JPS631209A - Pulse width modulation circuit - Google Patents

Abstract

PURPOSE:To prevent generation of an over-short-circuit current when the power supply voltage has a drop by using an output breaking circuit which detects the abnormality of the power supply of the circuits set at the preceding stages including a modulation circuit and preventing forcibly the output of the final pulse width modulation signal received from a switching element. CONSTITUTION:A modulation circuit 20 modulates the input signals S into the complementary pulse width modulation signals Pm1 and Pm2 in response to the amplitude levels of the signals S. An output breaking circuit 30 supplies signals Pm1 and Pm2 to an earth line via transistors Q1 and Q2 to prevent forcibly the output of the final pulse width modulation signal G delivered from an H-shaped amplifier 25 after detecting through a power supply voltage detecting circuit 33 that the power supply voltage levels of the circuit 20 and a signal amplifier 22 are reduced less than the prescribed value. 21:triangular wave generating circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a pulse width modulation circuit that is applied to power amplification of audio signals, push-pull amplification circuits for motor control, and the like.

(Prior art) Pulse width modulation (PWM) uses a comparison wave such as a triangular wave with a repetition frequency sufficiently higher than the frequency band of the input signal, and uses this comparison wave and the input signal to determine the input signal amplification level. This is to obtain a pulse width modulation signal with a corresponding pulse width.
High power efficiency can be obtained by performing pulse amplification with little loss on this pulse width modulated signal. Demodulation of the pulse width modulation signal can be easily performed by passing it through a low-pass filter circuit that blocks the frequency band of the pulse signal. By the way, some of these D-pulse width modulation circuits use their pulse width modulation output as a drive signal for push-pull amplifier circuits and H-type amplifier circuits used for servo motor control, and the circuit configuration diagram is shown in Figure 3. shows. When applied to a push-pull amplifier circuit or an H-type amplifier circuit as described above, it is first necessary to modulate the input signal into complementary pulse width modulation signals having mutually different phases by 180 degrees.

Therefore, each pulse width modulation signal is created as follows. To explain with reference to FIG. 4, each triangular wave E1 with bias level +eo, -eo as a cross comparison wave,
E2 is set, and these triangular waves E1, E2 and input signal 5L
f) Compare i width and bell. As a result of this comparison, when the amplitude level of the input signal S becomes higher than the level of the triangular wave E1, a first pulse width modulation signal P1 having a high level during that period is created. When the level becomes lower than the level of the triangular wave E2, a second pulse width modulation signal PII12 is created to be at a high level during this period.

Then, each pulse width modulated signal P1 obtained in this way
, pm2 are each exciter 1 to 4 of the H-type amplifier circuit shown in FIG.
Specifically, the pulse width modulation signal Pn+1 is sent to exciters 1 and 2, and the negative pulse width modulation signal Pm2 is sent to exciters 3 and 4. Note that the exciters 1 to 4 control the conduction and non-conduction of the power transistors 5 to 8, respectively, and are electrically insulated from each other. Further, the power transistors 5 to 8 are power transistors 5.7 and 6.8 connected in series and connected in parallel. and power transistors 5, 7 and 6
, 8, a filter 9 and a load 10 such as a servo motor are connected between the contacts. Therefore, when the pulse width modulation signal P1 becomes high level, both the power transistors 5 and 6 become conductive, and a current flows in the direction a, and the pulse width modulation signal pi2
When becomes high level, both power transistors 7 and 8 become conductive, and a current flows in the b direction. Thus, the input signal S
A power amplified signal proportional to is supplied to the load 10.

By the way, in the above circuit, each complementary pulse width modulation signal P
IIL PIl12 is obtained, so it is impossible for these pulse width modulated signals @PII11 and pm2 to become high level at the same time. However, each pulse width modulation signal Pm
Circuits such as comparators are used to generate Pml and Pm2, but when the power supply voltage supplied to these comparators decreases, the operation becomes unstable and the pulse width modulation signals Pml and Pm2 become high level at the same time. It may happen. If the level becomes high at the same time like this, power transistors 5 and 7 or 6 and 8 become conductive at the same time, and the power source 11 becomes short-circuited, causing a large yfi rating current to flow and burning out the power transistors 5 to 8, etc. .

(Problems to be Solved by the Invention) As described above, the operation becomes unstable due to the drop in power supply voltage, and an over-short circuit current flows.

SUMMARY OF THE INVENTION In order to solve the above problems, it is an object of the present invention to provide a pulse width modulation circuit that can prevent over-short circuit current from occurring when the power supply voltage drops.

[Structure of the Invention] (Means for Solving the Problems) The present invention modulates an input signal into complementary pulse width modulation signals having different phases using a modulation circuit, and then modulates each pulse width modulation signal using these pulse width modulation signals. In a pulse width modulation circuit that operates switching elements for each pulse width modulation signal to obtain a power-amplified R final pulse width modulation signal, switching is performed by detecting a power supply abnormality in a preceding stage circuit including a modulation circuit for driving each switching element. This pulse width modulation circuit attempts to achieve the above object by using an output cutoff circuit that forcibly blocks the output of the final pulse width modulation signal from the element.

(Function) By providing such a means, when an abnormality in the power supply of the front stage circuit including the modulation circuit is detected, the output of the R final pulse width modulation signal from the switching element is forcibly blocked.

(Example) Hereinafter, a first example of the present invention will be described with reference to the drawings. Note that the same parts as in FIG. 3 are given the same reference numerals.

FIG. 1 is a block diagram of a pulse width modulation circuit. In the same figure, 20 is a modulation circuit which inputs the triangular wave from the triangular wave generating circuit 21 and the input signal S passing through the signal amplifier 22, and outputs the input signal S with a phase difference of 180 degrees from each other according to the amplitude level of the input signal S. Each complementary pulse width modulation signal P
It has a function of modulating to Il11 and PI3.

The specific configuration includes comparators 23 and 24, and a triangular wave and an input signal S are respectively input to these comparators 23 and 24. Note that the triangular wave sent to the comparator 23 is biased by +eO by a bias circuit (not shown), and the triangular wave sent to the comparator 23 is
The triangular wave sent to 4 is biased by -eO by the bias circuit. Each of the pulse width modulated signals P1 and Pm2 is sent to the H-type amplifier circuit 25 through the output cutoff circuit 30. This H-type amplifier circuit 25 receives each pulse width modulation signal pm1, Pm2 and amplifies the power to obtain the final pulse width modulation signal G@, and its configuration is the same as the circuit shown in FIG. There is. Note that the obtained final pulse width modulation signal G is supplied to a load such as a servo motor through a filter circuit or the like. Further, a power source is connected between the terminals e%e'.

Now, the output cutoff circuit 30 is connected to the comparator 23.2.
4 and the signal amplifier 22, and when it is detected that the voltage has dropped below a predetermined voltage value, the pulse width modulation signals P1 and PI112 are sent to the ground line to the H-type amplifier 25.
It has the ability to forcibly prevent the output of the final pulse width modulated signal G from the output of the final pulse width modulated signal G.

Specifically, the collectors of N P N-type transistors (hereinafter abbreviated as transistors) Ql and Q2, which are switching elements required to function as gate circuits, are connected to the lines 31 and 32 through which the pulse width modulation signals pm1 and pm2 pass, respectively. On the negative side, a power supply voltage detection circuit 33 is provided which detects when the power supply voltage of the comparators 23, 24 and the signal amplifier 22 has decreased below a predetermined voltage value, and when a decrease in the N source is detected, each transistor Q1 , Q2, and sends a high-level detection signal to the base of each transistor Q1, Q2.
2 is made conductive.

Next, the operation of the circuit configured as described above will be explained. If the power supply voltage supplied to each comparator 23, 24 and signal amplification circuit 22 is at a normal level, the power S voltage detection circuit 33 sends a low level detection signal to each transistor Q1.
, Q2, so each transistor Q1, Q2
is in a non-conducting state. Therefore, each comparator 2
3. Each pulse width modulation signal pm1, P output from 24
m2 are respectively sent to the H-type amplifier circuit 25 through lines 31 and 32. As a result, the pulse width modulation signal Pml
When is at a high level, power transistors 5.6 are both conductive, and when pulse width modulation signal pm2 is at a high level, power transistors 3.4 are both conductive, thus responding to the amplitude level of input signal S. A final pulse width modulated signal G is output.

However, each comparator 23, 24 and signal amplification circuit 2
When the power supply voltage level supplied to transistors Q1 and Q2 drops below a predetermined voltage level, power supply voltage detection circuit 33 detects this drop and sends a high level detection signal to the bases of each transistor Q1 and Q2. As a result, each transistor Q1, Q
2 is in a conductive state. Therefore, each pulse width modulated signal pH
, pm2 are transistors Q1., pm2, respectively. It flows through Q2 to the ground line. As a result, the pulse width modulation signals Pm1 and Pm2 are no longer sent to the H-type amplifier circuit 25,
This is the same state as when the operation of the H-type amplifier circuit 25 has stopped. Thus, at this time, each pulse width modulation signal pm1, Pm
2 becomes high level at the same time, no over-short circuit current flows through the H-type amplifier circuit 25.

In this way, in the first embodiment, the transistors Q1 and Q2 for shielding switching are connected between the modulation circuit 20 and the H-type amplifier 25, and each transistor Q1 and Q2 is made conductive when a power drop is detected. pulse width modulation signal p
ml, PI112 was configured to flow into the ground line, so
Even if the voltage level of the power supply voltage decreases and the pulse width modulation signals PIl11 and Pm2 become high level at the same time, the H-type amplifier circuit 25 can be in the same state as not operating at this time, and the over-short circuit current will flow. can be prevented. Therefore, the power transistors 5 to 8, etc. are prevented from being burnt out, and malfunctions of the overcurrent switches can also be eliminated.

Next, a second embodiment of the present invention will be described with reference to the configuration diagram shown in FIG. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted. In this circuit, the configuration of the output cutoff circuit 40 is such that the excitation type power source 41 that supplies power to each of the exciters 1 to 4 is directly cut off upon detection of a power drop. Therefore, when a power drop detection signal is sent from the power drop detection circuit 33, the power supplied to each exciter 1 to 5 from the exciter power supply 41 is forcibly cut off, and each pulse width modulation signal Pm1, pm2 is H
Even if the signal is sent to the shaped amplifier circuit 25, each power transistor 5
~8 is not conductive. Thus, in the second embodiment as well, no over-short circuit current flows and the same effects as in the first embodiment can be achieved.

Note that the present invention is not limited to the above embodiments, and may be modified without departing from the spirit thereof. For example, instead of the transistors Q1 and Q2, a relay may be used to send each pulse width modulation signal to the ground line. Also,
It is possible to maintain the H-type amplifier circuit 25 in a non-operating state, or to configure the H-type amplifier 25 to return to normal operation in response to a rise in the power supply voltage.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide a pulse width modulation circuit that can prevent generation of over-short circuit current when the FA voltage decreases.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of a pulse width modulation circuit according to the present invention, FIG. 2 is a block diagram showing a second embodiment of the circuit of the present invention, FIG. 3 is a block diagram of a conventional circuit, and FIG. FIG. 4 is a diagram for explaining the pulse width modulation effect. 1-4... Exciter, 5-8... Power transistor, 20... Modulation circuit, 22... Signal amplifier, 23.
24... Comparator, 25... H-type amplifier, 30
...output cutoff circuit, 33...power supply voltage detection circuit,
Ql. Q2...NPN transistor, 40...Output cutoff circuit, 41...Exciter power supply. Applicant's agent Patent attorney Takehiko Suzue Figure 3 Figure 4

Claims (3)

[Claims] (1) The input signal and each comparison wave with different bias levels are inputted and modulated into complementary pulse width modulation signals with different phases by a modulation circuit, and then each switching element is controlled by these pulse width modulation signals. In the pulse width modulation circuit that operates each of the pulse width modulation signals to obtain a power-amplified final pulse width modulation signal, the switching element is activated by detecting a power supply abnormality in a pre-stage circuit including the modulation circuit for driving each of the switching elements. A pulse width modulation circuit comprising an output cutoff circuit for forcibly blocking output of the final pulse width modulation signal from the element. (2) The output cutoff circuit connects a switching element for shielding between the modulation circuit and each switching element, turns on the switching element for shielding when a power drop is detected, and transmits the pulse width modulation signal to the ground line. A pulse width modulation circuit according to claim (1). (3) The pulse width modulation circuit according to claim (1), wherein the output cutoff circuit cuts off the power supply to the exciter that excites the switching element when a drop in the voltage of the power supply is detected.