Circuit Ideas

Circuit Designs present tips and tricks for solving problems of interest to power supply designers. Here is where PI Applications Engineers turn their training and experience into practical circuit designs that can be employed to quickly and straightforwardly address problems of the sort that working designers often encounter.

Note: These ideas are presented for informational purposes only and Power Integrations makes no warranty herein expressed or implied.

Active Shunt Regulator and Pre-Load

For multi-output power supplies, an active shunt regulator and pre-load circuit may be used to prevent rising output voltages under unbalanced loading conditions.

Buffered Line Sense Resistors

A scaling buffer circuit for sensing a high DC input voltage is shown. The circuit can be used with a power converter controller.

Core Coupled Foil and Capacitance for Reduction of Common Mode Current

Reduction of common-mode current in the input lines may be achieved by attaching copper foil between the core of the transformer and the switching node of a power switch. Further reduction can also be achieved by connecting a capacitor between an input-referenced bias winding and a copper foil attached to the core of the transformer.

Ferrite Magamp on Flyback PS

For a dual output flyback power supply, a ferrite magamp is used to regulate within tolerances levels when one output goes to no-load.

Improved PFC Feedback Loop

An improved feedback loop process is introduced for power factor correction (PFC) controllers in single-stage AC-DC power converters. It reduces external component count and simplifies end-user tuning for the external components of error compensation.

Phase Controlled Active Filter for an LED Driver

LED driver with a controlled active filter which is activated by a secondary-side phase detection circuit to enable the controlled active filter during low conduction angles of a dimmer circuit, such as a TRIAC dimmer. The controlled active filter can reduce shimmer and flicker of an LED load due to the asymmetry of TRIAC dimmers.

The controlled active filter can be used with single-staged LED drivers with power factor correction (PFC).

Primary-Side Control for CCM Flyback PS

A primary-side controller for an isolated flyback power supply operating in continuous conduction mode (CCM) may use a primary-side winding to sense and to regulate the output voltage.

Primary-Side Control for DCM Flyback PS

A primary-side controller for an isolated flyback power supply operating in discontinuous conduction mode (DCM) may use a primary-side winding to sense and to regulate the output voltage.

V Pin Protection Circuit

A controller may use an internal clamp circuit that conducts current from the V pin to prevent damage to the internal ESD (electrostatic discharge) protection structure.