JPH0297111A - Pwm chopping circuit - Google Patents

Abstract

PURPOSE:To prevent the malfunction of RWM control and thermal runaway due to the rise of power consumption by providing first and second transistor TRs and a diode connected between the output terminal and the second potential supply source and inputting a control signal to the base of the first TR. CONSTITUTION:A coil 30 is charged by turning off a TR Q10. At this time, the Darlington output is obtained because a bias is impressed to the base of a TR Q20. Therefore, a current is supplied to the coil 30 of the load through an output terminal 20 to charge the coil 30. When the TR Q10 is turned on, the TR Q20 is turned off because the base current of the TR Q20 is absorbed. Therefore, the Darlington output is cut off to discharge the coil 30. That is, charging and discharging are repeated on a certain condition to perform RWM chopping. Thus, the chopping operation due to PWM control is stabilized, and thermal runaway does not occur.

Description

[Detailed description of the invention] [Purpose of the invention] ′ (Industrial application field) The present invention relates to semiconductor integrated circuits, and particularly relates to semiconductor integrated circuits.

(Prior Art) Conventionally, circuits shown in FIGS. 2 and 3 are known as circuits for chopping the output using PWM (Pulse Width Modulation). In the example of FIG. 2, the control signal input to the base of the transistor Q1 causes the transistor Ql to
The PWM chopping operation is performed by turning on and off. Specifically, when the transistor Q1 is turned off, a bias is applied to the base of the transistor Q2 from the power supply VCC through the constant current source 1, so that the load is applied from the power supply VCC through the output of the transistor Q3 (hereinafter referred to as "Darlington output"). Current is supplied to coil 2 of
The coil 2 is charged. Furthermore, when the transistor Ql is turned on, the base current of the transistor Q2 is absorbed and the Darlington output is cut off. Therefore, a coil current flows through the diode 3, and the coil 2 is discharged. Note that the coil current is monitored by various methods, and PWM control is performed by keeping the increase/decrease at a constant level. In the example of FIG. 3, the PWM chopping operation is controlled by a switch Sw.

In the former example, the diode 3 is formed from a substrate (p type) in a semiconductor integrated circuit and an island (n type) formed on this substrate. Therefore, the forward voltage VF of this diode 3 equivalently includes the voltage drop of the series resistance. That is, the forward voltage V increases as the large current operation is performed. Therefore, when the coil 2 is discharged, the output terminal 4 drops to the master potential by the forward voltage vF, but if this becomes more than twice the base-emitter voltage VBE of the transistor, the transistor Q
When the constant current absorbed by the transistor Q1 is no longer able to be absorbed completely, or when the transistor Q1 performs an inverse operation, a base current begins to flow into the transistor Q2. As a result, there is a drawback that thermal runaway occurs due to malfunction of PWM control and increase in power consumption pD. In the latter example, such a problem does not occur because the PWM chip-zipping operation is controlled by the switch SW.

However, there is a drawback that the chopping frequency cannot be increased because of the delay in the time until the charge accumulated in the base of the transistor Q2 is discharged, that is, the time to turn off the Darlington output.

(Problems to be Solved by the Invention) As described above, the conventional technology has the drawback that it is not possible to simultaneously prevent malfunction of PWM control and thermal runaway due to increased power consumption, and increase the chopping frequency.

Therefore, an object of the present invention is to provide a PWM chopping circuit that can ensure high frequency stability of chopping operation and prevent malfunction of PWM control due to parasitic effects and thermal runaway due to increase in power consumption. .

C. Configuration of the Invention (Means for Solving the Problems and Their Effects) In order to achieve the above object, the PWM chopping circuit of the present invention has an emitter connected to an output terminal, and a collector connected to a first a first transistor connected to a potential supply source, a collector connected to the first potential supply source, a base connected between the constant current source and the collector of the first transistor, and an emitter connected to the first transistor; the second connected to the output terminal
and a diode connected between the output terminal and a second potential supply source. and,
By inputting a control signal to the base of the first transistor, a PWM chopped output can be taken out from the output terminal. Note that the second
The transistor consists of an output power transistor and a driver transistor.

According to such a configuration, even if the output terminal becomes a negative potential, the control transistor is saturated, so the chopping operation by PWM control is stable and thermal runaway does not occur. Further, since the charge accumulated in the base of the driver transistor can be instantaneously discharged by the control transistor, chopping operation can be performed stably even in a high frequency range.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a PWM chopping circuit according to the present invention. NPN for control where the control signal is input to the base
The emitter of transistor Qto is connected to output terminal 20. In addition, the collector of this transistor QIO is connected to the base of the driver npn transistor Q20, and a constant current source IO is connected between this connection point and the power supply VCC.
is connected. The collector of the transistor Q20 is connected to the power supply VCC, and the emitter is connected to the base of an output npn power transistor Q30. The collector of the transistor Q30 is connected to the power supply VCC, and the emitter is connected to the output terminal 20. Furthermore, a diode DIO is connected between the output terminal 20 and the ground point GND. Also, the coil 3 as a load
0 is connected between the output terminal 20 and the ground point GND.

In such a configuration, the control transistor Q1o
controls the PWM chopping operation by a control signal input to its base.

Furthermore, the output power transistor Q30 and its driver transistor Q20 are Darlington connected, and a Darlington output can be obtained from the power transistor Q30.

Constant current source 10 is Darlington connected transistor Q.
30 and Q20.

The diode Di(l) is provided for discharging the load.

Next, the operation of the PWM chopping circuit will be explained based on the same figure. The coil 30 is charged by the transistor Q.
This is done by turning off +o.

At this time, since a bias is applied to the base of transistor Q20, a Darlington output can be obtained. Therefore, current is supplied to the load coil 30 via the output terminal 20, and the coil 3o is charged. Next, when transistor Q1o is turned on, transistor Q
Since the base current of Q20 is absorbed, this transistor Q20 is turned off. Therefore, since the Darlington output is cut off, a coil current flows through the diode DIO, and the coil 30 is discharged. That is, by repeating this charging and discharging under certain conditions, PW
M can be chopped. By the way, during discharging, the output terminal drops to a negative potential as the higher power operation is performed, but since the transistor Q+o is saturated,
Darlington connected transistors Q2o and Q30
Do not apply on-voltage to Note that the constant current is transistor Q+.

Although the current is supplied to the coil 30 through the current, there is no problem because the current is sufficiently small compared to the chopping operation current.

As described above, in the PWM chopping circuit of the present invention, even if the output terminal 20 becomes a negative potential, since the transistor QIO is saturated, no on voltage is applied to the Darlington-connected transistors Q20 and Q3o. Therefore, the chopping operation by PWM control is stable and thermal runaway does not occur. Also, transistor Q
Since the charges accumulated in the base of the transistor Q1o can be instantaneously discharged by the transistor Q1o, the chopping operation can be performed stably even in a high frequency range.

[Effects of the Invention] As explained above, the PWM chopping circuit of the present invention provides the following effects.

When the load is discharged, the control transistor is saturated, so the chopping operation by PWM control is stable.
No thermal runaway occurs. Further, since the charge accumulated in the base of the driver transistor can be instantaneously discharged by the control transistor, the chopping operation can be performed stably even in a high frequency region.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for explaining the PWM chopping circuit of the present invention, and FIGS. 2 and 3 are circuit diagrams showing conventional PWM chopping circuits, respectively. 10... Constant current source, 20... Output terminal, Q+. Q2 o + Q3 o...Transistor, Dlo・
...Diode, VCC...power supply, GND...ground point.

Claims (1)

[Claims] a first transistor whose emitter is connected to the output terminal and whose collector is connected to the first potential supply source via a constant current source; whose collector is connected to the first potential supply source and whose base is connected to the constant current source; a second transistor connected between the source and the collector of the first transistor and having an emitter connected to the output terminal; and a diode connected between the output terminal and the second potential supply source. comprising: the first
A PWM chopping circuit characterized in that a PWM chopped output is obtained from the output terminal by inputting a control signal to the base of the transistor.