JPH0441369Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic load device using a transistor as an electronic load, and particularly to prevention of thermal runaway due to heat generation of the transistor.

BACKGROUND ART Conventionally, electronic load devices are known that vary the impedance seen from a DC power supply connected between the collector and emitter by controlling the base current of a transistor. FIG. 1 is a block diagram showing an example of such an electronic load device, in which an external power source _Eio is connected between positive and negative test terminals P and N.
An NPN type load transistor Tr is connected between the test terminals P and N through an emitter resistor _Re and a current detection resistor _Rs in series. Then, apply a control voltage VC to the non-inverting input of the differential amplifier DF,
Apply the terminal voltage E _i of the current detection resistor R _s to the inverting input,
This output is applied to the base of the load transistor Tr to control its collector current IC.
In other words, the differential amplifier DF has both input voltages VC, E _i
Since the collector current IC is controlled via the load transistor Tr so that the values are equal, the collector current IC is given by the following equation (1).

IC=E _i /R _s =VC/R _s ……(1) In other words, as is clear from this equation (1), the control voltage
Collector current IC can be controlled according to VC.

Furthermore, since most of the power consumed by such a load device is converted into heat by the load transistor Tr, it is important to control this heat dissipation. Therefore, when a large current capacity is required, the two load transistors Tr ₁ and Tr ₂ are connected in parallel, for example, in a configuration as shown in the block diagram shown in FIG.

However, such a load device must be operated within the wide voltage range of the power supply _Eio and within the allowable power.
The collector currents _IC1 , IC2 of _Tr1 , _Tr2 are large, and in the region where the voltage of the power supply _Eio is low _, i.e., the voltage between the collector and emitter of the load transistors _{Tr1 , Tr2} is low, the collector currents IC1, _IC2 of the load transistors _Tr1 , _Tr2 connected in parallel by the emitter resistor _Re are equal.
In this situation, the specific load transistor Tr
The collector current of the load transistor Tr1 and the collector current of the load transistor Tr2 are large, and the load transistor Tr1 and the collector current of the load transistor Tr2 are not overloaded. On the other hand, when the collector current IC is small and the voltage of the power supply _Eio is high, the voltage drop in the emitter resistor R _e is small. Therefore, the collector currents _IC1 and _IC2 of the load transistors _Tr1 and _Tr2 are large.
The difference between the base-emitter voltage _Vbe and the DC current gain _hfe causes the load transistors Tr to lose balance. The collector current of a particular load transistor Tr increases significantly. On the other hand, the temperature coefficient of the base-emitter voltage _Vbe of a transistor is negative, so a load transistor with an increased collector current will experience thermal runaway as more collector current flows through it, resulting in destruction in a short time.

This problem also occurs in an electronic load device in which N load transistors Tr ₁ , . . . , T ₀ are connected in parallel, as shown in FIG. 3, for example. That is, the collectors of N load transistors Tr ₁ , . . . , T _o are connected in parallel and connected to the terminal P. Further, the bases of the load transistors Tr ₁ ...T ₀ are connected in parallel and connected to the emitter of the drive transistor Tr _p . Also this load transistor
The emitters of Tr ₁ , . . . T _o are connected in parallel via emitter resistors Re ₁ , . . . Re _o, respectively, and connected to the terminal N'. And the above drive transistor Tr _p
The collector may be connected to the terminal P, and the output of a differential amplifier as shown in FIG. 2 may be applied to the base for control. By the way, in such a case, the V _be voltage Vbe 1 ,... of each load transistor Tr ₁ ,...T _{o is} Vbe ₁ ,...
The following equation (1) holds true between ...Vbe _o , each collector current I ₁ , ... I _o , and each emitter resistance Re ₁ , ... Re _o .

V _be 1+I ₁・R _e 1=V _be 2+I ₂・R _e 2=...=Vbe _o +I _o・Re _o ...(1) In other words, in such an electronic load, where the input voltage V is high, Since the value of collector current I is small, variations in V _be voltage and emitter resistance Re ₁ ,
...Due to the variation in Re _o , the collector current I ₁ , ...
It makes a difference in _Io . Since the temperature coefficient of V _be is negative, current concentrates on a specific load transistor, which tends to destroy it due to thermal runaway or cause it to become inoperable. This is especially true for electronic loads that operate at high voltages, and there is no perfect solution to this problem. Furthermore, a large-capacity electronic load device has a plurality of cooling packages, and as the number increases, problems such as thermal interference become more serious, and current concentration tends to occur on a specific cooling package.

Figure 4 is a diagram showing an example of the voltage-current characteristics of an electronic load device, for example, maximum current 100A, maximum voltage
If the voltage is 100V and the maximum power is 600W, the curve for 600W power will be as shown in Figure 4. In this characteristic diagram, particularly in the portion A shown in the figure where the voltage V is high, current concentration tends to occur, easily resulting in breakdown due to thermal runaway, an inoperable state, etc.

This idea was made in view of the above circumstances.
An object of the present invention is to provide an electronic load device having a plurality of cooling packages each having a plurality of load transistors, which can maintain thermal balance between the cooling packages with a simple configuration.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the circuit diagram shown in FIG. In other words, Figure 5 shows 3
cooling packages CL ₁ , CL ₂ , CL ₃ each with N load transistors.
_Tr11 to _Tr1o , _Tr21 to _Tr2o , and _Tr31 to _Tr3o are provided. and each cooling package CL ₁ , CL ₂ ,
CL ₃ is, for example, the load transistors Tr ₁₁ to Tr _1o ,
Tr ₂₁ to _{Tr 2o} and Tr ₃₁ to _{Tr 3o} are attached to a radiator to form a hollow cylindrical body, and a fan is attached to one end of the radiator to perform forced air cooling with cooling air. each load transistor of
Tr ₁₁ to Tr _1o , Tr ₂₁ to _{Tr 2o} , and Tr ₃₁ to _{Tr 3o} are thermally coupled via a radiator and placed under the same conditions. Therefore, within the same cooling package, each load transistor Tr ₁₁ ~Tr _1o , Tr ₂₁ ~
Tr _2o , Tr ₃₁ to _{Tr 3o} are abbreviations that can maintain thermal equilibrium and eliminate problems such as thermal interference.
It occurs in units of CL ₁ , CL ₂ , and CL ₃ .

And each load transistor Tr ₁₁ ~ Tr _1o , Tr ₂₁
~Tr _2o , Tr ₃₁ ~ _{Tr 3o} share the collector with terminal P
The bases are commonly connected to the emitters of each drive transistor Tr ₁₀ , Tr ₂₀ , Tr ₃₀ , and the emitters are connected to respective emitter resistors R ₁₁ ~ R _1o , R ₂₁ ~
It is connected to terminal N' via R _2o and R ₃₁ to R _3o .
And each drive transistor Tr ₁₀ , Tr ₂₀ ,
The collector of Tr ₃₀ is connected to the terminal P, and the drive signal S given to the base via the terminal T is connected to the diode.
D ₁ , D ₂ , and D ₃ are applied in series in the forward direction. Note that the number of diodes D is 1 to 3.
are inserted in series and thermally coupled to a load transistor of a cooling package different from the cooling package corresponding to the drive transistor providing the drive signal S. Therefore, the diode D ₁ which supplies the drive signal S to the first cooling package CL ₁ is thermally coupled to the third cooling package CL ₃ and the diode D which supplies the drive signal S to the second cooling package CL ₂ . ₂ is thermally coupled to the first cooling package CL ₁ and provides a drive signal S to the third cooling package CL ₃ . Diode D ₃ is thermally coupled to the second cooling package CL ₂ .

Note that the terminal T has a configuration such as that shown in FIG. 2, where the difference between the terminal voltage of the current detection resistor and the control voltage corresponding to the desired load current I _p is obtained by a differential amplifier, and this output is obtained by using a differential amplifier. give. Also, terminal P
Connect the positive terminal of an external power supply (not shown) to
A negative terminal is connected to the terminal N' via a current detection resistor in series.

With such a configuration, for example, the current flowing from the terminal P is I _p , each cooling package CL ₁ ,
If the currents flowing through CL ₂ and CL ₃ are Io ₁ , Io ₂ , and Io ₃ , the above-mentioned currents Io ₁ , Io ₂ , and Io ₃ are equal in a steady state. Here, for some reason, the above currents Io ₁ , Io ₂ ,
Suppose that the balance of Io ₃ is no longer maintained and, for example, the current Io ₁ increases. Then, due to the increase in current Io ₁ , the first
When the heating value of the cooling package CL ₁ increases, the temperature of the diode D ₂ thermally coupled thereto increases. However, when the diode D ₂ heats up, since it has a negative temperature coefficient similar to the transistor V _BE , the forward voltage V _F decreases, thereby reducing the drive transistor Tr ₂₀ of the second cooling unit CL ₂ . Increase the base current and thereby increase the current _Io2 . This increase in current Io ₂ causes the second cooling unit to
As the heat generation of CL ₂ increases, the temperature of the diode D ₂ thermally coupled thereto increases, and therefore the forward voltage V _F of this diode D ₃ also decreases. The base current of the drive transistor Tr ₃₀ of the third cooling unit CL ₃ is therefore increased, thereby increasing the current Io ₃ . The current Io ₁ of the first cooling unit CL ₁ is therefore equal to that of the second cooling unit CL 1 .
Current in cooling units CL ₂ and CL ₃ in Figure 3
It is relatively small compared to Io ₂ and Io ₃ , and by similar control, each cooling unit CL ₁ , CL ₂ , CL ₃
The currents Io ₁ , Io ₂ , and Io ₃ can be made equal. Therefore, each cooling unit CL ₁ , CL ₂ ,
By thermally balancing CL ₃ , it is possible to prevent only the current in a particular cooling unit from increasing, overloading it and eventually destroying the load transistor due to thermal runaway.

As detailed above, the present invention provides a plurality of cooling packages in which a plurality of load transistors are thermally coupled via a heat sink, and connects the collector and emitter of each load transistor in each cooling package in parallel. An electronic device characterized in that it is connected to an external power source, and its base is connected in parallel to each cooling package to provide a drive signal via a diode that is thermally coupled to another cooling package different from the cooling package. load device.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing examples of different conventional electronic loads, FIG. 3 is a diagram explaining an electronic load having N load transistors, and FIG. 4 is a diagram illustrating an electronic load having N load transistors. A diagram showing an example of voltage-current characteristics, and FIG. 5 is a circuit diagram showing an embodiment of the present invention. CL ₁ , CL ₂ , CL ₃ ... Cooling package cage,
Tr ₁₁ to Tr _3o ...Load transistor, _D1 to _D3 ...
Diode, P, N', T... terminal.

Claims (1)

[Scope of utility model registration request] It has a cooling package in which multiple load transistors are connected in parallel and thermally coupled via a heat sink, and the collectors and emitters of each load transistor in the multiple cooling packages are connected in parallel and connected to an external power source. With,
An electronic load device characterized in that a base is connected in parallel to each cooling package and a drive signal is applied via a diode that is thermally coupled to another cooling package different from the cooling package.