Push-Pull Converter Control for Low EMI and Voltage Spike Suppression
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Solution Overview
Problem
Power supplies in aerospace and automotive systems face challenges in adhering to stringent Radio Frequency Emissions standards due to discontinuous input currents, which lead to unwanted interference, and must handle voltage transients while maintaining system reliability and efficiency.
Innovation Solution
A cascaded dual-mode power supply circuit with a push-pull converter that operates in three modes: normal, overvoltage, and hold-up, using a transformer and inductor configuration with PWM control to manage input voltage and provide continuous current during normal operation, while minimizing interference and ensuring voltage regulation across multiple outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If discontinuous input current topology (flyback or buck-derived converter) is used, then isolated topology requirement and multiple outputs are satisfied, but conducted emissions increase and interfere with surrounding circuitry
Solution Approach 1:
The power supply is divided into two distinct stages: a pre-regulator stage that provides continuous current to minimize emissions, and a push-pull converter stage that provides isolation and multiple outputs. This segmentation allows each stage to optimize for its specific function without compromising the other.
Solution Approach 2:
The pre-regulator stage acts as an intermediary between the input voltage source and the push-pull converter. It conditions the input voltage to provide continuous current, thereby reducing conducted emissions before the signal enters the isolated converter stage.
2Object-generated harmful factors
If significant differential mode filtering is added to reduce conducted emissions, then emissions requirements are met, but device complexity, size, and cost increase
Solution Approach 1:
The pre-regulator stage performs preliminary action by establishing continuous current flow before the power reaches the isolated converter. This proactive approach to current conditioning reduces emissions at the source, eliminating the need for complex downstream filtering.
3Reliability
If pre-regulator is used to convert input voltage for entire powered phase, then hold-up capability is provided, but power dissipation, cost, weight, size, and reliability are adversely impacted
Solution Approach 1:
The system dynamically switches between two operational modes: normal mode where the pre-regulator is active and provides continuous current regulation, and hold-up mode where energy storage capacitors maintain output voltage during input failures. This dynamic operation optimizes both reliability and efficiency.
Solution Approach 2:
The pre-regulator operates periodically during normal operation to recharge energy storage capacitors, which then sustain the system during hold-up conditions. This periodic recharging provides hold-up capability without requiring the pre-regulator to operate continuously.
4Object-affected harmful factors
If transient voltage suppressor is used to reduce voltage spikes, then transient protection is provided, but residual transient voltage remains that can still damage application circuits
Solution Approach 1:
The control system continuously monitors input voltage and detects transient conditions. When transients are detected, the controller adjusts the pre-regulator and push-pull converter operation to actively clamp and suppress the transient voltage, preventing residual damage to downstream circuits.
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
The solution effectively reduces electromagnetic interference, ensures continuous input current during normal operation, and provides stable output voltages across a wide input voltage range, enhancing compliance with industry standards and system reliability.
Implementation Method 1
a transformer having a primary winding and a secondary winding
Implementation Method 2
an inductor having a first terminal thereof connected to an input voltage via a third switch, wherein a second terminal of the inductor is connected to a centre tap on the primary winding
Implementation Method 3
a controller arranged to monitor the input voltage, to apply a first pulse width modulated (PWM) signal to the first switch, and to apply a second PWM signal to the second switch
Data Source
AI summary
A power supply circuit has a push-pull portion having a transformer; first and second terminals of the primary winding, each connected to ground via first and second switches; an inductor connected between an input voltage and the primary winding centre tap via a third switch; an energy storage portion connected between the primary winding and ground, and to the inductor via a fourth switch; a controller arranged to monitor the input voltage and to apply partially overlapping first and second PWM signals to the first and second switches; when input voltage is between first and second thresholds, the controller closes the third switch and opens the fourth switch; above the second threshold, the controller applies a third PWM signal to the third switch and opens the fourth switch; and below the first threshold, the controller closes the third switch and applies a fourth PWM signal to the fourth switch.