ON Semiconductor Introduces Reference Design for 40W (normal) and 80W (peak) Printer Power Supplies
ON Semiconductor unveiled its latest GreenPoint™ reference design – this one for 40W power supplies used to power desktop printers. The design is a blueprint which the company claims will help engineers quickly deliver power adapters to market that provide both low active-mode and low standby-mode power consumption.
Providing active-mode energy efficiency above 83% when delivering an output power between 5 and 40W, this reference design achieves a no-load power consumption of <150mW. Typical 40W printers in use today consume on average 450mW in similar conditions. The frequency foldback technique implemented in the design, keeps the efficiency of the power supply very high under light load conditions. (e.g. with an output power from 0.5 to 2W, the efficiency varies from 66 to 79%). The combination of these characteristics makes this GreenPoint™ reference design compliant with the most stringent requirements from ENERGY STAR® to the Group for Energy Efficient Appliances (GEEA) via the US Executive Order "1-Watt Standby" Order and the Japanese Eco Mark program.
The new 40W reference design enables a peak power of 80W to be transiently delivered – a feature that makes it particularly suitable for printer applications. An over power protection below 100W has been implemented for the entire input voltage range (88 ~ 265Vac) to comply with the Limited Power Source (LPS) test. In addition, the design uses a smaller bulk capacitor than those typically utilized in 40W power adapter designs with similar performance. This helps reduce both board space and the overall system cost.
The enabling device for the 40W reference design is the newly introduced NCP1351, a current mode controller targeting low power off-line flyback Switched Mode Power Supplies (SMPS). Based on a fixed peak current technique (quasi fixed TON), the controller decreases its switching frequency as the load becomes lighter. As a result, a power supply using the NCP1351 naturally offers excellent no-load power consumption, while optimizing the efficiency in other loading conditions. When the frequency decreases, the peak current is gradually reduced down to approximately 30% of the maximum peak current to prevent transformer mechanical resonance. The risk of acoustic noise is thus greatly diminished while keeping good standby power performance.
An externally adjustable timer permanently monitors the feedback activity and protects the supply in the presence of a short circuit or an overload. Once the timer elapses, NCP1351A and NCP1351C stop switching and stay latched, while NCP1351B and NCP1351D attempt restart. Both NCP1351C and NCP1351D feature a dual over current protection, a better fit for applications facing large output power transients. The internal structure of the device features an optimized arrangement which allows one of the lowest available startup currents, a fundamental parameter when designing low standby power supplies. The negative current sensing technique minimizes the impact of the switching noise on the controller operation and allows the user to select the maximum peak voltage across the current sense resistor. Power dissipation can then be optimized for the application.
The NCP1351 A, B, C and D are all offered in Pb-free SOIC-8 packages, and are priced at $0.32 per unit in 2,500 unit quantities.
