Bootstrap Compensation Circuit for Power Semiconductor Devices
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Solution Overview
Problem
Existing power semiconductor devices face challenges in sufficiently charging bootstrap capacitors due to the complexity and size increase caused by the need for high voltage switches and level shifting signals across voltage sides, especially when the high side switching element is ON.
Innovation Solution
A power semiconductor device design that includes a totem-pole connected high side and low side switching elements, a bootstrap capacitor, a bootstrap diode, and a floating power supply with a bootstrap compensation circuit that monitors and supplies current to the capacitor when the high side drive circuit is ON and the low side is OFF, ensuring sufficient charging without increasing circuit complexity or size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a refresh circuit with high voltage switches SW1 and SW2 is used to charge the bootstrap capacitor, then the bootstrap capacitor can be sufficiently charged, but the circuit becomes complicated and increases in size
Solution Approach 1:
The invention extracts the high voltage switching function from the bootstrap charging circuit by using the existing high side switching element itself to control the charging path. The high side switching element's ON/OFF state directly controls whether the bootstrap capacitor charges from the floating power supply, eliminating the need for separate high voltage switches SW1 and SW2 in the refresh circuit.
Solution Approach 2:
The high side switching element serves dual functions: it acts as both the power switching element for the motor drive and simultaneously controls the bootstrap capacitor charging path. This multi-functionality eliminates the need for dedicated refresh circuit switches, reducing circuit complexity while maintaining reliable bootstrap charging.
2Reliability
If high voltage switches and level shifting circuits are added to refresh the bootstrap capacitor, then the bootstrap capacitor can be charged when high side switching element is ON, but the circuit size increases
Solution Approach 1:
The invention merges the bootstrap charging function with the existing high side drive circuit by using the same power supply terminal and control signals. The charging path is integrated into the existing circuit topology, utilizing the floating power supply and high side switching element's control terminal, thereby avoiding additional circuit components and reducing overall circuit size.
3Ease of operation
If level shift circuits are used to transmit drive signals across voltage sides, then high voltage switches can be controlled, but the circuit becomes more complex
Solution Approach 1:
The high side switching element's control terminal self-adjusts its potential based on the ON/OFF state, automatically enabling or disabling the bootstrap charging path without requiring external level shifting circuits. The control mechanism uses the inherent electrical characteristics of the switching element to manage signal levels across different voltage domains.
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
This design allows for efficient charging of the bootstrap capacitor, simplifies the circuit, and downsizes the apparatus by maintaining a constant voltage between the drive and emitter potentials, ensuring the high side drive voltage is secured even when the high side switching element is ON, while reducing power consumption and heat loss.
Implementation Method 1
a bootstrap capacitor having first and second terminals and supplying a drive voltage to the high side drive circuit
Implementation Method 2
a bootstrap diode having an anode connected to a power supply and a cathode connected to the second terminal of the bootstrap capacitor and supplying a current from the power supply to the second terminal of the bootstrap capacitor
Data Source
AI summary
A power semiconductor device comprises: high side and low side switching elements; high side and low side drive circuits; a bootstrap capacitor supplying a drive voltage to the high side drive circuit and having a first terminal connected to a connection point between the high side switching element and the low side switching element and a second terminal connected to a power supply terminal of the high side drive circuit; a bootstrap diode having an anode connected to a power supply and a cathode connected to the second terminal and supplying a current from the power supply to the second terminal; a floating power supply; and a bootstrap compensation circuit supplying a current from the floating power supply to the second terminal, when the high side drive circuit turns ON the high side switching element and the low side drive circuit turns OFF the low side switching element.