POWER AND LINEAR IC SOLUTIONS

Controllers Ease LED Drive Designs

The SGP100 controller from Fairchild Semiconductor allows designers to implement AC-input LED lighting systems without the traditional secondary-side control circuit and optocoupler. This reduces overall system cost and size, and simplifies safety standardisation.



LED applications with AC mains input require an electronic circuit to convert the AC input voltage into a constant current, usually 350mA, 700mA or 1A. In some applications there is an additional requirement that the load be isolated from the mains input.

One effective way of implementing this approach is to use a flyback converter with a constant current output. In most applications, a control circuit on the secondary side using an operational amplifier and a reference (or a dedicated control IC) regulates the constant current and sends the control information to the PWM controller on the primary side via an optocoupler.

In contrast, designs based on Fairchild´s SGP100 PWM controller removes the need for the secondary-side control circuit and also the optocoupler.

The SGP100 is a highly integrated PWM controller that provides several features to enhance the performance of low-power flyback converters. Its patented topology enables simplified circuit design for a range of applications, including display drivers and battery chargers. This produces lower cost, smaller and lighter products than can be implemented using a conventional design or a linear transformer.

To minimise standby power consumption, a proprietary green-mode function provides off-time modulation to decrease PWM frequency linearly under light-load conditions. This green-mode function allows the power supply to meet power conservation requirements. The start-up current is only 10µA for further power saving.

PWM Controller Specifications

Part No.	Constant Voltage Accuracy	Constant Current Accuracy	Status
SGP100	±10%	±10%	Released
FAN102	±5%	±5%	Sampling

Features

• Constant-Voltage (CV) and Constant-Current (CC) control without secondary-feedback circuitry
• Green-mode function: PWM frequency linearly decreasing
• Fixed PWM frequency of 42kHz with frequency hopping to solve EMI problems
• Low start-up current: 10µA (typical)
• Low operating current: 6.5mA (typical)
• Peak-current-mode control in CV mode
• Cycle-by-cycle current limiting
• OverVoltage Protection (OVP) with latch
• UnderVoltage LockOut (UVLO)
• Gate output maximum voltage clamped at 18V
• Fixed over-temperature protection with latch

Applications

• Lighting drivers
• Battery chargers for portable equipment

For further information, including the Fairchild SGP100 Specification Sheet, please click here