Lighting Power Controllers

Apr 6, 2009 12:11 PM

Texas Instruments' UCC28810 and UCC28811 are general lighting power controllers for low to medium power lumens applications requiring power factor correction and EMC compliance. It is designed for controlling a flyback, buck or boost converter operating in critical conduction mode. It features a transconductance voltage amplifier for feedback error processing, a simple current reference generator for generating a current command proportional to the input voltage, a current-sense (PWM) comparator, PWM logic and a totem-pole driver for driving an external FET.

In the critical conduction mode operation, the PWM circuit is self-oscillating with the turn-on being governed by a transformer zero energy detector (TZE pin) and the turn-off being governed by the current sense comparator. Additionally, the controller provides features such as peak current limit, restart timer, overvoltage protection (OVP), and enable.

The efficient system performance is attained by incorporation of zero power detect function which allows the controller output to shut down at light load conditions without running into overvoltage. The device also features an innovative slew rate enhancement circuit which improves the large signal transient performance of the voltage error amplifier. The low start-up and operating currents of the device result in low power consumption and ease of start-up. The highly-accurate internal bandgap reference leads to tight regulation of the output voltage in normal and OVP conditions, resulting in higher system reliability. The enable comparator ensures that the controller is off if the feedback sense path is broken or if the input voltage is very low.

There are two key parametric differences between UCC28810 and UCC28811, the UVLO turn-on threshold and the gM amplifier source current. The UVLO turn-on threshold of the UCC28810 is 15.8 V and for the UCC28811 it is 12.5 V. The gM amplifier source current for UCC28810 is typically 1.3 mA, and for the UCC28811 it is 300µA. The higher UVLO turn-on threshold of the UCC28810 allows quicker and easier start-up with a smaller VDD capacitance while the lower UVLO turn-on threshold of UCC28811 allows operation of the critical conduction mode controller to be easily controlled by the downstream PWM controller in two-stage power converters. The UCC28810 gM amplifier also provides a full 1.3-mA typical source current for faster start-up and improved transient response when the output is low either at start-up or during transient conditions. The UCC28811 is suitable for applications such as street lights and larger area luminaires where a two-stage power conversion is needed. The UCC28810 is suitable for applications such as commercial or residential retrofit luminaires where there is no down-stream PWM conversion and the advantages of smaller VDD capacitor and improved transient response can be realized.

Devices are available in the industrial temperature range of 40°C to 105°C. Package offering is an 8-pin SOIC (D) package.

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