PWM Timer Control Circuit for Forward Converter Transistors
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Solution Overview
Problem
Existing pulse width modulated (PWM) timers in digital power supplies, such as those used in STM32 MCUs, are not optimized for power converter control, leading to complex timing requirements and a need for programmable delays between transistor control signals in forward converters.
Innovation Solution
A control circuit with multiple delay timers and comparators is implemented to generate control signals for transistors in a forward converter, allowing for programmable timing and phase relationships between control signals, including the use of autoreload registers, up counters, and multiplexers to manage delay timers and comparator thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a motor controller (STM32 MCU) is used to control power converter transistors, then the basic PWM control function is achieved, but the timing control precision and flexibility are insufficient for complex power converter requirements
Solution Approach 1:
The control circuit is segmented into dedicated functional blocks: separate delay timers for different transistor groups, individual comparators for each timing threshold, and specific logic circuits for dead-time insertion. This segmentation allows each component to be optimized for its specific function, achieving precise timing control without requiring a complex general-purpose microcontroller.
Solution Approach 2:
Dedicated delay timer circuits serve as intermediary components between the PWM signal source and the transistor gate drivers. These intermediate delay timers introduce precise programmable time delays to coordinate the switching of primary and secondary transistors, enabling accurate timing control that general-purpose MCUs cannot provide efficiently.
2Adaptability or versatility
If general-purpose PWM timers are used in power converters, then basic switching control is achieved, but programmable delays between control signals cannot be implemented
Solution Approach 1:
The control circuit employs programmable delay timers with adjustable time constants, allowing the timing parameters to be dynamically configured for different operating conditions. This dynamic adjustability enables the system to adapt to various power converter topologies and operating modes while maintaining precise timing control through dedicated hardware timing circuits.
3Productivity
If multiple transistors are controlled with fixed timing relationships, then circuit simplicity is maintained, but the ability to optimize for both voltage and current control modes is lost
Solution Approach 1:
The control circuit is designed with universal functionality to support both voltage control mode and current control mode operations. The same delay timer and comparator architecture can be configured for different control modes by adjusting the timing parameters and comparator thresholds, eliminating the need for separate control circuits for each mode while maintaining the ability to optimize performance for both modes.
Data Source
AI summary
A forward converter circuit includes a transformer having a primary winding and a secondary winding. A first transistor is coupled in series with the primary winding and a second transistor is coupled in series with the secondary winding. A control circuit generating control signals for controlling operation of the first and second transistors. The control signals are generated responsive to the values in certain triggered counting circuits satisfying programmable thresholds.