Transistor Drive Circuit Parallel Operation Overheating Control
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Solution Overview
Problem
The existing drive circuits for bipolar-type transistors and MOSFETs in parallel configurations face issues such as high loss due to overheating, delayed turn-on timing, increased drive loss, tail current generation, and poor controllability in PWM control, leading to inefficiencies and potential short-circuit currents.
Innovation Solution
A transistor drive circuit that employs temperature and current detection elements to evaluate the heat-generation state of the transistors, adjusting the drive configuration to prevent overheating by controlling the parallel operation of bipolar-type transistors and MOSFETs, including dynamic voltage application and timing adjustments to optimize turn-on and turn-off sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a MOSFET with smaller chip size is used in parallel with RC-IGBT, then loss reduction is achieved, but the MOSFET may enter overheating state when conduction amount increases
Solution Approach 1:
The patent implements dynamic switching between RC-IGBT and MOSFET based on conduction amount detection. When conduction amount exceeds a threshold, the system switches from parallel operation (DC assist mode) to RC-IGBT only operation, preventing MOSFET overheating while maintaining loss reduction benefits during normal operation
Solution Approach 2:
The system changes the operational parameters by detecting conduction amount and adjusting the drive configuration accordingly. The control unit modifies the operating state from dual-transistor parallel operation to single-transistor operation based on real-time conduction levels, optimizing both loss and temperature performance
2Reliability
If negative potential is applied to MOSFET gate when turned off, then off-state is reliably maintained, but drive loss increases due to larger potential difference with high-level voltage
Solution Approach 1:
The patent applies negative potential to the MOSFET gate only when necessary (during DC assist mode operation) rather than continuously. This partial application of negative voltage maintains off-state reliability when needed while reducing drive loss by avoiding continuous large potential difference application
Solution Approach 2:
The negative gate voltage is applied periodically based on operational mode rather than continuously. During DC assist mode, negative voltage is applied to ensure reliable off-state; during RC-IGBT only mode, negative voltage is not applied, reducing drive loss while maintaining reliability when required
3Reliability
If fixed delay time is used for MOSFET turn-on timing, then variations in switching characteristics are accommodated, but turn-on timing is delayed and loss reduction effect is insufficient
Solution Approach 1:
The system uses real-time detection of RC-IGBT turn-on completion status to trigger MOSFET turn-on, creating a feedback-based timing mechanism. This eliminates fixed delay limitations by dynamically adjusting MOSFET turn-on timing based on actual RC-IGBT switching state, reducing switching loss while ensuring reliable operation
Solution Approach 2:
The system prepares for MOSFET turn-on by monitoring RC-IGBT gate voltage in real-time and triggers MOSFET turn-on immediately upon detecting RC-IGBT turn-on completion. This preliminary monitoring approach ensures optimal timing without excessive delay, improving loss reduction effectiveness
4Ease of operation
If MOSFET is turned off first in DC assist, then IGBT turn-off can be performed subsequently, but tail current flows and electric power loss occurs
Solution Approach 1:
The patent inverts the conventional turn-off sequence by turning off the RC-IGBT first and then turning off the MOSFET. This reversed sequence prevents tail current flow from the IGBT, eliminating the associated power loss while maintaining ease of control through coordinated switching
5Reliability
If MOSFET turn-off is started first in PWM control, then parallel drive configuration is maintained, but turn-off completion time increases and controllability becomes poor
Solution Approach 1:
The system dynamically adjusts the turn-off sequence based on PWM signal characteristics and operational requirements. By making the turn-off sequence flexible rather than fixed, the system can optimize for either parallel drive stability or fast turn-off speed depending on the specific operating conditions
Solution Approach 2:
The control unit changes the turn-off sequence parameter based on operational mode. In certain PWM conditions, MOSFET turns off first to maintain parallel drive; in other conditions, RC-IGBT turns off first to improve speed. This parameter adjustment optimizes both stability and speed performance
Data Source
AI summary
A transistor drive circuit drives a bipolar-type transistor and a MOSFET that are connected in parallel to each other. A temperature detection element that detects a temperature of a the bipolar-type transistor or the MOSFET. When the temperature is equal to or less than a threshold, the transistor drive circuit turns on both of the MOSFET and the bipolar-type transistor. When the temperature exceeds the threshold, the transistor drive circuit turns on only the bipolar-type transistor.