JPH03163913A - Power source fluctuation detecting circuit - Google Patents

Abstract

PURPOSE:To easily enable the circuit to detect the fluctuation of a power source by operating an A/D converter by a fluctuating power source, inputting a reference voltage, which is generated by a reference voltage generator, to the said A/D converter and defining the conversion output of the said A/D converter as a power source fluctuation detecting signal. CONSTITUTION:The fixed reference voltage is generated by a reference voltage generator 12 and this voltage is inputted to an A/D converter 11. Since the A/D converter 11 executes the A/D conversion of this reference voltage, the A/D output is not changed when a power supply voltage is fixed. However, when the power supply voltage is fluctuated, the internal voltage of the A/D converter 11 to be compared with an A/D input is also changed and accordingly, the A/D output is changed. The ratio of the change in this A/D output is correspondent to the power source fluctuation. The power source of the A/D converter 11 is B<+> as well. The reference voltage generator 12 serially connects a resistor R3 and a Zener's diode D1 between power sources B<+> and B<-> and a Zener voltage to be generated at the said diode D1 is inputted to the A/D converter 11 as a reference voltage. A correcting circuit 13 corrects (analogly inverts) the conversion output of the A/D converter 11 and inputs it to a PCM/PWM converter 22.

Description

[Detailed Description of the Invention] [Summary] Regarding a power supply fluctuation detection circuit using an A/D converter, the purpose is to output the fluctuation width of the power supply voltage as a digital value. Operate with a power supply, input the reference voltage generated by the reference voltage generator to the A/D converter, use the conversion output of the A/D converter as a power supply fluctuation detection signal, or set the A/D converter to a constant voltage. Operated by the output of the circuit, the A/D
A power supply voltage that fluctuates is input to the converter after being divided by a voltage dividing circuit, and the converted output of the A/D converter is used as a power supply fluctuation detection signal.

[Industrial application field]

The present invention relates to a power supply fluctuation detection circuit using an A/D converter.

In a circuit where power supply voltage fluctuations affect the output, it is desirable to suppress the power supply fluctuations or to detect the fluctuations and correct the output. However, when the power supply of in-vehicle equipment is directly connected to the battery, it is not possible to stabilize the power supply voltage (it fluctuates greatly depending on changes in load, etc.), so there is no way to detect power fluctuations and correct the equipment output. Effective.

[Conventional technology]

As the source (sound source) of in-vehicle audio equipment becomes digital, there is a tendency for each part to become digital as well. One example is the power amplifier that drives a speaker, and if a digital amplifier called a Swiss-isolating amplifier is used here, a large output can be achieved.

Figure 7 is an explanatory diagram of a switching amplifier, where SP is a speaker, Q1 to Q4 are switching elements, A is a control signal,
λ is its inverted signal, Vcc is the power supply, and GND is the ground. Elements Q, , Q3 are turned on when signal A is H (high), and drive current flows through speaker SP with the polarity indicated by the solid line arrow. On the other hand, elements Q2 and Q4 are turned on when signal λ is H, causing currents of opposite polarity (indicated by broken line arrows) to flow through speaker SP. Although this example uses a BTL system, the number of elements is large, but simply grounding one end of the speaker SP and using the element pair Q, , Q2 or Q3, Q4 at the other end is sufficient.

Control signal A. A is, for example, a PWM (pulse width modulation) signal in which the duty of each pulse of a pulse train (carrier) of a constant period is changed according to the amplitude of the audio signal. When elements Q1 to Q4 in Fig. 7 are driven with this PWM signal, a driving current that is integrated according to the power supply voltage and the duty of the PWM signal flows through the speaker SP, and when this is smoothed, it is restored to the original analog value. The audio signal is reproduced from the speaker SP. The power supply voltage determines the amplitude of the PWM signal.

FIG. 8 shows the carrier of the PWM signal, the voltage waveform (similar to the PWM signal) applied to the speaker SP, and the smoothed waveform of the drive current flowing to the speaker SP.

[Problem to be solved by the invention]

If the power supply Vcc of the circuit shown in FIG. 7 is the vehicle's battery, its voltage will vary greatly depending on the increase or decrease of the load (for example, the air conditioner). As a result, when the voltage applied to the speaker SP decreases, for example, from Vcc to vcc' in FIG. The sound pressure decreases.

The present invention attempts to easily detect the above-mentioned harmful power supply voltage fluctuations using an A/D converter.

[Means to solve the problem]

FIG. 1 is a first principle diagram of the present invention, where 11 is an A/D converter;
12 is a reference voltage generator, and 13 is a correction circuit used as necessary.

FIG. 3 is a second principle diagram of the present invention, in which 11 is an A/D converter;
14 is a voltage dividing circuit, and 15 is a constant voltage circuit.

[For production]

The A/D converter l1 in FIG. 1 operates on a fluctuating power supply. If this A/D converter 11 uses the power supply voltage as an A/D input, the A/D output will always be constant regardless of power supply fluctuations, so power supply fluctuations cannot be detected. Therefore, in this example, a constant reference voltage is generated by the reference voltage generator 12, and this is
The signal is input to the D converter 11. Since the A/D converter If converts this reference voltage into A/D, if the power supply voltage is constant, A/D converter If converts this reference voltage into A/D.
/D output also remains unchanged. However, when the power supply voltage fluctuates, A
Since the internal voltage of the Δ/D converter 11 compared with the /D input also changes, the A/D output changes. The rate of change in this A/D output corresponds to power supply fluctuations.

Figure 2 is a waveform diagram showing this operation, where (a) is the power supply, (b)
) is the A/D input (reference voltage), and (C) is the A/D output. Although this A/D output is a digital value, it is expressed as an analog value for ease of explanation.

As shown in these figures, when the A/D input is constant and the power supply increases (decreases), the A/D output decreases (increases).

Incidentally, if it is desired that the direction of change in the A/D output is the same as the power supply fluctuation, a correction circuit 13 such as an inverting circuit may be used. FIG. 2(d) shows an analog representation of the output of such a correction circuit 13.

The A/D converter 11 in FIG. 3 operates on the output of the constant voltage circuit 15, and A/D converts the divided voltage output of the fluctuating power supply voltage divided by the voltage dividing circuit 14. The voltage dividing circuit 14 includes a series resistor R,
, R2, as shown in Figure 4 (al Tb
) shows a voltage fluctuation of N times that of the power supply. N is a voltage division ratio, whereby the voltage division output is set to be less than or equal to the maximum input level of the A/D converter 11. This A/D converter l1
When the output is converted into an analog form and shown as shown in FIG. 4 (Cl), it corresponds to power supply fluctuations. In this case, the correction circuit 13 shown in FIG. 1 is not required.

〔Example〕

FIG. 5 is a structural diagram of a first embodiment of the present invention.

This example is applied to in-vehicle audio equipment.
is a digital source such as a CD (compact disc), 2
2 is P which converts the output (PCM signal) into PWM signal
The CM/PWM converter 23 is a Swiss switching type power amplifier whose final stage is configured as shown in FIG. 7, the SP speaker, B+ is the positive side of the bass terminal, and B1 is the negative side of the bass terminal. Corresponding to Figure 7, B 11, V cc, B
= GND.

This power source B1 is used as an operating power source for all circuits.

In this example, the method shown in Figure 1 is applied, so the A/D converter I1
The power source is also B0. The reference voltage generator 12 connects a resistor R3 and a Zener diode 1/D1 in series between power supplies B1 and B-, and inputs the Zener voltage generated at the diode D1 to the A/D converter 11 as a reference voltage. . The correction circuit 13 corrects (inverts in analog terms) the converted output of the A/D converter 11 and inputs it to the PCM/PWM converter 22 .

This PCM/PWM converter 22 has a digital source 21
The PCM signal (audio signal) from
This is converted into a PWM signal and supplied to the power amplifier 23, and the operation as explained in FIGS. 7 and 8 is performed. At this time, the PCM/PWM converter 22
The PWM signal is corrected by the output as follows.

As shown in Figure 8, when the amplitude of the speaker applied voltage decreases from Vcc to Vcc' due to power supply fluctuations, the duty is increased to compensate for this (make the area the same) and the speaker drive current changes from the broken line. Try to return it to a solid line (if the power increases, correct it in the opposite direction). For example, PC
If the M signal is converted to a PWM signal using a pulse width counter, the value to be input to the counter is
A configuration may be considered in which the value indicated by the correction signal is added to the value indicated by the M signal. Or PCM/PWM converter 22
If this is implemented using software using a DSP (digital signal processor), this duty correction may also be performed using software. Note that if the PCM/PWM converter 22 has a function equivalent to that of the correction circuit 13, the correction circuit 13 may be omitted.

FIG. 6 is a structural diagram showing a second embodiment of the present invention. In this example, the system shown in FIG. 3 is adopted for the power supply fluctuation detection circuit 10, and the other parts are the same as those shown in FIG. The constant voltage circuit 15 is a resistor R
4 and a Zener diode D2 are connected in series between power supplies B1 and B1, and the Zener voltage of the diode D2 is used as the operating power supply for the A/D converter 11. This A/D converter 11 is connected to a power supply B0, whose voltage is divided by the resistors R, , R2 of the voltage dividing circuit 14.
The divided voltage of B is the A/D input, and the A/D output is the PC.
This value is input to the M/PWM converter 22 as a correction value. In this example, the operating power for the PCM/PWM converter 22 is also supplied from the constant voltage circuit 15.

〔Effect of the invention〕

9 As described above, according to the present invention, for a system in which power supply fluctuations directly lead to output fluctuations, the range of power supply fluctuations can be detected as a digital value and provided as a correction parameter.

[Brief explanation of the drawing]

Figure 1 is the first principle diagram of the present invention, Figure 2 is its operating waveform diagram, Figure 3 is the second principle diagram of the present invention, Figure 4 is its operating waveform diagram, and Figure 5 is the present invention. FIG. 6 is a configuration diagram of a second embodiment of the present invention, FIG. 7 is an explanatory diagram of a switching amplifier, and FIG. 8 is an operating waveform diagram thereof. In the figure, 11 is an A/D converter, l2 is a reference voltage generator, 1
3 is a correction circuit, 14 is a voltage dividing circuit, and 15 is a constant voltage circuit.

Claims (1)

[Claims] 1. The A/D converter (11) is operated with a fluctuating power supply, and the reference voltage generated by the reference voltage generator (12) is input to the A/D converter; A power fluctuation detection circuit characterized in that a conversion output of a /D converter is used as a power fluctuation detection signal. 2. The A/D converter (11) is operated by the output of the constant voltage circuit (15), and the fluctuating power supply voltage is applied to the A/D converter by the voltage divider circuit (14).
), and the converted output of the A/D converter is used as a power fluctuation detection signal.