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Speed Does Not Kill - Power Supplies with Fast Switching Frequency Just Got a Lot Safer

[ Edited ]

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Introduction

 

Isolated power supply systems are prevalent in server systems, industrial applications, and telecommunication and networking equipment. In this bandwidth-hungry age of the Internet of Things (IoT), a growing number of these systems need to be efficiently powered, driving up the need for power-efficient, cost-effective solutions.
As devices get smaller, power supplies have to follow suit. Thus, designers today have one overriding objective—to maximize power per volume (W/mm3). One way to achieve this is to use higher performance power switches.There have been significant innovations in this area and exciting new products are now available that have highspeed switching capability, offering increased system efficiency and a lower component size.
These new power switches include the next generation of faster silicon-based MOSFETs as well as newer technologies like Gallium-Nitride (GaN) or Silicon-Carbide (SiC) substrates. The new technologies’ lateral structure, compared to vertical for silicon, makes them low-charge devices and
therefore capable of switching hundreds of volts in nano-seconds (ns). This is ideal for fast switching systems.


Other advantages include a higher electric field strength and electron mobility, which means the size of the switch is much smaller for a given breakdown voltage and on-resistance. Also, they have a wider band gap, which means they can operate safely at a higher current at higher frequencies.

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However, for power supplies, fast switching does not come for free—it produces high noise transients that could cause loss of modulation, or permanent damage to the overall system due to latch-up. To solve this problem, the noise immunity of components used to drive these new power switches has to be improved significantly. This article explains these new technologies and how designers can arm themselves to meet the power challenges of tomorrow.

 

Power Converter Systems

Let’s look more closely at the widespread switched mode power supplies (SMPS), where power switching is most relevant. SMPS convert their input power from ac to dc (ac-dc) or from dc to dc (dc-dc), and in most cases, they also change voltage levels to suit the needs of the application.

Typical ac-dc SMPS Block Diagram.png

Typical ac-dc SMPS Block Diagram

 

The figure shows a typical ac-dc SMPS block diagram. The ac input voltage is first rectified into a dc voltage. This dc voltage is then modulated by the power switch stage using the gate drivers to control the modulation. The controller generates the control signal that the gate drivers use to modulate the power switches. This switched voltage couples through an isolated transformer with the desired turns ratio to obtain the right voltage level at the output. This voltage is then rectified by the sync FETs back to dc. The sync FETs also require gate drivers to control their switching. Current and/or voltage sensors monitor the output and provide feedback to the controller for fine tuning the modulation scheme for maximum performance.

 

Download and read the complete white paper here.