BACKGROUND

Isolated converters refer to converters that provide full galvanic isolation between input and output circuits using a power transformer with a primary winding and a secondary winding. Some isolated converters use a power transformer with an auxiliary winding separate from the secondary winding to supply power (a bias supply voltage) to control circuitry (e.g., a pulse-width modulation controller) for one or more isolated converter switches. For isolated converters with wide output voltage range (e.g., a USB power delivery adapter or light-emitting diode driver), it is challenging to provide a usable bias supply voltage to the control circuitry directly from the auxiliary winding of the power transformer. This is because some regulation circuitry is needed to provide a usable bias supply voltage in a wide output voltage range scenario, which undesirably increases cost, size, and power consumption of the converter. Previous regulation circuitry options to supply power to control circuitry of an isolated converter using an auxiliary winding of the power transformer are lossy and increase the controller cost with a higher voltage rating in order to handle the higher rectified positive auxiliary winding voltage at the high output voltage condition.

SUMMARY

In accordance with at least one example of the disclosure, a system comprises an isolated converter having a power transformer with a primary winding, a secondary winding, and an auxiliary winding. The isolated converter also comprises a first switch coupled to the primary winding and a switch controller coupled to the first switch. The isolated converter also comprises a bias power regulator circuit coupled to the auxiliary winding and the switch controller, wherein the bias power regulator circuit includes a second switch. The bias power regulator circuit is configured to provide a bias supply output voltage to the switch controller based on a first set of modes that modulate a switching frequency of the second switch and based on a second mode in which the second switch stays off.

In accordance with at least one example of the disclosure, a control circuit for an isolated converter with a power transformer having an auxiliary winding is provided. The control circuit comprises a bias supply input node and a bias supply output node. The control circuit also comprises a pulse-width modulation (PWM) controller coupled to the bias supply output node. The control circuit also comprises a bias power regulator circuit between the bias supply input node and the bias supply output node. The bias power regulator circuit comprises a forward path between the bias supply input node and the bias supply output node. The bias power regulator circuit also comprises a switch coupled between the forward path and a ground node. The bias power regulator circuit also comprises a modulation circuitry coupled to a control terminal of the switch. The bias power regulator circuit also comprises a mode controller coupled to the modulation circuitry.

In accordance with at least one example of the disclosure, an integrated circuit comprises an isolated converter switch control node, an auxiliary winding node, and a bias supply voltage node. The integrated circuit also comprises an isolated converter switch controller coupled to the bias supply voltage node and the isolated converter switch control node. The integrated circuit also comprises a bias power regulator circuit coupled to the auxiliary winding node and the bias supply voltage node, wherein the bias power regulator circuit comprises a switch. The bias power regulator circuit is configured to provide a bias supply voltage to the isolated converter switch controller based on a plurality of modulation modes that modulate a switching frequency of the switch and based on a forward mode in which the switch stays off.

In accordance with at least one example of the disclosure, an integrated circuit comprises a bias supply input node and a bias supply output node. The integrated circuit also comprises a bias power regulator circuit between the bias supply input node and the bias supply output node. The bias power regulator circuit comprises a switch. Also, the bias power regulator circuit is configured to provide a bias supply output voltage to the bias supply output node based on modulating a switching frequency of the switch if a voltage level at the bias supply input node is greater than a bias supply input threshold and based on using a forward path with the switch off if the voltage level at the bias supply input node is not greater than the bias supply input threshold.

