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Exxelia introduces the CCM family at ESA / SPCD 2022

Magnetic components for space applications, optimized for multi output Flyback transformers

SUMMARY

  • Introduction : evolution of magnetic components in space

Definition – How to satisfy it?

  • Part 1 : Family qualification by ESA/CNES

Why choose Technology Flow over QPL products?

Qualification steps.

  • Part 2 : Performance characterization of CCM technology

Thermal behavior.

Frequency response and Current saturation (standard CCM inductors).

  • Part 3 : Optimization for multi output Flyback transformers

The cross regulation problem or voltage deviations on some outputs.

PhD thesis definition – Different stages of work – Present and future results.

  • Conclusion

Components that meet present and future customer needs

 

WHAT IS A CCM?

 

CCM family : INTRODUCTION

 

What are the new technical needs and constraints for specific transformers?

 

First : Applications with more outputs.

Need for more In/Out pins.

More different voltages and power levels.

 

Second : Increase in the power to volume and power to weight ratios.

We can no longer take large safety margins.

  →  need to know all the technical limitations of the product.

Reliability, internal heating, frequency response, current saturation.

 

Third : Development time is getting shorter

Breadboards/Prototypes must work the first time  →  design method must be accurate.

Even specific products must avoid qualification time.

  →  have to be already qualified before BreadBoard/Prototype step.

 

Part 1 : ESA qualification 

 

 

  • CCM family : What is this, and what is it for?

1 technology for 5 shapes

Ferrite circuit around windings wound in a bobbin, cabled on a leadframe and moulded.

For both standard and custom components

Different types of functions : inductors (DMC, CMC), pulse/SMPS/measurement transformers

  →  QPL qualification not adapted  Technology Flow is better

 

  • What is a Technology Flow?

Exxelia must prove that CCM technology is space compliant.

1st step Evaluation (Exxelia), 2d step Qualification (ESA/CNES).

Exxelia has to define : bill of materials / manufacturing process / design rules and list of tests to be performed.

 

Bill of materials

3 key raw materials : Bobbin, leadframe and magnetic circuit.

Other materials : wires, solid insulation, glue/resin/varnish, weld, ink, package.

 

Manufacturing process

3 key steps : winding, cabling, moulding.

Other steps : gluing, assembling, marking, testing, packaging.

 

Design rules

All theoretic actions the designer has to do upstream to prevent surprises downstream.

 

Test campaigns

All those in Charts F4 SG1, SG2 and SG3.

Thermal shocks, Temperature rise, Overload, Soldering heat, Vibrations, Mechanical shocks Operating life, Permanence of marking, Solderability, Terminal strength, Dielectric, Moisture.

 

  • Summary of work carried out

- More than 100 components designed, manufactured, and tested

  many configurations of  functions / shapes / tests.

- Some components destroyed to identify security margins

  on thermal, mechanical, dielectric aspects.

- Evaluation took several years to complete

 Result :  Qualification was successful on first try.

 

  • Conclusion

Respecting BOM, process and design rules qualified  ... Exxelia has the right to offer any function in CCM shapes without any mandatory testing for customer.

 

Part 2 : CCM technology performances

 

 

  • Security margins must be reduced

Maximum permissible loss value  →  leads to internal heating (Tmax <  125 °C).

Maximum operating frequency  →  above resonant frequency component is no more inductive.

Saturation curve  →  which inductor value at which excitation current?

 

  • How can these characteristics be determined ?

We decided to carry out 3 experimental campaigns :

  1. Thermal resistance determination for each of 5 shapes.
  2. Inductance versus frequency curves for standard inductors.
  3. Inductance versus current curves for standard inductors.

 

  • Thermal resistance Rth of CCM4, CCM5, CCM6, CCM20 and CCM25

  • Definition of test conditions

Use of inductors with one winding connected to all pins one side.

 

Measurements in vacuum are very complex.

  →  in natural convection in the air first.

Copper losses (heating source) only.

  →  DC current excitation / measurement of Rwind.

Component on PCB / all pins soldered  / no glue / no copper except for large current paths.

Component in a (pierced) box inside a ventilated oven  / temperature controlled.

 

  • Measurement bench

Measurements realised for each of 5 shapes.

2 L values  /  5 Tenv : 25, 50, 75, 100, 125 and 150°C  / up to 15 meas. points for each Tenv.

 

  • Complements and further work

Results applied for all CCM components  /  We have a math model air convection → vacuum.

3D simulations in progress to validate these curves  …  1st results are promising.

Measurements in vacuum are planned.

 

  • Frequency behavior for CCM4, CCM5, CCM6, CCM20 and CCM25 standard inductors

 

  • Definition of test conditions

Use of inductors with one winding connected to all pins one side.

Constant excitation, between 100µT and 1mT.

Components soldered on a brass plate.

RLC meter calibrated after 1 hour functioning.

 

Measurement device

 

  • Measurements realised for each of 5 shapes

2 L values  / up to 15 meas. points for each inductor value.

 

 

  • Result overview
    • Majority of inductors are usable at least up to 1MHz.
    • All of inductors are usable at least up to 400kHz.

 

  • Saturation behavior for CCM4, CCM5, CCM6, CCM20 and CCM25 standard inductors

 

  • Definition of test conditions

Use of inductors with one winding connected to all pins one side.

0,5 phase shift full bridge DC supply.

DC+AC (300kHz) excitation with duty cycle > 0,5.

ΔI constant as long as no saturation.

Period nb controlled to achieve desired DC current.

L value measured with current rise slope.

 

  • Measurements realised for each of 5 shapes

2 L values  / 2 Tenv, ambiant and 125°C / up to 15 meas. points for each Tenv.

2 types of curves L function of Idc or Imax (Idc+ΔI/2).

 

  • Result overview

Big ≠ between 25 and 125 °C : taking account of thermal behavior of ferrite is mandatory.

Main interest : to detect the beginning of saturation.

 

Part 3 : multi Flyback optimization

 

 

  • What are voltage deviations also named cross regulation problem ?
  1. At nominal point of load, some output voltages are different from theoretical values.
  2. If power level at regulated output varies, some non-regulated output voltages values vary.
  3. Current waveform on some auxiliary outputs is very different from theoretical triangle shape.

 

  • Observation :

The more different output / voltage levels / power levels …

The greater the probability to have voltage deviations.

Actual solution : linear regulators.

  →  more volume/weight, less efficiency, more heating.

 

  • Charge :  Transformer is mostly responsible

Problem seriousness depends on application and even on piece inside a manufacturing batch.

Magnetic root cause (transformer), but power electronics consequence (converter).

  →  need to work in both electromagnetism and power electronics.

 

  • Exxelia decided to manage a PhD thesis on this subject

Aims :

  1. Understand scientific problem, Identify root causes (transformer, other components?),
  2. Find solutions, Take account of voltage deviations in design and manufacturing process

Partners : G2Elab laboratory, D. Motte Michellon student, CNES, Steel Electronique

 

  • PhD step 1 : Understanding the scientific problem, identify root causes

Study of magnetic behavior of several transformers

  →  use of FLUX finite element simulation software

Identification of a circuit model compliant with several softwares (Psim, Spice, other)

  →  extended Cantilever magnetostatic model

Calculation of all output voltages for different transformers/converters

  →  use of Psim circuit software

 

  • Result of analysis :
  •  3/4 problem comes from transformer : magnetic coupling between all secondaries
  •  1/4 problem comes from drawbacks of some other components of converter

 

  • Actions :
  1.   Creating an analytic model to take account of leakage inductances between secondaries,
  2.   Use this model to quick calculate all output voltages.

 

  • PhD step 2 :  Finding theoretical and industrial solutions

We identified relationship between   CCM winding process, couplings between secondaries and voltage deviations.

We identified which other components and which drawbacks are concerned.

For the moment, one method of winding CCM to avoid worst cases of voltage deviations and to minimize variations from one piece to another applied since 01/01/2022 for all designed Flyback in CCM.

In progress, a software to optimize (minimize) voltage deviations and to identify best cases of CCM winding processes.

    →  Increase of know-how for customer benefit.

 

CCM family : CONCLUSION

 

 

  • Whatever the function you need

Component is already qualified  →  Reliability and security.

Many pins  ==  many input/output possibilities.

You know its thermal behavior  →  have a good idea of its energy/power limit.

 

  • For inductor applications

You can have standard or custom components.

You know frequency and current responses.

 

  • For multi output Flyback transformers

Design method focused on :

  1. meeting customer’s need as close as possible,
  2. volume and weight reductions.

 

Understanding voltage deviations  =  problem minimization + ability to assist customer.

 

                                                                CCM technology is well adapted for space   …  and we continue to improve it.

 

 

 

Autor : Bruno COGITORE  –  Jean PIERRE

Magnetic Expert / Innovation  –  Space product Manager  •  Exxelia Magnetics

 

Published on 05 Oct 2021 by Stephane PERES

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High Voltage Resistor Selection Checklist

Introduction to High Voltage Resistor Selection Checklist The resistor is the most common and well-known passive electrical component. A resistor is a device connected into an electrical circuit to introduce a specified resistance. The resistance is measured in Ohms. As stated by Ohms Law (E=IR), the current through the resistor will be directly proportional to the voltage across it and inversely proportional to the resistance. Resistors have numerous characteristics that determine their accuracy during use. The performance indices affect the accuracy to a greater or lesser extent depending on the application. Some of these indices are: Tolerance at DC, Temperature Coefficient of Resistance (TCR), Voltage Coefficient of Resistance (VCR), Noise, Stability with respect to Time and Load, Power Rating, Physical Size, and Mounting Characteristics. Resistor networks typically require temperature and voltage tracking performance. Please refer to the application note: Glossary of Resistor Terminology for an expanded explanation of resistor terminology. Selection Requirements 1. Determine the resistance in ohms and watts. 2. Determine the proper physical case size as controlled by voltage, watts, mounting conditions, and circuit design requirements. 3. Select the resistor that meets your needs for type, termination and mounting. Step 1 : Determine the resistance in ohms and watts. Ohm’s Law: E=IR or I=E/R or R=E/I Ohm’s Law, as shown in the above formula, enables one to define the voltage (E), current (I), or resistance (R) when two of the three terms are known. When current and voltage are unknown they must be measured in the model circuit.   Power Law: W=I2R or W=EI or W=E2 /R Watts (power) can be determined from the above formulas that are derived from Ohm’s Law. R is measured in Ohms, E in volts, I in amperes, and W in watts. Watts must be accurately determined before resistor selection. Simply stated any change in voltage or current produces a much larger change in wattage (heat dissipated by the resistor). The effects of relatively small increases in voltage or current must be determined because the increase in wattage may be significant enough to influence resistor selection. As stated in the above formulas the wattage varies as the square of the current or voltage. Allowances should be made for maximum possible voltage. Step 2 : Determine the proper physical case size as controlled by voltage, watts, mounting conditions, and circuit design requirements. Power Rating and Physical Size: A resistor operated at a constant wattage will reach a steady temperature that is determined largely upon the ratio between the substrate size (surface area) and the wattage dissipated. Temperature stabilizes when the sum of the heat loss rates (by radiation, convection, and conduction) equals heat input rate (wattage). The larger the resistor surface area per watt to be dissipated, the greater the heat loss rate and therefore the lower the temperature rise. Free Air Wattage Rating (Maximum Power Rating) is defined as the wattage rating of resistors as established under specified standard conditions. The absolute temperature rise for a specific resistor is roughly related to the area of its radiating surface. It is also dependent upon a number of other factors such as thermal conductivity, ratio of length to width, heat-sink effects of mounting, and other minor factors. The precise temperature limits corresponding to 100% rated wattage are somewhat arbitrary and serve primarily as design targets. Once a wattage rating has been assigned on the basis of an empirical hot spot limit, the verification of its correctness must be established through long term load life test (see Application Note: Life Test Data – High Voltage Chip Resistors) based on performance and stability standards rather than the measurement of hot spot temperature. Step 3 : Select the resistor that meets your needs for type, termination and mounting. ✔ Resistor Selection: Select the most suitable resistor that meets the requirements of the application. OhmCraft resistors are made to your specification. Refer to the appropriate data sheet to determine part number or call OhmCraft for assistance. ✔ Wattage Rating: To allow for the differences between actual operating conditions and the Free Air Wattage Rating it is a general engineering practice to operate resistors at less than the nominal rating. ✔ Voltage Rating: Determine maximum applied (working) voltage that the resistor will be exposed to and select the appropriate package size. ✔ Pulse Operation: When a resistor is operated in a pulse application, the total power dissipated by the resistor is a function of the pulse’s duty cycle. Typically, one will define the number of joules of energy the resistor must dissipate and choose a resistor accordingly. For additional information refer to our Pulse Resistor white paper or contact OhmCraft. ✔ High Frequency: OhmCraft resistors, due to their design and construction, have very low capacitance and are inherently a non-inductive design. For additional information refer to our High Frequency Attributes Application Note. ✔ Military and Other Specification: The special physical operating and test requirements of the applicable industrial or military specification must be considered. Contact OhmCraft for additional information. Effect of the power ratings on components All the components of an electrical apparatus including resistors, capacitors, rectifiers, and semiconductors have their own limitations as to the maximum temperature at which they can reliably operate. The attained temperature in operation is the sum of the ambient temperature plus the temperature rise due to the heat dissipation in the equipment. Ambient Temperature Derating, below defines the percent of full load that power resistors can dissipate as a function of ambient temperature. Temperature Coefficient of Resistance Temperature Coefficient of Resistance (TCR) is expressed as the change in resistance in ppm (0.0001%) with each degree of change in temperature Celsius (C). MIL STD 202 Method 304 is often referenced as a standard for measuring TCR. This change is not linear with temperature. TCR is typically referenced at +25C and changes as the temperature increases or decreases. It can be either a bell or S shaped curve. It is treated as being linear unless very accurate measurements are required, then a temperature correction chart is used. A resistor with a TCR of 100 ppm will change 0.1% over a 10-degree change and 1% over a 100-degree change. An example of a TCR curve can be found in the application note: Glossary of Resistor Terminology. The following formula expresses the rate of change in resistance value per 1 C in a prescribed temperature range. TCR (ppm/°C) = (R-R0)/R0 X 1/(T-T0) X 106 - R: Measured resistance (Ω) at T °C - R0: Measured resistance (Ω) at T0 °C - T: Measured test temperature °C - T0: Measured test temperature °C In the context of a resistor network, this TCR value is called absolute TCR in that it defines the TCR of a specific resistor element. The term TCR tracking refers to the difference in TCR between each specific resistor in the network. Voltage Coefficient of Resistance The Voltage Coefficient of Resistance is the change in resistance with applied voltage. This is entirely different and in addition to the effects of self-heating when power is applied. A resistor with a VCR of 100 ppm/V will change 0.1% over a 10 Volt change and 1% over a 100 Volt change. VCR becomes very important in high Ohmic value resistor (100M Ω and above) where typical VCRs can be greater than 1000 ppm/V to specify the voltage that will be applied. Failing to do this may result in a resistor that will not meet your specification. The rate of change in resistance value per 1 volt in the prescribed voltage range is expressed by the following formula: VCR (ppm/V) = (R0-R)/ R0 X 1/(V0-V) X 106 - R: Measured resistance (Ω) at base voltage - R0: Measured resistance (Ω) at upper voltage - V: Base voltage - V0: Upper voltage In the context of a resistor network, this VCR value is called the absolute VCR in that it defines the VCR of a specific resistor element. The term VCR tracking refers to the difference in VCR between each specific resistor network. Please refer to the application note: Voltage Ratio Tracking and Voltage Coefficient of Resistance. Summary When specifying a resistor, the following parameters MAY be of interest. Please use this chart to help you define the operating characteristics for your specific application. All of them may not important for your specific application. Also, please do not hesitate to contact Ohmcraft for application help. At Exxelia Ohmcraft, our commitment transcends the creation of resistors. We are dedicated to empowering the visionary innovations that define the future of military technology. Our team is poised to collaborate and customize solutions that perfectly align with the evolving needs of military applications. In a landscape where reliability is non-negotiable and precision is imperative, Exxelia Ohmcraft stands as the beacon of unwavering support, fortifying military operations with resilient, high-performance resistors. Download our White Paper   Exxelia Ohmcraft’s sister division, Exxelia Micropen Medical is at the forefront of medical device product development, providing design engineers with unique insights on conceiving and implementing new designs and features. 
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