1. Overall Circuit Design & Purpose

️· This documentation details the design of a flyback power supply using a Power Integrations TinySwitch-II (TNY266) controller.
️· Input: 85-265VAC (Universal Input)
️· Output: 7.8VDC at 5.26W (This appears to be a regulated output).
️· Efficiency: Target of approximately 70%.
️· The design focuses on creating a compact and efficient power supply suitable for applications requiring a low-voltage, relatively low-power output.

2. Key Components & Specifications

️· TinySwitch-II (TNY266): The heart of the design. It's a primary-side switched-mode controller optimized for low-power flyback converters. Key specs:
- Switching Frequency (fS): 132kHz
- Minimum Current Limit: 325mA
- Maximum Current Limit: 375mA
️· Transformer: A custom-designed flyback transformer is critical. Important parameters in the datasheet:
- Core Type: EE13
- Effective Area (AE): 0.171 cm²
- Effective Path Length (LE): 3.02 cm
- Primary Turns (NP): 77
- Secondary Turns (NS): 8
- Primary Inductance (LP): 1114 uH
️· Diode: Fast recovery diode is used for rectification on the secondary side.

3. Transformer Design Details

️· The transformer design is a significant part of the documentation. The spreadsheet includes calculations for:
- Core parameters (AL, AE, LE).
- Inductance (Primary, Leakage).
- Flux Density (Bm). Important Note: The documentation *highlights that the calculated Bm value (3167 Gauss) is high*. This suggests potential saturation issues. The designer notes the need to *reduce* this, potentially by increasing the number of secondary turns, selecting a larger core, or choosing a different TinySwitch with a lower current limit.
- Turns Ratio: Calculated based on the desired output voltage and input voltage range.

4. Design Considerations & Calculations

️· Efficiency: The design targets around 70% efficiency. The spreadsheet factors in losses due to switching, core, and conduction.
️· Current Limiting: The TinySwitch-II's current limit is a crucial design parameter. It sets the upper bound on the primary current.
️· Duty Cycle: The spreadsheet calculates the duty cycle of the switching waveform.
️· Flux Density (Bm): As noted above, this is a critical parameter to monitor to avoid core saturation.
️· Ripple Current: Calculations for primary ripple current are also performed to ensure proper circuit operation.

5. Key Design Parameters for the Transformer

Parameter	Value
Core Type	EE13
Effective Area (AE)	0.171 cm²
Effective Path Length (LE)	3.02 cm
Primary Turns (NP)	77
Secondary Turns (NS)	8
Primary Inductance (LP)	1114 uH
Flux Density (Bm)	3167 Gauss (potentially too high)

6. Circuit Operation (Inferred)

️· The TinySwitch-II operates as a primary-side controller, generating a PWM signal to drive the primary winding of the flyback transformer.
️· Energy is stored in the transformer core during the on-time of the switch.