Introduction
How should EMC and protection be handled for the peripheral circuits of modular power supplies? With increasing electronic integration and continued miniaturization of devices and components, power supplies are also moving toward higher power density, smaller size, thinner profiles, and chip-scale packaging. What factors mainly determine power supply miniaturization?
1. Switching frequency
Raising the switching frequency of a switched-mode power supply can increase power density. For the same performance requirements, a higher switching frequency requires power switches that operate at higher frequency, which allows the use of smaller output inductors and filter capacitors. This reduces the volume and weight of inductors and capacitors and therefore the overall circuit.
However, as switching frequency increases, losses in switching devices and passive components also rise, and issues such as high-frequency parasitics and increased high-frequency EMI must be considered.
In traditional switch-mode power supplies, the transformer often occupied a large portion of the supply volume. Increasing the operating frequency significantly reduces transformer size.
Transformer effective volume:
In the expression above, r is the current ripple ratio, r = △I / IDC; f is the switching frequency; PO is the rated output power.
The magnetic core volume is inversely proportional to the switching frequency f, so higher frequency allows a smaller core and therefore a smaller transformer. High-frequency transformers can easily operate at several hundred kHz, which leads to much smaller size compared with mains-frequency transformers at the same power level.
2. Use of new transformer types
With improvements in manufacturing, planar transformers and piezoelectric transformers can further reduce transformer volume, enabling compact, thin, high-power-density high-frequency power converters. Planar cores enable flat transformer designs; because planar transformers require flat cores and windings, multilayer PCB windings are typically used. Planar transformers are characterized by high frequency, low profile, and very small height at high operating frequency. Piezoelectric transformers use the voltage-to-vibration and vibration-to-voltage conversion properties of piezoelectric ceramics to transmit energy; their equivalent circuit resembles a series-parallel resonant circuit and they are a research and application focus in power conversion.
3. Modularization and integration
A large number of passive components increases the volume of a power supply. Integrating these passive components can reduce size and lower manufacturing cost. Integrating the power system onto a single chip makes the power product more compact, reduces volume, and shortens lead lengths, which reduces parasitics. Low-temperature co-fired ceramic (LTCC) integration technology has become a mainstream method for passive integration. Applying LTCC allows embedding passive components from the power circuit and integrating them together; LTCC also supports three-dimensional circuit designs, further reducing circuit volume and lowering assembly costs.
In addition, component selection and PCB layout should be considered: simplify circuits, choose small-package components, and apply compact PCB layout techniques to further reduce the power supply volume.
