SG6848T

The SG6848 is a highly integrated PWM controller designed for low-power switching-mode power supplies and flyback converters.

It incorporates several functions intended to reduce standby power consumption.

The proprietary Green Mode function uses off-time modulation to linearly reduce the switching frequency under light-load conditions, significantly reducing standby power consumption.

The BiCMOS process allows a very low 5 µA start-up current and approximately 2 mA operating current. This makes it possible to use a high-value start-up resistor.

Built-in synchronized slope compensation provides stable peak-current-mode control.

Internal compensation provides a relatively constant output power limit over the universal 90 VAC to 264 VAC input range.

Cycle-by-cycle current limiting provides protection during overload and short-circuit conditions.

The SG6848 Gate output is internally clamped to approximately 15 V, protecting the external power MOSFET from excessive gate-drive voltage.

Features

• Green-Mode PWM
• Blue Angel standard support
• 5 µA low start-up current
• 2 mA low operating current
• Leading-Edge Blanking
• Constant output power limit
• Universal AC input
• Built-in synchronized slope compensation
• Current-mode operation
• Cycle-by-cycle current limiting
• Under-Voltage Lockout (UVLO)
• Programmable PWM frequency
• 15 V Gate-output clamp
• Low external component count
• Low-cost implementation
• 8-pin DIP and 6-pin SOT-26 packages

Applications

• General-purpose SMPS
• Flyback power converters
• Cellular-phone chargers
• Cordless-phone chargers
• PDA and digital-camera power supplies
• Power-tool chargers
• Ink-jet printer adapters
• Video-game-console adapters
• Portable-audio power supplies
• TV/DVD standby supplies
• Auxiliary supplies for consumer electronics
• Replacement for linear transformer supplies
• Replacement for RCC SMPS
• PC 5 V standby supplies

Practical repair summary

For a non-starting SG6848 Flyback supply, the most important checks are:

VCC → start-up resistor → VCC capacitor → MOSFET → current-sense resistor → transformer primary → feedback circuit.

A failed MOSFET, dried VCC capacitor, increased start-up resistor, damaged current-sense circuit, or faulty feedback loop can all result in the same symptom: no startup or repeated startup attempts.

Tags: SG6848T, SG6848, PWM Controller, Green Mode, Flyback, 70kHz, SOT-26, SMPS, Power Supply Controller