DC/DC Forward Converter Active Clamp Reset Duty Cycle Extension
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Solution Overview
Problem
DC/DC forward converters with active clamp reset face limitations in achieving high duty cycles due to power loss constraints, particularly with wide input ranges, which restrict efficiency and component optimization.
Innovation Solution
A control system that dynamically adjusts delay periods for the reset switch and secondary switch in a DC/DC forward converter, using PWM control circuits and delay control circuits to minimize power loss by reducing delay periods as the on-time interval approaches its maximum value, thereby extending the achievable duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fixed delay period is set between reset switch turn-off and primary switch turn-on to minimize power loss, then power loss is reduced, but the achievable duty cycle is limited
Solution Approach 1:
The patent implements dynamic delay adjustment where the delay period between reset switch turn-off and primary switch turn-on is no longer fixed but varies based on operating conditions. The control system monitors the on-time interval and dynamically adjusts the delay period to extend the achievable duty cycle while maintaining power loss minimization, directly resolving the contradiction between fixed delay benefits and duty cycle limitations
Solution Approach 2:
The patent changes the parameter of delay period from a static value to a dynamically adjustable value. By modifying the delay period parameter based on the on-time interval and operating conditions, the system can extend the duty cycle beyond what is achievable with fixed delay, while still maintaining the power loss minimization benefit through optimized delay timing
2Productivity
If delay period is reduced to extend duty cycle, then achievable duty cycle increases, but power loss increases
Solution Approach 1:
The patent employs feedback control where the control system monitors the on-time interval and uses this information to dynamically adjust the delay period. This closed-loop approach ensures that the delay is optimized in real-time to extend duty cycle while preventing excessive power loss, as the system can detect when duty cycle extension is occurring and adjust delay accordingly to maintain efficiency
Solution Approach 2:
The system transitions from static delay to dynamic delay adjustment based on operating conditions. The delay period is continuously adapted based on feedback about the on-time interval and power loss conditions, allowing the system to extend duty cycle when beneficial while automatically reducing delay to minimize power loss when needed
3Adaptability or versatility
If transformer turns ratio is optimized for wide input range, then component optimization is improved, but voltage stress on MOSFETs increases
Solution Approach 1:
The patent utilizes parameter changes in the delay period to compensate for the effects of optimized transformer turns ratio. By dynamically adjusting the delay based on input voltage conditions and operating mode, the system can maintain extended duty cycle capability across wide input ranges while managing voltage stress on MOSFETs through optimized switching timing rather than relying solely on turns ratio optimization
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 allows for increased duty cycle operation while minimizing power loss, enhancing efficiency and optimizing component selection for wider input ranges without compromising transformer turns ratio or increasing voltage stress on MOSFETs.
Implementation Method 1
A DC/DC forward converter uses transformer windings to provide voltage conversion and galvanic isolation for the load
Implementation Method 2
The converter 10 further includes a clamp capacitor C C arranged on the primary side of the transformer PT
Implementation Method 3
If the FG and the SG switch immediately when the AG turns off, significant power will be lost in the body diode of the SG
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
Novel system and methodology are provided for controlling a DC/DC forward converter (200) having a transformer (PT) with primary and secondary windings, a reset switch (AG), and a first switch (PG) coupled to the primary winding of the transformer. The control system involves a PWM control circuit (202,204,206) responsive to an output signal (Vout) of the converter (200) for producing a PWM signal to control switching of the reset switch (AG), and the first switch (PG). A period of the PWM signal includes an on-time interval for enabling transfer of power via the transformer (PT) when the first switch (PG) is on, and a reset time interval for enabling reset of the transformer (PT) when the reset switch (AG) is on. A maximum value of the on-time interval is pre-set to provide sufficient time for the reset. The reset switch (AG) is turned off when the PWM signal goes from a first level to a second level. A first delay period is set between time when the reset switch turns off and time when the first switch turns (PG) on. A first delay control circuit (206) is provided for reducing the first delay time when the on-time interval approaches the maximum value. Further, the converter (200) may include a second switch (FG) coupled to the secondary winding of the transformer (PT). A second delay period shorter than the first delay period may be set between time when the reset switch (AG) turns off and time when the second switch (FG) turns on. A second delay control circuit (204) may be provided for reducing the second delay period when the on-time interval approaches the maximum value.