JPH0350914A - Output driving circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction of a device to be driven by applying on/off control to an output drive transistor(TR) via a Zener diode with an output signal of a gate circuit. CONSTITUTION:When a power-on reset IC 1 is not normally operated with a voltage within a prescribed range at the time of rising a power voltage, an output voltage in the IC 1 and an AND gate IC 2 of emitter follower TR output system rises as a power voltage rises. A potential difference between an output terminal of the IC 2 and ground, an operation minimum base-emitter voltage of a driving TR 3 and a Zener voltage of a Zener diode 4 are set to a prescribed relation. Thus, even when the IC 1 is not completely operated at the time of rising the power voltage, the TR 3 is turned on and the output signal is set and malfunction of a device to be driven is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an output drive circuit, and more particularly to an output drive circuit that prevents malfunctions when the power supply voltage rises.

[Prior Art] Conventionally, in order to drive devices connected to the outside of a semiconductor circuit, such as relays, light emitting diodes, receiver ICs, etc., high voltage and high current have been used in accordance with the characteristics of the devices to be driven. An output drive circuit is used that incorporates a drive transistor that can also handle

FIG. 2 shows a NAND type output drive circuit which is a typical example of such a conventional output drive circuit.

In Figure 2, when the power supply voltage rises, the output signal I
To ensure the IOII level, a power-on reset ICI is connected to one of the input terminals of the AND gate IC2. The AND gate IC2 is an AND gate IC that outputs a signal from the emitter of an emitter follower transistor, which is an internal element. AND gate I
The output terminal of C2 is connected to a resistor 5 whose one end is grounded and the base of the drive transistor 3. The emitter of drive transistor 3 is connected to ground,
The collector is connected to a drive signal output terminal 51.

For example, +5■ is applied to the power supply line, and when the logic signal input terminal 50 of the emitter-follower transistor output type AND gate IC2 is given a logic signal of °゛O゛O゛ level, the inside of the AND gate IC2 The emitter follower transistor is turned off, and the AN
Since no voltage is generated between the output terminal of the D-gate IC2 and the ground, the drive transistor 3 is turned off, and the drive signal output terminal 51 is also turned off.

As a logic signal, °
When the level ゛1°゛1°゛ is given, AND gate I
The emitter follower transistor, which is an internal element of C2, is turned on, and a potential difference is generated between the output terminal of AND gate IC2 and the ground. This potential difference turns on the drive transistor 3, and the drive signal output terminal 51 is also turned on. .

Although FIG. 2 shows a case in which a two-manpower emitter follower transistor output type AND gate IC2 is used, an IC of a type that performs a larger number of logical products is also used for input.

[Problems to be Solved by the Invention] The conventional output drive circuit described above uses a power-on reset ICI to turn off the emitter follower transistor, which is the output element of the AND gate C2, when the power supply voltage rises. is connected to one of the input terminals of AND gate IC2, but power-on reset ICI
may not be able to completely guarantee the °゛0''° level when the power supply voltage rises, and as the power supply voltage rises, the output level of the power-on reset ICI also increases, and the output level will not be maintained until the power supply voltage reaches a certain level. The level continues to rise by the amount of power supply voltage, and when the power supply voltage exceeds a certain level, the output level of power-on reset IC1 becomes "O".
” may occur.

Furthermore, when the power supply voltage rises sufficiently, the output signal level cancels the 0° level and becomes 1111 levels. Therefore, when the power supply voltage rises, the output of the emitter follower transistor output type AND gate IC2 A voltage is generated between the terminal and ground, and when this voltage exceeds the operating minimum base-emitter voltage of the drive transistor 3, the drive transistor 3 turns on, the external drive output signal turns on, and the driven There is a problem that the device may malfunction.

[Means for Solving the Problems] The present invention has been made in view of the above-mentioned problems, and it is possible to turn on the output signal even if the power-on reset circuit does not fully operate when the power supply voltage rises. In order to achieve this purpose, a gate circuit that outputs a signal from an emitter follower transistor, which is an internal element, and a gate circuit that outputs a signal from the emitter follower transistor are used. a power-on reset circuit connected to the input terminal of the gate circuit so that the voltage becomes zero level when the power supply voltage rises; an output drive transistor that is controlled on and off by the output signal of the gate circuit; and an output terminal of the gate circuit and the output drive. A Zener diode connected in the opposite direction to the base of the transistor is provided, and the output drive transistor is turned on and off using the output signal of the gate circuit via the Zener diode.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a circuit diagram showing one embodiment of an output drive circuit according to the present invention.

In Figure 1, when the power supply voltage rises, the output signal
A power-on reset ICI is connected to one of the input terminals of the AND gate Ic2 in order to guarantee the "LOT" level.AND gates 1 to IC2 receive a signal from the emitter of an emitter follower transistor, which is an internal element. It is an AND gate IC that outputs.AND gate I
The output terminal of c2 is connected to the cathode of a Zener diode 4 connected in the opposite direction.

The anode of the Zener diode 4 is connected to a resistor 5 whose one end is grounded and to the base of the drive transistor 3. The emitter of the drive transistor 3 is connected to ground, and the collector is connected to the drive signal output terminal 51. The resistor 5 has one end grounded and the other end connected to the base of the drive transistor 3 in order to determine the base-emitter voltage of the drive transistor 3.

For example, +5V is applied to the power supply line, and when an O''° level signal is applied as a logic signal to the logic signal input terminal 50 of the AND gate IC2 of the emitter follower transistor output type, the internal elements of the AND gate IC2 Some emitter follower transistors are turned off and the AN
Since no voltage is generated between the output terminal of the D gate E C2 and the ground, the drive transistor 3 is turned off, and the drive signal output terminal 51 is also turned off.

When a "1" level signal is applied as a logic signal to the logic signal input terminal 50 of the emitter follower transistor output type AND gate IC2, the AND gate IC
The emitter follower transistor, which is an internal element of 2, is turned on, and a potential difference is generated between the output terminal of AND gate IC 2 and the ground. This potential difference turns on the drive transistor 3, and the drive signal output terminal 51 is also turned on. .

Although FIG. 1 shows a case in which a two-manpower emitter follower transistor output type AND gate Ic2 is used, an IC of a type that performs a larger number of ANDs may also be used for input.

If the power-on reset ICI does not operate normally within a certain range from 0 when the power supply voltage rises, the power supply voltage will appear as is at the output of the power-on reset ICI, and the complete゛Because the level is not reached,
Regarding the emitter follower transistor output type AND gate Ic2, as the power supply voltage increases, the voltage at its output section also increases.

Here, emitter follower transistor output method AN
The potential difference between the output terminal of D gate IC2 and the ground is V
OUT, and the lowest operating base-emitter voltage of the drive transistor 3 is V BEonmin1, and the Zener voltage of Zener diode 4 is Vz, VX==VOUT, VY=VBEonmin+V
z, the on state or off state of the drive transistor 3 is determined by the magnitude relationship between vx and VY. That is, when vx>vy, the drive transistor 3 is turned on, and when vx<vy, the drive transistor 3 is turned off.

Therefore, if a Zener diode 4 is selected that has a Zener voltage Vz that satisfies V However, the problem of the output signal turning on and causing the driven equipment to malfunction can be completely prevented.

[Effects of the Invention] As explained above, the present invention includes a gate circuit that outputs a signal from an emitter follower transistor, which is an internal element, and a gate circuit that outputs a signal from the emitter follower transistor, which is an internal element, so that the output signal of the gate circuit becomes zero level when the power supply voltage rises. A power-on reset circuit connected to the input terminal of the gate circuit, an output drive transistor controlled on and off by the output signal of the gate circuit, and a power-on reset circuit connected in the opposite direction between the output terminal of the gate circuit and the base of the output drive transistor. The output drive transistor is controlled on and off via the Zener diode by the output signal of the gate circuit, so even if the power-on reset circuit does not fully operate when the power supply voltage rises, the output signal can be maintained. This makes it possible to prevent the power from turning on and to prevent any adverse effects on the driven equipment.

[Brief explanation of drawings]

FIG. 1 shows an output drive circuit according to the present invention: -Power-on reset IC AND gate IC Drive transistor Zener diode resistance Logic signal input terminal Drive signal output terminal

Claims (1)

[Claims] A gate circuit that outputs a signal from an emitter follower transistor that is an internal element, and a power-on reset circuit that is connected to the input terminal of the gate circuit so that the output signal of the gate circuit becomes zero level when the power supply voltage rises. , an output drive transistor that is turned on and off by an output signal of the gate circuit, and a Zener diode connected in a reverse direction between the output terminal of the gate circuit and the base of the output drive transistor,
An output drive circuit characterized in that the output drive transistor is controlled on/off by the output signal of the gate circuit via the Zener diode.