Engineering Trends in Power Supplies to Reduce Environmental LoadImproving the Efficiency of AC-DC Converters through Synchronous Rectification

－Well then, could you please explain some specific solutions.

ROHM has developed the BM1R001xxF series of controller ICs which resolve the problem of synchronous rectification in AC-DC converters. They support all modes, from discontinuous through critical to continuous, and a special protection circuit is unnecessary even when used in continuous mode operation. They can also be used in PWM converters, and make possible stable synchronous rectification operation.

The BM1R001xxF series basically offers synchronous control of external MOSFETs which replace the rectifying diodes of a diode rectification type circuit and an output setting circuit that includes a shunt regulator. I think circuit examples will make this easy to understand.

In the BM1R001xxF series, the synchronous rectification control unit and the shunt regulator unit are configured to be independent. The synchronous rectification control unit automatically enters a sleep mode under no-load conditions to reduce the operating current. The shunt regulator unit achieves a small 40 μA operating current, far lower than that of an individual shunt regulator. In a comparison of ROHM products, the no-load power consumption was reduced by 25 mW or more over systems using general-purpose shunt regulator ICs with diode rectification.

－And what is the efficiency like?

Here are graphs that compare the efficiency with diode rectification methods.

In a comparison of ROHM products, an efficiency improvement of 3% or more was confirmed for power modules overall compared with conventional diode rectification.

The graph on the left compares 115 VAC input products. The efficiency with the diode rectification method is not low at all, but with synchronous rectification a high efficiency of up to 91% is attained, for an improvement of 4% or more over the diode rectification design. The graph on the right compares efficiencies for 230 VAC input. Because the input voltage is higher, the efficiency is somewhat lower, being from somewhat below 88% to higher percentage, higher than the efficiency for diode rectification at 115 VAC. The efficiency improvement with synchronous rectification is up to 3% or more.

－As a whole, do synchronous rectification AC-DC converters that use BM1R001xxF series products meet the U.S. regulations that you mentioned earlier?

Strictly speaking, evaluations under the required conditions are needed, but as the graphs of efficiency presented above indicate, high efficiency levels that cannot be attained using diode rectification methods are achieved, so we believe that our products will enable customers to meet these regulation standards.

－Well then, allow me to ask about the other issue, “industrial waste”.

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