POWER AND LINEAR IC SOLUTIONS

Reference Design for LED-Based MR16-Compatible Lamps

Zetex Semiconductors has developed a novel dedicated chipset and reference design for MR16-compatible LED lamps. Reducing the component count of existing solutions by up to 50%, the chipset significantly decreases the size of the required driver circuitry and the overall cost of lamp manufacture.

Designed to fit into the base connector space within the neck of the lamp, the highly integrated MR16 chipset handles all the required power rectification and LED current control. It consists of two key devices, the ZXLD1350 monolithic LED Driver and the ZXSBMR16PT8 full bridge.

The ZXSBM16PT8is a thermally efficient device that also includes a freewheeling diode and is designed for LED current drive applications of up to 350mA. Realised using extremely low leakage 1A, 40V Schottky diodes, the device delivers much higher efficiency levels than standard silicon diodes, whilst retaining a compact form factor. It allows operation at a nominal 12VAC input level.

The ZXLD1350 provides a cost-effective die size and contains an internal 30V, 400mA NDMOS switch. This rating, combined with its hysteretic mode of operation (the reference-design inductor-current waveform will ramp ±15% about the nominal current set point) provides sufficient margin for MR16 type applications. The device can accommodate a wide input voltage range from 7V to 30V, can switch at up to 1MHz and provides high power efficiency ratings of more than 90%.



Because the ZXLD1350 has a hysteretic switching topology, the switching frequency is dependent on several factors including input voltage, target current and number of LEDs. Zetex provides a spreadsheet-based calculator for initial system evaluation and component choice.

Lighting manufacturers are increasingly looking to LED technology to provide much longer lifetime and greater energy efficiency than traditional halogen technology. Designing the driver electronics for such products, however, is demanding. Zetex created the MR16 reference design 'top-down', to provide both efficiency and ease of manufacture.

In addition to the ZXLD1350 and ZXSBMR16PT8, the design includesa bill of materials for the required associated passive devices and a circuit board layout. The driver design can be used with up to three 1W LEDs and includes facilities to bypass the bridge rectifier should the final lamp design be used for purely DC operation. However, the bridge should still be used if the power supply can be reversed. As standard, the reference specifies use of a 100µH screened inductor that sets the nominal frequency to around 250kHz, while minimising radiated EMI.

As with any switching regulator, circuit board layout is crucial to reducing radiated EMI: the design keeps critical track lengths to a minimum and maximises ground areas around such tracks.

Features

• Chipset and reference design for driving MR16 LED lamps
• Reduces component count by up to 50%
• Fits within the neck of the lamp
• Full bill of materials and circuit layout
• Can drive up to three 1W LEDs
• Up to 350mA drive current
• Low leakage 1A, 40V Schottky diodes
• Nominal 12V AC input level.
• Hysteretic switching topology
• Spreadsheet-based calculator allows initial system evaluation and component choice
• Bridge rectifier can be bypassed for purely DC operation
• Nominal 250kHz switching frequency

Applications

• Directional lighting
• Residential
• Retail
• Office

For further information, including the MR16 Datasheet, please click here