JPH05315931A - Level shifting circuit - Google Patents

Abstract

PURPOSE:To prevent the generation of a through current and to stabilize a circuit in a high voltage source system by providing a level shifting circuit with a gate circuit for fixing the potential of the level shifting circuit at the occurance of abnormality. CONSTITUTION:The gate circuit is constituted by adding a detection circuit 10 for monitoring a low voltage source VCC and detecting its abnormal rise and two transistors(TRs) QP1, QN1 for receiving an output from the circuit 10 by their gates to a convensional level shifting circuit. The n-channel TR QN1 is connected between ground and the output terminal T1 of the level shifting circuit, and if abnormality is detected in the VCC, it is turned on to fix the output terminal T1 to the ground. Thereby an output terminal 5 is initialized to a high impedance state. On the other hand, the sources of two p-channel TRs Q1, Q3 in the level shifting circuit are connected to a high voltage source VDD through the p-channel TR QP1, and when the VCC is abnormal, the QP1 is turned off, so that the level shifting circuit is disconnected from the VDD and a current flow disappears.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a level shift circuit.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing an example of a driver circuit using a conventional level shift circuit. The input terminal T is connected to the input of an inverter 2 whose source is a low voltage source (hereinafter referred to as VCC), and the output of the inverter 2 is also input to an inverter 3 whose source is VCC. The outputs of these two inverters 2 and 3 are connected to the gates of two N-channel insulated gate field effect transistors (hereinafter referred to as N-channel transistors) Q2 and Q4 that form a level shift circuit. The level shift circuit is a P-channel insulated gate field effect transistor (hereinafter, referred to as “VDD”) between a high voltage source (hereinafter referred to as VDD) and the ground.
A P-channel transistor Q1 and an N-channel transistor Q2, and a P-channel transistor Q3 and an N-channel transistor Q4 are connected in series. The P-channel transistor Q1 has a gate connected to the P-channel transistor Q3 and the N-channel transistor Q4. Q4
Of the P-channel transistor Q3 is connected to the connection point T1 of the P-channel transistor Q1 and the N-channel transistor Q2.

The output T1 of the level shift circuit passes through an inverter 4 whose source is VDD, and its drain is input to the gate of a P-channel transistor Q5 connected to an output terminal 5. Here, a high voltage is applied to the transistors Q1 to Q5 and the inverter 4 after the level shift circuit, so that the design is high withstand voltage.

In operation, the VCC input to the input terminal T
The level signal is converted into a VDD level signal by the level shift circuit, and the input terminal T is 0 at the output terminal 5 of the IC.
Is output at high impedance, and when T is 1 or VCC, 1 or VDD is output.

As shown in the waveform diagram of FIG. 5, when VCC rises abnormally (time t _o ), the VCC transistor breaks down and the potential of T1 becomes indefinite and becomes T11 level (FIG. 5 (c)). .. The output terminal 5 is turned on or off according to this signal level (FIG. 5 (d)).

[0006]

Generally, a high voltage source from a battery and a low voltage source obtained by stepping down the high voltage source from a battery are used for an IC having two power sources used in an automobile.

When the low voltage source rises due to the abnormality of the three-terminal regulator and the withstand voltage of the transistor of the low voltage source system is exceeded,
The transistor breaks down and its output becomes insufficient.

Since the input of the level shift circuit also becomes insufficient, a shoot-through current is generated, and the output of the level shift circuit and I
There is also a problem that the output terminal of C becomes undefined and causes an abnormality in the entire system.

[0009]

SUMMARY OF THE INVENTION A level shift circuit of the present invention monitors a low voltage source and detects an abnormal rise, and receives the signal to stop the operation of the level shift circuit when an abnormality occurs. A gate circuit for fixing the electric potential is provided.

[0010]

The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of the first embodiment of the present invention. Figure 3
Low voltage source (VCC) for the conventional level shift circuit of
Of the detection circuit 10 that monitors the voltage and detects an abnormal rise thereof, and two transistors QP1 and Q that receive the output at their gates.
N1 is added to form a gate circuit. The N-channel transistor QN1 is connected between the ground and the output terminal T1 of the level shift circuit, and is turned on when an abnormality is detected in VCC, and the output terminal T1 is fixed to the ground. As a result, the output terminal 5 is initialized to the high impedance state. On the other hand, the sources of the two P-channel transistors Q1 and Q3 of the level shift circuit are P-channel transistors QP.
QP1 when connected to VDD via 1 and VCC is abnormal
Is turned off, the level shift circuit is disconnected from VDD, and no current flows.

As described above, it is possible to prevent the shoot-through current and initialize and fix the output.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

In contrast to FIG. 3, N-channel transistor QN
1, QN2 are added to form a gate circuit. The N-channel transistor QN2 is the N-channel transistor Q2
It is connected to the gate of the
2 is turned off to prevent shoot-through current. On the other hand, the N-channel transistor QN1 is similar to that of the first embodiment shown in FIG. As described above, the same effect as that of FIG. 1 can be obtained.

The VCC abnormality detecting circuit can be easily constructed by using the comparator 6 as shown in FIG. VD
Two resistors R1 and R connected in series between D and ground
It is sufficient to input the level to be detected above the VCC rating to the (-) side input of the comparator by using the voltage division by 2. VCC or a voltage corresponding thereto is input to the (+) side input V5.

The operation of the level shift circuit according to the present invention will be described with reference to FIG.

When VCC exceeds the abnormality detection level at time t _o (FIG. 5A), the output signal of the detection circuit 10 becomes 1
That is, it becomes VDD (FIG. 5 (b)), so that T1
Is fixed to 0 (FIG. 5 (c)), and the output terminal 5 has a high impedance (FIG. 5 (d)).

[0017]

As described above, according to the present invention, a gate circuit for detecting an abnormal rise of a low voltage source due to a failure of the power supply system and fixing the potential of the level shift circuit in that case is provided. This has the effect of preventing and stabilizing the circuit of the high voltage source system.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional technique.

FIG. 4 is a circuit diagram of an example of the low voltage source abnormality detection circuit shown in FIGS. 1 and 2.

FIG. 5 is a waveform diagram showing the operation of the level shift circuit according to the related art and the present invention.

[Explanation of symbols]

2, 3, 4 Inverter 5 Output terminal 6 Comparator 10 Low voltage source abnormality detection circuit Q1, Q3, Q5, QP1 P-channel transistor Q2, Q4, QN1, QN2 N-channel transistor T input terminal T1, T2 Output of level shift circuit Edge VDD High voltage source VCC Low voltage source

Claims (1)

[Claims] 1. A level shift circuit for converting a circuit of a low voltage source system into a circuit of a high voltage source, a detection circuit for detecting a rise of the low voltage source above a rating, and a level for receiving a signal from the detection circuit. A level shift circuit having a gate circuit for fixing the potential of the shift circuit.