JPS6111543B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a transistor chopper device, and more particularly to a power transistor drive device that supplies an optimal base current in a power transistor switching operation.

[Background of the invention]

Conventionally, a method for controlling the base current of a transistor chopper device that controls a DC motor has been described, for example, in JP-A-52
It is known from the publication No.-60930.

In general, current transformers, including those cited above, simply control the base current in a proportional relationship according to the magnitude of the load current, in other words, the load current is controlled from 0 to the maximum load. There is a problem in that simply changing the base current proportionally increases the power loss in the drive circuit of the transistor chopper.

[Purpose of the invention]

An object of the present invention is to provide a power transistor base current control device that can reduce power loss in a drive circuit.

[Summary of the invention]

In a transistor chopper, the present invention detects the instantaneous value of the collector or emitter current of the transistor, flows the minimum necessary constant base current until the current reaches a certain value, and when the current exceeds a certain value, the current is proportionally reduced. Control is performed to increase the base current, and control is also performed to compensate for fluctuations in the base current according to fluctuations in the power supply voltage.

[Embodiments of the invention]

In Figure 1, M is a DC motor having a series field winding F, 1 is a transistor chopper, D is a flywheel diode, B is a DC power source such as a battery, 2 is a drive transistor, and 3 is a current limiting resistor. , 4 is a conduction rate control circuit. 5 is Batsuteri B
and a current detector 7 provided in series with the transistor chopper 1, and the output terminal of the control circuit is connected to the current limiting resistor 3.
base current control transistor 6 connected in parallel with
connected to the base of.

Next, a specific embodiment of the base current control circuit will be explained with reference to FIG. In the figure, 1 is a transistor chopper, which is controlled by a base current I _B . Transistor 2 controls I _B on and off, and its collector is connected to the base of the chopper transistor via base resistor R _B , and its emitter is connected to the positive terminal of battery power supply B via current limiting resistor 3. ing. The drive transistor 2 is
The base is connected to the conduction control circuit 4 via the base series resistor _R13 , and the conduction rate control circuit 4 is
ON/OFF control is performed based on ON/OFF signals. 9 is an operational amplifier with input resistances R ₁₀ , R ₁₁ ,
It is a current detection circuit that has a feedback resistor R ₁₅ and a feedback resistor R ₁₂ , and detects the voltage across the current detector 7 and detects the transistor current _I.sub.C. 8 is an operational amplifier that detects the transistor current and battery voltage and generates an output for controlling the transistor 10. The + terminal of the input of the operational amplifier 8 is connected to the input resistor 5.
to the negative of battery B via
It is connected via _R4 to the midpoint between voltage dividing resistors _R1 and _R2 , which divide the voltage of battery B. The other negative terminal is connected to the output via a feedback resistor R ₆ and also to the output of the operational amplifier 9 for the transistor current I _C detection circuit via an input resistor R ₃ . 6 is a base current control transistor;
The emitter and collector are connected to both ends of the current limiting resistor 3, respectively. Further, a base parallel resistor R ₁₄ is connected between the collector and the base, and the base is connected to the collector of the transistor 10 . transistor 10
The emitter is connected to the negative battery B via the emitter resistor _R9 , and the base is connected to the parallel resistor _R8.
and the base series resistor _R7 is connected, and the resistor
The other end of _R7 is connected to the output terminal of the operational amplifier 8 via a Zener diode _ZD . The base current control circuit is configured by the above circuits, and the operation of these circuits will be explained. First, the operational amplifier 9 detects the instantaneous value of the current I _C of the transistor chopper. The gain of the operational amplifier in that case is
R ₁₂ /R ₁₀ and the output voltage V _I is output. When this output voltage V _I and the divided voltage of the battery B are added, the output voltage V _C of the operational amplifier 8 has the following relationship.

V _C =V _B・R ₂ /R ₁ +R ₂・R ₅ /R ₄ −R ₆ /
R ₃ V _I (1) The transistor 10 is controlled by this output signal V _C. That is, the relationship between the control signal V _C and the base current of the transistor 10 is expressed by the following equation.

However, the emitter current I _E10 of the transistor 10
is I _C10 + I _B10 .

V _C =V _Z +R ₇ (I _B10 −V _BE +I _E10 R ₉ /R ₈ ) +V _BE +R ₉・I _E10 ………(2) Here, V _Z : Zener voltage I _B10 : Base current of transistor 10 I _C10 : Collector current of transistor 10 In addition, collector current I _C10 is h _FE (direct current amplification factor) times I _B10 as shown in the following equation.

I _C10 = h _FE I _B10 (3) Therefore, when the control voltage V _C is sufficiently larger than the Zener voltage V _Z , a large amount of base current I _B10 flows, and the voltage between the collector and emitter of the transistor 10 is saturated. However, as the control voltage V _C decreases, I _B10 decreases. I _C10 is also proportionally changed and controlled.

Then, the collector current I of transistor 10
The relationship of _C8 etc. is as follows.

V _B =I _C10 R ₁₄ +V _CE8 +R ₉ I _E10 ...(4) Here, V _B : Battery voltage V _CZ8 : Collector-emitter saturation voltage of transistor 10 Furthermore, base current I _B flowing through chopper transistor 1 The relationship between the collector-emitter voltage V _CE6 of the base current control transistor 6, etc. is expressed by the following equation.

V _B = V _CE6 + V _CE2 V _BE1 + V _S + I _B R _B …(5) Here, V _CE2 : Collector-emitter saturation voltage of transistor V _BE1 : Base-emitter voltage of chopper transistor V _S : Current detector Now, in equation (5), V _CE6 , I _B R _B ≫ V _CE2 , V _BE1 ,
When V _S is assumed, equation (5) becomes the following equation.

V _B ≒ V _CE6 + I _B R _B (6) Therefore, it can be seen that by changing the collector-emitter voltage V _CE6 of the base current control transistor 6, the base current I _B of the transistor chopper can be controlled. .

FIG. 3 shows the operating waveforms of these base current control circuits during chopper operation. FIG. 3a shows the case where the collector current is small, and the base current I _B is at the minimum current state. b indicates that when the collector current I _C exceeds a certain value, I _B increases proportionally. Further, c represents a case where the collector current is large, and I _B increases in proportion to I _C from the start of the chopper.

In the above embodiment, as can be seen from the characteristics in Figure 4, the base current I _B is controlled with respect to the collector current I _C so that the battery voltage has characteristics b when it is normal, a when it is low, and c when it is high. It is something that These characteristics basically approximate the relationship of the inverse function of the DC current amplification factor of the power transistor. Note that the base current I _Bnio in the range where I _B remains constant even if I _C increases is due to the current limiting resistor 3 (R _B ) and battery voltage because the base current control transistor 6 in FIG. 2 is in the cut-off state. It is determined by the voltage V _B of B and changes in an analog manner, resulting in the value of the following equation.

I _Bnio = V _B /R _B (7) Therefore, in the characteristic of a where the battery voltage has decreased, it is necessary to secure the minimum base current necessary to saturate transistor 1. I understand.

The characteristics shown in FIG. 4 are characteristics that compensate for battery voltage fluctuations when I _B is made proportional when I _C exceeds a certain value, and can be obtained as follows.
In Fig. 2, when the voltage of battery B decreases,
During a certain period of the base current, the current control transistor 6 is in an off state, and the base current I _B of the transistor 1 becomes a current expressed by the above equation (7). In a region where the collector current I _C increases and the base current I _B rises, the base current control circuit 5 controls the conduction state of the transistor 6 in accordance with fluctuations in the battery voltage. In other words, the battery voltage decreases,
Alternatively, in the case where the collector current I _C is in the same state, the conduction state of the transistor 6 is controlled so that the base current I _B is constant, so that the characteristics shown in FIG. 4 are obtained. The characteristics of this control method are that when the collector current I _C is large, the relationship with I _B is not affected by fluctuations in the power supply voltage, and in the section where the base current is constant, the power supply voltage decreases (a) in Fig. 4.
The characteristic of this is that it ensures a minimum base current.

In this way, by controlling the base current of the transistor chopper according to the collector current,
Since the base current consumption is lower than in the conventional method, the loss of the base current supply circuit is small and the efficiency of the chopper is improved.

According to the embodiment of the present invention described above, the collector current and battery voltage of the transistor chopper are detected, and the base current of the chopper transistor is controlled in accordance with the changes in the collector current and battery voltage, so that the base current of the chopper transistor is kept in an optimal state, so that the switching of the transistor is The necessary base current is secured. In addition, when the load is light, that is, when the collector current is small, the base current is small, so the loss in the base current control circuit is small, improving chopper efficiency, and at the same time, the cooling structure of the chopper device is simplified. There is.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a power transistor base current control device that can reduce power loss in a drive circuit.

[Brief explanation of the drawing]

Fig. 1 is a motor control circuit diagram using the transistor chopper device of the present invention, Fig. 2 is a detailed view of the main part of Fig. 1, and Fig. 3 is an output of the main part showing the operating principle of the present invention. The waveform diagram and FIG. 4 are I _C - I _B operating characteristic diagrams in chopper operation of the present invention. 1... Transistor chopper, 2... Drive transistor, 3... Current limiting resistor, 4... Conductivity control circuit.

Claims (1)

[Claims] 1. In a power transistor base current control device comprising a transistor chopper including a power transistor connected between a DC power source and a load, and means for supplying a base current of the power transistor, means for detecting the current flowing through the load. and,
means for detecting the voltage of the DC power source; a function generator for operationally amplifying and biasing the output based on the output signal of each of the detection means; and a base of a power transistor controlled by the output of the function generator. A transistor that controls a transistor that controls a current, and is provided between the transistor chopper and the base current control transistor, and is controlled by an output signal of a conduction rate control circuit, and controls the transistor chopper. A base current control device for a power transistor, comprising a drive transistor to be controlled.