SMPSU With A Relay

Switched mode power supply units (SMPSUs)
are popular but difficult to build oneself as well problematic when it
comes to understanding their design principles. Building your own SMPSU
typically requires a lot of expertise, hard to find components and
time. The circuit shown here is educational only and devised to
demonstrate the principle of the step-up switch mode circuits. It is not
intended to be incorporated in a ‘real’ design. Relay Re1 has a
normally-closed (NC) change-over contact and is connected toact as a
vibrator. When power is applied to the circuit, the relay is energized
and actuates its contact.

Circuit diagram:

This action may appear to break the circuit. However, the energy
stored in the relay coil will produce an induced voltage which is fed to
D1 and C1 for rectification and smoothing. The output voltage will be
of the order of 150 V and strongly dependent on the type of relay used.
In general, the faster the relay, the higher the output voltage. The
circuit will oscillate at a low frequency (100-200 Hz), and a buzzing
sound will be heard from the relay.
SMPSU With A Relay Circuit Diagram

Author: Myo Min – Copyright: Elektor July-August 2004

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