High-Side Half-Bridge Drive Circuit Against Common-Mode Transients
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Solution Overview
Problem
High voltage half bridge circuits face issues with common mode voltage transients, which can lead to erroneous control and potential destruction of transistors due to high current spikes, and existing solutions either fail to eliminate these transients or slow down the switching rate.
Innovation Solution
A high side control circuit that includes composite current mirror circuits and comparators to manage the common mode voltage transients, ensuring proper control of the half bridge without limiting switching speed by using differential current comparisons and current generators to overcome transient voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional level shifters are used to control high side transistors, then control voltage range is achieved, but common mode voltage transients cause erroneous control and potential transistor destruction
Solution Approach 1:
The patent introduces an intermediary circuit between the control signal source and the high side transistor gate. This intermediary level shifter circuit translates control voltages while isolating the control logic from harmful common mode transients. The circuit uses a bootstrap capacitor and voltage translation mechanism to provide stable gate drive voltages without directly exposing control elements to high voltage transients, thus preventing erroneous control and transistor damage.
Solution Approach 2:
The control circuit is segmented into separate functional blocks: low voltage control logic, voltage translation stage, and high voltage output stage. This segmentation allows each block to operate within its optimal voltage range and protects sensitive control logic from high voltage transients. The level shifter acts as an isolated intermediate stage that handles voltage translation without transmitting harmful transients to the control logic.
2Reliability
If protection circuits are added to prevent transient damage, then transistor reliability improves, but switching speed decreases
Solution Approach 1:
The bootstrap capacitor is pre-charged during the off-state to store the necessary voltage for rapid gate turn-on. This preliminary energy storage enables fast switching action when needed, without requiring slow charging during the critical switching transition. The circuit prepares voltage conditions in advance, allowing rapid response when switching is commanded.
Solution Approach 2:
The harmful common mode transient component is extracted and isolated from the control signal path using the level shifter architecture. By separating the transient-prone high voltage node from the control logic through capacitive coupling and voltage translation, the protection function is achieved without introducing slow protective elements into the critical switching path, maintaining high switching speeds.
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 solution effectively reduces or eliminates the impact of common mode voltage transients, ensuring reliable and fast switching of the half bridge circuit, thereby preventing transistor damage and maintaining control accuracy.
Implementation Method 1
a capacitor 16 coupled at one end to the node, HS, and coupled at the other end to provide a voltage VB (a bootstrap supply) as a power supply to portions of the high voltage control circuit 10
Data Source
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AI summary
A level shift circuit (204) is configured to control a high side transistor (17) of a half bridge circuit (19). The level shift circuit has composite current mirrors (not shown in 204) and other circuits that reduce the effect of transient voltages that are produced as the half bridge circuit (19) is switched.