JPS594293Y2 - Circuit that monitors the temperature of semiconductor junctions - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a means for monitoring the temperature of a semiconductor, in particular a means for monitoring the temperature of a junction in a power semiconductor through which a large current flows.

Solid state devices such as diodes and thyristors are currently well known for power applications.

It is also well known that most of the heat generated in power semiconductors is generated at their junctions that carry current.

As a result, the junction reaches the highest temperature in the semiconductor and is typically the site of semiconductor failure if this temperature gets too high.

The temperature of the junction cannot be determined with satisfactory accuracy by measuring the temperature of the structures used to conduct heat away from the semiconductor device.

Due to the slow heat transfer characteristics of this structure, external temperature measurements do not accurately reflect the temperature of the junction.

In power semiconductor applications, it is not practical to directly measure the temperature of a junction.

As a result, the protective devices used are indirect.

The oldest and most well-known protection device is, of course, the fuse, and the particular fuse used is set to blow at a value of current that is considered safe for the semiconductor.

This is a rather rough and simple method,
This does not utilize the full current carrying capacity of the semiconductor and tends not to be fast enough to protect the semiconductor against all transient conditions.

Additionally, when fuses are used, there is the problem of matching the thermal properties of the fuses to those of the semiconductor.

Solid state electronic circuits that protect power semiconductors from excessive temperatures are also known.

Naturally, such circuits are more sensitive and faster than fuses.

A circuit of this type is described in US Pat. No. 3,622,849.

The circuit described in this patent combines a signal representative of the temperature of a semiconductor heat dissipating structure and a signal representative of the current flowing through the semiconductor into a third signal representative of the temperature of the semiconductor junction.

Quoting from this patent, it is stated as follows.

A temperature monitoring device is provided that determines whether the temperature of a conductive thyristor junction has reached a preselected level corresponding to a dangerously high junction temperature.

The monitoring device has a circuit for synthesizing the thermal response of a portion of the thyristor and an associated pressurization assembly between an internal PN junction of the thyristor and an external reference point on a heat sink in close proximity to the junction. .

A synthesis circuit takes a measured signal representing the level of current flowing through the junction and exchanges this signal for a signal representing the power dissipated in the junction.

This latter signal is fed to a heat transfer simulator where it is converted into a signal representative of the temperature difference between the junction and the reference point of the heat sink.

This signal is combined with a measurement signal representing the temperature of the heat sink in an adder circuit to produce an output signal representing the temperature of the junction itself.

Preferably, the output of the adder circuit is provided to a level detector to generate a stop signal when the input is above a preselected level.

Means responsive to this stop signal can then be used to suppress the gate signal to the conducting thyristor, causing it to turn off and cool.

A somewhat related, but somewhat related, purpose of this invention is to provide a monitoring circuit that more directly determines the temperature of the junction.

As is well known, power semiconductors vary in the number of junctions used to conduct current from the anode to the cathode.

For example, a diode has one junction, and a thyristor has several junctions.

In the following description, the term "junction" includes both semiconductors with one junction and semiconductors with multiple junctions.

The semiconductor temperature monitoring device of this invention essentially comprises means for determining a signal representative of the current flowing through the junction, a current controller, a resistance-capacitance analog circuit of the semiconductor thermal system, and a direct current source.
Consists of a voltage level detector.

A current controller is connected to a similar circuit and the combination is connected to a direct current source.

The controller is controlled by a signal representative of the junction current and passes current through the analogous circuit.

The control is such that the relationship between the passed current and the control signal approximates the power dissipation characteristics of the semiconductor junction.

The voltage across the similar circuit represents the junction temperature, which is measured with a level detector.

When this monitoring device is used to protect semiconductor circuits against overheating, this voltage can be used to stop operation of the circuit when a level indicative of excessive junction temperature is reached.

The voltage measured by the level detector takes into account the power dissipation in the junction, the rate of heat diffusion, and the thermal conditions of the semiconductor structure.

The rate at which heat diffuses from the junction is a function of the transient thermal impedance of the structure.

A semiconductor structure refers to the combination of a semiconductor cell and a heat dissipating structure for the cell.

For example, it refers to a cell attached to a heat dissipation section. Transient thermal impedance is a heat dissipating structure expressed as a time relationship.
That is, it is the ratio of the temperature rise of the junction higher than the temperature of the heat dissipation part and the power consumed by the junction.

This is a function of several factors, including (1
) the dimensions of the heat sink to which the semiconductor is attached; (2) the type and speed of the cooling fluid that exchanges heat with the heat sink; and (3) the heat dissipation capacity of the heat sink.

If the power consumption in the junction is known, and the transient thermal impedance is known, the temperature of the junction can be determined.

The transient thermal impedance of a semiconductor structure as well as the power dissipation characteristics of the junction are both structure specific.

In the case of a cell, these characteristics are usually available from the cell manufacturer, and when the cell is combined with a heat sink, these characteristics are determined from measurements by the person installing the cell on the heat sink.

Next, this invention will be explained in more detail with reference to the drawings.

A temperature monitoring circuit 10 is shown in FIG. 1 and is coupled to a current conversion circuit 11 by a current sensing device 12. As shown in FIG.

The circuit 11 essentially consists of a power input line 13, a circuit breaker 14, a current converter 15, and a power output line 16.

This power circuit can be used for various purposes, such as converting polyphase alternating current on line 13 to direct current on line 16, converting polyphase alternating current on line 13 to direct current on line 16,
Convert the DC on line 13 to polyphase AC with another frequency of
It can be used to convert to 6 AC.

Alternatively, the current conversion device can be configured to serve as a circuit breaker.

The converter itself has a number of semiconductors, such as cynostars or diodes, connected in series and parallel in a bridge or other manner, depending on the voltage and current conditions.

High-power conversion devices that most require semiconductor protection include a large number of semiconductors.

The temperature monitoring circuit 10 essentially includes a current-to-voltage converter 17, a current controller 18, and a resistance-capacitance analog circuit 1.
9, a voltage level detector 20, and a DC source 21,22.

Transducer 17 receives the input signal from sensing device 12 and generates a signal to controller 18 .

A controller 18 and a similar circuit 19 are interconnected between buses 21 and 22, and a level detector 20 is connected to the similar circuit 19.

The level detector may be operatively coupled to circuit breaker 14, as shown by dashed line 23.

A sensing device 12 senses the current flowing through a semiconductor junction in a converter 15, and a converter 17 converts the output of the sensing device to a DC voltage that is a function of the junction current.

This voltage is also a function of the current flowing through any one semiconductor, since the semiconductors inside the converter are the same or approximately the same and are connected in a current-sharing circuit fashion with each other.

For this reason, the signal applied to controller 18 to control it is a voltage representing the current flowing through the junction of one semiconductor, and in response to this voltage, the controller A current is caused to flow between the busbars 21.22 via 19.

The analogous circuit 19 is a resistive-capacitive circuit configured to simulate the thermal circuit of semiconductors of the type used in converter devices.

The voltage from converter 17 controls the current through controller 18.

The control of this controller is such that when a graph is drawn using the current of the controller and the voltage of the converter as coordinates, the resulting curve approximates the power consumption characteristics of a semiconductor junction.

Therefore, the parameters of the circuit can be selected with respect to the voltage of the analogous circuit 19 representing the junction temperature.

This voltage may be measured by a detector 20 and displayed as a temperature or for other purposes, such as initiating a control function, e.g. tripping the circuit breaker 14, when the junction temperature becomes too high. It can be used.

In the circuit shown in FIG. 1, the current controller may be connected to a similar circuit as either a current source or a current absorber, the result being only that the direction of the current through the controller is different.

In this section, we define that current flows from the source and flows into the absorber.

FIG. 2 shows a similar circuit when operating as a current absorbing section.

A preferred embodiment of this invention will now be described with reference to FIG.

This figure shows the temperature monitoring circuit in more detail.

The circuit of FIG. 2 has an input 24, an input buffer 25, a current controller 26, a similar circuit 27, an output buffer 28, a voltage level detector 29, and a pair of DC busbars 30,31.

Input terminals 33 and 34 are connected to series resistors 35, 36, 37
connected to a voltage divider made up of.

Zener diode 38 connects resistor 36 at buffer 25
and 37.

One side of the voltage divider is connected to the negative bus 31.

The positive output of the voltage divider is passed through the operational amplifier 39 of the buffer 25 to the operational amplifier 40°41.4 in the current controller 26.
2 direct input.

The output of amplifier 40 is connected to the base of an NPN transistor 43 whose collector-emitter path is connected in series with a resistor 44.45 between buses 46 and 31.

The inverting input of this amplifier is connected directly to the emitter of the transistor.

The output of amplifier 41 is connected to the base of transistor 47, whose collector-emitter path is connected in series with resistor 48, 49 between busbars 46 and 31.

The inverting input of this amplifier is connected to the emitter of the transistor via a resistor 50, and resistors 51, 52, 53
It is also connected to the busbar 30.31 via.

Amplifier 42 is circuit-connected to transistor 54 and resistors 55 to 60 in the same manner as amplifier 41.

Block 27 in FIG. 2 is an approximate electrical analog circuit for the semiconductor thermal system used in converter 15. Block 27 in FIG.

That is, it is a resistance-capacitance circuit. In these circuits, capacitance corresponds to heat capacity, electrical resistance corresponds to thermal resistance, current corresponds to the rate of heat transfer or heat generation, and voltage corresponds to temperature.

Therefore, the circuit 27 that electrically represents the thermal state of the semiconductor is as follows.

The capacitances of the capacitors 61 to 64 correspond to the heat capacities of the junction, weber, main body, and heat dissipation part, respectively, and the capacitances of the resistors 65 to 6
The resistance values of 8 correspond to the thermal resistances from the junction to the webber, from the webber to the main body, from the main body to the heat dissipation part, and from the heat dissipation part to the surroundings, respectively.

In other words, the capacitance of the capacitors 61 to 64 is
It can be considered that the effective heat capacity of the junction, webber, main body, and heat dissipation part corresponds to the main body, respectively, and the resistance values of resistors 65 to 68 can be considered to roughly correspond to the effective thermal resistance between these elements. It's fine.

It should be noted that the electrical circuit of capacitors 61-64 and resistors 65-68 only approximates the semiconductor thermal system.

This particular circuit uses the minimum number of capacitors and resistors considered necessary for a monitoring device.

By increasing the number of capacitors and resistors, even stricter similarity can be achieved.

A circuit of capacitors and resistors is connected to busbar 30.46.

A voltage level detector 29 is connected across the capacitor 61 of the analogous circuit.

This connection is made through a buffer circuit 28 that includes an operational amplifier 69, and is configured in such a way that the detector can monitor the voltage on the capacitor while drawing little current from the capacitor.

The power supply for the particular temperature monitoring circuit shown in FIG. 2 is a dual voltage DC source.

That is, a positive 15V bus, a negative 15V bus, and a 0
or a source with a common bus line.

Preferably, this power supply is an inhibit type power supply, such as that described in US Pat. No. 3,866,094, which inhibits its output when voltage transients are present.

A level detector such as that shown at 29 operates by comparing the changing voltage level to a constant voltage level.

Since a constant voltage is available from the power supply, transient conditions in the power supply tend to cause spurious operation of the detector, and it is therefore preferable to provide the power supply with means for inhibiting such operation.

Next, the operation of the circuit shown in FIG. 2 will be explained with reference to the graph shown in FIG.

The voltage at terminals 33.34 of input 24 is the voltage obtained from a current-to-voltage converter operatively coupled to current converter 15 and represents the current flowing in the semiconductor of the converter;
In other words, it is a DC voltage that is a function of junction current.

This voltage is applied to voltage dividers 35-37. The adjustment at 37 allows the voltage to be selected to the appropriate value for use in current controller 26.

Zener diode 38 is provided to protect the operational amplifier against excessive voltage.

The positive voltage selected at the midpoint of the voltage divider is applied via the buffer 25 to the direct inputs of the operational amplifiers 40, 41, 42.

A buffer operational amplifier 39 converts a high input impedance to a low output impedance.

Although the buffer is not essential to the operation of this circuit,
It makes a voltage divider a current controller in the sense that the controller does not disturb the equilibrium of the currents in the voltage divider, i.e. the current drawn by the controller does not disturb the proportionality of the voltage in the voltage divider and the current in the junction. It is very useful to use it in terms of isolation from the environment.

Therefore, the voltage applied to the direct inputs of operational amplifiers 40-42 is a function of the junction current.

A positive voltage generated by operational amplifier 40 is applied to the base of transistor 43 and is applied to bus bar 46 via the collector-emitter path of this transistor and resistor 44.45.
The current ■□ is passed from the bus bar 31 to the bus bar 31.

The control of the amplifier depends on the positive voltage applied to its direct input.
8 and a positive feedback voltage applied from the emitter of the transistor to its inverting input.

The current 11 carried by the transistor is equal to the output of the amplifier and the resistor 4.
It is determined by the resistance value of 4.45.

Therefore, there is a direct relationship between the current 11 and the voltage 8.

This relationship is shown in the graph of FIG. 3, where the vertical axis represents the current (2) and the horizontal axis represents the voltage (8).

This graph shows that the current 1 is linear starting from the current and voltage 0.

In reality, this current is not necessarily perfectly linear, but
It is so close to linear that it can be considered linear for convenience of explanation.

Amplifier 41. Transistor 47, resistor 48, 49 separate element 4 apart from the signal applied to the inverting input of the amplifier.
A circuit similar to the circuit composed of 0.43 and 44.45 is constructed.

In this case, resistor 50 changes the feedback voltage, and resistors 53, 5
A negative bias is applied by 2.51.

This bias increases the voltage v8 required to turn on the transistor.

Figure 3 shows that the current ■2 passed by the transistor 47 is the voltage ■1
It is shown that the current starts from 0 at , and rises linearly with a slope different from that of the current 1.

This slope is determined by the voltage to the base of the transistor as well as the resistance value of resistor 48.49.

Amplifier 42, transistor 54, and resistors 55-60 constitute a circuit similar to that previously described.

In this case, the current ■3 passed by the transistor 54 is caused by the voltage ■
It is shown in FIG. 3 that from zero at 2 it rises linearly with a slope different from that of the other two currents.

As shown in FIG. 2, currents II, I2. I3 is obtained from bus bar 46, which is also connected to analogous circuit 27 at capacitor 61.

Therefore, the sum of these currents can be expressed as .

From a similar circuit, the current ■ is the capacitor 61 and the resistor 65.
It is obtained at the connection point with.

In FIG. 3, the current 11. I2. When I3 is summed up on a graph (as shown in FIG. 2 when summed up algebraically), the sum can be represented by curve 8.

The curve IR is composed of a series of straight lines as an approximation of the dashed curve marked as ideal.

The ideal curve represents the power dissipation characteristics of the junction.

That is, it is a graph of the junction current shown as a function of the wattage consumed in the junction plus the loss due to the resistance value of the semiconductor material.

Since the current in the controller corresponds to the rate of heat generation, the current (2) in FIG. 3 can be expressed in wattage, and of course the voltage (8) represents the junction current.

Therefore, the broken line curve shown in this figure also represents the power consumption characteristics of the junction.

This characteristic curve can be obtained from the semiconductor manufacturer or by testing.

Axis line ■ in Fig. 3 indicates parts 40 to 45 and 47 to 6.
By appropriately selecting 0, it is possible to approximate this power consumption characteristic.

That is, the resistance value of the selected resistor and the operating characteristics of the amplifier and transistor are such that II, I2 . I3 is generated.

FIG. 2 shows the third stage current controller 26.

That is, the parts 40 and 43 of the controller that generate the current 11
45 to 45 can be considered as the first stage, components 41 and 47 to 53 that generate current I2 can be considered as second stage, and components 42 and 54 to 60 that generate current I3.
can be considered as the third stage.

In a preferred embodiment of the invention, three stages of current 1, .
L, I3 yields a reasonable approximation IR of the power dissipation characteristics of the junction.

However, there may be cases where a more rigorous approximation is required, in which case a fourth or more stages can be added.

It will be readily apparent to those skilled in the art that additional stages may be added.

The resistor-condenser circuit shown at 27 in FIG. 2 is a similar circuit that approximately electrically represents the thermal system of a semiconductor.

At any given time, the current flowing through capacitor 61 corresponds to the rate of heat generation in the semiconductor junction, and the voltage across the capacitor corresponds to the temperature rise of the junction.

Components 62 to 68 of the circuit represent a semiconductor structure that removes heat from the junction; the power dissipation characteristic of the junction effectively represents the heating of the junction, and the current , approximates that characteristic. Therefore, in a similar circuit as shown in 27, the voltage across the capacitor 61 represents the junction temperature.

The voltage across the capacitor 61 is detected by the voltage level detector 29.
monitored by.

A buffer 28 in the circuit leading from bus 46 to the level detector prevents the level detector from drawing significant current from this bus.

The buffer 28 shown in FIG. 2 is essentially an operational amplifier, and its circuit type is such that the current drawn from the bus is negligible, but it can follow the voltage of the capacitor.

Any change in the value of current IR will be reflected in the voltage across capacitor 61.

Therefore, if the level detector is to accurately read the junction temperature, this current must not be disturbed.

The detector 29 can be used for a number of functions, such as displaying the junction temperature, recording the junction temperature, or shutting down the exchanger if the semiconductor temperature becomes too high.

In the circuit of FIG. 2, a similar circuit 27 is used with a current regulator 26 operated in the manner previously defined as a current absorber.

The temperature monitoring circuit may use a similar circuit with a controller acting in the form of a current source as previously defined.

As defined earlier, current is considered to flow from a source and into an absorber.

A case in which the controller is operated as a current source is shown in FIG. 4, which will now be described.

In the case of a current source, many of the components shown in FIG. 2 for controller 26 and analogous circuit 27 are arranged as shown in FIG.

Rearranged parts have the same reference numerals with 100 added.

For example, amplifier 40 in FIG. 2 is amplifier 140 in FIG. 4, and NPN) transistor 43 in FIG.
NP) transistor 143.

Figure 4 shows the circuit components that generate current ■1.
The components that generate the currents 2 and 13 are similarly arranged.

In the case of similar circuits, only enough components are shown in FIG. 4 to indicate the new arrangement.

The operation of the temperature monitoring circuit is the same whether the controller is used as a current absorber or a current source.

In a practical application of the invention to protect a converter such as that shown at 15 in FIG. 1, a single supervisory circuit as shown in FIG. 2 will usually be sufficient.

When determining the parameters of the monitoring device, consider the worst operating condition for the semiconductor in the converter, and increase this condition by a safety factor of, for example, 20%.

For example, if the current sharing between the semiconductors in the converter is such that the maximum current through one of them is 10 OA, the monitoring device should be designed as if it were 12 OA.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram of the invention, FIG. 2 is a circuit diagram of a preferred embodiment of the temperature monitoring circuit, FIG. 3 is a graph illustrating the operation of the circuit shown in FIG. FIG. 4 is a circuit diagram of a modification of the circuit shown in FIG. Explanation of main symbols 12: Current sensing device, 18, 26:
Current controller, 19.27: Similar circuit, 20.29:
Voltage level detector, 21.22; 30, 31: DC bus.

Claims (1)

[Scope of utility model registration request] means for generating a direct current voltage that is a function of the current through the semiconductor; a first capacitance means representative of the heat capacity of the junction of said semiconductor; another capacitance means representative of the heat capacity of the wafer, body and heat sink; A resistance-capacitance similar circuit of the semiconductor thermal system including resistance means representing thermal resistance to the surroundings to which it is connected, and a large number of stages, the magnitude of the current passed through each stage being the value of the DC voltage. and each stage is connected in parallel with a current controller having one side of said parallel connection connected to one side of said first capacitive means and one pole connected to said other side of said parallel connection. applying the DC voltage to each stage of the current controller and a DC current source connected to the other side of the first capacitor, the other pole of which is connected to the other side of the first capacitance, so that each stage passes. The magnitude of the current is controlled according to the value of the DC voltage, and by this control, the sum of the currents passed by each stage becomes a curve that approximates the power consumption characteristics of the semiconductor junction in a graph that coordinates the current and voltage. and a voltage level detector connected to said first capacitive means for measuring a voltage level thereon, said voltage level being indicative of the temperature of said semiconductor junction. A circuit that monitors temperature.