JPH02161810A - Pwm pulse generating device - Google Patents

Abstract

PURPOSE:To always obtain a PWM signal having the prescribed pulse width regardless of the temperature change by using a comparator which compares the output of a level shift circuit with the output of an absolute value circuit to obtain the pulse width modulation output. CONSTITUTION:The voltage obtained at the lower edge of a triangular wave is fixed at a prescribed level of a level shift circuit 12 which is formed by a diode circuit. For the reference voltage of an absolute value circuit 4, the input signal is switched between the positive and negative states by the reference voltage V0 decided by a diode. Thus the difference of both voltage levels can be set at a prescribed level with substantially no control. Then the forward drop voltage change if caused by the temperature characteristics of the diode can be offset since the diodes are used to both a voltage generating circuit 11 and the circuit 12. As a result, the same PWM pulse signals can be obtained regardless of the temperature change.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a PWM pulse generator that performs pulse width modulation according to an input signal.

[Conventional technology]

Conventionally, a PWM pulse generator used in, for example, a power steering device of a vehicle detects a signal from an l-lux sensor and a circuit current from a motor, and generates a PWM pulse with a duty ratio corresponding to the deviation thereof.

FIG. 4 is a block diagram showing an example of a conventional PWM pulse generation circuit.

In this figure, the deviation between the torque signal from the torque sensor 1 and the current signal obtained from the current detection circuit 2 is determined by the deviation amplifier 3.
The signal is amplified by and transmitted to the absolute value circuit 4 and polarity switch 5. The absolute value circuit 4 has the input/output characteristics shown in FIG. 5(a), and if the input signal is at a positive level, it will be output as is, and if it is at a negative level, it will be inverted and output.
Its output is given to comparator 6. Also, triangular wave generation circuit 7
As shown in FIG. 5 (bl), generates a triangular wave with a constant amplitude value that does not have a DC component, and the output is given to the comparator 6 via the level shift circuit 8. The level is shifted by the voltage AvP-P+vl, which is the sum of the amplitude 4 of the amplitude value v, -p and the voltage V1 for generating a constant dead zone, for example, 0.2V. ), the level-shifted triangular wave signal and the output of the absolute value circuit 4 are output to the comparator 6.
compared by.

Then, by comparing these signals, the comparator 6 outputs the signal shown in Fig. 6 (
A PWM pulse signal as shown in d) is obtained, and the steering motor 10 is driven via the PWM drive circuit 9.

[Problem to be solved by the invention]

However, according to such a conventional PWM pulse generator, it is necessary to precisely add the voltage V of the fuwa band and the voltage 'AVp-p of the triangular wave to perform a level shift due to fluctuations in the amplitude value of the triangular wave. The disadvantage is that it requires skill and effort to make adjustments while observing the waveform.

The present invention has been made in view of the problems of the conventional PWM pulse generator, and an object of the present invention is to automatically generate a PWM signal with a predetermined pulse width without requiring such adjustment. is a technical issue.

[Means to solve the problem]

The present invention is a PWM pulse generator that performs pulse width modulation according to an input signal, which includes a voltage generation circuit that provides a reference voltage according to the forward voltage drop of a diode, and a voltage generation circuit that generates an input signal that changes between positive and negative. An absolute value circuit that discriminates based on the obtained reference voltage, outputs signals that exceed the reference voltage as they are, and inverts and outputs input signals that are below the reference voltage, a triangular wave generator that generates a triangular wave, and a triangular wave generator. The resulting triangular wave output is given, and a pulse width modulation output is generated by comparing the outputs of the level shift circuit and the absolute value circuit with a level shift circuit that sets the lowest level voltage to a predetermined value based on the forward drop voltage of the diode. The present invention is characterized in that it has a comparator that obtains .

[Effect]

According to the present invention having such features, a reference voltage is applied from the voltage generation circuit to the absolute value circuit, and the input signal is discriminated and outputted based on this voltage.

This reference voltage is obtained from the forward voltage drop of the diode and has predetermined temperature characteristics. Similarly, the shift voltage of the level shift circuit also has temperature characteristics due to the diode, and is controlled so that the voltage difference between the voltage at the lower end of the voltage generating circuit and the lower end of the triangular wave is always constant. Therefore, the voltage in the dead zone region during this period can always be kept constant regardless of temperature changes.

〔Effect of the invention〕

Therefore, according to the present invention, there is no need to perform adjustment while monitoring the waveform using a variable resistor, and the effort required for adjustment can be significantly reduced. Further, it is possible to obtain a pulse generating circuit that always has constant characteristics regardless of temperature characteristics.

[Explanation of Examples]

FIG. 1 is a block diagram showing the overall configuration of a PWM pulse generator according to an embodiment of the present invention. In this figure, the same parts as in the conventional example are given the same reference numerals and detailed explanations are omitted. Also in this embodiment, the output from the torque sensor 1 and the output from the current detection circuit 2 are given to the deviation amplifier 3, and the output thereof is given to the absolute value circuit 4 and the polarity switch 5. Now, in this embodiment, the output of the voltage generating circuit 11 is given to the absolute value circuit 4. Further, the output of the triangular wave generating circuit 7 is given to a level shift circuit 12. Level shift circuit 12
is a level shifting circuit that fixes the lowest level voltage of the triangular wave to a predetermined value. The level-shifted signal and the signal from the absolute value circuit 4 are applied to a comparator 6 and compared, thereby generating a pwM pulse.

The other configurations are the same as those of the conventional example described above.

FIG. 2 is a circuit diagram showing the detailed configuration of the main parts of this embodiment. In this figure, the absolute value circuit 4 includes an operational amplifier 4a that provides the absolute value of an input signal, and an operational amplifier 4b for inverting and adding that level-shifts and inverts and amplifies the output. As shown in the figure, the voltage generating circuit 11 is connected to a power source by a resistor R1,
Diode D1. A resistor R2 is commonly connected, a resistor R3 is connected between the common connection point of the resistor R1 and the diode D1, and the other end is applied as a reference voltage V0 to the inverting input terminal of the operational amplifier 4b). Therefore, the Mm voltage V of the output of the voltage generating circuit 11. is the value obtained by adding the voltage drop of the resistor R2 to the forward voltage drop of the diode DI, and the characteristics of the absolute value circuit 4 including the characteristics of the voltage generating circuit 11 are shown in FIG. 3(a).
It will be as shown in

On the other hand, the triangular wave generation circuit 7 is composed of an operational amplifier 7a, and generates a triangular wave signal of a predetermined width V p -p centered on Ov as shown in FIG. 3(b), as in the conventional example, and this signal is The signal is transmitted to the level shift circuit 12.

The level shift circuit 12 has a capacitor C1 connected to an input terminal, and a diode D2 and a resistor R4 connected in parallel between the other end of the capacitor CI and a ground terminal. And that common connection end is level shift! -(No. 8 is connected to the input terminal of the operational amplifier 6a constituting the comparator 6.

Here, the level shift circuit 12 fixes the voltage at the lower end of the triangular wave to a predetermined value corresponding to the forward drop voltage of the diode, for example 0.5.

Therefore, the level shift circuit 12 provides the comparator 6 with a triangular wave signal as shown in FIG. 3(C).

The output of the deviation amplifier 3 from the absolute value circuit 4 is shown in FIG.
It is converted into an absolute value with the characteristics shown in FIG. Therefore, the comparator 6 generates a PWM signal as shown in FIG. 3(d).
A pulse signal is obtained, and the steering motor 10 is driven via the PWM drive circuit 9. and the third
Even when the amplitude VP-P voltage of the triangular wave shown in FIG.

In this way, in the present invention, the voltage at the lower end of the triangular wave is fixed to a predetermined value of the level shift circuit 12 formed by the diode circuit, and the reference voltage of the absolute value circuit 4 is also the reference voltage (2) determined by the diode. The input signal is switched between positive and negative.

Therefore, the voltage difference can be kept at a predetermined level with almost no need to be adjusted, and even if the forward drop voltage changes depending on the temperature characteristics of the diode, diodes can be used in both the voltage generation circuit 11 and the level shift circuit 12. Therefore, the changes are canceled out and the same PWM pulse signal can be obtained regardless of temperature changes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of a PWM pulse generator according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of the main parts of this embodiment, and FIG. 3 shows waveforms of each part. FIG. 4 is a block diagram of a conventional PWM pulse generator, and FIG. 5 is a waveform diagram showing waveforms of various parts of the conventional PWM pulse generator. Figure 2■--Torque sensor 2-...Current detection circuit 3-
... Deviation amplifier 4--------One absolute value circuit
5.Polarity switch 6---1.Comparator 7---
--1 Triangular wave generation circuit 8, 12...-Level shift [-Circuit 9--PWM drive circuit i o-1---
-Steering motor 11・--11--Voltage generating circuit Fig. 10 Fig.

Claims (1)

[Claims] (1) A voltage generation circuit that provides a reference voltage according to the forward voltage drop of the diode, and input signals that change between positive and negative are discriminated based on the reference voltage obtained from the voltage generation circuit, and signals that exceed the reference voltage are left as they are. an absolute value circuit that inverts and outputs an input signal that is below a reference voltage; a triangular wave generating circuit that generates a triangular wave; and a triangular wave output obtained from the triangular wave generating circuit is given and and a comparator that obtains a pulse width modulation output by comparing the outputs of the level shift circuit and the absolute value circuit. Pulse generator.