CN-122026874-A - Power failure detection circuit and isolator circuit

CN122026874ACN 122026874 ACN122026874 ACN 122026874ACN-122026874-A

Abstract

The invention discloses a power failure detection circuit and an isolator circuit. The power down detection circuit comprises a voltage detection circuit, a pulse width modulation circuit and a logic circuit, wherein the voltage detection circuit receives a supply voltage and compares the supply voltage with a threshold voltage to generate a pre-power-down electric signal, and when the supply voltage is smaller than the threshold voltage, the pre-power-down electric signal jumps from a first state to a second state. The pulse width modulation circuit generates a pulse width modulation signal according to an input signal, wherein the duty cycle of the pulse width modulation signal is related to the value of the input signal. And the logic circuit generates a power-down control signal according to the pre-power-down signal and the pulse width modulation signal, wherein the power-down control signal controls the pulse width modulation signal to be kept in the first state when the first preset edge of the pulse width modulation signal is temporarily changed from the first state to the second state.

Inventors

ZHU JIANIAN
CHEN QIHUI
LIN JIANFENG

Assignees

上海纳矽微电子有限公司
苏州纳芯微电子股份有限公司

Dates

Publication Date: 20260512
Application Date: 20260122

Claims (11)

1. A power down detection circuit, comprising: The voltage detection circuit receives the power supply voltage and compares the power supply voltage with the threshold voltage to generate a pre-power-down electric signal, wherein the pre-power-down electric signal jumps from a first state to a second state when the power supply voltage is smaller than the threshold voltage; a pulse width modulation circuit for generating a pulse width modulation signal based on an input signal, wherein a duty cycle of the pulse width modulation signal is related to a value of the input signal, and And the logic circuit generates a power-down control signal according to the pre-power-down signal and the pulse width modulation signal, wherein the power-down control signal controls the pulse width modulation signal to be kept in the first state when the first preset edge of the pulse width modulation signal is temporarily changed from the first state to the second state.
2. The power down detection circuit of claim 1, wherein the power down control signal transitions from the first state to the second state upon a first predetermined edge of the pulse width modulated signal after the pre-down electrical signal transitions from the first state to the second state.
3. A power down detection circuit according to claim 1 or 2, wherein the first preset edge of the pulse width modulated signal after the transition of the pre-down electrical signal from the first state to the second state is a falling edge.
4. The power down detection circuit of claim 2, wherein the first state of the pre-down signal is a logic high state and the first state of the pulse width modulated signal is a logic low state.
5. The power down detection circuit of claim 1, wherein the logic circuit comprises: an inverter having an input and an output, wherein the input receives the pulse width modulated signal; A flip-flop having a first input terminal receiving the pre-down signal, a second input terminal coupled to the output terminal of the inverter, and an output terminal The OR gate is provided with a first input end, a second input end and an output end, wherein the first input end is coupled with the output end of the trigger, the second input end receives the pre-power-down electric signal, and the output end outputs a power-down control signal.
6. The power down detection circuit of claim 1, wherein the input signal is sinusoidal and the frequency of the input signal is between 1K and 100MHz.
7. The power down detection circuit of claim 1, wherein the supply voltage is in the range of 3V-6V and the threshold voltage is in the range of 2.5V-4V.
8. An isolator circuit is provided which includes a pair of isolation circuits, characterized by comprising the following steps: A power down detection circuit as recited in any one of claims 1-7, and And the edge modulation circuit is used for receiving the pulse width modulation signal and generating an edge signal according to the pulse width modulation signal, wherein the edge signal is provided with a first pulse when the rising edge of the pulse width modulation signal comes and is provided with a second pulse when the falling edge of the pulse width modulation signal comes, and the width of the first pulse is different from the width of the second pulse.
9. The isolator circuit of claim 8, further comprising: An isolation circuit receiving the edge signal and transmitting the edge signal to the output circuit, and And the output circuit outputs an output signal, wherein the duty ratio of the output signal is the same as that of the pulse width modulation signal, and the frequency of the output signal is the same as that of the pulse width modulation signal.
10. The isolator circuit of claim 9, wherein the isolation circuit comprises a capacitor or an inductor.
11. The isolator circuit of claim 9, wherein the output signal remains in the first state when the pulse width modulated signal remains in the first state.

Description

Power failure detection circuit and isolator circuit Technical Field The invention relates to the technical field of edge modulation isolation, in particular to a power failure detection circuit and an isolator circuit. Background Currently, isolators employing edge-modulated isolation are widely used for various current-voltage detection in industry and automobiles (e.g., on-board chargers, inverters, and motor drives). For example, motor drive systems typically have two voltage domains, a "high voltage" domain (also referred to as the primary side) and a "low voltage" domain (also referred to as the secondary side). A microcontroller or digital signal processor, typically located in the low voltage domain, receives feedback signals (voltage, current, etc.) from the three-phase IGBT power stages and generates pulse width modulated signals to control the power switching transistors and other high side circuits. These systems typically require the detection and indication of such anomalies to be timely and accurate when the primary power source is powered down. Therefore, a power failure detection circuit capable of accurately detecting the power failure of the primary side is needed. Disclosure of Invention The invention mainly aims to provide a power-down detection circuit which aims to eliminate the condition that an output signal of a secondary side is uncertain so as to realize a primary side power-down detection function. In order to achieve the above object, a power-down detection circuit according to the present invention includes: The power-on circuit comprises a voltage detection circuit for receiving a power supply voltage and comparing the power supply voltage with a threshold voltage to generate a pre-power-on signal, wherein the pre-power-on signal jumps from a first state to a second state when the power supply voltage is smaller than the threshold voltage, a pulse width modulation circuit for generating a pulse width modulation signal according to an input signal, wherein the duty ratio of the pulse width modulation signal is related to the value of the input signal, and a logic circuit for generating a power-on control signal according to the pre-power-on signal and the pulse width modulation signal, wherein the power-on control signal controls the pulse width modulation signal to be kept in the first state temporarily at a first preset edge of the pulse width modulation signal after the pre-power-on signal jumps from the first state to the second state. According to the technical scheme, when the power supply is powered down to be smaller than the threshold voltage, the pulse width modulation circuit is not turned off immediately after the preset edge of the pulse width modulation signal is started, namely the pulse width modulation signal is kept in the first state (can be logic low), so that the secondary side circuit can output a continuous preset level (in one circuit, the primary side power supply is powered down, the secondary side output can only be one of low level or high level) when the primary side circuit is powered down, the normal working state is distinguished, a reliable power failure detection function is realized, the problem that the conventional primary side power failure secondary side circuit outputs an unstable state is solved, and the system safety is further improved. Drawings In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the structures shown in these drawings without inventive effort for a person skilled in the art. Fig. 1 is a circuit diagram of a conventional isolator with a power down detection circuit. FIG. 2 is a waveform diagram of signals when the power supply voltage VDD is powered down in the conventional power-down detection circuit; FIG. 3 is a waveform diagram showing signals of another case when the power supply voltage VDD is powered down in the conventional power-down detection circuit; Fig. 4 shows a circuit diagram of an isolator circuit 400 in accordance with an embodiment of the present application; fig. 5 shows waveforms of signals in the isolator 400 of fig. 4; fig. 6 shows waveforms of signals in the isolator 400 of fig. 4; fig. 7 shows a circuit diagram of a power down detection circuit according to an embodiment of the application. Detailed Description The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodimen