Power Electronics

Power Supply Design Keeps LCD Monitor Standby Usage Under 80 mW

Power Integrations has published a new Design Engineering Report (DER-229) that details the design of a 27-watt power supply for LCD monitors and similar applications. Based on Power Integrations' TNY380PN, a member of the TinySwitch PK product family, the design is more than 80% efficient at full load under worst-case conditions. This 15 volt main output, 5-volt auxiliary output, power supply draws comfortably less than 80 mW input power when delivering 30 mW to the system in standby mode. Such ultra-low standby consumption ensures that there is ample power available for designers to incorporate remote ON/OFF functionality without exceeding the limits of several prominent OEM PC system integrators, and greatly exceeds the 1-watt specification of ENERGY STAR and the mandatory 500 mW requirement of the European Union Tier 2 Ecodesign Directive for Energy-Using Products (EuP).

TinySwitch-PK includes control and regulation functions that minimize power consumption at no-load. The IC also uses frequency jittering to reduce the size of the EMI (electromagnetic interference) filter, eliminating the need for X capacitors and their associated bleed resistors (required for safety compliance), which can themselves dissipate more than 30 mW.

The transformer used in DER-229 was designed using Power Integrations' popular PI Expert power supply design software to reduce parasitic losses between windings. High switching frequency at full load suppresses acoustic noise from the power supply and enables the use of very small magnetic components, making the new design ideally suited for slim form-factor LCD monitors and similar space-constrained applications.

Comments Andrew Smith, product marketing manager at Power Integrations: "Many information technology equipment OEMs are embracing the philosophy that if low standby is good, then really low standby is even better. By delivering a power supply with a no-load consumption of less than 80 mW, customers can easily meet all known standby power regulations and the most advanced market-driven requirements, while leaving a large power budget available for other circuit functions. The design is also highly efficient in normal operation, enabling PSUs that easily meet full-load efficiency requirements."

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