Figure 1: A switch-mode power supply driving a fixed load
can be designed and optimized specifically for that load.
Having said that, there are some applications that by their very nature surpass four channels. Moreover, some of these applications concern circuits and devices that are produced in extremely high volumes. A case in point is switch-mode power supplies, such as those typically found in notebook PCs, tablets, or embedded systems.
Figure 2: When power-supply loads vary, so does
efficiency, a scenario common in computing tasks.
NCP81141, a device with an Serial VID (SVID) interface for desktop and notebook CPU applications. SVID, by the way, is the communications protocol Intel concocted for its VR12/VR12.5 specification for PWM control.
In a fixed-load scenario, a switch-mode power supply may be purpose-built for the specific application and thus be highly efficient, on the order of >90% (Figure 1). A device like the NCP81141 would be employed to regulate the current delivered to the supply while maintaining a constant voltage.
Figure 3: A multi-phase switch-mode controller dynamically
switches in more phases are required to service
a variable load.
The answer to this is a multi-phase controller such as ON Semiconductor's NCP81140, which dynamically switches multiple phases in (or out) depending on load changes (Figure 3). The response from such a device to changing loads is very fast, whether it is adding phases to shore up current to increasing loads, or shedding them when a single phase is able to keep up with the power requirements. In this fashion, high efficiency is maintained across the load spectrum with a huge corresponding reduction in heat stress on the supply's components. Moreover, the circuit is scalable in terms of the number of phases and the output per phase.
|Figure 4: Proper debugging of this four-phase power supply|
circuit requires six oscilloscope channels
It gets even more complex when the power supply is for a server. Such power supplies call for six phases, so you'd be looking at eight channels. There are many other embedded applications for multi-phase switch-mode power supplies as well.
One example of an oscilloscope well suited for an application of this nature is Teledyne LeCroy's HDO8000 series, which sports eight analog input channels as well as 16 digital channels as an option.