JPH066194A - Malfunction prevention circuit for electronic device - Google Patents

Abstract

PURPOSE:To prevent malfunction by connecting Zener diode between an emitter of a drive transistor(TR) and ground and connecting a diode between one terminal of the Zener diode and a 1st power supply terminal and between the one terminal of the Zener diode and a 2nd power supply terminal respectively. CONSTITUTION:When a power switch is turned on, an emitter potential of a drive TR 5 rises with a voltage having a faster follow-up speed in either of voltages V1 and V2 via a resistor 12, a diode 14, a resistor 13 and a diode 15 and the potential reaches a Zener voltage of a Zener diode 16. Since an output of a drive IC 1 is in a high impedance state until such time as it reaches its minimum operating voltage, noise is generated in an output voltage VA for a period T1 with respect to an input voltage Vi of the IC 1 synchronously with the rising of a level of a power supply terminal 8. However, the TR 5 is not turned on because a reverse bias is applied to the TR 5. Since a TR 17 is kept off, malfunction due to noise caused for the period T1 is prevented in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a malfunction prevention circuit for an electronic circuit which prevents malfunction of a driving (driver) IC connected to a power supply terminal when the power supply is turned on and off.

[0002]

2. Description of the Related Art Generally, various electronic circuits are connected to a power supply terminal to form a circuit having various functions and operations. An AC power supply or a DC power supply such as a battery is used as a power supply circuit and a power switch is turned on. , To supply power to the load circuit.

In this case, when the power switch is turned on, due to the charging / discharging characteristics of the smoothing circuit connected to the power circuit, the waveform does not become a square wave but an exponential waveform when rising or falling.

As shown in FIGS. 5 and 6, an output transistor (TR) is connected to the output side of a driving IC (IC in the drawings), and the output voltage V is applied to a load (Z _L ) to this. _In order to supply ₀ , the above IC has an input voltage of Vi
However, V ₁ is added as a power supply voltage, and V ₂ is added as a power supply voltage to TR.

In this case, the power supply voltages V ₁ and V ₂ have curves of rising and falling as shown in FIGS. 6 (a) and 6 (b) as the power switch is turned on and off. Figure 6 on the input side of the IC
When the pulse voltage shown in (c) is applied, the period from t ₁ to t ₂ when the power switch is turned on and t ₃ from when the power switch is turned off
An unnecessary voltage waveform is generated in the output voltage V _A of the IC (FIG. 6 (d)) during the period of t ₄ , which causes the voltage V V shown in FIG. 6 (e).
Noise appears in the above period as ₀ , and the normal input signal Vi
An extra voltage is applied to the load (Z _L ) other than the pulses corresponding to the periods T ₁ and T ₂ of.

[0006] As a conventional example, "Transistor circuit design" P.I. The smoothing circuits shown at 253-256 are provided, and these smoothing voltages are supplied as the voltage V ₁ or V ₂ shown in FIG.

[0007]

In the above-mentioned prior art,
When the power switch is turned on and off, an unnecessary voltage appears in the load and the load malfunctions. The present invention provides a novel electronic circuit malfunction prevention circuit that eliminates the above drawbacks. is there.

[0008]

According to the present invention, there is provided a first DC power supply terminal connected to a driving IC, a second DC power supply terminal connected to a driving transistor in the next stage of the driving IC, An output transistor connected to the output side of the driving transistor, and a load connected to the output side of the output transistor. A Zener diode is connected between the emitter of the driving transistor and ground and the first and second A diode is connected between the DC power supply terminal and the Zener diode to eliminate noise appearing at the output end of the driving IC when the power supply to the first and second DC power supply terminals is turned on and off. It is a composition.

[0009]

According to the present invention, the driving I generated due to the rising and falling characteristics of the power supply voltage when the power switch is turned on and off.
The noise appearing on the output side of C causes the driving transistor and the output transistor to malfunction. The diode and Zener diode provided between the power supply terminal and the ground prevent the driving transistor from reaching the predetermined Zener voltage. Since the off state is maintained, the generation of noise voltage can be prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a malfunction prevention circuit for electronic equipment of the present invention.
4 is an explanatory waveform diagram of FIG. 1, FIG. 5 is a circuit diagram of a main part of a conventional electronic device, and FIG. 6 is an explanatory waveform diagram of FIG. In the drawing, (1) is a driving IC, (2), (3) and (4) are bias resistors, (5) is a driving transistor, (6) and (7) are base resistors, and (8) and (9) are respectively. First and second power supply terminals, (10) is an input terminal, (11) is a voltage dividing resistor (12)
(13), diodes (14) and (15) connected in the forward direction to both power supply terminals, and a zener diode (1 for constant voltage
6 is a voltage regulator circuit, 17 is an output transistor, and 18 is a load.

Next, the operation of the circuit of the present invention will be described. The power supply terminal (8) of the driving IC (1) is shown in FIG.
Applied power supply voltages V ₁ shown in, on the power switch, each voltage falls rising or falling timing t ₀ and t ₃ by off. At this time, the input terminal (1
The input signal shown in FIG. 2C is added to 0).

The IC (1) is generally an open collector type driving IC and has resistors (2) and (3).
(4) The next stage of the driving transistor to the output signal of the IC (1) (5) the base current of the driving transistor so as to transmit to the base (5) of (I _B) and the base voltage (V _B) Is a bias resistor for supplying the drive transistor (5) to drive the output transistor (17). The emitter of the driving transistor (5) is held at a predetermined voltage (V _DZ ) by the Zener diode (16).

Now, a power switch (not shown) for supplying power to the electronic apparatus main body is turned on, and V ₁ and V ₂ rise at timing t _{0 as} shown in FIGS. 2A and 2B. Then, the resistance (12) and the diode (14), the resistance (1
3) and the driving transistor (5) via the diode (15) by the voltage having the faster following speed of V ₁ or V _2.
Emitter potential rises and Zener diode (16)
Zener voltage (V _DZ ) is reached. (Timing t ₁ ) At this time, the output of the driving IC (1) becomes high impedance until it reaches the minimum operating voltage. Therefore, the input voltage of the driving IC is synchronized with the rise of the power supply terminal (8). The output voltage V _A for Vi (FIG. 2C) is shown in FIG.
As shown in (d), noise is generated in the period T ₁ . However, with respect to the voltage V _A , the base-emitter voltage (V _EB ) of the driving transistor (5) becomes V _EB = V _B0 -V _Z , and a reverse bias is applied until V _B0 = V _Z. become. (V _B0 is the base voltage of the driving transistor, V
_Z is the voltage applied to the Zener diode (16). Therefore, when V _B0 = V _Z , the voltage V _EB becomes V _EB = 0,
Until this time, the driving transistor (5) is not turned on.

Further, the voltage V _{B0 of the} driving transistor (5)
Is never higher than V ₁ , so V is maintained during the period T _{1.
Since EB} ≦ 0, the driving transistor (5) does not operate until the operation guarantee voltage value of the driving IC (1) is exceeded. The pattern is enlarged and shown in FIGS. 3A to 3B. As shown in FIG. 3B, the driving transistor (5) is forcibly kept off during the period (T _P ). Be done.

Therefore, since the output transistor (17) is kept off during the period (T _P ) described above, malfunction due to noise generated during the period T ₁ shown in FIG. 2D can be prevented.

On the other hand, when the power switch is turned off,
From timing t _{3 of} FIG. 2, the voltages V ₁ and V ₂ of the power supply terminals (8) and (9) gradually decrease as shown in FIGS.

At this time, from the period (T ₂ ) in which the driving IC (1) has a high impedance, the output transistor (1
Since the OFF period of 7) becomes long, the driving transistor (5) is forcibly turned OFF during the period (T ₃ ) of FIG. 4B from the characteristics shown in FIG. The collector voltage (V _c ) of () becomes a positive voltage, the output transistor (17) is turned off, and the malfunction of the output transistor (17) due to the noise generated in the period T ₂ does not occur.

As can be seen from the above description, the output voltage V ₀ shown in FIG. 2 (E) is applied to the load (18), and the malfunction that has conventionally occurred can be prevented.

[0019]

According to the malfunction prevention circuit for an electronic device of the present invention, the power supply voltage changes according to the conventional power switch being turned on and off, and noise generated at this time causes noise to be added to the load. Was malfunctioning because the output transistor can be forcibly set to off during the noise period by connecting the drive transistor, Zener diode, and diode, preventing malfunction of the output transistor. obtain.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram for explaining the operation of FIG.

FIG. 3 is a detailed characteristic diagram for explaining when the power switch is turned on in FIG.

FIG. 4 is a detailed characteristic diagram for explanation when the power switch is turned off in FIG.

FIG. 5 is a circuit diagram of a main part of a conventional electronic device.

FIG. 6 is a characteristic diagram for explaining FIG.

[Explanation of symbols]

 (1) Driving IC (5) Driving transistor (8) First power supply terminal (9) Second power supply terminal (10) Input terminal (11) Voltage adjustment circuit (16) Zener diode (17) Output transistor ( 18) Load

Claims (2)

[Claims] 1. A driving IC to which an input signal is applied, a driving transistor whose base is connected to the output side of the driving IC, and a load circuit connected to the output side of the driving transistor, A Zener diode is connected between the emitter of the driving transistor and the ground, and diodes are respectively connected between one end of the Zener diode and the first and second power supply terminals, so that the driving IC is turned on and off. A malfunction prevention circuit for electronic equipment, which eliminates noise generated on the output side of the. 2. A series circuit including a resistor and a diode connected in a forward direction is connected between the first and second power supply terminals and one end of the Zener diode, respectively. Malfunction prevention circuit for electronic devices.