Switching converter
Laboratory exercise 2
Switching converter (DC converter)
A switching converter is an electrical device that converts the unregulated DC input to a
controlled DC output with a desired voltage level.
Applications: DC motor control, switched-mode power supply (SMPS), battery chargers, etc.
ton
U
UdAV
Ucontrol
toff
+
IdAV
E
Pic 1 Buck converter (step-down)
An average output voltage:
t
U dAV  U  on  U  d
T
(2.1)
ton – switch on time, d – duty cycle
Ripple current:
id  idMAX  idMIN 
U
 d 1  d 
f L
(2.2)
Inductance:
U
 d 1  d   L
f L
id  idMAX  idMIN 
d  d 


U 100  100 
L 
f
id
2
(2.3)
Resistance:
U
R  dAV
I dAV
(2.4)
1
Ing. Lukáš Odlevák, Ing. Petr Vaculík
Switching converter
Task
1. Measure characteristic UdAV = f (d) for RL load. Add measured and calculated (2.1)
waveform to the same graph. Find out resistance R (2.4) as an average value.
2. Measure characteristic Δid = f (d) for RL load and make the graph. Find out
inductance L (2.3) as an average value.
3. Buck converter (step-down) with RL+E load: display waveforms of voltage Ud and
current id in case of continuous and discontinuous current. Add these pictures to this
protocol.
4. Boost converter (step-up) with RL+E load: display waveforms of voltage Ud and
current id in case of continuous and discontinuous current. Add these pictures to this
protocol.
Pic 2 Wiring diagram
Device:
L1 – L3
D1 – D6
Rb
V3
C
3-phase supply
Rectifier (6-pulse)
braking resistor
switching of Rb
electrolyte capacitor
V1, V01
V2, V02
R
L
E
2
Buck converter (step-down)
Boost converter (step-up)
variable resistor
inductor
DC motor
Ing. Lukáš Odlevák, Ing. Petr Vaculík
Switching converter
Laboratory measurement
Buck converter (step-down):
Switching frequency f =
DC supply voltage
U=
d
[%]
UdAV
[V]
IdAV
[A]
Δid
[A]
5
15
25
[Hz]
[V]
35
45
50
55
65
75
85
95
Average
R
[Ω]
L
[H]
Optional reference:
http://en.wikipedia.org/wiki/DC_to_DC_converter  Usage, Switched-mode conversion
3
Ing. Lukáš Odlevák, Ing. Petr Vaculík