JPS5826566B2 - Switch circuit for preventing malfunction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention resides in means for preventing malfunctions in electronic devices such as desktop computers and registers.

In other words, when the power is turned OFF in a desktop computer, for example, the power for the control unit (drive signal generation source) such as an LSI rises earlier (from the negative level to the ground level) than the power for the load (driven unit). During this period, drive signals were randomly output from the drive signal generation source, causing the driven section to malfunction.

The present invention provides a circuit that prevents the above-mentioned malfunction.

A feature of the present invention is that the above-mentioned malfunction prevention circuit is achieved with a simple circuit configuration and can be constructed at extremely low cost.

As shown in Fig. 1, the above-mentioned malfunction is caused by the drive signal generation source (
When the potential ■□ supplied to the control section) and the potential V2 supplied to the driven section (load) are turned off, they rise to the ground level as shown in the figure.

In this case, the rise of the potential ■1 operates faster than the rise of the potential v2.

Point E at potential (1) indicates the limit point of the LSI specifications constituting the control section, and point D at potential (2) indicates the point at which the load becomes inoperable.

When the potential (1) reaches point E due to the power OFF operation, the drive signal generation source (control unit) becomes unstable between the point E and the ground level.

Further, due to the power OFF operation, the potential V2 reaches the point D compared to the time the potential V1 reaches the point E.
It takes time.

For this reason, if a signal is randomly output in an unstable state from the drive signal generation source within the time t0, a malfunction occurs in the load, which is the driven section.

Therefore, conventionally, in order to prevent the above-mentioned malfunction, a configuration as shown in FIG. 2 has been adopted.

In other words, in FIG. 2, block 1 is a drive signal generation source constituting a control section such as an LSI, and block 2 is a block 3.
1 shows a drive circuit for driving a driven part, which is a load shown in FIG.

Zl is a constant voltage element like a Zener diode, R1-R
3 is the resistor s Qt and Q2 are switch transistors, Vl is the power supply voltage for block 1, ■2 is the power supply voltage for block 3, Ein is the power supply voltage before regulation of ■2, Zener diode Z2 and resistor The circuit consisting of R4 and transistor Q3 represents a regulator of power supply voltage 2.

In this normal operating state, IVII>IVZI (Vz: Zener voltage), a base current flows through Ql, and Ql is in the ON state.

Therefore, since the base potential of Q2 is clamped to approximately the ground level, Q2 is in an OFF state, and the power supply potential v2 is normally output without affecting the base potential of Q3.

When the power is turned off in the above normal operating state, the power supply voltages (1) and (2) rise as vl and V2 shown in Figure 1, so when the power supply voltage v1 reaches Vz, Ql becomes 0.
FFL...This turns Q2 into the ON state.

When Q2 is turned ON, the base of Q3 is clamped to approximately the ground level, so Q3 is turned OFF, and as is clear from Figure 1, this power supply voltage (■2) decreases when ■1 reaches Vz. Canted off.

Namely 1. By cutting off the power source (2) of the driven section 3 until the power source (1) of the drive signal generation source 1 reaches the limit point E, malfunctions when the power is turned off are prevented.

The above-mentioned malfunction prevention circuit configuration is extremely complicated, requires two stages of expensive constant voltage elements (Zener diodes) and transistors, and is extremely disadvantageous in terms of cost. There are drawbacks such as power loss due to Ql's collector current when Ql is in the ON state at times, and it cannot be said to be a desirable malfunction prevention circuit.

The present invention provides a novel malfunction prevention structure in which a malfunction prevention circuit is provided using inexpensive parts and a simple circuit configuration.

The present invention will be described below with reference to the circuit configuration shown in FIG. 3 and the operational diagram shown in FIG. 4.

In FIG. 3, block 1 shows a drive signal generation source constituting a control section such as an LSI, and block 2 shows a drive circuit for driving a driven part, which is a load shown by block 3.

Further, 1 indicates the power supply voltage for block 1, and 2 indicates the power supply voltage for block 3, which is the same as 1°v2 in FIG. 2 above.

And s Q4 is a switching transistor, R3-R6
C1 is a resistive element, C1 is a capacitor that maintains the voltage difference between the power supply voltage v1 and the smaller voltage v3 mentioned above, and F is the base voltage of Q4.

In this normal operating condition, the base current of Q4 is R5
When the drive signal (ground level signal) is generated from the drive signal generation source 1, the voltage Q4 is supplied from the voltage Q4.
ONL, , 1 The driven section 3 is driven via the drive circuit 2.

At this time, the capacitor C1 has l■11 1 ■s
A potential difference of 1-V4 is maintained.

When the power is turned off from the normal operating state, the power supply voltages ■ and ■2 rise as shown in Figure 4) Q4
As shown by F, the base potential of is raised to a potential higher than ■1 by V4.

Therefore, at the point when 1 reaches the limit voltage E, a reverse bias voltage (a potential higher than the ground level) is applied between the base and emitter of Q4, and Q4 is completely turned off.

That is, since Q4 is cut off before the power supply voltage v1 reaches point E, even if the drive signal generation source 1 generates a drive signal in an unstable state after point E, the driven part 3 does not operate.
This prevents malfunctions.

As described above, in the present invention, a switch element is provided to control the signal from a drive signal generation source to one drive circuit, and when the power is turned off, the switch element A switch element control circuit comprising a capacitor and a current limiting resistor element that maintains the difference between the voltage to the drive signal generation source and another voltage different from the voltage is provided so as to cause the switch to act in an OFF state. Since it does not use expensive parts such as constant voltage elements, it only requires an inexpensive capacitor, and it only requires one stage of transistors, the circuit configuration can be extremely simplified compared to conventional circuits, and it is also cost-effective. It becomes a malfunction prevention circuit that can significantly reduce the amount of noise.

In addition, the transistor has features such as no extra current flowing through the transistor during normal operation and no power loss, and is extremely effective in practical use.

Note that the circuit configuration of the present invention requires a voltage like (3), but since many LSIs generally use a two-power supply system, a voltage equivalent to (3) exists. In addition, the circuit can be constructed using appropriate voltages of other driving elements, and there is no practical inconvenience.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the conventional operating state, Fig. 2 is a block diagram of the conventional malfunction prevention circuit, Fig. 3 is a block diagram of the malfunction prevention circuit of the present invention, and Fig. 4 is an explanatory diagram of the operation of Fig. 3. be. 1: Drive signal generation source, 2: Drive circuit, 3: 1 driven part (
Load), ■1: Power supply voltage of drive signal generation source, ■2: Power supply voltage of driven part, ■3: Voltage smaller than ■1, Q4: Switch transistor, R5 and R6: Resistance element, 0□: Capacitor .

Claims (1)

[Claims] 1 In a device that causes a driven part (load) to perform a predetermined operation via a drive circuit in response to a signal from a drive signal generation source, a switch element is provided to control the signal from the drive signal generation source to the drive circuit, and a power supply The voltage to the drive signal generation source is set to another voltage different from the voltage, so that the voltage to the drive signal generation source acts on the switch element in the OFF state before the voltage to the drive signal generation source reaches the operating limit voltage value of the drive signal generation source when the drive signal generation source is turned off. A switch circuit for preventing malfunction, which is provided with a switch element control circuit composed of a capacitor that maintains a voltage difference and a current limiting resistor element.