电磁元件培训教材应用.ppt

变压器设计 Function: Voltage transformation Galvanic isololation Design: Turns ratio Core losses Winding losses Capacitance * 变压器设计 Turns ratio n = N1:N2 * 变压器设计－绕组损耗 * 变压器设计－分布电容 Capacitances CM noise Switch losses * 变压器设计－温升 SA = Surface Normal Convection Ferrites Toroids * 变压器设计－减小漏感的方法 减小漏感的方法： 1 初级级采用分层交叉绕制 2 初次级绕组双线并绕 3 尽可能减少绕组间绝缘厚度 4 使用环形磁芯时绕组均匀分布 5 减少绕组匝数 * 变压器设计－减小分布电容的方法 减小分布电容的方法： 1 减小对应面积 2 绕组分段绕制 3 采用介电常数小的绝缘材料 4 适当增加绝缘材料的厚度 5 正确安排绕组极性，减小绕组间的电位差 6 采用静电屏蔽 * 变压器设计 H8411T1 * 安培定律MMF示意图 * D＞＞δ时MMF示意图 * 多次夹绕时的MMF * 部分夹绕时的MMF * 单层的总的铜损 * 双绕组变压器的铜损的增加 * 双绕组变压器的总铜损 * 电感设计－共模磁芯选择 CM inductors Use ferrite toroids Use materials with m 10k due to freq.response If size a problem, try amorphous/nanocrystalline cores * 电感设计－差模磁芯选择 Small power: use toroids of powder material Input DM: Iron powder due to price PFC: KoolMy, HighFlux, MPP Output: Iron Powder Large power: consider ferrites due to price Be aware of airgap effects Be aware of temp dependence of saturation Highest power: Use amorphous core due to space Be aware of airgap effects * 磁芯材料长度比较 * 电感设计－导线材料 Magnet wire + cheap, high utilization - not reinforced insulation Cu-foil + best utilization, reinforced insulation if taped in two layers - can cause failures because of sharp edges etc. Tripple insulated wire + reinforced insulation - bad utilization, expensive, limited in sizes Litz and twist wire + excellent high freq performance - expensive, difficult in production, not reinforced ins. * 电感设计－电路基础 Vac Look at the inductors in an AC/DC-converter function design realization material * 电感设计－共模电感 Function: attenuate the conducted CM-noise to mainsthrough high impedance for f ? fsw high Z low Z * 电感设计－共模电感 Building High impedance ? high-μi core Current compensation ? 2 windings toroid, no residual airgap ? high AL * isolation ? lindningarna p? varsin halva av k?rnan E-core, residual airgap * isolation ? 2-section bobbin * 电感设计－共模电感 R LDM LCM Cw Simple represent