JPH04119136U - switch circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the saturation voltage between the emitter and collector of a transistor used as a switching element, and to reduce the amount of heat generated in this part. [Structure] A transistor Tr 3 is connected to the base circuit of a transistor Tr 2 used as a switching element,
A diode is connected between the power supply Vcc and the collector of the transistor Tr 2.
Insert the heat dissipation diode D1. Then, the collector current of the transistor Tr 3 is used as the base drive current of the transistor Tr 2, and the anode side of the diode D1 and the emitter of the transistor Tr 3 are connected.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

This invention relates to switch circuits, particularly switch circuits using transistors. do.

0002

[Conventional technology]

Traditionally, switch circuits using transistors have been configured to control the voltage applied to the load. Techniques for turning pressure on and off are well known. However, in this case, the Heat generation due to power loss in transistors is a problem in circuit design and heat dissipation design.

0003 Therefore, in the past, the one shown in FIG. 3 has been first proposed.

0004 This turns on the transistor Tr 1 by the output VIN of the control circuit 1, and A driving current is applied to the base of the transistor Tr 2 through R1, and thereby the transistor This turns on the resistor Tr 2 .

[0005] By the way, in this case, in the transistor Tr 2 , the emitter and collector when ON are Power loss due to inter-saturation voltage and switching loss during turn ON/turn OFF occurs. In this case, switching loss is caused by switching frequency This can be reduced by lowering the emitter-collector saturation. Power loss due to sum voltage cannot be reduced. In this case, the value of resistor R1 should be reduced. In this case, the drive current of the transistor Tr 2 can be increased by The power consumption of the resistor R1 increases in inverse proportion to the resistance value of the resistor R1, which impairs the efficiency of the entire circuit.

[0006] Therefore, as shown in Figure 4, the base circuit of the switching transistor Tr 2 is , a technique is used in which the transistor Tr 3 is arranged in a Darlington connection. This person According to the method, the current amplification factors of transistors Tr 3 and Tr 2 are significantly improved, and the resistance Power consumption in anti-R1 is reduced.

[0007] However, in this example, the emitter-collector saturation of transistor Tr 2 The voltage is Tr 3 assuming that the emitter-collector of transistor Tr 3 is sufficiently saturated. Since the base-emitter forward voltage of transistor Tr 2 is added, The base-emitter forward voltage is divided between the emitter and collector of the transistor Tr 2. You can't get into it.

[0008] In the above, a PNP type transistor is used as the switching transistor Tr 2. In this case, an NPN type transistor is used as the switching transistor Tr 2. A case in which transistors are employed will be described with reference to FIG. 5.

[0009] In this example, the switching transistor Tr 2 has a resistor R1 connected to the power supply Vcc. The base current is supplied through the control circuit 1, and the transistor By turning on Tr 1, the base current of transistor Tr 2 is bypassed. This turns off the transistor Tr 2 .

0010 By the way, in this case, when the transistor Tr 2 is ON, the supply to the load L is In order to supply a base bias current commensurate with the supply current, there is a potential difference between both ends of the resistor R1. occurs, and this voltage component and the base-emitter forward voltage of transistor Tr 2 occurs between the collector and emitter of transistor Tr 2 .

[0011] Therefore, in this example as well, in order to reduce the saturation voltage when the transistor Tr 2 is turned on, For this purpose, the resistance value of resistor R1 must be set sufficiently small. Also, transition When the starter Tr 2 is OFF, the resistor R1 is inserted between the power supply and ground. , this also necessitates large power losses.

0012 Therefore, the circuit shown in FIG. 6 is often employed.

[0013] This uses a second transistor Tr 3 instead of the resistor R1 in FIG. This drives the base of transistor TR 2 .

[0014] In this case, the transistor Tr 1 is turned on by the output VIN of the control circuit 1, and this As a result, transistor Tr 3 is turned on via resistor R1, and the saturation voltage is sufficiently low. The voltage can connect the power supply VCC and the base of the transistor Tr 2 .

[0015] However, even in this case, the base-emitter forward voltage of transistor Tr 2 is This cannot be ignored, and the voltage between the collector and emitter of transistor Tr 2 when it is ON is It cannot be interrupted.

[0016]

[Problem that the idea aims to solve]

In the conventional switch circuit as described above, for example, the one shown in FIG. The current amplification factor in resistors Tr 3 and Tr 2 has been greatly improved, and the power consumption in resistor R1 has been reduced. Although it is reduced, the emitter-collector saturation voltage of transistor Tr 2 is Even if the emitter-collector of transistor Tr 3 is sufficiently saturated, the transistor The base-emitter forward voltage of transistor Tr 2 is added, and the emitter voltage of transistor Tr 2 is The base-emitter forward voltage cannot be interrupted between the emitter and collector. Can not. Therefore, when the transistor Tr 2 is turned on, the emitter-collector saturation is The power loss due to the sum voltage is large, and in this case, the heat generated by the power loss is localized. Since this phenomenon occurs in a concentrated manner, it can be very difficult to design circuits and heat dissipation. There was a problem.

[0017] In addition, in the case shown in FIG. 6, the power supply Vcc and the transistor T The base of transistor Tr 2 can be connected to the base of transistor Tr 2 . The emitter forward voltage cannot be ignored, and the collector emitter voltage when the transistor Tr 2 is on is The emitter saturation voltage cannot exceed the base-emitter forward voltage; The power loss due to collector-collector saturation voltage is large, resulting in the same problem as shown in Figure 4. There was a coincidence.

[0018] This invention was made in view of the conventional problems as mentioned above, and its purpose is to The rollers are the emitter and collector of a transistor used as a switching element. A switch that can reduce the saturation voltage between The purpose of this invention is to provide a circuit.

[0019]

[Means to solve the problem]

In order to achieve the above object, the present invention uses a transistor to apply power to the load. In a switch circuit that opens and closes a voltage, the first transformer is used to open and close a load circuit. a second transistor connected to the base circuit of the first transistor; a collector circuit of the first transistor; and a diode whose conduction direction is the forward direction.

[0020]

[Effect]

In this invention, the first transistor and the base circuit of this first transistor are A large current amplification factor is obtained by the connected second transistor, and If there is no diode, the power loss consumed by the first transistor is It can be distributed into one transistor and diode.

[0021] Therefore, the saturation voltage between the emitter and collector of the first transistor can be made sufficiently small. This can also reduce the power loss of the first transistor. I can do that.

[0022]

【Example】

The present invention will be explained below based on the drawings.

[0023] FIG. 1 is a circuit diagram of an embodiment to which the present invention is applied.

[0024] First, to explain the configuration, the transistor (first transistor) Tr 2 is the load A switching element that turns on and off the voltage applied to L, which connects the power supply Vcc and the transistor. A diode (heat dissipation diode) D1 is inserted between the collector of the transistor Tr2. Ru.

[0025] Furthermore, the base circuit of the transistor Tr 2 includes a transistor Tr 3 (a second transistor). transistor) is arranged, and the collector current of the transistor Tr 3 is The base drive current of transistor Tr 3 is set to 2, and the emitter of transistor Tr 3 is Connected to the anode side of the ode D1.

[0026] 1 is a control circuit that controls ON/OFF of the entire switch circuit; The output VIN of 1 is supplied to the base of the transistor Tr 1 .

[0027] Also, there is a resistance between the collector of the transistor Tr 1 and the base of the transistor Tr 3. Resistor R1, resistor R2 between the base and emitter of transistor Tr3, R3 is connected between the emitter of Tr 2 and the collector of transistor Tr 3. Furthermore, between the emitter of the transistor Tr 1 and the emitter of the transistor Tr 2 A diode D2 is connected in parallel with the load L.

[0028] The above is the configuration of this embodiment, and its operation will be explained next.

[0029] First, the control circuit 1 outputs the base drive current VIN of the transistor Tr 1. Then, the transistor Tr 1 is turned on, and the voltage is transferred to the transistor Tr 3 via the resistor R1. Base current is supplied.

[0030] As a result, the transistor Tr 3 is connected to the power supply Vcc at a sufficiently low saturation voltage. and the base of the transistor Tr 2 are connected. As a result, the transistor Tr 2 becomes It is turned on and supplies current to the load L.

[0031] By the way, the emitter voltage VOUT of the transistor Tr 2 at this time is Expressed in terms of the voltage of the base circuit of the transistor Tr 2, the power supply voltage is VCC, and the voltage of the transistor Tr 2 is The collector-emitter voltage of transistor Tr 3 is VCE3, and the base-emitter voltage of transistor Tr 2 is It can be expressed by the following equation, assuming the forward voltage of the motor as VBE2.

[0032] VOUT =VCC-VCE3-VBE2 (1) On the other hand, the voltage of the collector circuit of transistor Tr 2 causes the emitter of transistor Tr 2 to The forward potential of the diode D1 is VF, and the transistor potential VOUT is expressed as the forward potential of the diode D1. Tr 2 Letting the collector-emitter voltage be VCE2, it can be expressed by the following equation.

[0033] VOUT =VCC-VF-VCE2 (2) Therefore, from equations (1) and (2) above, the following equation can be obtained.

[0034] VCC−VCE3 −VBE2 =VCC−VF −VCE2 (3) Here, the forward voltage VBE2 of the transistor Tr 2 is equal to the forward voltage VBE2 of the diode D1. If it is equal to the pressure VF, the following equation can be obtained from the above equation (3).

[0035] VCE3 = VCE2 (4) In other words, the collector-emitter voltage VCE3 of transistor Tr3 and The collector-emitter voltage VCE2 of star Tr 2 becomes equal, and the already mentioned sufficient The saturation voltage of transistor Tr 3 which is low due to This means that it can be treated as the collector-collector saturation voltage.

[0036] In this embodiment, the transistor Tr 3 is connected to the base circuit of the transistor Tr 2. Therefore, the current amplification factor should be set sufficiently large in both transistors Tr 2 and Tr 3. , and a resistor with a small resistance value can be used as the resistor R1. Power consumption can be reduced.

[0037] In addition, in this case, in this embodiment, the power loss consumed by the transistor Tr 2 is can be distributed between the diode D1 and the transistor Tr 2, and the low The emitter-collector voltage is the emitter-collector voltage of the transistor Tr 2. Therefore, the power loss of the transistor Tr 2 can be sufficiently reduced. can be done.

[0038] In addition, even when the switch frequency is set high, most of the voltage drop when the switch is turned on is Since the diode D1 carries the load, the transistor Tr2 mainly performs switching. Only loss needs to be considered, increasing flexibility in device circuit design and heat dissipation design. do.

[0039] In addition, as mentioned above, since the heat generating parts are distributed, the heat dissipation mechanism is simplified and greatly improved. This enables cost reduction.

[0040] Next, a second embodiment of the present invention will be explained with reference to FIG. The same components will be described with the same reference numerals.

[0041] By the way, in this second embodiment, PNPs are used as the transistors Tr 2 and Tr 3 . A Darlington type transistor is used, and a Darlington connection is made to the base circuit of the transistor Tr 2. Next, a transistor Tr 3 is arranged, and a heat dissipation diode D1 is connected to the transistor. It is connected between the collector of transistor Tr 2 and the collector of transistor Tr 3. , the other configurations are exactly the same as the first embodiment, so redundant explanation will be omitted. do.

[0042] Also in this embodiment, the output VIN of the control circuit 1 causes the transistor Tr 1 to turn to O. When the voltage is set to N, a drive current is supplied to the base of the transistor Tr 3 via the resistor R1. It will be done. As a result, the transistor Tr 3 becomes a transistor at a sufficiently low saturation voltage. Connect the base of Tr 2 and the load circuit.

[0043] Here, the voltage drop from the emitter of transistor Tr 2 to the load circuit is The emitter-base forward voltage of transistor Tr 2 and the Consisting of emitter-collector saturation voltage, as in the first embodiment above, Between the emitter and collector of transistor Tr 2 due to the forward voltage of diode D1 The voltage is reduced. Therefore, it has the same effect as the first embodiment described above.

[0044] .

[Effect of the idea]

As explained above, in the present invention, the first diode and the second diode collector-emitter of the first transistor while maintaining a large current amplification factor. This is possible by keeping the saturation voltage between the transistors sufficiently low. It is possible to reduce power loss and the amount of heat generated.

[0045] In addition, the heat generating parts are not concentrated in one place, but are distributed among diodes, transistors, etc. Therefore, the heat dissipation mechanism is simplified and costs can be reduced.

[0046] Furthermore, even when the switching frequency is set high, the voltage drop when turned on is large. The switching loss is borne by the diode, so the first transistor The degree of freedom in circuit design and heat dissipation design is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a switch circuit diagram in a conventional example in which a PNP transistor is used as a switching element.

FIG. 4 is a circuit diagram in which a switch circuit is configured by adding one transistor to the switch circuit of FIG. 3;

FIG. 5 is a switch circuit diagram in a conventional example in which an NPN transistor is used as a switching element.

FIG. 6 is a circuit diagram of a switch circuit in which one transistor is further added to the switch circuit of FIG. 5;

[Explanation of symbols]

1 Control circuit D1 diode (heat dissipation diode) D2 diode Tr 1 transistor Tr 2 transistor (first transistor) Tr 3 transistor (second transistor) L load R1, R2, R3 resistance

Claims (1)

[Scope of utility model registration request] 1. A switch circuit that uses transistors to open and close a voltage applied to a load, comprising: a first transistor used to open and close the load circuit; and a second transistor connected to a base circuit of the first transistor. 1. A switch circuit comprising: a second transistor; and a diode connected to a collector circuit of the first transistor, the diode having a conduction direction of the first transistor as a forward direction.