High Voltage Driver With Diode Strings For Transistor Stress Relief
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Solution Overview
Problem
High voltage stress on transistors occurs due to the slow stabilization of intermediate voltages in low voltage processes, leading to potential damage and overshooting of output voltages in charge pump circuits.
Innovation Solution
A high voltage driver design incorporating a charge pump, level shift circuit, and two strings of diodes to manage and control driving and feedback voltages, with the first string providing divisional voltages to reduce stress and the second string ensuring responsive feedback, along with a comparator to adjust the pump frequency if necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If stacked transistors controlled by intermediate voltages are used to control high voltage with low voltage process elements, then high voltage control is achieved, but voltage stress damages the transistors due to slow stabilization of intermediate voltages
Solution Approach 1:
The circuit raises the intermediate voltage before raising the high voltage output. By using control transistors that are enabled before the main stacked transistors, the intermediate voltage reaches its target level in advance, ensuring that when the high voltage is applied, the transistors are already protected from excessive voltage stress.
Solution Approach 2:
The circuit dynamically controls the timing of voltage raising by using separate control signals for control transistors and main transistors. The control transistors are activated first to establish safe intermediate voltage levels, then the main transistors are activated to deliver the high voltage output, creating a time-dependent protection mechanism.
2Reliability
If intermediate voltages are raised in a slower pace than charge pump output voltage, then transistor voltage stress is reduced, but output voltage overshoot occurs due to late feedback
Solution Approach 1:
Control transistors are introduced as intermediary elements between the charge pump and the main stacked transistors. These control transistors manipulate the intermediate voltage to rise at a controlled pace, acting as a buffer that prevents both excessive voltage stress and output voltage overshoot by mediating the timing between voltage generation and transistor activation.
3Manufacturing precision
If intermediate voltages are raised faster to improve feedback response, then output voltage precision is improved, but high voltage stress damages the transistors
Solution Approach 1:
The control transistors are activated in advance to establish the intermediate voltage at safe levels before the main transistors are turned on. This preliminary action ensures that even though the intermediate voltage rises quickly to improve feedback response, the transistors are already protected from voltage stress because they are enabled only after the intermediate voltage reaches safe levels.
Data Source
AI summary
A high voltage driver includes a charge pump, a level shift circuit, a first string of diodes, and a second string of diodes. The charge pump adjusts a driving voltage according to a feedback voltage. The level shift circuit generates an output voltage according to the at least one control signal, and the level shift circuit includes a plurality of stacked transistors for relieving a high voltage stress caused by the driving voltage, and a plurality of control transistors coupled to the plurality of stacked transistors for controlling the output voltage. The first string of diodes provides a plurality of divisional voltages between the driving voltage and a reference voltage, and each of the stacked transistors has a control terminal receiving a corresponding divisional voltage of the plurality of divisional voltages. The second string of diodes provides the feedback voltage.