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# Pulsiv nomogram simplifies discontinuous fly-back converter design

Pulsiv, a Plymouth University spin-out that specialises in power electronics technology, has announced the development of a nomogram that will help design engineers to determine critical transformer parameters in DCM flyback designs.

An intuitive tool, it can be used to replace more complex equation-based methods, providing a fast and accurate visual process for identifying primary side inductance and minimum duty cycle.

In terms of using the Pulsiv nomogram there are four steps.

Step 1:  Switching frequency & maximum duty cycle

Note the switching frequency and maximum duty cycle of your chosen flyback controller.

Step 2:  Peak current & minimum operating voltage

Select the required peak current (based on the output power) and minimum flyback operating voltage.

Step 3:  Primary side inductance & minimum duty cycle

Draw straight lines across the nomogram to identify suitable values for primary side inductance (for the DCM flyback) and minimum duty cycle (based on the maximum flyback operating voltage).

Step 4:  Check the flyback controller datasheet

According to Pulsiv, it is important to check the flyback controller datasheet to ensure that the minimum duty cycle, calculated from Step 3, can be achieved. Some controllers change the switching frequency based on the operating voltage of the flyback, and this must be considered when using the nomogram to determine the minimum duty cycle.

“The field of nomography was invented in 1884 by French engineer and mathematician, Philbert Maurice d’Ocagne to provide engineers with a precise and practical method for calculating complicated formulas using a parallel coordinate system. Results from a nomogram are obtained quickly and reliably by simply drawing one or more lines, without needing to solve algebraic equations," said Pulsiv.

DCM flybacks are used in low to medium power designs where isolation is required. They are often paired with a boost PFC front-end stage with significant switching losses under low load conditions and poor average efficiency.

Pulsiv has a patented switching technique that applies intelligence to an active valley fill approach for converting AC to DC. The company’s OSMIUM technology offers several advantages:

• A front-end efficiency of 97.5% (99.5% peak) and 90% at 2W
• A totally flat efficiency profile across the entire load range
• Input voltage derating is eliminated
• Inrush current is eliminated
• Extending the range of single-switch flybacks to 180W
• Meeting the latest ecodesign regulations

According to Pulsiv, its OSMIUM technology can improve the efficiency of flyback converters by reducing the peak operating voltage reducing primary side inductance and leakage inductance while increasing the total winding area, enabling engineers to select a smaller transformer core size, while reducing overall weight and cost.