FEATURES
* Green-Mode PWM
* Supports the “Blue Angel” Standard
* Low Start-up Current (9uA)
* Low Operating Current (3mA)
* Leading-Edge Blanking
* Constant Output Power Limit
* Universal Input
* Built-in Synchronized Slope Compensation
* Current Mode Operation
* Cycle-by-cycle Current Limiting
* Under Voltage Lockout (UVLO)
* Programmable PWM Frequency with Frequency Hopping
* VDD Over Voltage Protection (Auto Restart)
* Gate Output Voltage Clamped at 17V
* Low Cost
* Few External Components Required
* Small SOT-26 and Dip 8 Packages

APPLICATIONS
General-purpose switching mode power supplies and flyback power converters, such as
* Battery chargers for cellular phones, cordless phones, PDAs, digital cameras, and power tools
* Power adapters for ink jet printers, video game consoles, and portable audio players
* Open-frame SMPS for TV/DVD standby and other auxiliary supplies, home appliances, and consumer electronics
* Replacements for linear transformers and RCC SMPS
* PC 5V standby power.

DESCRIPTION
This highly integrated PWM controller provides several special enhancements designed to meet the low standby-power needs of low-power SMPS. To minimize standby power consumption, the proprietary green-mode function provides off-time modulation to linearly
decrease the switching frequency under light-load conditions. This green-mode function enables the power supply to easily meet even the strictest power conservation requirements.
The BiCMOS fabrication process enables reducing the start-up current to 9uA, and the operating current to 3mA. To further improve power conservation, a large start-up resistance can be used. Built-in synchronized slope compensation ensures the stability of peak current
mode control. Proprietary internal compensation provides a constant output power limit over a universal AC input range (90VAC to 264VAC). Pulse-by-pulse current limiting ensures safe operation even during short-circuits.
To protect the external power MOSFET from being damaged by supply over voltage, the SG6859’s output driver is clamped at 17V. SG6859 controllers can be used
to improve the performance and reduce the production cost of power supplies. The SG6859 is the best choice for replacing linear and RCC-mode power adapters. It is available in 8-pin DIP and 6-pin SOT-26 packages.

SG6859TZ
SG6859DZ

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Design Highlights
• Extremely low component count
• High efficiency – 85% using Schottky rectifiers
• No current sense resistor or transformer required
• Accurate input under/over voltage meets ETSI standards
• Operates to zero load with no pre-load required
• Output overload, open loop and thermally protected
• 400 kHz operation minimizes size of magnetics

Operation

DPA-Switch greatly simplifies the design compared to a discrete implementation. Resistor R1 programs the input under/over voltages to 33 V and 86 V, respectively. Including tolerances
these thresholds guarantee the converter is operational between 36 V and 75 V, without the cost of additional line sense components.
Resistor R3 programs the internal current limit of the DPA425R to 50% of nominal. The larger DPA-Switch selection reduces conduction losses, raising efficiency without circuit changes or increased overload power.
Zener VR1 clamps leakage inductance spikes, keeping the DRAIN voltage below BVDSS. The bias supply for U1 is provided from an auxiliary flyback transformer winding.
On the secondary, a snubber across D2 (C9, R5 and R13) limits the secondary leakage inductance spikes generated by diode reverse recovery. Inductor L2, C13 and C14 form a
post-filter to reduce high frequency output switching ripple. A soft-finish network, C18, D3 and R7, eliminates output turn-on overshoot. The remaining components provide output voltage regulation and loop compensation.

Key Design Points
• For nominal under-voltage set point VUV: R1 = (VUV-2.35 V)/50μA. VOV = (R1×135 μA)+2.5 V.
• Zener VR1 voltage is 130 V to safely limit the DRAIN voltage below VDSS of 200 V.
• Opto U2 should have a CTR of between 100% and 200% for optimum loop stability.
• Set resonance of L2 and C13 + C14 to beyond loop crossover frequency (typically 5% to 10% of switching frequency).
• Good layout practices should be followed:
- Locate C5, C6 and R4 close to U1, with grounds returned to the SOURCE pin.
- Primary return should be connected to the DPA-Switch tab, not the SOURCE pin.
- Minimize the primary and secondary loop areas to reduce parasitic leakage inductance.


DPA425R

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The STR-A6259H is a 100 kHz PWM topology (with ±5% frequency jittering for minimum EMI) regulator specifically designed to satisfy the requirements for increased integration and reliability in flyback converters. It incorporates a primary control and drive circuit with an avalanche-rated power MOSFET.

 Covering the power range from below 17 watts for a 230 VAC input, or to 13 watts for a universal (85 to 264 VAC) input, this device can be used in a wide range of applications,
from DVD players and VCR player/recorders to ac adapters for cellular phones and digital cameras. An auto-burst standby function reduces power consumption at light load, while multiple protections, including the avalanche-energy guaranteed MOSFET, provide high reliability of system design.

 Cycle-by-cycle current limiting, undervoltage lockout with hysteresis, overvoltage protection, and thermal shutdown protect the power supply during the normal overload and fault conditions.
Overvoltage protection and thermal shutdown are latched after a short delay. The latch may be reset by cycling the input supply.

 Low start-up current and a low-power standby mode selected from the secondary circuit completes a comprehensive suite of features. It is provided in an 8-pin mini-DIP plastic package with pin 6 removed. The leadframe plating is pure Sb, and the package complies with RoHS.

FEATURES AND BENEFITS
•100 kHz PWM with ±5% frequency jittering for EMI noise filtering cost reduction
•Rugged 650 V avalanche-rated MOSFET:
- Simplified surge absorption
- No VDSS derating required
•Low RDS(on) : 6 Ω maximum
•Auto-burst mode for stand-by operation or light loads; less transformer audible noise
•Built-in leading edge blanking
•Soft start and low start-up current; start-up circuit disabled in operation
•Auto-burst stand-by (intermittent operation) input power <0.1 W at no load
•Built-in constant-voltage/constant current (CV/CC)
•Multiple protections:
- Pulse-by-pulse overcurrent protection (OCP)
- Overload protection (OLP) with auto restart
- Latching overvoltage protection (OVP)
- Undervoltage lockout (UVLO) with hysteresis
- Latching thermal shutdown (TSD)

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