JPH1197989A - Pulse signal generating device with malfunction preventing function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the loss of an element, etc., controlled with pulses generated by the pulse generating device by preventing the pulse signal generating device from malfunctioning. SOLUTION: A triangular wave generating circuit 2 generates a triangular wave by using the output of an oscillator 1. A comparator 3 generates a pulse signal according to the result of comparison between the triangular wave and the output of a control circuit 4. The result of AND between the output of the comparator 3 and the output of the oscillator 1 is inputted to the set terminal of a latch circuit 21. To the reset terminal of the latch circuit 21, the result of AND between the inverted signal of the output of the comparator 3 and the inverted signal of the output of the oscillator 1 is inputted. The output of the latch circuit 21 is regarded as the output of this device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse signal generating device having a malfunction preventing function, and more particularly to a device for generating a pulse signal for controlling a switching element and the like.

[0002]

2. Description of the Related Art Many circuits for controlling a switching element or the like using a pulse signal have been known. For example, in a charger, a DC / DC converter, a DC / AC inverter, etc., a power MO
There are many cases where the voltage or current supplied to a load is adjusted by controlling a switching element such as S.

FIG. 3A is a block diagram of a general pulse signal generator. Here, a configuration in which the switching element is controlled by the PWM method is shown. The oscillator 1 generates a square wave having a predetermined frequency. The triangular wave generation circuit 2 generates a triangular wave from the square wave generated by the oscillator 1. The comparator 3 compares the level of the triangular wave generated by the triangular wave generation circuit 2 with the output level of the control circuit 4.
The control circuit 4 outputs a potential for adjusting the duty of the pulse signal supplied to the switching element 11 (the ratio of the period during which the pulse signal is at the “H” level to the period during the “L” level). For example, when this pulse signal generation device is used in a charger, the output of control circuit 4 changes based on the voltage of the battery to be charged. The drive circuit 5 drives the switching element 11 by amplifying the output of the comparator 3.

The output of the pulse signal generating device having the above configuration is
As shown in FIG. 3B, when the level of the triangular wave is higher than the output level of the control circuit 4, the level is "H", and when the level of the triangular wave is lower than the output level of the control circuit 4, the level is "L". It becomes a pulse signal of a level. In this case, the switching element 11 is turned on when the pulse signal changes from the “L” level to the “H” level, and conversely, is turned off when the pulse signal changes from the “H” level to the “L” level.

[0005]

However, as is well known, when a switching element or the like is turned on or off, noise is generated accordingly.
This is so-called switching noise.

FIG. 4 is a diagram for explaining the influence of a malfunction when switching noise occurs in the configuration shown in FIG. Here, an example is shown in which switching noise is superimposed on a triangular wave.

When a triangular wave on which switching noise is superimposed is input to the comparator 3, chattering (a state in which the ON state and the OFF state are alternately repeated at high speed) occurs in the output of the comparator 3. Thus, the comparator 3
When chattering occurs in the output of (1), a signal that alternates between the “H” level and the “L” level at high speed alternately is input to the switching element 11. Therefore, the switching element 11 alternately switches between the ON state and the OFF state at a high speed during that time. Where, in general,
A large loss occurs when the switching element is turned on and off. Therefore, as described above, when the switching element 11 repeatedly turns on and off at a high speed, heat is increased and not only loss is increased, but also the switching element itself may be damaged in some cases. This can also occur when switching noise is superimposed on the output of the control circuit 4.

An object of the present invention is to prevent a malfunction of a pulse signal generating device, thereby suppressing a loss in an element or the like controlled by a pulse generated by the device, and
The purpose is to avoid damage to the element and the like.

[0009]

A pulse signal generating device according to the present invention is based on an oscillator, a triangular wave generating circuit for generating a triangular wave using an output of the oscillator, and a comparison result between the triangular wave and a control signal. A comparator that generates a pulse signal; a first logic circuit that outputs a logical product of the output of the oscillator and the output of the comparator; a logical product of an inverted signal of the output of the oscillator and an inverted signal of the output of the comparator And a latch circuit that holds a first state by an output of the first logic circuit and holds a second state by an output of the second logic circuit, The output of the latch circuit is used as an output pulse signal.

Generally, a circuit driven by a pulse signal generates noise immediately after the timing when the level (L / H) of the pulse signal changes. On the other hand, the timing at which the level of the pulse signal generated by this device changes is
Synchronizes with the output of the oscillator. Therefore, by holding the output of the device using the output of the oscillator for a predetermined period after the level of the pulse signal changes, noise generated immediately after the timing when the level of the pulse signal changes can be removed. .

The malfunction prevention circuit according to the present invention is based on a configuration provided for an apparatus that generates a triangular wave using an output of an oscillator and generates a pulse signal based on a comparison result between the triangular wave and a control signal. While the output of the oscillator is in the first state, the triangular wave is latched in the first state at the timing when the level of the triangular wave first exceeds the level of the control signal, and the output of the oscillator is in the second state And a latch circuit that is latched in the second state at a timing when the level of the triangular wave first falls below the level of the control signal, and the output of the latch circuit is used as the output pulse signal of the pulse signal generation device. The operation of this circuit is basically the same as that of the pulse signal generating device.

[0012]

FIG. 1 is a block diagram of a pulse signal generating device according to the present embodiment. Of the reference numerals used in FIG. 1, those used in FIG. 3 (a) represent the same parts. That is, the pulse signal generating device of this embodiment is basically different from the general device shown in FIG. 3A in that the latch circuit 21, the AND circuits 22 and 23, and the inverting circuit 2
4 and 25 are provided.

The AND circuit 22 receives the output signal of the comparator 3 and the output signal of the oscillator 1, and outputs a logical product of them. On the other hand, the AND circuit 23 includes the comparator 3
And the inverted signal of the output of the oscillator 1 are input, and the logical product thereof is output. The comparator 3
Is inverted by an inverting circuit 24, and the output of the oscillator 1 is inverted by an inverting circuit 25.

The latch circuit 21 is, for example, an SR type flip-flop circuit. The output signal of the AND circuit 22 is input to its set terminal, and the output signal of the AND circuit 23 is input to its reset terminal. Then, the output of the latch circuit 21 (or a signal obtained by amplifying the output of the latch circuit 21 by the drive circuit 5) is the output of the pulse signal generation device of the present embodiment. That is, in the example shown in FIG. 1, the switching element 11 is driven by the output of the latch circuit 21 (actually, a signal obtained by amplifying the output of the latch circuit 21 using the drive circuit 5).

Next, the operation of the pulse signal generation circuit of the present embodiment will be described with reference to FIG. The oscillator 1 outputs a clock signal that determines a switching frequency. The duty of this clock signal is 50 in this embodiment.
Percentage (a signal in which the “H” level period and the “L” level period have the same length). Triangular wave generation circuit 2
Generates a triangular wave according to the clock signal output from the oscillator 1. Here, a triangular wave is generated such that the clock signal ramps up during the “H” level period and ramps down during the “L” level period.

The comparator 3 compares the triangular wave with the potential output from the control circuit 4 and determines whether the level of the triangular wave is
When the level of the triangular wave is lower than the level of the output of the control circuit 4, “H” is output. The output of the comparator 3 is a pulse signal subjected to PWM control by the control circuit 4.

As described as a conventional problem, switching noise is superimposed on this pulse signal. That is, the noise accompanying the turn-on or turn-off of the switching element 11 is superimposed on the triangular wave (or the output of the control circuit 4), so that the pulse signal output from the comparator 3 causes chattering. The pulse signal generation device according to the present embodiment focuses on the fact that the chattering occurs immediately after the switching element 11 is turned on or off, and includes a latch circuit 21, AND circuits 22, 23, and invert circuits 24, 25. Malfunction prevention circuit (or noise elimination circuit)
To prevent the switching element 11 from being turned on or off by chattering. Hereinafter, a specific description will be given.

The AND circuit 22 allows the output (pulse signal) of the comparator 3 to pass only while the output of the oscillator 1 is at the "H" level. The output of the AND circuit 22 is input to the set terminal of the latch circuit 21. on the other hand,
The AND circuit 23 allows the inverted signal of the output (pulse signal) of the comparator 3 to pass only while the output of the oscillator 1 is at the “L” level. The output of the AND circuit 23 is input to the reset terminal of the latch circuit 21.

When a rising edge is input to the set terminal, the latch circuit 21 keeps its output at "H" level thereafter until a rising edge is input to the reset terminal. Here, while the output of the oscillator 1 is at the “H” level, the output of the inverting circuit 25 is at the “L” level, so that the output of the AND circuit 23 is always at the “L” level, and the latch circuit 21 is reset. It will not be done. Therefore, once set by the first rising edge of the output of AND circuit 22, latch circuit 21 outputs the "H" level without being reset while the output of oscillator 1 is at the "H" level. Keep doing.

Here, considering the method of generating the triangular wave using the output of the oscillator 1, the timing at which the level of the triangular wave exceeds the output level of the control circuit 4 for the first time (time 1) exists during a period when the output of the oscillator 1 is at the “H” level. In FIG. 1, the triangular wave is depicted as rising linearly. However, in actuality, the switching noise is superimposed on the triangular wave as shown in FIG. Therefore, it is expected that the triangular wave and the output of the control circuit 4 intersect a plurality of times. Also, when the level of the triangular wave exceeds the output level of the control circuit 4 for the first time, the oscillator 1
During the period from the time when the clock signal output from the clock signal changes from the “H” level to the “L” level, that is, from time 1 to time 2 shown in FIG. 2, the output level of the control circuit 4 is the peak level of the triangular wave. Except when it is near or longer, it is enough time for the chattering that occurs immediately after time 1 to disappear. During this period, the output of the oscillator 1 is at the “H” level and the output of the AND circuit 23 is always at the “L” level, so that the latch circuit 21 is not reset.

Therefore, when the level of the triangular wave exceeds the output level of the control circuit 4 for the first time while the level of the triangular wave rises, the output of the latch circuit 21 becomes "L".
After the change from the level to the “H” level, even if chattering occurs in the output of the comparator 3, the latch circuit 21 is not reset due to the chattering, and the output state of the latch circuit 21 does not change. In other words, even if chattering occurs in the output of the comparator 3, the switching element 11 is not turned on or turned off by that. In the device of the present embodiment, noise such as chattering is removed from the pulse signal in this manner.

On the other hand, when a rising edge is inputted to the reset terminal, the latch circuit 21 keeps its output at "L" level until a rising edge is inputted to the set terminal thereafter. Here, while the output of the oscillator 1 is at the “L” level, the output of the AND circuit 22 is always “L”, and the latch circuit 21 is not set. That is, while the output of the oscillator 1 is at the "L" level, once the latch circuit 21 is reset by the first rising edge of the output of the AND circuit 22, the latch circuit 21 changes the "L" level without being set thereafter. Continue to output. Therefore, as in the case described above, when the level of the triangular wave falls below the output level of the control circuit 4 for the first time (for example, at time 3) while the level of the triangular wave is decreasing, the output of the latch circuit 21 becomes the “H” level. After that, the output state of the latch circuit 21 does not change even if chattering occurs in the output of the comparator 3 after the signal changes from "L" to "L" level.

Considering the above two operations together, the output of the latch circuit 21, that is, the pulse signal generated by the pulse signal generation device of the present embodiment is a signal during the period when the output of the oscillator 1 is at the "H" level. In the period from when the level of the triangular wave first exceeds the output level of the control signal 4 to when the level of the triangular wave first falls below the output level of the control signal 4 during the period when the output of the oscillator 1 is at the "L" level. During the period in which the output of the oscillator 1 is at the "L" level, the output of the oscillator 1 is changed to "H" from the time when the level of the triangular wave first falls below the output level of the control signal 4. During the period of the “H” level, the “L” level is maintained until the level of the triangular wave first exceeds the output level of the control signal 4. Here, the timing when the output of the latch circuit 21 changes from the “L” level to the “H” level is when the level of the triangular wave first exceeds the output level of the control signal 4. And the timing in the original state where no noise is superimposed.
Further, the output of the latch circuit 21 changes from “H” level to “L” level.
The timing of changing to the level is when the level of the triangular wave first falls below the output level of the control signal 4 and coincides with the timing in the original state where noise is not superimposed on the triangular wave or the output of the control circuit 4. . Thus, even if a circuit for preventing a malfunction (a circuit for removing noise) is provided, the timing and duty of the pulse signal to be generated do not change.

As described above, according to this embodiment, the switching noise can be easily removed, and the switching element 11 is not turned on or off by the noise. For this reason, it is possible to suppress the waste of power in the switching element 11, and accordingly, the heat generation in the switching element 11 is reduced, so that heat damage is less likely to occur. If thermal damage is less likely to occur, the output power of the switching element 11 can be set higher.

Further, since the noise in the pulse signal generator including the analog circuit is removed by using the digital circuit, the noise resistance becomes equal to that of the digital circuit. In the above embodiment, the switching element is used to supply the pulse signal. However, the present invention is not limited to this. Noise is generated due to the pulse signal generated by the device of the present invention. This is useful when a circuit is to be supplied with a pulse signal.

The triangular wave used by the device of the present invention is:
It is assumed that the rising slope and the falling slope include asymmetric waveforms. For example, it is assumed that a sawtooth wave is also included in the triangular wave of the present invention.

[0027]

When a pulse signal for driving a switching element or the like is generated, noise generated due to the operation of the switching element or the like can be removed from the pulse signal. Therefore, the switching element and the like are not unnecessarily turned on or off, and the switching loss can be suppressed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a pulse signal generation device of the present embodiment.

FIG. 2 is a diagram illustrating the operation of the pulse signal generation device according to the present embodiment.

FIG. 3A is a block diagram of a general pulse signal generating device, and FIG. 3B is a diagram for explaining the operation thereof.

FIG. 4 is a diagram for explaining the influence of a malfunction when switching noise occurs in the configuration shown in FIG. 3 (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillator 2 Triangular wave generation circuit 3 Comparator 4 Control circuit 5 Drive circuit 11 Switching element 21 Latch circuit 22, 23 AND circuit 24, 25 Invert circuit

Claims (2)

[Claims] An oscillator, a triangular wave generating circuit that generates a triangular wave using an output of the oscillator, a comparator that generates a pulse signal based on a comparison result between the triangular wave and a control signal, and an output of the oscillator A first logic circuit that outputs a logical product of the output of the comparator, a second logical circuit that outputs a logical product of an inverted signal of the output of the oscillator and an inverted signal of the output of the comparator, Holds the first state by the output of the logic circuit of
And a latch circuit for holding a second state by an output of the second logic circuit, wherein the output of the latch circuit is used as an output pulse signal. 2. A malfunction prevention circuit provided for a device that generates a triangular wave using an output of an oscillator and generates a pulse signal based on a comparison result between the triangular wave and a control signal, the device comprising: During the period when the output is in the first state, the level of the triangular wave is latched in the first state at the timing when the level of the control signal first exceeds the level of the control signal, and in the period when the output of the oscillator is in the second state, A latch circuit latched in a second state at a timing when the level of the control signal first falls below the level of the control signal, and a malfunction prevention circuit using an output of the latch circuit as an output pulse signal of the pulse signal generation device.