Swtched - Mode Power Supply
Swtched - Mode Power Supply
Swtched - Mode Power Supply
(SWTCHED - MODE
POWER SUPPLY)
An OVERVIEW
A - bridge rectifier
B - Input filter
capacitors
C - Transformer
D - output filter
coil
E - output filter
capacitors
SMPS and Linear Power
Supply
A switched-mode power supply or SMPS, is an electronic power supply
unit (PSU) that incorporates a switching regulator. While a
linear regulator maintains the desired output voltage by dissipating
excess power in a "pass" power transistor, the SMPS rapidly switches
a power transistor between saturation (full on) and cutoff (completely
off) with a variable duty cycle whose average is the desired output
voltage. The resulting rectangular waveform is low-pass filtered with
an inductor and capacitor. The main advantage of this method is
greater efficiency because the switching transistor dissipates little
power in the saturated state and the off state compared to the
semiconducting state (active region).
Other advantages include smaller size and lighter weight (from the
elimination of low frequency transformers which have a high weight)
and lower heat generation from the higher efficiency.
Disadvantages include greater complexity, the generation of high
amplitude, high frequency energy that the low-pass filter must block
to avoid EMI, and a ripple voltage at the switching frequency and the
harmonic frequencies thereof.
How an SMPS works
Input rectifier stage
If the SMPS has an AC input, then the
first stage is to convert the input to DC.
This is called rectification.