Decoupling Circuit for DC-DC Converter Transient Mitigation
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Solution Overview
Problem
High power density DC-DC converters face issues with parasitic elements causing voltage stress and power loss due to ringing in high side transistors, which conventional methods either reduce efficiency or increase area, and existing solutions fail to effectively manage parasitic inductance from package bondwire and PCB routings.
Innovation Solution
A decoupling circuit comprising a series connection of three diodes and parallel capacitors that charge and discharge energy during overshoot and undershoot transient voltages, respectively, to neutralize the effects of parasitic inductances and enhance reliability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gradual switching of power MOSFET is used to reduce voltage stress, then reliability is improved, but power efficiency deteriorates due to increased current-voltage overlap loss
Solution Approach 1:
The patent introduces an intermediary circuit (decoupling circuit with capacitors and diodes) between the power supply and the transistor to handle voltage transients. This mediator absorbs voltage overshoots and undershoots caused by parasitic inductance, allowing the transistor to switch without experiencing extreme voltage stress while maintaining fast switching speeds and efficiency.
Solution Approach 2:
The decoupling capacitors are pre-charged to anticipate and prepare for voltage transients before they occur during transistor switching. By having energy stored in the capacitors in advance, the circuit can immediately counteract voltage overshoots and undershoots without waiting for the transients to develop, thus protecting the transistor while maintaining fast switching.
2Reliability
If higher voltage rated power MOSFET is used to handle voltage overshoots, then reliability is improved, but device area increases
Solution Approach 1:
Instead of relying on the MOSFET itself to withstand voltage overshoots through higher voltage ratings, the patent uses an intermediary decoupling circuit to absorb and mitigate these transients. This allows the use of lower voltage rated, smaller area MOSFETs while still protecting them from damaging voltage spikes.
Solution Approach 2:
The patent converts the harmful effect of parasitic inductance (which causes voltage overshoots) into a beneficial effect by using the same inductance in conjunction with capacitors to create a resonant circuit that actively counteracts the transients. The energy that would otherwise damage the MOSFET is instead used to charge and discharge the decoupling capacitors, protecting the device.
3Reliability
If driver switching speed is reduced to minimize PVIN transients, then voltage stress is reduced, but power efficiency deteriorates
Solution Approach 1:
The decoupling circuit acts as an intermediary that isolates the power supply from the effects of fast transistor switching. The capacitors absorb the high-frequency transients generated by fast switching, allowing the driver to operate at high speeds without causing damaging PVIN transients, thus maintaining both efficiency and reliability.
Solution Approach 2:
The decoupling circuit dynamically responds to transient conditions by charging and discharging capacitors in real-time during switching events. This dynamic behavior allows the circuit to maintain stable PVIN during fast transitions without requiring slow driver switching, preserving power efficiency while mitigating transients.
4Reliability
If external decoupling capacitor is added close to supply PVIN, then some voltage stress is reduced, but package bondwire inductance effects remain unresolved
Solution Approach 1:
The patent segments the decoupling function into multiple capacitors placed at different locations in the circuit (at the transistor drain and at the power supply). This segmentation allows each capacitor to address specific transient issues locally, with the first capacitor handling drain-side transients and the second capacitor handling supply-side transients, collectively eliminating the effects of bondwire inductance.
Solution Approach 2:
The patent applies different decoupling capacitance values and positions tailored to local circuit conditions. The first decoupling capacitor is placed close to the transistor drain where voltage overshoots occur, while the second is placed at the power supply where undershoots occur. This localized approach optimizes the decoupling effect at each critical point, effectively addressing the bondwire inductance problem.
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 decoupling circuit effectively reduces voltage stress and power loss by absorbing and neutralizing transient voltages, improving the reliability and efficiency of DC-DC converters without increasing area or degrading power efficiency.
Implementation Method 1
A first capacitor connected in parallel with the first diode and second diode; and a second capacitor is connected in parallel with the second diode and third diode. The first capacitor and second capacitor charge and store energy during an overshoot transient voltage from the voltage supply
Implementation Method 2
The first capacitor and second capacitor discharge energy to a transistor during an undershoot transient voltage
Implementation Method 3
A decoupling circuit includes a first diode, a second diode, and a third diode connected in series with one another
Data Source
AI summary
Described herein is a technology for implementing a decoupling circuit (104) to increase reliability of a DC-DC power converter (100). To absorb an overshoot transient voltage, the decoupling circuit includes a first capacitor (214) and a second capacitor (216) that charge energy during a short burst of upward electrical energy. During an undershoot transient voltage, however, the first capacitor and second capacitor discharge energy to a transistor (108). In certain embodiment, such as the transistor that requires higher voltage switching, the decoupling circuit is connected in series with another decoupling circuit.