DC-DC开关模式变换器.讲义
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Example 7-1 In the Buck dc-dc converter of Fig. 3-5a, L =24μH . It is operating in dc steady state under the following conditions: Vin = 20V , D = 0.6 , Po = 12W , and fs = 200kHz . Assuming ideal components, calculate and draw the waveforms shown earlier in Fig. 3-5d.
iL = 1 8 0.6 5 (Vin Vo ) DTs = = 1A L 24
Po 12 I L = Io = = = 1A Vo 12
Therefore, iL=IL+iL,ripple , as shown in Fig. 3-6. When the transistor is on, iin=iL, otherwise zero. The average input currents is Iin=DIo =0.6A .
Chapter 7： DC-DC Switch-Mode Converters: 7-1 Introduction 7-2 Control of dc-dc Converters 7-3 Step-Down (Buck) Converter 7-4 Step-Up (Boost) Converter 7-5 Buck-Boost Converter 7-6 Cuk dc-dc Converter 7-7 Full Bridge dc-dc Converter 7-8 dc-dc Converter Comparison
7-3 BUCK CONVERTER
7-3 Step-Down (Buck) Converter
7-3 BUCK CONVERTER
Practical Buck Converter
Simplifying Assumptions 1.Transistors, diodes and other passive components are all ideal. 2. The input is a pure dc voltage Vd. 3. The output voltage is purely dc without any ripple, that is vo(t) ≈ Vo, 4. Continuous conduction mode, CCM
Vo can be controlled by varying the duty ratio D.
7-3 BUCK CONVERTER
In the dc steady state: Neglecting power losses associate with all the circuit elements.
iL
+
L
D iD is
+
+ VL -
Vd
-
C
R
Vo
-
7-4 BOOST CONVERTER
Operation principle
1) Turning on the switch applies the voltage Vd across the inductor, vL=Vd, and iL linearly ramps up, increasing the energy in the inductor. 2) turning off the switch forces the inductor current to flow through the diode, some of the stored energy is transferred to the output stage.
Pd = Po Therefore: Vd I d = Vo I o and :
IC = 0
Io 1 = Id D
Vo I L = Io = R
(7 4)
iC (t ) iL,ripple (t )
7-3 BUCK CONVERTER
In the dc steady state:
IC = 0 Vo I L = Io = R
7-3 BUCK CONVERTER
Solution With fs = 200kHz , Ts = 5 μs and Ton = DTs = 3μs . Vo=DVin =12V .The inductor voltage vL fluctuates between (Vin −Vo ) = 8V and (−Vo) =−12V , as shown inFig. 3-6.
7-4 BOOST CONVERTER
7-4 Step-Up (Boost) Converter Step-up converter is mainly applied in regulated dc power supplies and regenerative braking of dc motors.
id + Vd voi
O
iL
+ voi L + vL -
io + C vo=Vo R
(a)
Vd t on
TS = 1 fs
Vo
toff
(b)
t
7-3 BUCK CONVERTER
Operation principle 1) Turning on the switch increase the inductor current. 2) When the transistor is turned off, the inductor current “freewheels” through the diode.
iC (t ) iL,ripple (t )
iL (t ) = I L iL,ripple (t )
1 1 iL = (Vd Vo ) DTs = Vo (1 D)Ts L L
Ts2Vo (1 D) Vo = 8CL (7 23)
（7 22）
7-3 BUCK CONVERTER
id + (a) Vd vL (b) + voi (Vd-Vo)
A
iL
L + vL -
io + C vo=Vo R
t
B
(-Vo)
iL (c) id (d)
0 0
Ts
ton
toff
(IL=Io) t
iD
Baidu Nhomakorabea
t
(e)
0
t
7-3 BUCK CONVERTER
In the dc steady state:
VL = 0 （Vd Vo )ton = Vo (Ts ton ) Vo ton = =D Vd Ts (7 3)
iL = 1 8 0.6 5 (Vin Vo ) DTs = = 1A L 24
Po 12 I L = Io = = = 1A Vo 12
Therefore, iL=IL+iL,ripple , as shown in Fig. 3-6. When the transistor is on, iin=iL, otherwise zero. The average input currents is Iin=DIo =0.6A .
Chapter 7： DC-DC Switch-Mode Converters: 7-1 Introduction 7-2 Control of dc-dc Converters 7-3 Step-Down (Buck) Converter 7-4 Step-Up (Boost) Converter 7-5 Buck-Boost Converter 7-6 Cuk dc-dc Converter 7-7 Full Bridge dc-dc Converter 7-8 dc-dc Converter Comparison
7-3 BUCK CONVERTER
7-3 Step-Down (Buck) Converter
7-3 BUCK CONVERTER
Practical Buck Converter
Simplifying Assumptions 1.Transistors, diodes and other passive components are all ideal. 2. The input is a pure dc voltage Vd. 3. The output voltage is purely dc without any ripple, that is vo(t) ≈ Vo, 4. Continuous conduction mode, CCM
Vo can be controlled by varying the duty ratio D.
7-3 BUCK CONVERTER
In the dc steady state: Neglecting power losses associate with all the circuit elements.
iL
+
L
D iD is
+
+ VL -
Vd
-
C
R
Vo
-
7-4 BOOST CONVERTER
Operation principle
1) Turning on the switch applies the voltage Vd across the inductor, vL=Vd, and iL linearly ramps up, increasing the energy in the inductor. 2) turning off the switch forces the inductor current to flow through the diode, some of the stored energy is transferred to the output stage.
Pd = Po Therefore: Vd I d = Vo I o and :
IC = 0
Io 1 = Id D
Vo I L = Io = R
(7 4)
iC (t ) iL,ripple (t )
7-3 BUCK CONVERTER
In the dc steady state:
IC = 0 Vo I L = Io = R
7-3 BUCK CONVERTER
Solution With fs = 200kHz , Ts = 5 μs and Ton = DTs = 3μs . Vo=DVin =12V .The inductor voltage vL fluctuates between (Vin −Vo ) = 8V and (−Vo) =−12V , as shown inFig. 3-6.
7-4 BOOST CONVERTER
7-4 Step-Up (Boost) Converter Step-up converter is mainly applied in regulated dc power supplies and regenerative braking of dc motors.
id + Vd voi
O
iL
+ voi L + vL -
io + C vo=Vo R
(a)
Vd t on
TS = 1 fs
Vo
toff
(b)
t
7-3 BUCK CONVERTER
Operation principle 1) Turning on the switch increase the inductor current. 2) When the transistor is turned off, the inductor current “freewheels” through the diode.
iC (t ) iL,ripple (t )
iL (t ) = I L iL,ripple (t )
1 1 iL = (Vd Vo ) DTs = Vo (1 D)Ts L L
Ts2Vo (1 D) Vo = 8CL (7 23)
（7 22）
7-3 BUCK CONVERTER
id + (a) Vd vL (b) + voi (Vd-Vo)
A
iL
L + vL -
io + C vo=Vo R
t
B
(-Vo)
iL (c) id (d)
0 0
Ts
ton
toff
(IL=Io) t
iD
Baidu Nhomakorabea
t
(e)
0
t
7-3 BUCK CONVERTER
In the dc steady state:
VL = 0 （Vd Vo )ton = Vo (Ts ton ) Vo ton = =D Vd Ts (7 3)