JPH028550Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is a series-controlled chopper that has a main circuit that controls on/off the main transistor inserted into the direct current for the load, rectifies and smoothes the chopping output, and supplies it to the load. More specifically, the present invention relates to a chopper circuit incorporating a main transistor base current drawing circuit that can significantly reduce power loss during switching of the main transistor.

There are various types of switching regulators, one of which is a series-controlled chopper circuit. This series-controlled chopper circuit, for example, as shown in FIG. It is configured to chop the output from the oscillator, rectify and smooth the output in a rectifier and smoothing circuit 3, and supply it to the load 1. In this embodiment, in order to facilitate connection with the control circuit 2, a configuration is adopted in which a PNP type transistor Q2 is connected complementary to an NPN type main transistor Q1, but such a circuit configuration is not necessarily required. That doesn't mean you have to. Note that the resistors R1 and R2 are base bias resistors for switching each transistor.

In such a conventional chopper circuit, the switching speed of transistors Q1 and Q2 depends on the performance of each transistor, such as fall time and storage time. In other words, the switching speed will vary considerably due to variations in the characteristics of each transistor and changes in temperature.

If the switching speed of a transistor is slow, the area where the current waveform and voltage waveform overlap during switching increases, resulting in extremely large power loss. In particular, the power loss when the transistor is off is very large, and the increase in fall time and storage time is an extremely serious problem in increasing the speed of the chopper circuit.

By the way, in order to increase the switching speed of the transistor, the base bias resistor R1,
A method is used to reduce R2 and reduce the surplus base current, but such a method increases the power consumption in the base bias resistor, which not only causes problems with heat generation, but also increases the power consumption during switching. There is a problem that causes unsaturation of the transistor, and there is a limit to the measures that can be taken to reduce the excess base current. On the other hand, in order to saturate the transistor sufficiently, it is sufficient to supply a large amount of base current, but this increases the fall time and storage time, and as mentioned above, increases the power loss during switching. It turns out.

In any case, for these reasons, it has been technically a very difficult problem to reduce the power loss in the output stage of the series-controlled chopper circuit. However, due to the miniaturization of devices, for example, when incorporating such a chopper circuit into a hybrid IC, it is necessary to significantly reduce the power loss of resistors, transistors, etc., and make it possible to mount a large number of components. .

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to significantly reduce the power loss in the output stage of a series-controlled chopper circuit, thereby making it possible to implement it, for example, in a hybrid IC. The object of the present invention is to provide an improved chopper circuit.

The present invention, which can achieve these objectives, basically increases excess base current to sufficiently saturate each transistor before switching, thereby reducing transistor power loss during on and off periods as well as base bias resistance. In addition to reducing the power loss of the main transistor, it is designed to draw out excess base current when the main transistor is turned off, thereby preventing the storage time and fall time from increasing.
More specifically, a base current extraction transistor is connected in series to the base circuit of the main transistor,
In addition, a series circuit consisting of a resistor and a capacitor is connected between the base of this transistor for drawing base current and the input line from the DC power supply to the main transistor, so that when the main transistor is turned from on to off, the capacitor is The structure is devised so that the base current drawing transistor is turned on by the charging current.

Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 2 is a circuit diagram showing an embodiment of the series-controlled chopper circuit according to the present invention. For ease of understanding, parts corresponding to those in FIG. 1 are given the same reference numerals. The circuit that serves as a path for the load current, that is, the main circuit, has a configuration including a DC input power source E, a main transistor Q1 inserted in series with the load 1, and a rectifying and smoothing circuit 3 that rectifies and smoothes its output. . The output of the DC input power source E is stopped by the main transistor Q1, which is controlled on and off in response to the output of the control circuit 2.
The chopping output is rectified and smoothed by a rectifying and smoothing circuit 3 and then supplied to a load 1. As mentioned above,
The main transistor Q1 is an NRN type power transistor, and the PNP type transistor Q2
are complementary connected and connected to the control circuit 2 via a resistor R3. Resistors R1 and R2 are each base bias resistors. In the configuration up to this point, although there is a difference in resistance value, the connection relationship of each part is the same as that of the conventional circuit. The circuit of this embodiment is significantly different from the conventional circuit in that these chopper circuits are additionally provided with resistors R4, R5, R6, and R6.
7. A base current extraction circuit consisting of a capacitor C and a transistor Q3 is incorporated. Transistor Q3 is a transistor for drawing base current, and its collector is resistor R7 for surge absorption.
The emitter of the base current drawing transistor Q3 is connected to the emitter of the main transistor Q1. Furthermore, a resistor R4 and a parallel circuit of a capacitor C and a resistor R5 are inserted in series between the main circuit, that is, the collector of the main transistor Q1 here and the base of the base current drawing transistor Q3. A resistor R6 is inserted between the base and emitter of the transistor Q3. Here, the resistor R5 is for discharging the charge accumulated in the capacitor C, and the resistor R6 is for turning on the transistor for drawing the base current.
Furthermore, the resistor R7 is for surge absorption as described above.
Therefore, when considering the basic operation of this circuit,
It is only necessary to consider the series connection of resistor R4 and capacitor C.

Next, the operation of this circuit will be explained. The basic operation of the chopper circuit is the same as that of the conventional circuit shown in FIG. As mentioned above, the control circuit 2 generates an on/off pulse output at a duty ratio according to the output voltage, thereby controlling the transistor Q2 and the main transistor Q.
1 on/off control. This main transistor Q
By the chopping operation of step 1, the DC input power source E
The output of the circuit 3 is chopped, and the obtained pulse output is rectified and smoothed by a rectification and smoothing circuit 3, and then supplied to a load 1. Here, the base bias resistors R1 and R2 of the main transistor Q1 and the transistor Q2 are set to slightly low resistance values so that each transistor is sufficiently saturated when it is turned on, unlike the conventional technology. If this is done, the surplus base current of the main transistor Q1 increases, so that the problem in this case is an increase in the fall time and storage time when the main transistor Q1 is turned off. According to this circuit, the moment the main transistor Q1 is turned off, the output voltage of the DC input power source E is directly applied between the collector and emitter of the main transistor Q1. At this time, capacitor C is connected through resistor R4.
Therefore, a steep current flows to the base of the base current extraction transistor Q3. Due to this current, the base current drawing transistor Q3 becomes conductive and draws the excess base current of the main transistor Q1 as shown by the broken line arrow. Therefore, the moment the main transistor Q1 is turned off, its surplus base current is drawn out, so that the fall time and storage time of the main transistor Q1 become extremely short. next,
When the main transistor Q1 is turned on, its collector-emitter voltage usually becomes about 1V, and the charge stored in the capacitor C is discharged by the resistors R4, R6 and the main transistor Q1. By repeating such operations, it becomes possible to operate the chopper circuit with extremely high efficiency.

In the above description, a more detailed description focusing on the operation of the base current drawing transistor Q3 will be as follows.

That is, as the main transistor Q1 starts to turn off, a potential difference is generated between the collector and emitter of the main transistor Q1. This potential difference is the resistance R4
Since the voltage is applied between the base current drawing transistor Q3 and the emitter of the transistor Q3, the resistor R4 and the capacitor C
A base current is supplied to the base current drawing transistor Q3 through the resistor R7, so that the base current of the main transistor Q1 is drawn to the base current drawing transistor Q3 through the resistor R7.

In this way, the base current drawing transistor Q
3 turns on and draws the base current of the main transistor Q1, thereby increasing the speed at which the main transistor Q1 turns off. Furthermore, as the speed of turning off increases, the potential difference generated between the collector and emitter of the main transistor Q1 also increases sharply.
Therefore, the base current of the base current drawing transistor Q3 flowing through the resistor R4 and the capacitor C increases.

Then, due to this increase in base current, the base current drawing transistor Q3 is changed to the main transistor Q3.
It works to draw out more base current of 1,
As a result, the speed at which the main transistor Q1 turns off becomes very fast.

In addition, this base current drawing transistor Q
3 is on during the off period of the main transistor Q1. However, main transistor Q1
When it is time to turn off the main transistor Q1, an excessive current is supplied as the base current of the base current drawing transistor Q3 through the resistor R4 and the capacitor C. On the other hand, when the main transistor Q1 is in the off state, the excessive current is supplied through the DC input power supply E. A small current defined by the resistors R4 and R5 is supplied as the base current of the base current drawing transistor Q3.

Therefore, capacitor C is connected to main transistor Q1
The constant is appropriately set so that an excessive current can flow through the base current drawing transistor Q3 while the transistor Q3 is turned from on to off.

Since the present invention is a series-controlled chopper circuit configured as described above, it is possible to significantly speed up the rising waveform of the voltage between the collector and emitter of the main transistor, thereby reducing power loss during on/off transients. Since the power dissipation of the base bias resistor of the main transistor etc. is also small, the power loss of the entire circuit is significantly reduced, making this circuit suitable for hybrid
The practical effects are extremely large, such as being able to be implemented within an IC.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional technique, and FIG. 2 is a circuit diagram showing an embodiment of a chopper circuit according to the present invention. 1...Load, 2...Control circuit, 3...
Rectifying and smoothing circuit, E...DC input power supply, Q1...Main transistor, Q3...Base current extraction transistor, R1, R2, R3, R4, R5, R
6, R7...Resistor, C...Capacitor.

Claims (1)

[Claims for Utility Model Registration] On/off control of the main transistor inserted in series with the load, thereby chopping the output from the DC power supply, and rectifying and smoothing this chipping output before supplying it to the load. In the chopper circuit configured as above, a base current drawing transistor is connected in series to the base circuit of the main transistor, and between the base of the base current drawing transistor and an input line from the DC power source to the main transistor. , a series control type chopper circuit in which a series circuit of a resistor and a capacitor is connected, and the base current drawing transistor is turned on by the charging current to the capacitor when the main transistor is turned from on to off. .