Power Transistor Driver Circuit Reducing Voltage Spikes
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Solution Overview
Problem
Switching converters face challenges in reducing voltage spikes at the switching node due to parasitic inductance, leading to increased costs and potential EMI, while high load drivability is required for fast transistor switching.
Innovation Solution
A driver circuit comprising two transistors, where one transistor is turned on and off by a first driving signal, and the other is turned on and off by a second driving signal, with specific timing to manage the switching voltage and minimize voltage spikes, utilizing a control signal generating circuit to manage the switching process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If driver with high load drivability is used to fast turn on and off power transistor, then switching loss is reduced, but high SW voltage spikes are created due to parasitic elements
Solution Approach 1:
The driver circuit performs preliminary action by pre-charging the gate terminal before the power transistor switches on, and by proactively managing the gate voltage during switching transitions. The circuit prepares the gate charge in advance and controls the discharge timing to prevent voltage spikes before they occur, rather than reacting after the spikes are generated.
Solution Approach 2:
The driver circuit dynamically adjusts the gate voltage waveform by controlling the charging and discharging rates of the gate terminal. The circuit changes the driving characteristics in real-time during switching transitions, optimizing the gate voltage profile to achieve fast switching while minimizing voltage spikes through dynamic control of charge transfer rates.
2Reliability
If high voltage spikes are generated at switching node, then breakdown voltage of power transistor must be increased, but cost increases
Solution Approach 1:
The driver circuit converts the potentially harmful effect of gate charge discharge into a beneficial pre-charging action. By controlling the discharge of gate charge through a resistor before the switching event, the circuit transforms what would be a source of voltage spikes into a mechanism that prepares the gate for optimal switching, thereby reducing spikes without requiring higher breakdown voltage transistors.
3Speed
If high voltage spikes occur at switching node, then EMI is caused to nearby circuit, but switching speed must be maintained
Solution Approach 1:
The driver circuit introduces an intermediary element (resistor) between the gate charge source and the gate terminal. This intermediary component controls the rate of charge transfer, acting as a buffer that smooths the switching transitions. The resistor mediates the interaction between the fast switching requirement and the EMI reduction need by controlling the dv/dt of the gate voltage while maintaining overall switching speed.
Data Source
AI summary
A driver for driving a power transistor, the driver having: a first transistor, and a second transistor; wherein (1) when the first transistor is turned on, the second transistor is simultaneously turned on, and wherein after the second transistor remains on for a first time period, the second transistor is turned off for a second time period during when a switching voltage at a second terminal of the power transistor is rising, and the second transistor is turned on after the second time period is over; and (2) when the first transistor is turned off, the second transistor is simultaneously turned off.