204 is supplied to ₃₂₄ .

The second charge pump 330 includes a second capacitor C ₂₁ , a second sub driver 332, and a second rectifying element D ₂₁ . One end of the second capacitor C ₂₁ is connected to the lower power supply terminal 324 of the high side driver 322. The second sub-driver 332 synchronizes with the high-side driver 322, and at the other end of the second capacitor C ₂₁ , the second charge pump signal V that sets the bootstrap voltage V _BST to the high level and the switching voltage V _SW to the low level. _{Apply CPH} . The second rectifying element D ₂₁ is a diode provided such that the cathode is on the switching line 204 side and the anode is on the lower power supply terminal 324 side on the high side driver 322. Second rectifying element D ₂₁ may use a Zener diode.

The second level shifter 328 receives the high-side pulse S _H generated by a controller (not shown). The second level shifter 328, the high level power supply voltage _{V CC,} a high-side pulse _{S H} to the low level reference voltage _{V GND,} a high level of bootstrap voltage _{V BST,} the high side pulse to the voltage _{V CPOUTH} a low level Level shift to _SH '.

The above is the configuration of the switching circuit 300. Next, the operation will be described. FIG. 5 is an operation waveform diagram of the switching circuit 300 of FIG. Since the low side operation is similar to that of FIG. 3, only the high side operation is shown in FIG. Actually, the switching voltage V _SW is a pulse as shown in the lower part of the _drawing , but V _CPOUTH , S _H ′, and V _GH are shown as constant V _SW .

First, the operation of the second charge pump 330 will be described.

When the high-side pulse S _H becomes high level in the high output period T _H , the second sub-driver 332 applies V _CPH =V _BST4 to one end of the second capacitor C ₂₁ . When the forward voltage of the second rectifying element _{D 21} to Vf, is across the second capacitor _{C 21, V} BST -Vf is applied, a second capacitor _{C 21} is charged.

In the low output period _TL , when the high side pulse _SH goes to the low level, the output V _CPH of the second sub driver 332, that is, one end of the second capacitor C ₂₁ goes to the low level V _SW . Charge of the second capacitor _{C 21} is saved, since its voltage across _(V BST -Vf) is maintained in other words, the voltage _{V CPOUTH} the other end of the second capacitor _{C 21 is, V} CPOUTH = - _{(V BST} −V _SW )+Vf.

As described above, during the period in which the high-side transistor _MH should be turned off by the second charge pump 330, the lower power supply terminal 324 of the high-side driver 322 has a voltage higher than the voltage V _SW of the switching line 204 by (V _BST − A voltage lower than Vf) is supplied.

Next, operations of the high side driver 322 and the high side transistor _MH will be described. In the high-output period _{T H,} the high-side driver 322, a _V GH _{= V BST} is applied to the gate of the high side transistor _{M H,} turns on the high-side transistor _{M H.} As a result, the switching voltage V _SW becomes the high level V _IN .

In the low output period T _L , the high side driver 322 applies V _GH =V _BST to the gate of the high side transistor _MH . As a result, the high side transistor _MH is turned on, and the switching voltage V _SW becomes the high level voltage V _IN .

According to the switching circuit 300, the same effect as that of the switching circuit 200 of FIG. 2 can be obtained for the low-side transistor M _L. Further, according to the switching circuit 300, the same effect as that of the low-side transistor M _L can be obtained for the high-side transistor M _H.

(Third Embodiment)
FIG. 6 is a circuit diagram of a switching circuit 300A according to the third embodiment.
In the switching circuit 300A, the power supply voltage V _CC3 different from the ground voltage V _GND is supplied to the reference line 206. The power supply voltage V _CC3 may be positive or negative.

Further, a power supply voltage V _CC2 different from the power supply voltage V _CC1 of the upper power supply terminal 226 of the low side driver 222 is supplied to the upper power supply terminal of the first sub driver 232 of the first charge pump 230. The high side drive stage 320 is similar to that of FIG.

FIG. 7 is an operation waveform diagram of the switching circuit 300A of FIG. According to the switching circuit 300A, the low level of the gate voltage V _GL is arbitrarily set by preparing the power supply (power supply voltage V _CC2 ) for the first charge pump 230 separately from the main power supply (power supply voltage V _CC1 ). can do.

(Use)
Next, the usage of the switching circuit 300 (or 200) will be described. FIGS. 8A to 8D are diagrams showing the usage of the switching circuit 300. FIG. 8A shows a step-down DC/DC converter 500, which includes transistors M ₁ and M ₂ , an inductor L ₁ , a capacitor C _O1 , a controller 502, and a driving stage 504. The controller 502 generates the high-side pulse S _H and the low-side pulse S _L by feedback control so that the load state (for example, the output voltage V _OUT and the output current I _OUT ) approaches the target. The transistors M ₁ and M ₂ and the driving stage 504 correspond to the switching circuit 300.

FIG. 8B shows a step-up DC/DC converter 600, which includes transistors M ₃ and M ₄ , an inductor L ₂ , a capacitor C _O2 , a controller 602, and a drive stage 604. The controller 602 generates the high-side pulse S _H and the low-side pulse S _L by feedback control so that the load state (for example, the output voltage V _OUT and the output current I _OUT ) approaches the target. The transistors M ₃ and M ₄ and the driving stage 604 correspond to the switching circuit 300. The switching circuit 300 can also be used in a buck-boost converter.

FIG. 8C shows a three-phase motor driver 700, and each leg of the U-phase, V-phase, and W-phase is composed of a switching circuit 300.

FIG. 8D is a bidirectional isolated DC/DC converter 800, in which each leg of the primary H bridge circuit 802 and the secondary H bridge circuit 804 is configured using the switching circuit 300. ..

Although the present invention has been described based on the embodiments using specific terms, the embodiments merely show the principle and application of the present invention, and the embodiments define the scope of claims. Many modifications and changes in arrangement are possible without departing from the concept of the present invention.

200... Switching circuit, 204... Switching line, 206... Reference line, 208... Power supply line, 210... Output stage, 220... Drive stage, 222... Low side driver, 224... Lower power supply terminal, 226... Upper power supply terminal, 228... the first level shifter, 230 ... first charge pump, 232 ... first sub-driver, C _{11 ...} first capacitor, D _{11 ...} first rectifying element, M H _... high-side transistor, M L _... low-side transistor, 300 ... switching circuit , 302... Input line, 320... Driving stage, 322... High side driver, 324... Lower power supply terminal, 326... Upper power supply terminal, 328... Second level shifter, 330... Second charge pump, 332... Second sub-driver, 340... Bootstrap circuit.

Claims (10)

A low-side transistor provided between the switching line and the reference line,
A low-side driver for driving the low-side transistor,
A first charge that operates in a charge pump in synchronization with the low side driver and supplies a first voltage lower than a reference voltage of the reference line to a lower power supply terminal of the low side driver at least during a period when the low side driver should be turned off. A pump,
A switching circuit comprising: The switching circuit according to claim 1, wherein the output voltage of the first charge pump has a voltage level higher than the first voltage during a period when the low-side transistor should be turned on. The first charge pump is
A first capacitor whose one end is connected to the lower power supply terminal of the low side driver;
A first sub-driver that applies a first charge pump signal having a positive power supply voltage at a high level and the reference voltage at a low level to the other end of the first capacitor in synchronization with the low-side driver;
A first rectifying element provided between the one end of the first capacitor and the reference line;
The switching circuit according to claim 1, further comprising: The switching circuit according to claim 3, wherein the positive power supply voltage is common with the voltage of the upper power supply terminal of the low-side driver. The switching circuit according to claim 3, wherein the positive power supply voltage is different from a voltage of an upper power supply terminal of the low side driver. The switching circuit according to claim 1, wherein the low-side transistor is a normally-on type device. A high-side transistor provided between the input line and the switching line,
A high-side driver for driving the high-side transistor,
A charge pump operates in synchronization with the high side driver, and supplies a second voltage lower than the switching voltage of the switching line to a lower power supply terminal of the high side driver at least during a period when the high side transistor should be turned off. A second charge pump,
A bootstrap circuit for supplying a third voltage higher than the switching voltage to an upper power supply terminal of the high side driver;
The switching circuit according to claim 1, further comprising: 8. The switching circuit according to claim 7, wherein the output voltage of the second charge pump has a voltage level higher than the second voltage during a period when the high side transistor should be turned on. The second charge pump is
A second capacitor whose one end is connected to the lower power supply terminal of the high side driver;
A second sub-driver that applies a second charge pump signal that sets the third voltage to a high level and the second voltage to a low level to the other end of the second capacitor in synchronization with the high-side driver;
A second rectifying element provided between the one end of the second capacitor and the switching line;
9. The switching circuit according to claim 7, which includes: The switching circuit according to any one of claims 1 to 9, wherein the switching circuit is integrated on one semiconductor substrate.

Images