Photocoupler Isolation Switch Circuit for LCD Voltage Driving
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Solution Overview
Problem
In liquid crystal display technology, CMOS circuits in voltage driving chips are prone to latch up effects, which can lead to malfunction or breakdown, especially when the control voltage rises after the driving voltage, and existing timing control circuits are not always reliable in preventing these issues.
Innovation Solution
A photocoupler isolation switch circuit is introduced, comprising a power chip and a voltage driving chip with a photocoupler device that includes a light emitting device and a photosensitive device. The circuit controls the light emitting device based on the control voltage, turning it on or off to manage the driving voltage output, ensuring the driving voltage is only supplied when necessary to prevent latch up effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a timing control circuit is added inside the power chip to control that the control voltage rises up before the driving voltage, then the latch up effect is prevented, but the device complexity increases and reliability decreases if the timing control circuit is abnormal
Solution Approach 1:
The patent extracts the timing control function from the power chip and implements it externally using a photocoupler device. The photocoupler's light-emitting diode is connected to the power chip's control voltage output, while the phototransistor side controls the driving voltage output timing. This separation removes the complex timing control circuit from the power chip, reducing device complexity while maintaining reliability through optical isolation.
2Device complexity
If the control voltage rises up after the driving voltage, then the circuit operation is simplified, but the CMOS circuit generates latch up effect causing MOS tube breakdown
Solution Approach 1:
The patent implements preliminary action by using the photocoupler device to ensure the control voltage rises before the driving voltage. The light-emitting diode responds to the control voltage first, and only after this initial rise does the phototransistor enable the driving voltage output. This preliminary timing control prevents the latch up effect while keeping the overall circuit operation simple.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The photocoupler isolation switch circuit effectively prevents latch up effects in voltage driving chips by ensuring the driving voltage is only output when the control voltage is appropriate, thereby maintaining normal operation and preventing chip breakdown.
Implementation Method 1
the photocoupler device includes a light emitting device and a photosensitive device
Implementation Method 2
the photosensitive device is turned on or turned off according to the working status of the light emitting device
Data Source
AI summary
A photocoupler isolation switch circuit is disclosed. The circuit includes a power chip and a voltage driving chip including a photocoupler device having a light emitting device and a photosensitive device. A first output terminal of the power chip connects to a first terminal of the light emitting device, and a second terminal of the light emitting device connects to ground; a second output terminal of the power chip connects to a first terminal of the photosensitive device and outputs a driving voltage, a second terminal of the photosensitive device connects to an output terminal of the photocoupler device; the photocoupler device controls a working status of the light emitting device according to a control voltage, the photosensitive device is turned on or off according to the working status; the driving voltage is outputted through the output terminal of the photocoupler device when the light emitting device is turned on.