Switching Power Supply Delay Control for Dead Time Reduction
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Solution Overview
Problem
In switching power supply devices operating in continuous current mode, the intentional delayed operation of the primary-side switch leads to increased power loss due to a longer dead time and reverse current flow, especially when using silicon-MOSFETs with body diodes, as the forward voltage of the diode results in a larger power loss.
Innovation Solution
The implementation of a delay circuit and control voltage generation circuit that adjusts the delay time and ON period of the diode to minimize the dead time, using a delay time control circuit to determine the ON period of the diode based on the drain voltage, thereby reducing the delay time and minimizing power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intentional delayed operation of the primary-side switch is used to avoid simultaneous switching on, then switching conflicts are avoided, but dead time increases and power loss increases
Solution Approach 1:
The patent applies dynamics by making the delay time variable rather than fixed. The delay time is dynamically adjusted based on the output current magnitude: smaller delay time for larger output current and larger delay time for smaller output current. This dynamic adjustment allows the system to optimize between avoiding switching conflicts and minimizing dead time losses under different operating conditions.
Solution Approach 2:
The patent changes the parameter of delay time based on operating conditions. Specifically, the delay time is changed according to the output current magnitude, allowing the system to adapt the timing parameters to minimize power loss while maintaining reliable operation across different load conditions.
2Productivity
If diode is connected parallel to secondary-side switch to enable current flow during dead time, then continuous current mode is achieved, but forward voltage of diode causes larger power loss
Solution Approach 1:
The patent dynamically adjusts the delay time based on output current magnitude to minimize the duration during which diode current flows. By reducing delay time when output current is large, the system limits the period of diode conduction and associated power losses, while still maintaining continuous current mode operation when needed.
Solution Approach 2:
The patent converts the potentially harmful effect of diode forward voltage drop into a controlled phenomenon. By carefully managing the delay time and diode ON period, the system allows diode current flow only when necessary for maintaining continuous current mode, thereby converting what would be pure loss into a controllable operating parameter that supports high productivity when needed.
3Loss of energy
If delay time is reduced to minimize power loss, then power loss decreases, but risk of simultaneous switching on increases
Solution Approach 1:
The patent changes the delay time parameter based on operating conditions (output current magnitude) to find the optimal balance between minimizing power loss and maintaining switching safety. The system adjusts this critical parameter dynamically rather than using a fixed value, allowing adaptation to different operational requirements.
Solution Approach 2:
The patent implements feedback by monitoring the output current magnitude and using this information to adjust the delay time. This feedback mechanism ensures that the delay time is optimized for current operating conditions while maintaining sufficient margin to prevent simultaneous switching on, thereby balancing power loss reduction with switching safety.
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 approach reduces the period of diode current flow, decreases power loss, and prevents transistor destruction by minimizing the dead time and reverse current, while maintaining efficient operation in continuous current mode.
Implementation Method 1
a primary winding and a secondary winding... magnetically coupled to each other via a transformer
Implementation Method 2
a diode having a cathode coupled to the one end of the secondary winding and an anode at the reference potential
Data Source
AI summary
A switching power supply device includes a transformer including a primary winding and a secondary winding, a first transistor coupled to the primary winding, a first control circuit that outputs a first control voltage, a delay circuit that delays the first control voltage and supplies the delayed first control voltage to the first transistor, a second transistor that has a first terminal coupled to the secondary winding, a diode coupled to the secondary winding, a second control circuit that outputs a third control voltage used for controlling a switching operation of the second transistor, a control voltage generation circuit that generates the second control voltage, and a delay time control circuit that determines an ON period in which the diode is switched on and controls a delay time so that the delay time by which the delay circuit delays the first control voltage is shorter for a longer ON period.