JP2004088192A - Drive circuit for voltage driven device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain the switching loss or the surge voltage of a drive circuit for voltage-driven elements from increasing due to the variation of its threshold voltage. <P>SOLUTION: The drive circuit for voltage-driven elements comprises a turn-on time measuring means 11 and a turn-off time adjusting means 12. The latter means 12 corrects the gate discharge rate of the voltage-driven element IGBT (Q1) at turning off to correct the turn-off time so that the gate discharge rate at turning off decreases with the increase of the turn-on time and vice versa, and the former means 11 measures the turn-on time based on a voltage across a capacitor C1 for charging it during turning on. It comprises a PNP transistor (Q3) an emitter terminal and a collector terminal of which are connected to the gate of the IGBT (Q1) and the ground, respectively. The capacitor C1 is connected to the base of the PNP transistor (Q3). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a driving circuit for a voltage driving element.
[0002]
[Prior art]
Regarding the driving circuit of the conventional voltage driving element, for example, the transistor technology SPECIAL No. 54 "Special Feature: Introduction to Practical Power Electronics", page 56, CQ Publishing Company, 1996.
[0003]
As described in this document, current is switched using a power device such as an IGBT (Insulated Gate Bipolar Transistor), which is one of voltage driving elements (switching elements), or a power MOS. In this case, the switching loss and the surge voltage have a trade-off relationship.
[0004]
The surge voltage is a voltage generated by the main circuit inductance L and a current change rate di / dt at the time of current interruption, and is represented by Vs = L × di / dt.
[0005]
In order to prevent the power device from being destroyed, the power supply voltage + the surge voltage must be suppressed to a level lower than the withstand voltage of the power device.
[0006]
On the other hand, if the current change rate di / dt at the time of current interruption is reduced to suppress the surge voltage, that is, if the switching speed (turn-off speed) is reduced, the switching loss increases.
[0007]
When the current is continuously switched as in PWM (Pulse Width Modulation: pulse width modulation) driving, an increase in switching loss causes a rise in temperature, which may destroy a power device. The switching loss must be kept within an allowable range in consideration of the above.
[0008]
In the case of a voltage driving element such as an IGBT or a power MOS, which turns on / off a current depending on whether or not a voltage is applied to a gate, the switching speed is adjusted by adjusting the size of a gate resistor connected to the gate, and the surge voltage is adjusted. In many cases, a technique for keeping both the switching loss and the switching loss within an allowable range is adopted.
[0009]
[Problems to be solved by the invention]
In such a conventional method, if the threshold voltage fluctuates due to variations in IGBT or power MOS or temperature characteristics, the switching speed also fluctuates. When the switching speed (turn-off speed) is reduced, the switching loss becomes excessive, and there is a possibility that the switching element is destroyed by heat generation. Conversely, when the switching speed (turn-off speed) increases, an excessive surge voltage is generated, and the switching element may be broken. That is, when the turn-off speed is reduced due to the fluctuation of the threshold voltage, the switching loss increases, and when the turn-off speed is increased, the surge voltage increases.
[0010]
It is an object of the present invention to provide a drive circuit for a voltage drive element that can suppress an increase in switching loss and surge voltage due to a change in threshold voltage.
[0011]
[Means for Solving the Problems]
In order to solve the above problem, a drive circuit for a voltage drive element according to the present invention includes a drive circuit for driving a voltage drive element on and off, wherein a turn-on time that is a time required for the voltage drive element to drive from off to on is reduced. Turn-on time measuring means for measuring, and turn-off time correcting means for correcting the turn-off time, which is the time required for the voltage drive element to drive from on to off, based on the turn-on time measured by the turn-on time measuring means. It is characterized by having.
[0012]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a drive circuit of a voltage drive element that can suppress an increase in switching loss and surge voltage due to a change in threshold voltage.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, those having the same functions are denoted by the same reference numerals, and repeated description thereof will be omitted.
[0014]
FIG. 1 is a circuit diagram illustrating an example of a drive circuit when driving a load using an IGBT that is one of voltage drive elements.
[0015]
The load L1 is configured to be driven by an IGBT (Q1) as a voltage driving element, and the gate of the IGBT (Q1) is configured such that the NPN transistor Q2 can apply the power supply voltage Vcc via the resistor R1. The PNP transistor Q3 is configured to be grounded via the resistor R2. The base of the NPN transistor Q2 is connected to the input signal Vin, and the base of the PNP transistor Q3 is connected to the input signal Vin via the resistor R3, and can be turned on / off by the input signal Vin. When there is an input signal Vin, the NPN transistor Q2 is on and the PNP transistor Q3 is off. Conversely, when there is no input signal Vin, the NPN transistor Q2 is off and the PNP transistor Q3 is on.
[0016]
Further, the output of the constant current source 13 is connected to the collector of the IGBT (Q1) via the diode D1 and to the capacitor C1 via the diode D2, and the constant current source 13, the diode D1, the diode D2 and the capacitor C1 The turn-on time measuring means 11 for measuring the time required for turn-on (referred to as turn-on time) is configured.
[0017]
Further, the connection point between the diode D2 and the capacitor C1 is connected to the base of the PNP transistor (Q3) via the diode D3, and the time required for turning off (referred to as turn-off time) by the diode D3, the resistor R3, and the capacitor C1. The adjusting (correcting) turn-off time adjusting means 12 is configured. The capacitor C1 serves as a component of the turn-on time measuring means 11 and a component of the turn-off time adjusting means 12.
[0018]
FIG. 2 shows waveforms of the respective parts when the IGBT (Q1) is turned on and then turned off in response to a change in the input signal Vin. Vin is an input signal, Vc1 is the voltage of the capacitor C1, Ig (off) is the discharge current from the gate at the start of turn-off of the IGBT (Q1), Vce is the collector-emitter voltage of the IGBT (Q1), and Ic is the collector current. It is.
[0019]
The IGBT (Q1) enters a turn-on operation due to the change of the input signal Vin from L to H (time t1).
[0020]
The change of the input signal Vin from L to H turns off the PNP transistor (Q3), thereby starting the current supply from the constant current source 13 to the capacitor C1. As a result, the capacitor C1 is charged with electric charge from the constant current source 13 via the diode D2, so that the voltage generated in the capacitor C1 increases with time.
[0021]
When the turn-on of the IGBT (Q1) is completed and the collector-emitter voltage Vce becomes close to 0 V, the current from the constant current source 13 does not flow to the capacitor C1, but flows to the collector of the IGBT (Q1) via the diode D1. Therefore, the rise of the voltage Vc1 of the capacitor C1 stops (time t2).
[0022]
That is, the longer the turn-on time, the higher the voltage generated in the capacitor C1.
[0023]
Next, when the input signal Vin changes from H to L, the IGBT (Q1) enters a turn-off operation (time t3).
[0024]
At this time, assuming that the voltage generated in the diode D3 is Vf, the peak value Ip of the discharge current Ig (off) from the gate at the start of turn-off of the IGBT (Q1) is:
Ip = [Vge- {Vc1-Vf + Vbe2}] / R2
{Vge-Vc1} / R2
Can be represented by Vc1 is the voltage of the capacitor C1, Vge is the gate-emitter voltage of the IGBT (Q1), and Vbe2 is the base-emitter voltage of the NPN transistor Q2.
[0025]
That is, as the voltage Vc1 of the capacitor C1 increases (21 in FIG. 2), the base voltage of the PNP transistor (Q3) increases, and the peak value Ip of the discharge current Ig (off) from the gate decreases (FIG. 2). 23), the turn-off speed is reduced. Conversely, as the voltage Vc1 of the capacitor C1 decreases (22 in FIG. 2), the base voltage of the PNP transistor (Q3) decreases, and the peak value Ip of the discharge current Ig (off) from the gate increases (see FIG. 2). 2-24), the turn-off speed increases.
[0026]
Here, focusing on the relationship between the turn-on time and the turn-off time due to IGBT variations and characteristic fluctuations, the following is obtained.
[0027]
When the threshold voltage of the IGBT rises, it becomes difficult to turn on and tends to turn off, so that turn-on is slow and turn-off is fast. In this case, the surge voltage at the time of turn-off becomes a problem.
[0028]
Conversely, when the threshold voltage decreases, the characteristics are easily turned on and hard to be turned off, so that turn-on is fast and turn-off is slow. In this case, the turn-on switching loss is small and the turn-off switching loss is large.However, if the turn-off speed is originally moderate to suppress the surge voltage, the turn-off switching loss is dominant, so the total Losses are large and heat is a problem.
[0029]
In the present embodiment, when the turn-on is delayed due to the threshold voltage fluctuation of the IGBT, the voltage generated in the capacitor C1 increases, so that the discharge current from the gate at the time of turn-off decreases and the turn-off increases. It works to suppress. In addition, when the turn-on speed is increased, the voltage generated in the capacitor C1 decreases, so that the discharge current from the gate of the IGBT (Q1) at the time of turn-off increases, thereby suppressing the delay of the turn-off.
[0030]
That is, the IGBT characteristic fluctuation is detected by the turn-on time measuring means 11, and the switching speed at the time of turn-off is made variable by the turn-off time adjusting means 12, thereby suppressing the fluctuation of the switching characteristic at the time of turn-off.
[0031]
As described above, the drive circuit of the voltage drive element according to the present embodiment corrects the turn-off time based on the turn-on time measuring means 11 for measuring the turn-on time and the turn-on time measured by the turn-on time measuring means 11. It is characterized by comprising a turn-off time correcting means, that is, a turn-off time adjusting means 12. The voltage drive element has a slow turn-off speed when the turn-on time is short, and a high turn-off speed when the turn-on time is long. Therefore, the turn-off time is appropriately corrected by correcting the turn-off time based on the turn-on time. can do.
[0032]
Further, the turn-off time adjusting means 12 corrects the turn-off time by correcting the gate discharge speed at the time of turn-off of the IGBT (Q1) which is a voltage driving element. As described above, the turn-off time can be appropriately corrected by correcting the turn-off time based on the turn-on time by correcting the gate discharge speed at the time of turn-off.
[0033]
In addition, the gate discharge speed at the time of turn-off is set such that the longer the turn-on time measured by the turn-on time measuring means 11, the lower the gate discharge speed at the time of turn-off, and the shorter the turn-on time, the faster the gate discharge speed at the time of turn-off. The speed is corrected. If the turn-on time is long, the turn-off time is short and the surge voltage is large.If the turn-on time is short, the turn-off time is long and the switching loss is large, but the longer the turn-on time is, the slower the gate discharge speed is. The surge voltage and the switching loss can be suppressed by correcting the gate discharge speed such that the gate discharge speed increases as the time becomes shorter.
[0034]
Further, the turn-on time measuring means 11 includes a capacitor C1 for charging electric charge during turn-on, and the turn-on time is measured based on the voltage Vc1 of the capacitor C1. Thereby, the turn-on time measuring means 11 can be configured at low cost.
[0035]
An IGBT (Q1), which is a voltage driving element, includes a PNP transistor (Q3) having an emitter terminal connected to the gate and a collector terminal connected to the ground, and a capacitor C1 serving as a base of the PNP transistor (Q3). Connected to a computer. Thereby, the turn-off time of the voltage driving element can be controlled with an inexpensive configuration.
[0036]
Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and it is needless to say that various modifications can be made without departing from the gist of the present invention.
[0037]
For example, the constant current source 13 used in the present embodiment may be replaced with a resistor. In this case, the rise of the voltage Vc1 of the capacitor C1 leads to a charging curve determined by the resistance value of the resistor and the capacitance value of the capacitor C1.
[0038]
In the present embodiment, the turn-off time is controlled by the capacitor C1, but the turn-off time may be controlled in a software manner by, for example, a control device that measures the turn-on time and controls the turn-off time.
[Brief description of the drawings]
FIG. 1 is a circuit diagram illustrating an example of a drive circuit of a voltage driving element according to an embodiment of the present invention when driving a load using an IGBT that is one of voltage driving elements.
FIG. 2 is a diagram showing waveforms of various parts when an IGBT (Q1) is turned on and then turned off in response to a change in an input signal Vin in the embodiment of the present invention.
[Explanation of symbols]
11 Turn-on time measuring means 12 Turn-off time adjusting means 13 Constant current source VB Battery voltage (power supply voltage)
L1 Load Vin Input signal Vcc Power supply voltage Q1 IGBT (NPN transistor)
Q2: NPN transistor Q3: PNP transistors R1, R2, R3: Resistors D1, D2, D3, D4: Diode C1: Capacitor Vce: Collector-emitter voltage Vge: Gate-emitter voltage Vc1: Voltage Ig of capacitor C1 (off ) Gate discharge current Ic collector current t1, t2, t3 time Ip gate discharge current peak value 21, 22 voltage capacitor C1, voltage 23, 24 gate discharge current peak value

Claims (5)

In a drive circuit for driving a voltage drive element on and off,
Turn-on time measuring means for measuring a turn-on time, which is a time required for the voltage drive element to drive from off to on,
Turn-off time correction means for correcting a turn-off time, which is a time required for the voltage drive element to drive from on to off, based on the turn-on time measured by the turn-on time measurement means, Driving circuit for the voltage driving element. 2. The driving circuit according to claim 1, wherein the turn-off time correction unit corrects the turn-off time by correcting a gate discharge speed when the voltage drive element is turned off. As the turn-on time measured by the turn-on time measuring means is longer, the gate discharge speed at the time of the turn-off becomes slower,
As the turn-on time is shorter, the gate discharge speed at the time of the turn-off is higher,
3. The driving circuit according to claim 2, wherein the gate discharge speed at the time of turn-off is corrected. The turn-on time measuring means includes a capacitor that charges a charge during turn-on,
3. The driving circuit according to claim 1, wherein the turn-on time is measured based on a voltage of the capacitor. An emitter terminal is connected to the gate of the voltage driving element,
A PNP transistor having a collector terminal connected to the ground,
5. The driving circuit according to claim 4, wherein the capacitor is connected to a base of the PNP transistor.

Images