Simple SMPS, 85-265VAC Input with Output 12VDC @ 750mA

This compact Switch-Mode Power Supply (SMPS) is built around the TNY266 chip, offering a cost-effective solution for various applications, including power adapters and LED drivers. The SMPS consists of a bridge rectifier, a DC bus capacitor, the TNY266 switch IC, a rectifier diode, and a PC817 optocoupler for feedback and fault condition monitoring.

The board features screw terminals for easy connection of AC input and DC output, as well as an onboard LED indicator for output voltage. Notably, no auxiliary power is required to drive the chip, making it a highly efficient design.

A simple 4-pin transformer is used, which can be readily sourced from online marketplaces such as AliExpress and eBay. This makes it an ideal solution for DIY enthusiasts and professionals alike, looking for a reliable and affordable SMPS solution.

Features

• Power Input 85-265V AC
• Output 12V, 750mA (Output +/-5%)
• Screw Terminals for AC Input and DC Output
• Operating Switching Frequency 132Khz
• 4 x 4 mm Mounting Holes
• PCB Dimensions 69.06 x 25.88 mm

Transformer

• Primary winding 0.8mH, Turn ratio 90:10
• Magnetic Core EE16, with 6Pin Bobin, Pin 1, 3 + 4,6 (Pin 2, Pin 5 NC)
• Primary 4 in 6 out, 90T, 0.2mm, 0.8mH inductance
• Secondary 1 in 3 out, 11T, 0.5mmx2 double-wire winding

Chip Features

• Fully integrated auto-restart for short circuit and open loop fault protection – saves external component costs
• Built-in circuitry practically eliminates audible noise with ordinary dip-varnished transformer
• Programmable line undervoltage detect feature prevents power on/off glitches – saves external components
• Frequency jittering dramatically reduces EMI (~10 dB) – minimizes EMI filter component costs
• 132 kHz operation reduces transformer size – allows use of
• Very tight tolerances and negligible temperature variation on key parameters eases design and lowers cost
• Lowest component count switcher solution

Better Cost/Performance over RCC & Linears

• Lower system cost than RCC, discrete PWM and other integrated/hybrid solutions
• Cost effective replacement for bulky regulated linears
• Simple ON/OFF control – no loop compensation needed
• No bias winding – simpler, lower cost transformer
• Simple design practically eliminates rework in manufacturing

Tiny Switch™-II integrates a 700 V power MOSFET, oscillator, high voltage switched current source, current limit and thermal shutdown circuitry onto a monolithic device. The start-up and operating power are derived directly from the voltage on the DRAIN pin, eliminating the need for a bias winding and associated circuitry. In addition, the Tiny Switch-II devices incorporate auto-restart, line undervoltage sense, and frequency jittering. An innovative design minimizes audio frequency components in the simple ON/OFF control scheme to practically eliminate audible noise with standard taped/varnished transformer construction.

The fully integrated auto-restart circuit safely limits output power during fault conditions such as output short circuit or open loop, reducing component count and secondary feedback circuitry cost. An optional line sense resistor externally programs a line undervoltage threshold, which eliminates power down glitches caused by the slow discharge of input storage capacitors present in applications such as standby supplies. The operating frequency of 132 kHz is jittered to significantly reduce both the quasi-peak and average EMI, minimizing filtering cost.

Application Examples

The Tiny Switch-II is ideal for low cost, high efficiency power supplies in a wide range of applications such as cellular phone chargers, PC standby, TV standby, AC adapters, motor control, appliance control and ISDN or a DSL network termination. The 132 kHz operation allows the use of a low cost EE13 or EF12.6 core transformer while still providing good efficiency. The frequency jitter in Tiny Switch-II makes it possible to use a single inductor (or two small resistors for under 3 W applications if lower efficiency is acceptable) in conjunction with two input capacitors for input EMI filtering.  The auto-restart function removes the need to oversize the output diode for short circuit conditions allowing the design to be optimized for low cost and maximum efficiency. In charger applications, it eliminates the need for a second optocoupler and Zener diode for open loop fault protection. Auto-restart also saves the cost of adding a fuse or increasing the power rating of the current sense resistors to survive reverse battery conditions. For applications requiring undervoltage lock out (UVLO), such as PC standby, the Tiny Switch-II eliminates several components and saves cost.  Tiny Switch-II is well suited for applications that require constant voltage and constant current output.  As Tiny Switch-II is always powered from the input high voltage, it therefore does not rely on bias winding voltage. Consequently, this greatly simplifies designing chargers that must work down to zero volts on the output.

Connections

• CN1: Pin 1 = +12V DC Output, Pin 2 = GND
• CN2: Pin 1 = AC-L Input, Pin 2 = AC-N Input, (AC 85-265V Input)
• D1: Power LED

Schematic

Parts List

Connections

TNY266 Block Diagram

Gerber View

Photos

TNY266 Datasheet