JPH07168637A - Abnormal voltage detecting device - Google Patents

Abstract

PURPOSE:To decrease ports of a system control microcomputer by detecting an abnormal short circuit between plural power supply lines through a single A/D conversion port of the system control microcomputer. CONSTITUTION:In an electronic equipment which is equipped with the system control microcomputer 10 having a voltage comparing means, constituted by connecting a power supply line to the A/D conversion port P1 of the microcomputer and has a function for turning OFF the circuit in the device when the voltage of the power supply line is lower than a threshold voltage value, the circuit in the device is provided with plural power supply lines 8 and 9 thereby they are connected to an adding circuit 7 consisting of a resistance and a diode, and the output of the adding circuit is inputted to the A/D conversion port through a voltage converting means R14. Further, the threshold voltage value of the microcomputer is switched corresponding to the operation mode of the electronic equipment by the circuit wherein at least one of the power supply line which is turned ON and OFF according to the operation mode of the electronic equipment is present together.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormal voltage detector for a plurality of power supply lines in an electronic device such as a video tape recorder (hereinafter referred to as VTR).

[0002]

2. Description of the Related Art Generally, a power supply line of an electronic device is stabilized by connecting a capacitor between the grounds and reducing the impedance in order to suppress the effects of load fluctuations, abnormal electric shocks from other circuit blocks in the device. It is trying to make it. By the way, capacitors, especially electrolytic capacitors,
When used for a long time, the insulating property deteriorates, and a short-circuit condition rarely occurs. At that time, an excessive current flows into the circuit, which causes the device to heat up and ignite. As a countermeasure against this, an overcurrent protection circuit is provided in the power line or a fuse or the like is used, but it is difficult to balance with the current capacity required under normal use conditions, and it takes experience and time to study. .

[0003]

Therefore, as one of reliable and easy methods, when the voltage of the power supply line falls below a specified voltage while the voltage of the power supply line is monitored by a microcomputer, the equipment is brought to a system down. There is a means. However, since this method basically requires one port for each power supply line, it cannot be adopted when there are a plurality of power supply lines and the number of ports of the microcomputer is small. As a method of monitoring a plurality of power supply lines with one port, a method of pulling up a microcomputer port, connecting each power supply line to the port via a diode, and pulling in at the time of an abnormal short circuit is conceivable. Not applicable when the monitored line is turned on / off depending on the device mode.

[0004]

A system control microcomputer having voltage comparison means (hereinafter referred to as a microcomputer) is provided, a power supply line is connected to an analog / digital conversion port of the microcomputer, and the voltage of the power supply line is thresholded. In an electronic device that has the function of shutting down the circuit inside the device when the voltage is below the voltage value, provide multiple power supply lines in the circuit inside the device, connect each power supply line to the adder circuit, and output the output of the adder circuit to the voltage. The configuration is such that input is made to the A / D conversion port via the conversion means.
This adder circuit is configured to add the output of a series circuit of a resistor and a diode connected to each power supply line.

Further, in a circuit in which a power supply line in which at least one of the plurality of power supply lines is turned on / off is mixed according to the operation mode of the electronic device, the threshold voltage value of the microcomputer is selected according to the operation mode of the electronic device. To be switched.

[0006]

After adding currents from a plurality of power supply lines through an adder circuit consisting of a resistor and a diode, the voltage is converted by a resistor (voltage converting means) connected between grounds, and this output is A / Input to D conversion port. The microcomputer compares and judges with the threshold voltage, and when there is an abnormality, the system inside the device is shut down. Further, the threshold voltage of the microcomputer is switched according to the operation mode of the device such as the recording mode and the post-recording mode, and the abnormality of the power supply line is detected.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an essential part of the present invention, and FIG. 2 is a flow chart of a microcomputer. This proposal describes an example of the case where it is adopted in an audio recording circuit of a VTR.
In the figure, 1 is an audio recording / reproducing (R / P) head, 2 is an audio erasing (AE) head, 3 is a full width erasing (FE) head, and both are fixed heads. Reference numeral 4 is a recording amplifier for amplifying a recording signal, 5 is an oscillating circuit for generating a recording bias signal for an audio signal and an audio track erasing signal, 6 is an oscillating circuit for generating a full width erasing signal, 7
Is an adder circuit in which a resistor R12 and a diode D1, and a resistor R13 and a diode D2 are connected in series to the first power supply line 8 and the second power supply line 9, respectively.

Reference numeral 10 is a system control microcomputer having voltage comparison means, 11 is a constant voltage power supply circuit for the first power supply line 8 composed of a transistor Tr1 and resistors R3 and R4, and 12 is a transistor Tr3 and resistor R8. , R9, a constant voltage power supply circuit for the second power supply line 9, 13 is a switching circuit composed of a transistor Tr2 and resistors R5 and R6, 14 is a switching circuit composed of a transistor Tr4 and resistors R10 and R11, R2 , R7
Is a current limiting resistor, L1 and L2 are filter coils, C
Reference numerals 1 and C2 are capacitors for power supply decoupling, and R14 is a resistor for current / voltage conversion (voltage conversion means).

Next, the operation of the present invention will be described. VTR
The linear track audio magnetic recording circuit generally uses a single oscillation circuit for the bias signal for recording signal, the audio track erasing signal, and the full width erasing signal. , The bias signal / audio track erase signal oscillation circuit 5 and the full-width erase signal oscillation circuit 6 must be operated independently.
It has two dedicated oscillator circuits.

By operating a record button (not shown), the port P of the microcomputer 10 is connected to the switching circuits 13 and 14.
Control signals S1 and S2 are sent from P2 and P3, and the constant voltage circuits 11 and 1 are turned on by switching on the switching circuits 13 and 14.
2 works. A constant voltage power source (12 V in this case) is applied, and a predetermined current is supplied to the oscillation circuit 5 via the resistor R2 and the coil L1. The load of the power supply line 8 during oscillation is suppressed by the capacitor C1. The recording signal amplified by the recording amplifier 4 is superimposed via the bias adjusting volume VR1 with the output from the oscillation circuit 5 as a bias,
It is sent to the R / P head 1 and recorded on a tape (not shown). The output of the oscillation circuit 5 is also supplied to the AE head 2,
Erase the audio track on the tape. On the other hand, a predetermined voltage is similarly supplied to the oscillation circuit 6 via the resistor R7 and the coil L2, and an erasing current is supplied to the FE head 3 to erase the entire width of the tape. The heads are arranged in the order of the FE head 3, the AE head 2, and the R / P head 1 with respect to the tape path.

The current in the first power supply line 8 passes through the resistor R12 and the diode D1, and the current in the second power supply line 9 passes through the resistor R1.
It is added via 3 and diode D2, and current /
The voltage is converted and input to the A / D conversion port P1 of the microcomputer 10. The microcomputer 10 compares the input voltage VIN with a threshold voltage set in the microcomputer 10, and if it is lower than the threshold voltage, it determines that there is an abnormality and shuts down the device circuit.

When the dubbing button (not shown) is operated, only the control signal S2 is output from the microcomputer 10 and only the R / P head 1 and the AE head 2 are operated. In this case, the threshold voltage set in the microcomputer 10 is switched. In addition, R / P during playback
Only the head 1 operates. In that case, the control signal from the microcomputer 10 is not output.

FIG. 2 shows a flowchart of the microcomputer 10. Operate the VTR mode key (step 2)
1) and the microcomputer 10 is "REC" or "A.DUB"
It is determined whether or not (step 22). "YES"
In case of, the threshold voltage is switched (in case of REC: VHI, in case of A.DUB: VLO) (step 2
3), the mode is changed (step 24). That is, REC
In the case of A, the control signals S1 and S2 are generated, and A. In the case of DUB, only the control signal S2 is generated. After that, the voltage VIN input to the port P1 of the microcomputer 10 is monitored (step 25).

Compared with the threshold voltage VHI or VLO depending on the mode, and if it is lower than the threshold voltage,
The system of the device circuit is brought down (step 27).
If higher than the threshold voltage, continue monitoring until the mode ends. When the STOP key (not shown) is operated (step 28), voltage monitoring is stopped (step 2).
9) Then, the operation mode is stopped. That is, the control signal output is stopped (step 30), and the operation of the microcomputer 10 ends. On the other hand, if "NO" in the step 22, the mode is shifted to another mode (for example, PLAY, FFWD, etc.) (step 31), the STOP key is operated (step 32) after the operation mode is completed, and the microcomputer 10 is passed through the step 30. Operation ends.

Here, in the configuration of the present invention, the normal REC mode and the A.D. Since it is necessary to switch the threshold voltage depending on the DUB mode, a method of setting the voltage will be described. For convenience, it is assumed that the voltages VOSC supplied to both oscillator circuits 5, 6 are of equal value. First, in the normal REC mode, both oscillation circuits 5 and 6 operate, so that the voltage VI applied to the A / D port P1 of the microcomputer 10 is
N2 is VIN2 = (VOSC-0.6) * R14 / (R14 + R12 / 2), where R12 = R13. Incidentally, 0.6 is a drop voltage due to the diode.

If either capacitor C1 or C2 is abnormally short-circuited, the voltage in that case drops to VIN2 '= (VOSC-0.6) * R14 / (R14 + R12). Therefore, if the threshold voltage VHI in the normal REC mode is set in the vicinity of these intermediate potentials in consideration of the stability of judgment, an abnormality can be detected. That is, VHI = VIN2 '+ (VIN2-VIN2') / 2 is set.

On the other hand, A. In the DUB mode, the oscillation circuit 5
Only the voltage VIN1 input to the port P1
Is VIN1 = VIN2 ′ = (VOSC−0.6) × R14 / (R14 +
R12). Since the voltage of the capacitor C1 at the time of abnormal short circuit is 0, the threshold voltage VLO may be set to an appropriate voltage between 0 and VIN1. That is, VLO = VIN1 / 2 is set.

Therefore, the normal REC mode and A. DUB
As shown in FIG. 3, the voltage distribution in the mode is VIN1 (= VIN2 ') <VHI <V in the recording (REC) mode.
IN2 is set, and 0 <VLO <VIN1 is set in the audio dubbing (A.DUB) mode.

[0019]

According to the configuration of the present invention, as long as the conditions such as the tolerance of the electronic components used, the line load variation, and the resolution of the A / D port of the microcomputer allow, abnormal short circuits of a plurality of power supply lines can be performed with one port and at low cost. It will be possible to monitor. Therefore, it is effective in reducing the number of ports of the microcomputer.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main part of the present invention.

FIG. 2 is a flowchart of a microcomputer.

FIG. 3 is a voltage distribution diagram corresponding to modes.

[Explanation of symbols]

7 Addition Circuit 8 First Power Supply Line 9 Second Power Supply Line 10 System Control Microcomputer R14 Current / voltage conversion resistance (voltage conversion means)

Claims (3)

[Claims] 1. A system control microcomputer having a voltage comparison means is provided, a power supply line is connected to an analog / digital (A / D) conversion port of the microcomputer, and the voltage of the power supply line is a threshold voltage. In an electronic device having a function of shutting down the circuit in the device when the value is less than or equal to a value, a plurality of power supply lines are provided in the circuit, each of the plurality of power supply lines is connected to an adding circuit, and the output of the adding circuit is a voltage. An abnormal voltage detection device, characterized in that it is inputted to the analog / digital conversion port via a conversion means. 2. The abnormal voltage detection device according to claim 1, wherein the adder circuit adds outputs from respective lines of the plurality of power supply lines via a series circuit of a resistor and a diode. 3. A circuit in which a power supply line in which at least one of the plurality of power supply lines is turned on / off in a mixed manner according to an operation mode of the electronic device is mixed, a threshold voltage of the microcomputer depending on an operation mode of the electronic device. The abnormal voltage detection device according to claim 1 or 2, wherein the value is switched.