Isolated power supply control ICs combine power savings & reliability

3rd October 2016
Barney Scott

ROHM has announced isolated flyback-type DC/DC converter control ICs for Auxiliary Supply in High Power Industrial equipment such as FA/solar inverters and power storage systems. Following the BD7F100, the company now expands the series with the BD7F200, covering all applications with a power requirement from 1 to 10W, and including two different packaging options. In addition, ROHM introduces a BD7F100 evaluation kit that facilitates the design of flyback isolated applications.

Isolation is almost always built into electronic equipment to provide protection against shock and damage. With this respect, a broad range of applications such as power metering, industrial programmable logic controllers (PLCVs), Industrial Fieldbus, Industrial automation, insulated-gate bipolar transistor (IGBT) and SiC MOSFET gate drivers require isolated DC/DC converters. These devices provide galvanic isolation, improve safety and enhance noise immunity to the systems. With them it is possible to generate multiple output voltage rails and dual polarity (positive and negative) rails. High voltage, high power industrial applications (including power storage systems and solar inverters which are seeing increased adoption) are no exception, requiring even more stringent reliability demands due to the harsher temperature conditions and the need for continuous, long-term operation.

Conventional solutions utilize an optocoupler and other components for flyback-type isolated power supply control for the feedback  loop.

However, this generates challenges associated with current consumption and reliability (including circuit scale and product life). The BD7F series, thanks to its optocoupler-less architecture, allows designers to simplify the development of the transformer and to reduce costs.

It decreases the number of external parts by nearly half by eliminating the need for a photocoupler and a phase compensation network, providing greater energy savings, reliability, and miniaturization. In addition, a newly developed adaptive ON time control method is used to improve load response time (a drawback of conventional isolated power supply ICs), while voltage fluctuation during the load transient is limited to under 200mV, contributing to even higher reliability. Various protection functions add to it as well.

The BD7F series of isolated power supply control ICs are optimized for industrial equipment requiring continuous, long-term operation under extreme conditions. Utilizing state-of-the-art power BiCDMOS processes and leveraging proprietary advanced analog technology allow ROHM to detect the secondary side voltage and current from the primary side. This eliminates the need for an optocoupler or tertiary transformer winding required with conventional configurations, reducing the number of external parts by half which contributes to greater reliability, power savings, and end-product miniaturization.

ON time control, typically used in conventional isolated power supply control ICs, is adopted to minimize output voltage fluctuations caused by instantaneous changes in load current.

ROHM’s new adaptive ON time control method limits output voltage fluctuations to 200mV, 65% less than conventional solutions (at a load current of 1A and rise time of 100us). As a result, load response against instantaneous load current fluctuations is improved, increasing reliability considerably.

In addition to the control ICs, an evaluation board (BD7F100HFN-EVK-001) is offered integrating the BD7F100HFN-LB, making it easy to evaluate isolated power supply operation (24V input, 5V/800mA output). Moreover ROHM Semiconductor GmbH is preparing CE certified 6 variant evaluation boards (BD7F100HFN-EVK-30x) in October 2016.

In order to offer further support to designers during the device evaluation, and consequentially, in the application design phase, ROHM is also releasing a new evaluation kit BD7F100HFN-EVK-001, implementing the BD7F100HFN and featuring 6 different input and output configurations.

Samples, along with this evaluation board, will be available for purchase. This board enables to be designed for 24V input voltage and 5V output voltage with output current range of 13.8mA to 800mA for maximum output power of 4W. Due to its fully controlled supply chain, ROHM can guarantee long-term availability.

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