Design Challenge: Experimenting with Flyback Transformers
Title: EMC-Optimized SMPS for PEMF Therapy device
by Kamrul Hussain
Blog: 0 - Introduction
Date: 23 Jan 2024
Introduction:
Sorry for my late start. I received the kit vary late due to the customs clearance complications.
I am excited....
It's truly exciting to have this opportunity for exploring the world of flyback transformers and their applications. As an enthusiast deeply involved in medical device research and development, this design challenge with flyback transformers is very timely. I was looking for an optimum power supply solution for a project. And that propels me into the heart of a design challenge centered around the flyback transformer. The objective? To harness its versatile applications in crafting an efficient Switched-Mode Power Supply (SMPS) with EMC filters tailored for a specific cause – a pulsed electromagnetic field (PEMF) therapy device, developed by our research team.
The backdrop of this venture is no ordinary one. The PEMF therapy device in question is a testament to the commitment of our local research team. In the pursuit of developing low-cost medical devices specialized for third-world countries, we recognized the untapped potential of PEMF therapy. This non-invasive and drug-free therapeutic approach has shown promising results in various medical applications, from pain management to tissue regeneration.
In the upcoming installments of this blog series, I'll try to explore the fundamentals of flyback transformers, the intricacies of SMPS design, and the significance of EMC filters in ensuring a seamless and interference-free operation. Particularly this blog is intended for the introduction and planning of my project.
PEMF background:
PEMF stands for Pulsed Electromagnetic Field therapy, which involves the use of pulsed electromagnetic fields to stimulate cellular repair and promote healing in the body. This non-invasive treatment modality has gained recognition globally for its potential in addressing a variety of health conditions, particularly in the realms of muscle pain management and bone healing.
https://www.frontiersin.org/articles/10.3389/fbioe.2022.879187/full
A PEMF device generates pulsating electromagnetic fields through the use of coils that are placed in close proximity to the target area on the body. The pulsating electromagnetic fields induce electric fields within the body, particularly within the cells and tissues in the target area, leading to improved cellular activity, blood circulation, oxygenation, tissue regeneration and overall healing.
My Interest:
Previously we used double general purpose power transformer (50Hz) in series to provide the required isolation for safety. But this makes the device bulky. Moreover, it produces pulsatile signal of around 70 Hz with less than 6% duty cycle to drive the coil, an inductive load.
| {gallery}PEMF circuit and pulses |
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IMAGE TITLE: PEMF control circuit |
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IMAGE TITLE: PEMF pulses @ 70Hz 6-10% duty cycle |
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IMAGE TITLE: PEMF pulse across the coil |
As because it drives in pulsatile mode, when considering the power supply for PEMF therapy devices, flyback transformers may offer a valuable solution due to their ability to efficiently convert and regulate power for the electromagnetic field generation.
Potential of Flyback transformers in powering PEMF:
Isolation and Safety: Flyback transformers provide effective isolation between the primary and secondary circuits, ensuring the safety of the user during the therapy sessions.
Voltage Regulation: Flyback transformers can regulate the voltage levels required for generating the pulsating electromagnetic fields, enabling precise control over the intensity and frequency of the electromagnetic pulses.
Compact and Efficient Design: Flyback transformers can be designed to be compact and efficient, allowing for integration into portable and user-friendly PEMF therapy devices that can be easily used in clinical settings or at home.
Customization and Adaptability: Flyback transformers can be customized to meet the specific power requirements of different types of PEMF therapy devices, accommodating variations in voltage, current, and frequency settings to cater to the diverse needs.
Testing Parameters:
Voltage Regulation: Investigate how the primary and secondary windings affect the output voltage, and observe the impact of varying input voltage on the output.
Isolation Rating: Ensure that the transformer provides adequate isolation between the input and output circuits, meeting the required safety
Transient Response: Assess the transformer's ability to maintain stable output voltage under varying load conditions and during transient events, ensuring consistent and reliable power delivery
High-Frequency Operation: Evaluate the transformer's performance at the intended operating frequency, ensuring that it can efficiently handle the high-frequency switching
My Workflow –
Designing an Efficient SMPS with EMC Filters for the PEMF Therapy Device:
Initial Analysis and Requirements Gathering: Conduct a thorough analysis of the power requirements of the PEMF therapy device, considering the specific voltage and current levels needed to drive the inductive load and manage the parallel capacitors. This initial phase will establish the baseline specifications for the SMPS and EMC filters.
Image taken from: https://www.powerelectronictips.com/how-to-design-modular-dc-dc-systems/
My point of interest will be the highlighted modules –
- Input Filter
- Isolated, Regulated DC-DC module
- Output filter
Transformer Selection and Customization: Select low power flyback transformers best suited for the application, ensuring compatibility with the targeted input and output voltage levels. Customize the transformer design to accommodate the unique demands of the inductive load and the parallel capacitors, prioritizing stable power delivery and efficient energy transfer.
At this stage I’ll try to evaluate the 063929xx series SMPS transformers provided with the Kit.
SMPS Circuit Design and load simulation: Develop a comprehensive SMPS circuit incorporating the selected flyback transformer, integrating necessary control circuitry, and feedback mechanisms. Topologies need to be simulated / tested for the load characteristics.
In my case the PEMF coils are inductive load driven with pulses. IT means there will be negative spikes resulting EMI and performance challenges. This will be evaluated during the experiments.
Integration of EMC Filters and Compliance Testing: Integrate effective EMC filters within the SMPS design to mitigate electromagnetic interference, ensuring compliance with the stringent EMC standards against potential electromagnetic disturbances.
The supplied common mode chokes (071923, 093267) will be evaluated at this stage.
Diversifying the Experimentation Scope:
Battery Charging Optimization: Explore the utilization of the low power flyback transformers in developing efficient and reliable battery charging solutions. Focus on optimizing charging efficiency, ensuring precise voltage and current regulation, and implementing comprehensive safety features for effective battery management across various chemistries and capacities.
**PFBR45-ST13150S and SM13117EL transformers - I don’t have any plan with these right now.
In my next blog I'll post a review on the kit that I have received.
