Topologies
AC Output Filter
AC filter inductors like the one shown have several advantages over DC inductors. First, the current in AC inductors reverse their polarity every switching cycle making “soft switching” easier to achieve. Second, the average low frequency component of the voltage across an AC inductor remains zero, significantly reducing the risk of current run-away. Lastly, AC inductors are less sensitive to the output voltage waveform shape and distortion and to disturbances at either input or load side.
The current through output filter inductors consists of a fundamental AC Current, with some ripple current, which is the target of the filter. Distributed Gap materials can keep from saturating during the peaks of the fundamental current, while maintaining excellent high frequency inductance for filtering.
Output Filters are used to filter high frequency noise from a fundamental AC current. These filters are needed in such applications as DC/AC converters and AC/AC converters such as those used on Variable Speed Motor Drives. The inductors must not saturate during the expected peak AC current, and maintain enough inductance to provide adequate filtering of the high frequency noise.
Distributed Gap Powder Cores are a good choice for inductors in AC Output Filters due to high Saturation and Low Cost.
To contact our engineering group regarding Micrometals solutions for AC Filter Inductor applications please use our website contact form or send an e-mail to applications@micrometals.com
DC/DC Converter
Micrometals’ distributed gap powder cores are a good choice for inductors in DC/DC Converters and are available in a wide variety of shapes, Saturation levels, core loss and cost. Whether in a Buck, Boost, Buck/Boost or other topology, Micrometals On-line Inductor Design Software can help recommend core solutions and optimize your inductor design.
Our core solutions provide exceptional performance for DC inductor applications, especially in critical performance areas like:
• High Saturation Magnetization to maintain inductance under high biasing currents
o FS- FluxSan
o HF – HighFlux
o OD – Optimized DC Bias
• Low Core Loss to prevent excessive heating in response to ripple current
o MS-Sendust
o OC –Optimized Core Loss
For applications greater than 500 kHz, SH-High Frequency Sendust is a good choice, or Carbonyl Iron Powders for the highest frequencies. Use "DC" module in the Inductor Design Software for design assistance.
AC Input Filter
The current through an output filter inductor consists of a fundamental AC Current, with some ripple current, which is the target of the filter. Micrometals distributed gap materials can keep from saturating during the peaks of the fundamental current, while maintaining excellent high frequency inductance for filtering.
Differential Mode Filters must handle the entirety of the input current, while maintaining enough inductance to provide effective filtering of the high frequency noise. Lossier materials are sometimes needed to help suppress high frequency noise. Materials -26 and -52 are most commonly employed in this application. Use "AC" or "AC+ripple" modules in the Inductor Design Software.
For AC Input Filters, Micrometals Distributed Gap Powder Cores are commonly used for the Differential Mode Choke. Specifically, Iron Powder toroids made from Materials -26 or -52 provide an excellent balance between low cost and effective noise filtering.
Flyback Transformer
A flyback transformer inductor is a coupled inductor that can store energy and provide coupling and isolation for the flyback converter. The primary winding of the transformer is directly connected to the input voltage source storing energy in the transformer. A gap between the core helps to store the energy. When the primary winding is disconnected from the source, the energy is transferred to the secondary winding, thus supplying the load.
The flyback is the simplest and most commonly used topology in switch mode power supplies for small power supply applications. The biggest advantage of a switch mode power supply is the higher efficiency provided by low power losses. Also, the part size is smaller, has a lighter weight due to higher operating frequency (typically 50 kHz – 1 MHz), and features lower heat generation due to higher efficiency.
Flyback Transformers should have high energy storage capability, and exhibit low losses during the discharge mode. Commonly used for ignition coil applications. The three-dimensional flux carrying capability is also valuable in ignition coil designs.
Power Factor Correction
Power Factor is a ratio of the actual output capacity of the circuit at a particular time to the product of voltage and current in a circuit. If the power factor is low, it means that the current and voltage are not in phase such that the point at which voltage and current reach their maximum value will be different. So to avoid loss of power and to increase efficiency engineers must be sure to design their circuitry to keep the power factor value high.
A common method to achieve power factor correction is through the use of inductors to help keep the current and voltage in optimal phase. A PFC inductor is typically designed to adjust the value of power factor to make it unity. To achieve this, the effects of the load’s reactance needs to be canceled. The equal and opposite load needs to be added to the circuit to cancel the effects of the load reactance. Both capacitive and inductive effects can be canceled by using inductors and capacitors. An inductor can only cancel the capacitive effect and a capacitor can only cancel the inductive effect. There are two types of PFCs. Active PFC and passive PFC. In passive PFC, only passive electronic components like inductor and capacitor are used.
PFC inductors are used to cancel the capacitive effects. The goal here is to make the total inductance and total capacitance equal so that the actual output power and potential power will be matched and power factor will become closer or equal to one.
Micrometals core solutions provide exceptional performance for PFC inductor applications, especially in critical performance areas like:
• High Saturation Magnetization to maintain inductance under high biasing currents
o FS- FluxSan
o HF – HighFlux
o OD – Optimized DC Bias
• Low Core Loss to prevent excessive heating in response to ripple current
o MS-Sendust
o OC –Optimized Core Loss
For applications greater than 500 kHz, SH-High Frequency Sendust is a good choice, or Carbonyl Iron Powders for the highest frequencies. Use "PFC" module in Inductor Design Software.
Resonant Circuit
Capacitors and Inductors are reactive components. Unlike a resistor, they can store energy in the form of an electric or magnetic field, respectively, and return that energy to the circuit whenever required. At a resonance state as shown above the energy absorbed by the inductor is the same as the energy released by the capacitor at the interval t1 to t2. The opposite situation occurs at the interval t2 to t3. Therefore all the energy from the power supply is delivered to the resistor, and the current in the circuit is maximum.
Therefore, resonant inductors require materials that have linear inductance with current, and low losses at the intended frequency and current levels. Distributed gap cores are suitable for resonant inductors anywhere from low frequency up to 100 MHz. Carbonyl Iron Powder materials are best suited for frequencies greater than 1 MHz. Use the "AC" module within Micrometals Inductor Design Software with "Min %L" set to 95-99.
Class D Amplifier
Class D amplifiers typically use a low-pass LC type filter to attenuate the switching noise in the output waveform while passing the audio signal to the loudspeaker. So it is important that engineers design and specify the correct L-C filter values in addition to choosing the correct LC components for the amplifier to minimize losses and harmonic distortion.
When designing the filter inductor for class-D amplifiers engineers need to be certain that the DC current rating of the filter inductors be greater than or equal to the maximum current that it will experience and that the selected core material does not adversely affect the amplifier's harmonic distortion and incur very low hysteresis losses.
For decades, audio engineers have exclusively specified Micrometals iron powder cores for their filter designs, in particular our exclusive Mix-2, which exhibits low losses and lower operating flux density.
RF Filter
Carbonyl Iron Powders are suitable for moderate bandwidth applications.