JPH02202375A - Power semiconductor module - Google Patents

Abstract

PURPOSE:To protect elements from breakdown by detecting the interval when the voltage across a shunt resistor has reverse polarity as the conducting interval of circulation current and then blocking ON signal based on the detection. CONSTITUTION:A power semiconductor module is a circuit to be employed as a switch for an inverter circuit and comprises flywheel diodes D1-D2 connected in reverse parallel, for circulating current through NPN transistor NPN of a self arc-extinguishing semiconductor element and a shunt resistor Rs. A terminal T for detecting the polarity of terminal voltage of the shunt resistor Rs is provided, and control is made such that forward base current is not fed to the transistor Q3 based on the detection of reverse polarity output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power semiconductor module used in a power conversion circuit such as an inverter circuit or a chopper circuit.

[Conventional technology]

In recent years, the main elements used in power conversion devices have changed from the traditional thyristors, which only had an on function, to self-extinguishing types such as GTOs, bipolar transistors, <Gar, Bt MOS transistors, etc., which have both on and off functions. They are being replaced by semiconductor devices. This self-extinguishing semiconductor device operates faster than a thyristor, so
In the case of a power conversion device using this as a main element, not only can the power conversion efficiency be increased and the component configuration be simplified, but also the operation sequence can be simplified.

FIG. 4 is a circuit diagram showing the basic operating principle of a single-phase bridge voltage type PWM inverter, which is an example of a typical power converter. In the figure, switches A, B, C, and D are each constructed by connecting a flywheel diode in antiparallel to the above-mentioned self-extinguishing semiconductor element, such as a bipolar transistor. Connect the series circuit and the series circuit of switch C2D in parallel,
A constant voltage power supply (2) is connected between both terminals of the parallel circuit, and an inductance L is connected between the connection point of the switches A and B and the connection point of the switch C1D. Switches A, D and Switch B.

C are turned on and off in pairs. In other words, each transistor is controlled so that when the transistor of switch A turns on and off, the transistor of switch D also turns on and off, and when the transistor of switch B turns on and off, the transistor of switch C also turns on and off. .

FIG. 5 is a timing chart showing the operation of the above-mentioned inverter, of which FIG. 5 (1) shows each of the above-mentioned switches A-
5(2) shows the waveform of the output voltage Eout when the signal wave is at a high voltage. Figure 5 (
3) is the output voltage E when the signal wave is at low voltage. ut waveform is shown. 5(1) where the level of the modulated wave a is lower than the levels of the signal waves bl and b2 (for example, FIG.
2), (sections tl and t2 shown in (3)), ON signals are given to the bases of the transistors of switches A and D,
The level of modulated wave a is equal to signal wave b1. In an interval higher than the level of b2 (for example, the interval t3 to t4 shown in FIGS. 5(2) and 5(3)), ON signals are applied to the bases of the transistors of switches B and C. When the amplitude is large as in the case of the signal wave b1, the output power of the inverter increases as shown by the dotted line in FIG. 5(2), and when the amplitude is small as in the case of the signal wave b2, the As shown by the dotted line in Figure (3), the output power of the inverter decreases. Also, the frequency of the inverter output is the signal wave b1. b
Corresponds to frequency 2.

By the way, in the inverter circuit shown in Fig. 4, for example, from a state where the transistors of switches A and D are on and the load current shown by the arrow ■ is flowing, the transistors of switches A and D are turned off after a certain rest period. Assume that an on signal is applied to the transistors of switches B and C while switching. At this time, the current flowing through the inductance in the direction of the arrow (■) decreases, so a back electromotive force is generated in the inductance L, and a circulating current as shown by the arrow (■) flows. This circulating current flows through the flywheel diodes connected in antiparallel to the transistors of switches B and C, so that a voltage in the opposite direction to that during normal operation is applied to the transistors of switches B and C. Therefore, during this period, normal ON operation of the transistors of switches B and C cannot be expected, but despite this, ON signals are input to these transistors (this state will be described below). (referred to as "empty firing mode"). If the period during which the ON signal is applied to the transistors of switches B and C is very short as in the section t5 shown in FIG. The load current indicated by the arrow ■ shown in FIG. 4 does not flow, and only the "dry firing mode" occurs.

Even if the period during which ON signals are applied to the transistors of switches B and C is not short, the transistors of switches B and C enter a steady state after passing through the "dry firing mode."

On the other hand, when an on signal is applied again to the transistors of switches A and D, these transistors turn on while maintaining the voltage (power supply voltage) held when they were off. At this time, switch B.

If the ON signal is applied to the transistor C for a very short period of time, a large current will flow through the flywheel diode connected anti-parallel to the transistor of switch A and the transistor of switch 8. Similarly,
A large current flows through the transistor of switch C and the flywheel diode connected anti-parallel to the transistor of switch D. This is because freewheeling current was flowing through the flywheel diodes of switches B and C until at least just before this stage, so the flywheel diodes remain free until the charge accumulated inside these flywheel diodes is removed. This is because the diode is considered to be in a short-circuited state. At the end of the short-circuited period of these flywheel diodes, the voltage previously held by the transistors of switches A and D will be held by the transistors of switches B and C. This switching of voltage sharing generally occurs within a short period of time.

In the above operation, the transistors of switches A and D have l! Since a large current is caused to flow while maintaining the m voltage, it is predicted that these transistors are likely to be destroyed. The safe operating area of the transistor in this mode is indicated by the index "Short SOΔ".

However, in reality, it is known from experience that the transistors on the switch B and C sides, which operate in the "dry firing mode", are much more likely to be destroyed. In addition, it is also known empirically that when the forward base current is large in driving the bases of the transistors on the switch B and C sides, the transistors are more likely to be destroyed.

Note that the transistors of switches B and C are turned on, and the arrow ■
When the load current is flowing, switch △.

When an on signal is given to the transistor D, "dry firing mode" occurs in the transistor of switch A, t),
A large current flows through the transistors of switches B and C.

As measures to improve the breakdown resistance of transistors that correspond to the above-mentioned "dry firing mode", we have gained experience such as increasing the transistor margin and adding a circuit to the base drive circuit to prevent more base current than necessary from flowing. Correspondence was being taken.

Although the operation of the above-mentioned "dry firing mode" has not been sufficiently analyzed to date, the following mechanism is expected to be at work.

In other words, in "dry firing mode" operation, even if no collector current flows through the transistor, the forward base current applied creates a state in which a small amount of charge exists inside the transistor. In the saturated state, which can be assumed to be turned on, a given forward base current flows from the base to the collector). At the end of the period in which the flywheel diode connected in antiparallel to this transistor exhibits a short-circuit condition, as described above, a high voltage corresponding to the power supply voltage is applied to the transistor in such an internal state for a very short time. will be applied to Reference document <11. N15hiua+i e
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Taking into consideration the mechanism of such "empty firing mode",
As shown in Figure 6, the configuration of the base drive circuit that does not cause "dry firing mode" also improves the transistor breakdown resistance1.
This has been proposed as one countermeasure. In FIG. 6, two NPN transistors Q1. Q2 is Darlington connected, and a flywheel diode D is connected in antiparallel between the collector and emitter of the NPN transistor Q1. NPN transistor Q1. A current detection coil 1 that detects a reverse current (reflux current) is inserted into the circuit on the collector side of Q2, and the base amplifier AMP is inactivated while the detection output of the current detection coil 1 indicates a reverse current. , the structure is such that no forward base current flows through the NPN transistor Q2.

[Problem to be solved by the invention]

However, as mentioned above, countermeasures such as increasing the transistor margin or adding a circuit to the base drive circuit to prevent more base current from flowing than necessary have the problem of increasing costs. .

In addition, in the method using the current detection coil 1, the current detection coil 1 needs to be large enough to allow the main current to flow, and connecting such a large coil to each transistor takes time and increases costs. It has problems such as:

The present invention has been made to solve these problems, and an object of the present invention is to provide a power semiconductor module that has a simple configuration and can improve the breakdown resistance of a self-extinguishing semiconductor element.

[Means to solve the problem]

A power semiconductor module according to the present invention includes a self-arc-extinguishing semiconductor element, which is connected in antiparallel to the self-arc-extinguishing semiconductor element to flow a return current in a direction opposite to the conduction direction of the self-arc-extinguishing semiconductor element. A shunt consisting of a series circuit of a second diode and a shunt resistor is connected in parallel to the flywheel diode, and a return current is generated based on the polarity of the voltage between the terminals of the shunt resistor. It is designed to detect the presence or absence of current.

[Effect]

In this invention, since the voltage between the terminals of the shunt resistor has the opposite polarity when the freewheeling current is flowing, the freewheeling current is Destruction of the self-extinguishing semiconductor element due to current is prevented.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of a power semiconductor module according to the present invention. This power semiconductor module is a circuit used, for example, as a switch in the inverter circuit shown in FIG. Flywheel diode D1 for
is connected to the flywheel diode D1, and a series circuit consisting of a second diode D2, which has almost the same basic electrical characteristics as the flywheel diode D1 and is smaller in size, and a shunt resistor R8 is connected in parallel to the flywheel diode D1. A detection terminal T for detecting the polarity of the voltage between the terminals of the shunt resistor R3 is drawn out from the connection point between the shunt resistor R8 and the diode D2.

FIG. 2 is a sectional view showing an example in which the flywheel diode D1 and the second diode D2 of the power semiconductor module are formed on one chip. in this way,
By forming two diodes DI, D2 on the same chip, diodes D1 . D2 can be easily obtained. Regarding the shunt resistor R8 connected in series with the second diode D2, the diode D1. It can be easily formed on the same chip as D2 by a conventionally well-known technique. In FIG. 2, 2 is a diode oi.

This is the back electrode common to both.

In this power semiconductor module, when a freewheeling current flows through the flywheel diode D1, a current corresponding to the area of the flywheel diode D1 and the second diode D2 branches from the freewheeling current and flows through the diode D.
2. The current is shunted to a shunt consisting of a series circuit of shunt resistor R3, and the voltage between the terminals of shunt resistor R5 has opposite polarity. Therefore, based on the detection output of the opposite polarity detected from the detection terminal T, the occurrence of "dry firing mode" is prevented by controlling so as not to apply forward base current to the base of the NPN transistor Q3 during this period. , destruction of the NPN transistor Q3, that is, the self-extinguishing semiconductor element, due to the return current is prevented.

Note that the second diode D2 described above works as a sensor for detecting the freewheeling current, and the one whose reverse recovery time is shorter is the NPN transistor Q3, which is the main active element.
This is preferable because it can reduce the influence on Such reverse recovery time control can be easily achieved by using in-shell lifetime control techniques, whether the diodes DI and D2 are formed on the same chip or on separate chips. Can be done.

In addition, in recent years, as power semiconductor devices have become more sophisticated, attempts have been made to incorporate a drive circuit into the module, but the power semiconductor module of this example is implemented on the same chip as described above. diodes Di, D2,
Since the shunt resistor R8 is easy to form, a configuration in which the drive circuit is also formed on the same chip can be easily realized.

In the above embodiment, a case has been described in which one NPNt-transistor Q3 is used as the self-extinguishing semiconductor element, but the same operation can be performed using a Darlington transistor.

Furthermore, even when a cathode-shorted GTO or a collector-shorted IGBT is used as a self-extinguishing semiconductor element, the main voltage is applied to these self-extinguishing semiconductor elements in the opposite direction to normal operation. When an on signal is given in the state, the main current flows in the opposite direction to the normal state, similar to the case of a transistor, so a configuration similar to this example can be applied to these self-extinguishing semiconductor devices. By applying this, it is possible to perform the same operation as in the case described above.

Furthermore, as shown in FIG. 3, a MOS transistor Q5 is connected in cascode to the front stage of the bipolar transistor Q4 in a B1 MO.
In the case of 8 elements, the previous stage MOS transistor Q5 has the function of flowing current in the opposite direction regardless of the gate signal due to the function of its built-in diode, and this MOS transistor Q5 has a bipolar transistor essentially parasitic. It is known that On the other hand, this 81・MO
Since a resistor R is connected between the base and emitter of the bipolar transistor Q4 after the three elements, this B
When the i-MO8 element is used as a self-extinguishing semiconductor element in a power semiconductor module, a small amount of current flows in the previous stage MOS transistor Q5 in the opposite direction to normal when operating in "dry firing mode". Nari, Bi
The situation is somewhat different from that in the other elements mentioned above other than the -MO8 element, when an off signal is applied during operation in the "dry firing mode", the inflow of charges into the element is suppressed. That is, in the Bi-MO8 element, it is not possible to actively suppress the inflow of charges into the element. However, this B1・M
Even in the case of the O8 element, it is possible to send an off signal to the bipolar transistor 04 in the subsequent stage during the detection period of the feedback current, so at least the operation of the bipolar transistor Q4 in the subsequent stage, which is the main transistor, can be blocked. In this case, too, large current operation that could lead to destruction can be suppressed.

〔Effect of the invention〕

As described above, according to the present invention, the period in which the voltage between the terminals of the shunt resistor has the opposite polarity is detected as the period in which the freewheeling current is flowing, and during this period, the ON signal is sent to the self-extinguishing semiconductor element. I tried to control her so that she wouldn't give it to me, so
With a simple configuration, it is possible to prevent destruction of the self-extinguishing semiconductor element due to return current.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a power semiconductor module according to the present invention, and FIG. 2 shows a configuration in which a flywheel diode and a second diode are formed on the same chip in the power semiconductor module. 3 is a circuit diagram showing the configuration of a 1-MO8 element that can be applied as a self-extinguishing semiconductor element in a power semiconductor module, and FIG. 4 shows the operating principle of an example of a typical power conversion device. 5 is a timing chart showing the operation of the power converter, and FIG. 6 is a circuit diagram showing an example of a proposed circuit configuration for improving the breakdown resistance of self-extinguishing semiconductor elements in the power converter. It is. In the figure, Q3 is an NPN transistor (self-extinguishing semiconductor device), Dl is a flywheel diode, and D2
is a second diode, R8 is a shunt resistor, and R8 is a detection terminal. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] (1) Includes a self-extinguishing semiconductor element and a flywheel diode connected in antiparallel to the self-extinguishing semiconductor element to flow a return current in the direction opposite to the conduction direction of the self-extinguishing semiconductor element. In a power semiconductor module, a shunt consisting of a series circuit of a second diode and a shunt resistor is connected in parallel to the flywheel diode, and the presence or absence of the return current is detected from the polarity of the voltage between terminals of the shunt resistor. A power semiconductor module characterized by: