JPH04282920A - Multi-function power supply circuit for on-vehicle audio equipment - Google Patents

Abstract

PURPOSE:To suppress noise generated from a power IC by providing a power supply fluctuation detection circuit to a multi-function power supply circuit and generating a mute signal regardless of a fluctuation timing of a backup power supply when an accessory power supply is fluctuated. CONSTITUTION:A higher voltage from an ACC is dropped by a forward voltage of diodes D1, D2 is outputted from the diodes D1, D2 and an integration circuit comprising R, C1 charges a capacitor C1 by this voltage. A transistor circuit comprising T, ZD, C2 outputs a mute signal MUTE when a voltage of the ACC is lower than a sum of a base-emitter voltage of a transistor (TR) T and a Zener voltage of the ZD with respect to the charging voltage of the integration circuit. A mute signal is generated independently of a fluctuation timing of a backup power supply BU at the fluctuation of an accessory power supply ACC in this way, then a noise sound generated from a power IC is suppressed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multifunctional power supply circuit for in-vehicle audio equipment having a function of generating a mute signal when the power supply voltage drops.

0002

[Prior art] Cassette (CS), FM tuner, AM
In-vehicle audio equipment that has multiple sources, such as a tuner, does not use each source at the same time, so a power supply circuit that can be shared by all sources can be used.

[0003] A multifunctional power supply IC in which a source selection function, a mute signal generation function, etc. are added to the power supply circuit and is integrated can be made smaller overall than when a function-specific power supply circuit is provided for each source.

In-vehicle audio equipment uses a backup power supply BU directly connected to a battery, and an accessory power supply ACC connected to the battery via a switch operated by an engine key. Since these power supplies are also used by other loads, they may exhibit large temporary voltage fluctuations. This power supply voltage fluctuation causes audio noise, so it is necessary to mute it.

FIG. 3 shows an example of a conventional power supply fluctuation detection circuit. In this circuit, a backup power supply BU is connected to the emitter of a pnp transistor T, and an accessory power supply ACC is connected to the base side via a DC cut capacitor C2 and a Zener diode ZD.When the transistor is turned on, the collector A mute signal MUTE is output.

The condition for transistor T to turn on is the falling period of ACC when ACC is lower than BU by a certain value, and in the circuit of FIG. 3, the base-emitter voltage VBE (about 0.7 V) of transistor T and The sum with the Zener voltage Vz (selected to be about 3 V) of the Zener diode ZD becomes the constant value.

[0007]

Although the power supplies BU and ACC are branched from the same battery, subtle differences occur in power supply fluctuations due to differences in connected loads and differences in operation timing. Therefore, in the circuit of Fig. 3, A
If CC decreases in advance, mute signal MUTE
Even if it is possible to output the mute signal MUTE, there is a drawback that the mute signal MUTE cannot be output when the BU decreases in advance as shown in FIG.

An object of the present invention is to make it possible to reliably generate a mute signal when a power supply fluctuation occurs, regardless of the above-mentioned fluctuation timing.

[0009]

[Means for Solving the Problems] The present invention provides a multifunctional power supply circuit for in-vehicle audio equipment that uses a backup power supply directly connected to a vehicle battery and an accessory power supply connected to the battery via a switch. , a diode circuit that outputs the higher voltage of either the backup power supply or the accessory power supply, an integrating circuit that holds a first voltage output by the diode circuit, and the first
and a second voltage of the accessory power supply;
The present invention is characterized by comprising a transistor circuit that turns on a mute signal when the second voltage becomes lower than the first voltage by a certain value or more.

0010

[Operation] When ACC falls, the higher voltage of either BU or ACC is BU in the case of Figure 4 and ACC in the case of Figure 5.
Therefore, if this voltage is held in an integrating circuit and compared with the falling edge of ACC in real time, the falling edge of ACC will always be lower. Therefore, the mute signal can be turned on not only at the timing shown in FIG. 4 but also at the timing shown in FIG. 5.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of the main parts of the present invention, showing an example of a power supply fluctuation detection circuit. The power supply fluctuation detection circuit in this example is
Diode circuits D1 and D2 that output the higher voltage of either the backup power supply BU or the accessory power supply ACC, integrating circuits R and C1 that hold the first voltage output by the diode circuits, and the first voltage and accessory power ac
It is composed of transistor circuits T, ZD, and C2 that compare the second voltage of C and turn on the mute signal MUTE when the second voltage becomes lower than the first voltage by a certain value or more. That is,
The configuration of this example is shown in FIG. 3 (transistor circuits T, ZD,
C2) diode circuits D1, D2 and integration circuits R, C1
is added.

[0012] The diode circuits D1 and D2 are BU and ACC.
The higher voltage is lowered by the forward voltage (approximately 0.7 V) of the diode D1 or D2 and output, and this is set as the first voltage. Integrating circuit R, C1 charges capacitor C1 with this first voltage. R is a charging resistance at this time.

The transistor circuits T, ZD, and C2 have an ACC of (VBE+VZ) with respect to the charging voltage of the integrating circuits R and C1.
), the mute signal MUTE is turned on. VBE is the base-emitter voltage of transistor T, V
Z is the Zener voltage of the Zener diode ZD.

According to the power supply fluctuation detection circuit of this example, the charging voltage of the integrating circuits R and C1 is changed in real time at the falling edge of ACC, both when the ACC falls in advance as shown in FIG. 4, and when the BU falls in advance as shown in FIG. Since the voltage is higher than the voltage of ACC, both mute signals MUTE are turned on. This circuit only needs to turn on the mute signal in response to the fall of ACC, and subsequent muting can be left to processing by a microcomputer or the like.

FIG. 2 is a block diagram of a multifunctional power supply IC incorporating the power supply fluctuation detection circuit of FIG. 1. This IC has a common power output terminal COM and power output terminals CS, AM,
FM, and both output the backup power supply BU after being stabilized by the regulator 11. 12 is common terminal C
This is a switch that supplies regulator output to the OM, and is controlled in response to on/off of the accessory power supply ACC. 1
Reference numeral 3 denotes a changeover switch that supplies the regulator output to one of the source-specific terminals CS, AM, and FM, and the switching position is selected by a selection signal SEL input from an external microcomputer or the like. 14 is a mute circuit that generates a mute signal when the select signal SEL changes, and 15 is an OR circuit that outputs this mute signal and the mute signal output from the power supply fluctuation detection circuit 16 to the outside from the mute output terminal MO.

The power supply fluctuation detection circuit 16 includes a capacitor C1,
Only C2 is attached externally, and all other elements are integrated within the IC. Therefore, the overall mounting area can be reduced.

[0017]

[Effects of the Invention] As described above, according to the present invention, a power supply fluctuation detection circuit is provided in a multifunctional power supply circuit used in an in-vehicle audio device, and the detection circuit adjusts the timing of fluctuations in the backup power supply when the accessory power supply fluctuates. Since the mute signal can be generated without depending on the power IC, abnormal noise generated from the power IC can be reliably suppressed.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a power supply fluctuation detection circuit according to the present invention.

FIG. 2 is a configuration diagram of a multifunctional power supply IC showing an embodiment of the present invention.

FIG. 3 is a configuration diagram of a conventional power supply fluctuation detection circuit.

FIG. 4 is a waveform diagram when the ACC is lowered in advance.

FIG. 5 is a waveform diagram when BU precedence decreases.

[Explanation of symbols]

Claims (1)

[Claims] 1. A multifunctional power supply circuit for an in-vehicle audio device that uses a backup power supply directly connected to a battery of a vehicle and an accessory power supply connected to the battery via a switch, wherein the backup power supply and the accessory power supply are connected to the battery through a switch. a diode circuit that outputs a higher voltage, an integrating circuit that holds a first voltage output by the diode circuit, and a comparison between the first voltage and a second voltage of the accessory power supply; A multifunctional power supply circuit for an in-vehicle audio device, comprising: a transistor circuit that turns on a mute signal when the second voltage drops by a certain value or more than the first voltage.