Semiconductor Group

58

TDA 4605-2

Circuit Description

Application Circuit

The application circuit shows a flyback converter for video recorders with an output power rating of

70 W. The circuit is designed as a wide-range power supply for AC-line voltages of 180 to 264 V.

The AC-input voltage is rectified by the bridge rectifier GR1 and smoothed by

the rush-in current.

The IC includes an internal circuit to avoid the turn-on of the power transistor T1 because of static

charges applied to the transistors gate, during the turn-off state of the IC. The resistor

limit the spectrum of the radiated noise.

During the conductive phase of the power transistor T1 the current rise in the primary winding

depends on the winding inductance and the mains voltage.

The network consisting of

collector current. The resulting control voltage is fed into pin 2 of the IC. The RC-time constant given

by

The ratio of the voltage divider

switching power supply shall stop operation because of the low mains voltage. The control voltage

present at pin 3 also determines the correction current for the foldback point.

This current added to the current flowing through

order to reduce the turn-on phase of T1. This is done to stabilize the fold-back point even under

higher mains voltages.

The control of the switched-mode power supply is done by means of a control voltage applied to

pin 1. The control voltage of winding

and stepped down at an adjustable ratio by

by the IC so that the voltage applied across the control winding, and hence the output voltages, are

at the desired level.

When the energy stored in the transformer is transferred into the load the control voltage passes

crossings of the control voltage can also be produced by ringing of the transformer after the turn-off

of the power transistor for T1 or when a short-circuit is applied to the output of the SMPS.

The capacitor

a shorter duty cycle in order to keep the operating frequency outside the audible frequency range.

On the secondary side of the transformer 3 output voltages are produced using the windings

the resistors with implemented fuse

output circuits, which are designed to supply only small loads.