High Frequency Power Applications Research Articles

Preparation and Characterization of Mn-Zn Ferrite for High Frequency Power Applications

Manganese-zinc-ferrous ferrites of estimated structural compositions Zn0.216Mn0.706Fe0.078Fe204 and Zn0.197Mn0.683 Fe0.120Fe2O4 were ferritized at 1120° and 1090°C using air atmosphere during heating and soaking periods and argon atmosphere during cooling. This ferritized powder after grinding to ≅ 5 μm was pressed into toroid and cylindrical pellets. Sintering of shapes was done in air at temperatures of 1220° and 1250°C and for a soaking periods of 6 hours, while the heating and cooling were done in air and argon respectively. Lattice parameters were determined by the X-ray method; the values ranged between 4.487 and 4.497 A for materials ferritized under different conditions. Real and imaginary parts of complex permeability, μ' and μ″ and quality factor Q were determined in the frequency range 100–2000 kHz using impedance bridge on toroidal samples. The values varied in the range 370–648 (for μ'), 30–54 (for μ″) and 7–16 (for Q) at 100 kHz. The permeability at 100 kHz range was 373–651 against the expected value of 1500 for such applications. The d.c. resistivity was determined using complex impedance analysis and values ranged between 276 and 5762 ohm-cm as compared to values of ≅ 700 ohm-cm reported in the literature. The values of saturation magnetization (σs) ranged between 96 and 108 emu/gm and Curie temperatures for compositions 1 and 2 were found to be 245° and 281°C respectively.

Lattice matched and pseudomorphic In0.53Ga0.47As/InxAl1−x As resonant tunneling diodes with high current peak-to-valley ratio for millimeter-wave power generation

Lattice matched and pseudomorphic In0.53 Ga0.47 As/InxAl1−x As resonant tunneling diodes, with some of the best dc performance ever reported, have been fabricated and their high-frequency power generation capabilities have been theoretically studied. For the lattice matched system a peak-to-valley ratio of 7 (300 K) and 21 (77 K) with a peak current density of approximately 10 kA/cm2 is measured. The pseudomorphic system with a In0.53 Ga0.47 As well and AlAs barriers results in a peak-to-valley ratio of 24 (300 K) and 51 (77 K) with a peak current density of approximately 15 kA/cm2. Based on a quasistatic large signal waveform analysis the power generating capability of the InGaAs device is compared with a GaAs based device with an equally high peak current density and it is found that for very high-frequency power applications the InGaAs based device is better.

A multiple-output 400kHz switching power supply using a new ferrite material H63A

A multiple-output 400kHz switching power supply using a new ferrite material H63A was developed. The power supply, with an efficiency of 74% and an output power of 6.3cc/W, had a single-ended forward type main transformer. The core shape was EE- 30, determined by output power and the winding window area specified in safety standards. The temperature rise of the transformer in operation was examined while changing core materials. The least temperature rise was observed when H63A was used as the core material. H63A was also found to be suitable for high frequency power applications.

Power ferrites for high frequencies

MnZn ferrites with Sn and/or Ti substitutions meet all main requirements for high frequency power applications. The composition Mn 0,631 Zn 0,266 Ti 0,022 Sn 0,010 Fe 2,071 O 4 has been selected to demonstrate the advantages of these ferrites. By sintering under special conditions to a medium initial permeability of about \mu_{i} \approx 1500 one achieves a flat μ i (ϑ)curve which varies only slightly up to 1 MHz in a wide temperature range. Thus contributions of gyromagnetic and dielectric losses are suppressed. The influence of eddy current power losses are discussed. They can only be reduced by high dc resistivity ρ, low magnetic flux density \circ{B} and small core sizes. The measurement of ρ versus temperature shows that with-in the application temperature range the decrease of ρ is governed by the same activation energy independent of the absolute value of ρ and the composition. Examples for power losses versus \circ{B} , frequency and temperature are given.

Constant voltage scaling of FETs for high frequency and high power applications

A constant voltage scaling scheme is examined for the enhancement of frequency and power performance of FETs. For low electric fields, this scheme is self-consistent within Shockley's formulation and improves the overall frequency and power performance figure of merit by a factor of κ 6 with a κ times reduction in the device area. For high electric fields, the improvement is reduced to κ 3 times due to the velocity saturation effect. Reduced breakdown voltage further limit the improvement.