|
Buck Regulator
| Buck
DC to DC Converter
or Step Down regulator is the
basic topology for all switching power supplies, and the
functionality is the basics as well for the all switching power
supplies topologies. Fig 1 show how a switching element provides the
voltage output depending of the time is tuned ON or OFF, like a
simple network voltage divider |
| Just
like a linear regulator, topology is about the same, but instead all
elements are in switched mode ON or Off. see Fig No. 2 and it
works as following: |
| If
MOSFET is switching with a square wave of 50% time ON and the other
50% of the time OFF, then the RMS voltage output will be 50% of the
Voltage input or the voltage output can be expressed in Vo = Vi x
duty Cycle Vo = Vi x 0.5 = Vi /2 Example 2: if MOSFET is
totally OFF the voltage output will be Cero volts If the MOSFET is
always ON then the output voltage will be equal to Vi
PWM
the effect of move the time ON
or OFF of the switching MOSFET back and forward is called Pulse
Width Modulation on just PWM, then moving the PWM for
different values we can obtain different voltage level outputs
see Fig 3 |
| LC
removes the square signal from the MOSFET and provides a RMS voltage
output, the larger is the LC filter. the pure is the DC output (less
switching ripple) |
| Diode
works like a switch when inductor delivery negative energy at the
moment MOSFET are switched OFF or opened, providing more efficient
functionality of the inductor releasing the negative energy to
positive energy to the load. The voltage output is calculated just
like a linear regulator Vo = Vref. x ( R4/R5)
The
size of the inductor and capacitor is determinate by the switching
frequency and the power output |
Advantages/Applications:
High
Efficiency
Easy
thermal management
When
only one or two outputs are required
Large
input to output voltage difference
Battery
operated portable equipment
Disadvantages:
No
DC isolation between input and output
Output
ripple higher than Linear
Slow
transient response
MOSFET
selection
Vds
>1.2 Vin(max)
Idpk
> 1.2 Io(max)
Diode
Selection
Vr
> 1.2Vin(max)
If
> Io(max)
|
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