JPH0378493A - Pwm controller - Google Patents

Abstract

PURPOSE:To need no filter circuit and simplify a circuit to lower the cost by masking spike noise with the reverse signal of trigger pulse. CONSTITUTION:By a control circuit 7, transistors 11-14 are turned ON/OFF, and a motor 19 is driven. When the transistor 12 or 14 is shifted to a conducting state from a non-conducting state, then spike current flows by the capacity component and the like of the motor 19 and diodes 15, 17, and potential at a point F is heightened, and when it exceeds the voltage of a reference power source 6, then the output of a comparator 5 is reversed, and a pulse is generated. However, the output of a trigger pulse generator 2 is reversed and is applied to an AND gate 3, and so the pulse from the comparator 5 is checked with the AND gate 3 and does not reach a FF 4. Accordingly, disturbance due to the spike current can be prevented from being generated without filters.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pwMtIi control device that performs PWM control on the output of a switching circuit.

[Prior art]

Fig. 3 is a circuit diagram of a conventional device of this kind constructed using a semiconductor integrated circuit. Create pulse A. 4 is an R-S flip-flop, 5 is a comparator, 6 is a reference power supply that provides a reference potential (Vref), 7 is a controller, 8 and 9 are AND circuits, 10 is a resistor, and 11 to 14 are switching elements (NPN) diodes 15 to 18 are connected in antiparallel to each other, and a motor 9 serving as a load is connected between the output terminals BSC. 20 is a capacitor, and 21 is a resistor, both of which constitute a filter circuit. 100 indicates a DC power supply of the inverter, and 200 indicates a ground potential.

Next, the operation of this circuit will be explained with reference to the waveform time chart of FIG.

In this configuration, the trigger pulse A sent out by the trigger pulse generator 2 becomes the set input of the R-S flip-flop 4, so the R-S flip-flop 4 is set and its Q output changes to H level. At this time, the controller 7
Assuming that control signals of H level and L level are sent to AND circuits 8 and 9, respectively, and signals of L level and H level are sent to transistors 11 and 13, respectively, AND circuit 8 sends control signals of H level and L level to transistor 12, respectively. Since the AND circuit 9 sends an L level signal to the transistor 14, the transistors 12 and 13 are ON.
,,transistors 11 and 14 are turned off, and the DC power supply 1
00-) Ranjimetal 13-Motor 19-Transistor 1
Current flows through 2-resistor 10-ground potential 200.

When the current IF flowing through the resistor 10 increases and the voltage drop across the resistor 10 becomes larger than the reference potential Vref, the comparator 5 outputs an output, and the output of the comparator 5 becomes the reset input of the R-S flip-flop 4. , the Q output of the RS flip-flop 4 changes to the L level, the output of the AND circuit 8 changes to the L level, and the transistors 12 and 13 are turned off. As a result, the current flowing to the ground potential 200 is rapidly cut off, and the energy stored in the inductance component of the motor 19 generates a back electromotive force, causing the potential at point B to rapidly rise, causing direct current to flow through the diode. A current flows to the power source 100 and the energy is discharged. This motor current decreases in proportion to the time constant of the inductance component, and after a certain period of time, a trigger pulse A is generated and the transistor 12 is turned on again.

When the output of the controller 7 is inverted, L level and H level control signals are sent to the AND circuits 8 and 9, respectively.
Since H-level and H-level signals are sent to transistors 11 and 13, respectively, transistors 11 and 14 are ON, and current flows in the motor 19 in the opposite direction.

[Problem to be solved by the invention]

In this conventional circuit configuration, transistor 12 or 1
4 transitions from a non-conductive state to a conductive state, a spike-like current (hereinafter referred to as spike current) flows due to the capacitance components of the motor 19 and the diode 15 or 17, and the potential at point F rises, and this becomes the reference point. If the potential exceeds Vref, the comparator 5 is inverted and generates a reset pulse, causing the transistor 12 or 14 to malfunction.

In order to prevent this, the conventional device described above is provided with a filter circuit consisting of a capacitor 20 and a resistor 21, but since these are external components, the number of terminals of the semiconductor integrated circuit increases accordingly. , not only hinders the downsizing of the device but also increases the price.

This invention was made to solve the above problem.
An object of the present invention is to provide a PWM control device that can prevent malfunctions caused by spike noise without providing a filter circuit.

[Means to solve the problem]

In order to achieve the above object, the present invention uses the output of a comparator that provides a reset input for the flip-flop as the reset input for the flip-flop through an AND circuit that receives an inverted signal of a trigger pulse.

[Effect]

In this invention, when spike noise occurs, the spike noise is masked by the inverted signal of the trigger pulse and does not reach the flip-flop.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 3 denotes an AND circuit, in which an inverted signal of the trigger pulse A is given to the - input, and the output of the comparator 5 is input to the other input. The configuration is the same as that shown in FIG. 3, except that the filter circuit consisting of the capacitor 20 and resistor 21 shown in FIG. 3 is not included.

Next, the operation of this embodiment will be explained with reference to the waveform time chart of FIG.

As mentioned above, when the transistor 12 or 14 transitions from a non-conducting state to a conducting state, a spike-like current (hereinafter referred to as spike current) flows due to the capacitance components of the motor 19 and the diode 15 or 17, and the When the potential increases and this whisker-like spike voltage Vspik exceeds the reference potential Vref, the comparator 5 inverts and generates a pulse. At this time, the AND circuit 3 receives the trigger pulse A. Since the inverted signal (L level) of R is input, the output of AND circuit 3 is at L level, and R
- Resetting of the S flip-flop 4 does not occur.

For example, if transistors 12 and 13 are ONL and transistors 11 and 14 are OFF, then DC type aioo - transistor 13 - motor 19 - transistor 12 - resistor 1
〇- Current flows through the ground potential 200 as before, and the current IF flowing through the resistor 10 increases and the resistor 10
When the voltage drop becomes larger than the reference potential V ref, the comparator 5 outputs. At this time, one input of the AND circuit 3 is at H level, so the AND circuit 3 applies an H level signal to the reset input of the R-S flip-flop 4.
The Q output of the S flip-flop 4 changes to L level, the output of the AND circuit 8 changes to L level, and the transistor 1
2 and 13 are turned off.

〔Effect of the invention〕

As explained above, this invention uses an inverted signal of the trigger pulse to mask spike noise, eliminating the need for a conventional external filter circuit, making it more compact and less expensive than conventional methods. .

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of each part of the above embodiment, Fig. 3 is a circuit diagram of a conventional PWM control device, and Fig. 4 is a waveform diagram of each part of the above conventional device. It is. In the figure, 2-) trigger pulse generator, 3-AND circuit, 4-flip-flop, 5-comparator, 6--reference power supply, 7--control circuit, 8.9--AND circuit, 10--resistor, 11-14--Transistor, 19-Electric motor. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] An oscillation circuit that generates a trigger pulse at predetermined time intervals, a flip-flop that is set by the trigger pulse, a control circuit that controls the output of the switching circuit in synchronization with the output of this flip-flop, and a voltage that controls the input or output current of the switching circuit. A detection circuit that performs conversion and detection, a comparator that compares the output of this detection circuit with a reference voltage, the output of this comparator is used as a reset input for the flip-flop, and the switching circuit performs PWM control by connecting switching elements in a bridge. A PWM control device, wherein the output of the comparator is used as a reset input of the flip-flop through an AND circuit that receives an inverted signal of the trigger pulse.