Feature: Power supplies
Figure 1: Traditional (left) and (right) bridgeless totem-pole PFC circuits
Totem-pole PFC techniques and technologies for more
effi cient PSUs By Yong Ang, Strategic Marketing Director, ON Semiconductor
L
osses in an input bridge rectifi er are a hurdle in achieving the best effi ciency from AC-DC power supplies. T e bridgeless totem-pole power factor correction (PFC) is an elegant solution that replaces the lossy bridge rectifi er, PFC FET and boost diode with four active switching devices. However, the
topology must use a complex control algorithm, which may need a microcontroller – and that can be expensive. T e cost and complexity of these control elements present a barrier to adoption of the technique for some engineering teams.
16 October 2021
www.electronicsworld.co.uk
Figure 2: PFC boost inductor current waveform, critical conduction mode
Large energy draw AC-DC power supplies are ubiquitous, accounting for a large proportion of global energy draw, so their effi ciency aff ects system cost and the emissions they contribute. When discussing AC-DC power, there is another, very important parameter – input power factor. If the line current and voltage do not have the same sinusoidal waveshape and phase, the apparent power drawn by the supply is higher than necessary, resulting in ineffi ciencies propagating back through the utility network. T ese can be addressed through PFC, which has now become a statutory requirement in many countries and regions. A typical power supply unit (PSU) without active power factor correction can easily draw 70% more current than one with correction, which is why it is now mandatory to incorporate circuitry to correct power factor to a value close to unity. More correctly, EMC standards such as IEC 61000-3-2 place limits
on the power in line harmonics, up to the 40th, generated by the distorted line current. T e 80 Plus certifi cation program promotes 80% effi ciency, which relates to effi ciency at 20%, 50% and 100% loading. T e highest level of 80 PLUS standard is known as “80+ Titanium standard”, which specifi es at least 90% effi ciency from 10% loading, up to 100%.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46
