For a majority of applications implemented today, the Intermediate Bus Architecture has been the preferred power architecture. This power architecture has led to the development of the isolated, fixed ratio DC-DC converter known as the intermediate bus converter (IBC). Fixed ratio bus converters that employ a new power topology – known as the Sine Amplitude Converter – offer dramatic improvements in power density, noise reduction, and efficiency over existing semi-regulated and regulated IBC products.
Typically the IBA distributes semi-regulated 38-55 voltage range, therefore taking advantage of reduced distribution losses by means of an isolated, non-regulated bus converter. This voltage is reduced by a factor of 4 (or 5).
This intermediate 9.5-13.75V bus enables non-isolated Point-Of-Load converters to provide final step down and regulation function at the same time. These functions present some trade-offs, which need to be considered, for example:
- DC step-down ratio vs. efficiency
- Load voltage vs. efficiency
- Batterycell number and size vs. backplane voltage range
- Bus conductor size and current level versus losses
Moreover, recent trends on adoption of HighVoltage DC infrastructure distribution instead of standard AC line add an extra dimension.
To deal with the multiplicity of low voltages, IBA turned to niPOLs (non-isolated buck step down regulators), reducing the POL function to regulation from a low voltage bus.
IBA uses an “Intermediate Bus Converter” to transform the 48V bus to an intermediate bus voltage, typically 12V. This relatively low voltage is compatible with using “buck” type, step down switching regulators to supply POL voltages.
But, lacking voltage transformation, niPOLs bring about an inherent conflict, rooted in fundamental physics, between efficient power distribution and efficient power conversion duty cycle.
Because the niPOLs reduce costs by foregoing isolation, IBA architectures can offer cost-effective solutions. However the niPOLs’ lower costs are also partly due to their limited voltage transformation ratio, which means IBCs must have lower output voltages – typically 12 V – and be located close together to avoid I²R losses across the PCB. The niPOLs’ lack of isolation makes overvoltage-sensitive loads vulnerable to serious faults and the entire system to ground loop problems. The niPOLs’ ability to respond to dynamic loads is also limited by inductive inertia
Find out more in part 2. In the meantime, you may also be interested in hearing Tom Curatolo, our director of applications engineering, discuss the challenges faced by today’s power system designers and the advantages of the various power architectures. Listen to the rebroadcast of our web seminar, “The Three Approaches to Power”.