JPS586090A - Transistor chopper controller - Google Patents

Abstract

PURPOSE:To save the waste of electric power by reducing the base current of a power transistor as the temperature of the transistor becomes high. CONSTITUTION:The bases of power transistors PT1, PT2 of a transistor chopper circuit 4 are connected to the emitters of a transistor TR1 controlled ON or OFF by a current flowing rate control circuit 6. A voltage regulator 10 controls the ON and OFF times of a transistor TR2 in response to the deviation between the instruction voltage V2 and the voltage V1 of a capacitor C1. An operational amplifier OP3 outputs a current reference signal proportional to the base and emitter voltages of a transistor TR3 responsive to the temperatures of power trnsistors PT1, PT2. An operational amplifier OP3 controls the instruction voltage V2 responsive to the deviation between the current reference signal and the current detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a transistor chopper circuit that controls the speed of a DC motor, and particularly to control of the base current of a power transistor.

Conventionally, the base current of the power transistor in this type of device has been controlled by the collector current of the control transistor. In this case, considering that the power transistor is operated from a cooled state, the base current is set to a value larger than the required current of the power transistor alone in the cooled state.

However, after 10 minutes of operation, the temperature of the power transistor increases, and the base current required for the power transistor decreases. However, as mentioned above, the necessary base current is flowing even at this time when the temperature is low, so the conventional method has the disadvantage of causing unnecessary current to flow.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks, an object of the present invention is to provide a transistor chopper control device that allows a proper base current of a power transistor to flow at all times to avoid wasting power.

According to the invention, the above objects are achieved by sensing the temperature of the power transistor and reducing the base current as this temperature increases.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a transistor chopper control device according to the present invention.

A DC motor 2, a current detector 3, and a transistor chopper circuit 4 are connected in series from a positive power line 1 to a negative power line 5. Note that a diode DO is connected in parallel with the DC motor 2. The bases of the power transistors PTI and PT2 of the transistor chopper circuit 4 are connected to NPN transistors TR via resistors R1 and R2, respectively.
The collector of TR1 is connected to the capacitor C1 and the inductance L1.

Further, the base of the transistor TRI is connected to a conduction rate control circuit 6, and this circuit controls on/off of the transistor TR,1. For example, it is controlled by an accelerator C (not shown) and also by motor current.

The positive power supply line 1 is connected to the anode side of the diode D1 via the fuse 7 and the key switch 8, and the cathode side of this diode D1 is connected to the collector of the transistor TR2 and the constant voltage circuit 9, and the constant voltage circuit 9 is connected to the transistor TR2. A voltage is supplied to the circuit 9. The emitter of the transistor TR2 is connected to the capacitor C1 through a series connection of a resistor R3 and an inductance LL, and an inductance L1
The input terminal of and the negative power supply line 5 are connected via a diode T)2. When the transistor TR2 is turned on, the capacitor C1 is charged, and when the transistor TR2 is turned off, the magnetic energy stored in the inductance L1 circulates through the capacitor C1 and the diode D2 to charge the capacitor C1. Note that the resistor R3 is used to prevent excessive current from flowing through the transistor TR,2, and is normally a resistor of several ohms or less.

The transistor TR,2 is turned on and off by the transistor TR.
, 2, and the voltage V on capacitor C1.

The on/off time of the transistor TR2 is controlled by the total command signal and the deviation fed back from the vI voltage. When the deviation is small, the on time is short, and when the deviation is large, the on time becomes long.

The voltage V2, which is divided by connecting the dividing resistors R, 4, R, and 5 to the constant voltage line 11, is applied to the operational amplifier OP1 via the resistor R6.
The terminal voltage of capacitor C1, Vl, is connected to the inverting input terminal of OPI via resistor R9. The output terminal of OPI is input to the voltage adjustment circuit 10 via a resistor R8, and is also connected to the inverting input terminal via a resistor R7. This circuit controls voltage v1 to be equal to voltage v2. If it is desired to further increase the voltage vI, a dividing resistor R9 can be connected as shown in the figure. Resistor R that performs relative amplification in the same way
, 11 to R13, and the operational amplifier OP2, the current detection circuit 1 connected to the current detector 3 is connected to the non-inverting input composed of the operational amplifier OP2.
2 signals are applied. The output terminal of the operational amplifier OP2 is connected to the voltage v2 terminal via a resistor R10 and a diode D3. As a result, the voltage v2 increases as the current increases.

Next, the features of this embodiment will be explained. The operational amplifier OP3 and the resistors R, 14 to R, 17 constitute a proportional amplifier circuit. A resistor R connected to the inverting input terminal of OF2,
15 and a resistor 11.18 connected to the constant voltage line 11 is connected to the base of a transistor TR3, the emitter of this transistor TR3 is connected to the negative power supply line 5, and the collector is open. This transistor TR
3 is attached to the cooling base near the power transistors PTI and PT2, and depending on the temperature of the power transistors, the voltage between the base and emitter of the transistor TR3 V[
The temperature of the power transistor is detected using changes in Ig. Further, the output terminal of OF2 is connected to the inverting input terminal of OF2 via a resistor R,13.

Next, the operation of this embodiment will be explained. When the temperature of power transistors PTI and PT2 is low, transistor TR
The base-to-emitter voltages V and E of No. 3 are large, and the output voltage amplified by the operational amplifier OP3 is small. Therefore, since the inverting input terminal of operational amplifier OP2 becomes small, the voltage V2
becomes larger.

Therefore, the terminal voltage V of the capacitor c1 is increased by the action of the operational amplifier OPI and the voltage adjustment circuit 10.

(Note that V, = V, ) also increases. This increase in v means that the on time of the transistor TRI becomes longer and the base currents of the power transistors PTI and PT2 become larger. That is, when the temperature of the power transistor is low, the base current of the power transistor is large. Conversely, as the temperature of the power transistor increases, VIIE becomes smaller and OF2.
OF2. The voltage V1 decreases through the chain operation of OP1. Therefore, the base currents of power transistors PTI and PT2 become small. Figure 2 is a diagram explaining the above operation, in which the dashed line shows the change in V when the temperature of the power transistor is 120°C, and the broken line shows the change in V when the temperature of the power transistor is 60°C. The solid line shows the change characteristic of vl at the time of , and the solid line shows the change characteristic of temperature in between.

Of course, a single power transistor at 60°C is required.1
Since is the value shown by the two-dot chain line, the voltage V mentioned above is above the two-dot chain line at any temperature and has a voltage that can sufficiently operate the power transistors PTI and PT2.

According to this embodiment, the power transistor PTI.

The temperature rise of PT2 is detected by transistor TR3, and based on this detected value, power transistors PT1. PT2
By controlling the 0 pace current, the required V at cold temperature can be reduced.
If the transistor TR2 is operated at a high temperature while maintaining the same voltage, the amount of time that the transistor TR2 is on increases, which has the effect of preventing an increase in loss. That is, as the temperature of the power transistor increases with operating time, the base current of the power transistor is reduced, thereby reducing power loss and improving power efficiency.

FIG. 3 shows the main part of another embodiment of the present invention,
Portions corresponding to those in FIG. 1 are indicated using the same reference numerals.

This circuit is characterized by the use of a thermistor 13 for temperature detection, and this thermistor 13 is inserted on the input side of the operational amplifier OP3. The rest of the configuration is completely the same as that in FIG. 1, so the explanation will be omitted. Further, as yet another embodiment, a similar effect can be obtained by using a diode to detect the temperature of the power transistor.

As is clear from the above description, the present invention provides a transistor chopper control device that increases or decreases the base current of a power transistor depending on the temperature of the power transistor, thereby constantly flowing an appropriate base current to save power wastage. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of a transistor chopper control device according to the present invention, FIG. 2 is an explanatory diagram of the operation of the embodiment shown in FIG. 1, and FIG. FIG. 3 is a circuit diagram showing main parts. 2... DC motor, 4... Transistor chopper circuit, 9... Constant voltage circuit, C1... Capacitor, OP
l.

Claims (1)

[Claims] 1. It has a chopper circuit using a power transistor that controls the current of a DC motor, and a control transistor that conducts and interrupts the base current of the power transistor,
In the transistor chopper control device that controls the input voltage of the control transistor by the current of the DC motor, a temperature sensor that detects the temperature of the power transistor;
A transistor chopper control device comprising: a circuit for controlling the operation time of the control transistor based on the detected value of the temperature sensor, and increasing/decreasing the base current of the power transistor depending on the temperature of the power transistor.