This was achieved by having a green/active boot strap circuit internal to the control IC that was similar to that presented in Figure 2, which only dissipates/applies power to the controller during startup and turning off once the bias winding
of the transformer could deliver energy to power the control IC.
FSL206MRx Series Eliminates Auxiliary Bias Winding, Simplifies Design
The highly integrated PWM controller with avalanche-rugged SenseFET includes an internal regulator, eliminating the need for an auxiliary bias winding and includes a built-in high-voltage startup and full-protection circuitry that saves board space and total bill of material (BOM) costs.
If voltage increases at the output, it will result in increased voltage at the output of the bias winding across C10.
The power supply also features a time-triggered overload protection function which is sensed from the primary side bias winding.
TinySwitch-III also enables easy compliance with the most stringent standards for standby and no-load energy use, consuming less than 150 mW of no-load power without the use of a bias winding on the transformer.
New in TinySwitch-III Feature Benefit Selectable current Increased design flexibility -- three current limit limits available for each IC, allowing trade-offs between power output and efficiency/thermal rise Extended power Addresses universal-input power supplies with up to range 28 W of output, compared to 15 W for TinySwitch-II Even lower no-load Less than 150 mW at 265 VAC input without use of a consumption bias winding; Less than 50 mW achievable with bias winding On-time extension Typically reduces size of bulk capacitor required for low-line power delivery/hold-up time
Using the company's integrated EcoSmart technology, TinySwitch-II enables a power supply design with high standby efficiency and low noload power consumption of under 250 mW at 265V AC input without a bias winding
on the transformer.
The use of a transformer with a bias winding
further reduces no-load consumption to less than 50 mW.
By eliminating the separate bias winding
on the power supply transformer, system component cost is reduced compared to competitive switcher designs.
Once the circuit is started, the Vcc power for the IRIS4009 comes from the bias winding
of the main transformer.