JP3743168B2 - Switching control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a circuit that performs switching control by applying a multistage gate voltage having an intermediate level to a gate voltage controlled switching element such as an IGBT.
[0002]
[Prior art]
In order to gate drive a gate voltage controlled switching element such as an IGBT (hereinafter, IGBT is taken as an example), the conventional gate driver has a circuit as shown in FIG. Two types of power supply voltage (-Vee) are connected to the gate through the gate resistor Rg to control the gate voltage. The gate is driven by Vcc at the time of turn-on and by -Vee at the time of turn-off, and is not driven by an intermediate voltage between Vcc and -Vee.
[0003]
In a power converter using an IGBT as a switching element, the peak value of a surge voltage generated when the IGBT is turned off causes problems such as a decrease in available DC side voltage and an increase in switching loss. In order to reduce this surge voltage, the following measures are taken.
[0004]
(A) A method of slowing the switching speed.
[0005]
In FIG. 4, by increasing the time constant determined by the gate resistance Rg and the gate capacitance Cg of the IGBT by the resistance Rg, the switching speed of the IGBT is slowed down and the surge voltage is suppressed.
[0006]
(B) A method of providing a snubber circuit that absorbs surge voltage.
[0007]
The surge voltage is generated by energy stored in the stray inductance of the IGBT main circuit. Therefore, the surge voltage is kept low by absorbing this energy in the snubber circuit.
[0008]
In the method (A), slowing down the switching speed of the IGBT mainly causes a problem in the cooling of the IGBT and the power conversion efficiency because an increase in switching time leads to an increase in turn-off loss of the element.
[0009]
On the other hand, in the method (B), the snubber circuit complicates the main circuit configuration, leading to an increase in the number of parts and man-hours. Further, the wiring inductance component of the snubber circuit itself cannot sufficiently exhibit the snubber effect.
[0010]
As a method for solving the above problems, the applicant of the present application has already proposed a method of driving the IGBT with a pattern voltage obtained by changing the gate voltage of the IGBT in multiple stages.
[0011]
This method eliminates switching delay by increasing the pattern voltage from the start of IGBT turn-off to immediately before the start of current interruption, or by reducing the period during which the current interruption starts and the surge voltage rises. Switching loss is reduced by suppressing the voltage or by increasing the speed from the point when the current interruption proceeds to some extent and the surge voltage starts to decrease until the end of turn-off.
[0012]
The circuit configuration for this is the basic gate driver configuration shown in FIG. 5, and is composed of a gate voltage pattern generator A that generates a gate voltage pattern and a gate voltage drive amplifier B that actually drives the IGBT with the gate voltage. When the gate signal is input, the pattern generator A creates an appropriate gate voltage waveform, and the amplifier B controls the gate voltage of the IGBT so as to obtain this voltage waveform.
[0013]
The gate voltage pattern generator A is configured as shown in FIG. 6, for example, and includes a simple D / A converter 1 configured using a high-speed C-MOS type TTL, and a resistor and capacitor configuration that removes high-frequency components from the pattern voltage. The digital pattern data applied to the TTL is controlled by the digital sequence circuit 3 using the CR filter circuit 2. A high-precision crystal oscillator 4 is used as a clock for driving the digital sequence circuit 3.
[0014]
The gate voltage drive amplifier B is configured as shown in FIG. 7, for example. In the figure, a common collector type transistor amplifier is used to increase current drive capability, and a common IGBT gate voltage of + 15V to -10V is generated.
[0015]
The output of the D / A converter 1 is 0V to 5V because it uses TTL. Here, a ground (Gnd) level in which 2.5 V is virtually generated by a voltage follower 4A using an operational amplifier is set, and the output of the D / A converter is equivalently ± 2.5 V by this ground level. When this is amplified 5 times by the non-inverting amplifier 4B using the operational amplifier, it becomes ± 12.5V, and from the actual ground level, it becomes + 15V to −10V, and this is amplified by the transistor amplifier circuit 4C. Corresponding to typical gate voltage.
[0016]
[Problems to be solved by the invention]
In the conventional multistage gate driver system using a pattern generator and a gate voltage driving amplifier, a D / A converter is required to generate an intermediate voltage level. An operational amplifier is required to amplify the voltage of the output of the D / A converter.
[0017]
These circuit elements determine the performance of the gate driver (gate voltage control resolution, voltage change speed), and high-resolution D / A converters and high-speed operational amplifiers are expensive, making them expensive gate control circuits. Become.
[0018]
An object of the present invention is to provide a low-cost switching control circuit without degrading performance.
[0019]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention has a configuration in which a D / A converter is configured with a TTL element having a high breakdown voltage open collector output and a voltage dividing resistor circuit, or a configuration in which a high-speed transistor is interposed. The amplifier circuit can be driven and has the following configuration.
[0020]
A gate voltage pattern generator that generates a pattern voltage in which the voltage change rate is changed within a period from the start to the end of turn-off of the gate voltage control type switching element, and a gate voltage that drives the voltage control type switching element according to the pattern voltage In a switching control circuit with a drive amplifier,
The gate voltage pattern generator includes a sequence circuit that generates digital data of the pattern voltage, and a plurality of high-speed switching elements that obtain ON / OFF outputs according to the digital data. With D / A converter to switch to
The gate voltage drive amplifier is constituted by a transistor amplifier circuit that directly amplifies the voltage of the divided voltage output of the resistor voltage divider circuit of the D / A converter.
[0021]
The high-speed switching element is a TTL element having a high breakdown voltage open collector output.
[0022]
The high-speed switching element is a TTL element to which digital data is input and a high-speed transistor driven by the output of the TTL element.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a multistage gate driver circuit diagram showing an embodiment of the present invention. The sequence circuit 3 and the crystal oscillator 4 of the gate voltage pattern generator generate a gate voltage pattern as in the conventional case.
[0024]
A D / A converter 1A that generates a multi-stage gate voltage waveform corresponding to this pattern includes TTL (transistor / transistor / logic) elements G1 to G3 having a high breakdown voltage open collector configuration and voltage dividing resistors R1 to R3.
[0025]
The TTL elements G1 to G3 can use commercially available IC elements mounted with a large number of circuits such as 6 circuits, and obtain buffer functions for impedance conversion of 3-bit data from the sequence circuit 3, respectively. A high-impedance open state and a low-impedance reference potential state are obtained at the output obtained by inverting the on / off input of each element.
[0026]
The voltage dividing resistors R1 to R3 obtain a multistage gate voltage at a voltage dividing ratio according to the output pattern of the TTL elements G1 to G3. In the figure, one end of the resistor R1 is connected to the power supply voltage (25V), and the other end is The resistors R2 and R3 are connected to one end, the other ends of the resistors R2 and R3 are connected to the output ends of the TTL elements G1 and G2, the common connection end of each resistor is used as an output end, and the output end of the TTL element G3 Connected to.
[0027]
The transistor amplifier circuit 4C amplifies the output from the D / A converter 1A to obtain the gate voltage output of the IGBT, as in the conventional case.
[0028]
The operation of the switching control circuit configured as above will be described. When the output pattern of the sequence circuit 3 turns off all the TTL elements G1 to G3, that is, when all the outputs are set to high impedance, the output of the D / A converter 1A becomes the power supply voltage (25V).
[0029]
When the TTL element G1 is turned on and the other elements G2 and G3 are turned off, the output of the D / A converter 1A becomes an output voltage determined by the voltage dividing ratio of the resistors R1 and R2. Further, when the TTL element G2 is turned on from this state, the output voltage is determined by the voltage dividing ratio of the parallel resistance value of the resistor R1 and the resistors R2 and R3. Further, when the TTL element G3 is turned on, the output voltage becomes the reference potential.
[0030]
When the elements G1 and G3 are turned off and the element G2 is turned on, the output voltage is determined by the voltage dividing ratio of the resistor R1 and the resistor R3.
[0031]
Therefore, the D / A converter 1A can switch the output voltage, that is, the gate control voltage in accordance with the output pattern from the sequence circuit 3, as in the prior art.
[0032]
FIG. 2 shows a voltage pattern generated by the transistor amplifier circuit 4C and a driving pattern example of the TTL element of the D / A converter 1A. Until the time t ₁ to all elements G1~G3 off state, the output of the D / A converter 1A becomes + 15V. At time t ₂ , the element G 1 is turned on to be an intermediate voltage determined by the resistors R 1 and R 2, and at time t ₃ , the element G ₃ is turned on to be −10V. That is, three gate control voltages can be obtained.
[0033]
Therefore, according to the present embodiment, a D / A converter can be configured using a TTL element of a high withstand voltage open collector commercially available as an IC element and a voltage dividing resistor circuit, and an operational amplifier is used as a gate voltage driving amplifier. This eliminates the need for a low-cost circuit configuration that requires only a transistor amplifier circuit.
[0034]
In addition, the TTL element operates at a low cost and at a high speed, and a gate drive voltage at a high speed can be obtained because the output of the D / A converter is directly applied to the transistor amplifier circuit.
[0035]
In the embodiment, a case where a TTL element having a high withstand voltage open collector output is used is shown. However, an element that makes high-speed transition to high impedance, for example, an NPN type high-speed transistor can be used, A high gate drive voltage can be obtained.
[0036]
This example is shown in FIG. 3, and the portion where the D / A converter 1B is different from 1A uses TTL elements G4 to G6 that operate at a high speed with a low breakdown voltage instead of the TTL elements G1 to G3 that have a high breakdown voltage open collector output. The shortage of breakdown voltage is compensated by providing the high speed transistors TR1 to TR3 as drive elements. In this configuration, a high breakdown voltage can be obtained by the transistors TR1 to TR3, and a multistage gate drive voltage up to a power supply voltage of 50V can be obtained.
[0037]
【The invention's effect】
As described above, according to the present invention, the D / A converter is constituted by a TTL element having a high breakdown voltage open collector output and a voltage dividing resistor circuit, or a structure in which a high-speed transistor is interposed, and a transistor amplifier circuit is directly connected by this converter output The following effects are obtained.
[0038]
(1) A high-speed operational amplifier for voltage amplification is not required, and the cost can be reduced.
[0039]
(2) High-speed gate drive can be performed by using a TTL element or a high-speed transistor. In particular, since a TTL element and a high-speed transistor are remarkably fast in on-operation, the turn-off speed of a gate voltage controlled switching element such as an IGBT can be increased.
[0040]
(3) When a high-speed transistor is used, a high-speed and high-voltage gate drive voltage can be obtained.
[Brief description of the drawings]
FIG. 1 is a multistage gate driver circuit diagram showing an embodiment of the present invention.
FIG. 2 shows an example of a voltage pattern and a TTL drive pattern in the embodiment.
FIG. 3 is a multi-stage gate driver circuit diagram showing another embodiment of the present invention.
FIG. 4 shows a conventional gate driver configuration.
FIG. 5 shows another conventional gate driver configuration.
6 is an example of a gate voltage pattern generation circuit in FIG. 5;
7 is an example of a gate voltage driving amplifier circuit in FIG. 5;
[Explanation of symbols]
A ... Gate voltage pattern generator B ... Gate voltage drive amplifier 1, 1A, 1B ... D / A converter 3 ... Sequence circuit 4C ... Transistor amplifier circuit.
G1 to G3 TTL elements G4 to G6 with high breakdown voltage open collector output TTL elements TR1 to TR3 High speed transistors

Claims (3)

A gate voltage pattern generator that generates a pattern voltage in which the voltage change rate is changed within a period from the start to the end of turn-off of the gate voltage control type switching element, and a gate voltage that drives the voltage control type switching element according to the pattern voltage In a switching control circuit with a drive amplifier,
The gate voltage pattern generator includes a sequence circuit that generates digital data of the pattern voltage, and a plurality of high-speed switching elements that obtain ON / OFF outputs according to the digital data. With D / A converter to switch to
2. The switching control circuit according to claim 1, wherein the gate voltage driving amplifier comprises a transistor amplifier circuit that directly amplifies a current of the divided output of the resistance voltage dividing circuit of the D / A converter. 2. The switching control circuit according to claim 1, wherein the high-speed switching element is a TTL element having a high withstand voltage open collector output. 2. The switching control circuit according to claim 1, wherein the high-speed switching element is a TTL element to which digital data is input and a high-speed transistor driven by the output of the TTL element.

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