Service manual

Standby Power Supply (Diagram A2)
This power supply is of a SOPS type (Self-Oscillating Power Supply) and is regulated
by the controlled switching of an oscillator. It uses the so-called 'Flyback' principle:
Figure: Flyback principle
• After closing switch 'S', the current ID will increase linearly in time. The magnetic
energy in the primary coil is directly proportional with the self-inductance of the
coil and current ID (thus with time the switch is closed). The voltage polarity at
the secondary winding is negative (due to different winding direction), meaning
that diode D will block. Capacitor C will discharge via RL, and UOUT will
decrease.
• Opening switch 'S' will generate a counter-e.m.f. in the primary winding, trying to
maintain current ID. Through this, the polarity of the secondary voltage will invert.
The magnetic energy, stored in the coil, will now be transformed to the secondary
side. Diode D will now conduct, capacitor C will be charged and UOUT will
increase.