Power Module Variable Delay Circuit for Dead Time Margin
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Solution Overview
Problem
Intelligent power modules face challenges in ensuring a desired dead time margin due to the increase in high-side turn-off time with voltage-controlled switching elements, particularly at low collector currents, which can lead to dielectric breakdown from turn-off surge voltage.
Innovation Solution
A power module with a high-side switching element and a low-side switching element forming a half bridge circuit, including a high-side drive circuit with a variable delay circuit that adjusts the delay time based on the detected current, ensuring a consistent dead time margin by reducing the delay time when the collector current is low.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If voltage-controlled switching elements are used in the half bridge circuit, then the switching speed is improved, but the high-side turn-off time increases at low collector currents, causing dielectric breakdown from turn-off surge voltage
Solution Approach 1:
The patent applies dynamics by making the delay time variable rather than fixed. The high-side drive circuit includes a variable delay circuit that dynamically adjusts the delay time based on the collector current level. When collector current is low, the delay time is reduced to compensate for the increased turn-off time, ensuring consistent dead time margin. This dynamic adjustment resolves the contradiction between switching speed and reliability.
Solution Approach 2:
The patent changes the parameter of delay time from a constant value to a variable value that depends on collector current. The variable delay circuit modifies the delay time parameter according to the operating conditions (current level), allowing the system to maintain proper dead time margin across different operating points while preserving the benefits of voltage-controlled switching elements.
2Device complexity
If a fixed delay time is used in the high-side drive circuit, then the circuit complexity is reduced, but the dead time margin cannot be maintained consistently across different collector current levels
Solution Approach 1:
The patent introduces a variable delay circuit that automatically adjusts the delay time based on collector current detection. This dynamic mechanism maintains consistent dead time margin without requiring complex external control systems or multiple delay circuits for different operating conditions. The variable delay approach balances complexity and reliability by using a single adaptive circuit.
3Reliability
If the delay time is reduced to compensate for increased turn-off time at low current, then the dead time margin is maintained, but the switching timing becomes inaccurate at high collector currents
Solution Approach 1:
The patent changes the delay time parameter dynamically based on collector current level. At low collector currents where turn-off time increases, the delay time is reduced to maintain dead time margin. At high collector currents where turn-off time is shorter, the delay time is increased to maintain accurate switching timing. This parameter adaptation resolves both timing precision and dead time margin requirements.
Data Source
AI summary
A power module, including a high-side switching element and a low-side switching element connected to form a half bridge circuit, a high-side drive circuit which drives the high-side switching element, a low-side drive circuit which drives the low-side switching element, and a high-side current detection circuit which detects a current of the high-side switching element. The high-side drive circuit includes a high-side variable delay circuit which adjusts, according to a value detected by the high-side current detection circuit, a length of a high-side delay time from a time when a signal is inputted to the high-side drive circuit to a time when the high-side switching element is driven.