AN2349 Application note
Simple cost-effective PFC using Bipolar Transistors for low-to-medium power HF Ballasts
Introduction
This note deals with the implementation of a Power Factor Correction (PFC) in a Discontinuous-mode Boost Converter where a PFC stage is achieved with a power bipolar transistor driven in self oscillating configuration. The new solution proposed exploits the physical relation (tS, IC) of any bipolar transistor to achieve the Pulse Width Modulation (PWM) signal in a Boost Converter.
June 2006
Rev 1
1/30
www.st.com
Contents
AN2349
Contents
1 PFC solutions for low-medium power HF Ballasts . . . . . . . . . . . . . . . . 5
1.1 Application description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 3
Feedback block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Selection of boost output inductor L1 . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1 Selection of boost output capacitor C4 . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4
PFC driving network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1 Feed-Back block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5
T Transformer and L1 inductor specifications . . . . . . . . . . . . . . . . . . 23
5.1 5.2 220V design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 120V design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
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AN2349
List of tables
List of tables
Table 1. Table 2. Table 3. 40W Demoboard 220V bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 40W Demoboard 120V bill of materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
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List of figures
AN2349
List of figures
Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Valley Fill circuit schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Valley Fll input current waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Active PFC with IC and MOSFET in boost topology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Base schematic of Bipolar PFC in HF ballast voltage Fed . . . . . . . . . . . . . . . . . . . . . . . . . 6 Ts modulation in bipolar PFC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Imain achieved using the basic Bipolar PFC shown in Figure 4 . . . . . . . . . . . . . . . . . . . . . . 7 Detail of storage time value and Ic in t2 istant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Detail of storage time value and Ic in t1 istant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Complete electrical schematic of the Bipolar PFC in HF Ballast . . . . . . . . . . . . . . . . . . . . . 9 PFC stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Feed-back block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 PFC waveforms with Feedback block working . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Imain achieved by the proposed bipolar PFC solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Detail of Storage time value in t2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Detail of storage time value in t1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Pre-heating @ 220V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Current on the electrolytic capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Inductor current with di/dt>0 and transformer voltage shape . . . . . . . . . . . . . . . . . . . . . . . 16 Inductor current with di/dt=0 and transformer voltage shape . . . . . . . . . . . . . . . . . . . . . . . 16 Inductor current with di/dt<0 and transformer voltage shape . . . . . . . . . . . . . . . . . . . . . . . 17 Transformer Vout shape and base current shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Collector current and base current shape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Detail of T1 total charge during Ton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 40W demoboard electrical schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 40W demoboard PCB layout and mounting components . . . . . . . . . . . . . . . . . . . . . . . . . . 25
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AN2349
PFC solutions for low-medium power HF Ballasts
1
PFC solutions for low-medium power HF Ballasts
The Valley Fill circuit is an example of a low-cost passive PFC available on the market. Figure 1. Valley Fill circuit schematic diagram
AC INPUT
DC-AC CONVERTER/ BALLAST
LAMP
RECTIFIER+PFC+DC FILTER BLOCK
Figure 2.
Valley Fll input current waveform
The capacitors are charged in serie, and discharged, via the two diodes, in parallel. Current is drawn from the line from 30 to 150, and then from 210 to 330. Discontinuities occur from 150 to 210 and from 330 to 360, and then the cycle repeats itself. Disadvantages of this PFC solution are spikes on input current waveform and large zero current gaps between the half sinusoidal wave and the next one (meaning a lower power factor and high input current distortion), and high ripple in the DC output voltage that causes poor performance in High Power Lamps. On the other hand, high performances can be achieved by IC driver optimized for controlling PFC regulators in boost topology as shown in Figure 3.
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PFC solutions for low-medium power HF Ballasts Figure 3. Active PFC with IC and MOSFET in boost topology
AN2349
The proposed Bipolar PFC solution targets the low-cost HF Ballast market up to 80 W as it provides a simple cost-effective solution without sacrificing THD and PF levels. It does not need any ICs to achieve the PWM signal since it uses just a power bipolar transistor and a closed-loop feedback that performs the duty cycle modulation and a satisfactory output power regulation.
1.1
Application description
The active PFC solution with Bipolar transistor adopts the Boost topology working in Discontinuous Conduction mode. This is the most simple and cost-effective solution for 220V and 120V mains and low\medium power. Figure 4. Base schematic of Bipolar PFC in HF ballast voltage Fed
No IC is used to generate a PWM signal, but the physical relation (tS, IC) of any power bipolar transistor is exploited when the base current IB value is kept constant. Figure 5 shows two different storage time values at two different input VAC values: in t1 the bipolar reaches a higher saturation level than in t2, and this means tS1>tS2. The overall switch on time is given by the sum of "IBON time" plus the storage time, therefore, if the "IBON time" is constant, the duty cycle changes according to the ts modulation. This natural duty cycle variation generates an appropriate PWM signal to
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AN2349
PFC solutions for low-medium power HF Ballasts control the PFC stage and reduces the Imain distortion achieving a THD in the range of about 30%, with a shape of the current drawn from the main as shown in Figure 6. Figure 5. Ts modulation in bipolar PFC
IIN IIN AV
IL=Ic ts1 ts2
IB
t
t
Figure 6.
Imain achieved using the basic Bipolar PFC shown in Figure 4
Imain
Vce Ic
Figure 7 and Figure 8 show in a real situation, what has been explained before.
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PFC solutions for low-medium power HF Ballasts
AN2349
Figure 7.
Detail of storage time value and Ic in t2 istant
Figure 8.
Detail of storage time value and Ic in t1 istant
Ib
Injected charges S t o r a ge Storage time Vce Ic
Ib
Injected charges Storage time
Vce Ic
The PWM signal acts on T1 bipolar transistor base through an auxiliary winding T on the transformer normally used in the ballast.
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AN2349
Feedback block
2
Feedback block
The duty cycle modulation performed by the Basic Solution shown in Figure 4 is not enough effective to achieve high THD values and no protection task can be implemented against overoload or high VAC values. A negative feedback network has been introduced to further control the duty cycle modulation by modifying the total Qon charge which is injected into the T1 base. Chapter Figure 9. on page 9 shows the complete solution of the proposed PFC stage. Figure 9. Complete electrical schematic of the Bipolar PFC in HF Ballast
The feed-back block in Figure 11 changes the T1 QON charge by modifying both the IBON amplitude and duration through the intervention of the transistor T2. In particular the proposed network by the T2 conduction reduces the base current permitting to reduce the duty cycle of the main switch (T1) performing a further THD correction and output power regulation. Figure 10. PFC stage
D7 D5
Figure 11. Feed-back block
L1 L1
Input 1
R13
R14
Input 2
Input 1 Output
Input 2 Feed-Back Input 3 Block
C4
Dz3
Output
Ds T2 D8 R3 C3 Dz1
Input 3
T1
R2 R1
C2 T
9/30
Feedback block
AN2349
The network D8, R3, DZ1, and C3 in Figure 11 ensures the switch protection during start-up thanks to a smart combination of three input signals. 1. 2. 3. Input 1 comes from the Main Voltage and it'is used to limit the amount of the distortion improving the THD. Input 2 comes from PFC Vout : it'is used to further regulate the power factor and to regulate the PFC Vout against supply voltage variations. Input 3 signal is a voltage proportional to the pre-heating current during start up and it' is used. to protect the power switch against over voltage . The Output signal is the base current driving the T1 main switch.
The transistor T2 during its On-state modifies the natural modulation imposed by the storage time variation of the transistor T1 since:
It reduces the time constant during the charge of the capacitor C2 thus reducing the time length of the On base current of T1 It shunts part of the same current to ground thus reducing its amplitude.
The combination of the previous two effects implies a reduction of the duty cycle of the transistor T1 helping to correct the THD and the power factor level . The schottky diode Ds in series with the collector of the transistor T2 by blocking any reverse current on the transistor itself ensures a low voltage drop during T2 on state. The steady state waveforms associated to the new proposed circuit are below reported in Figure 16. Figure 12. PFC waveforms with Feedback block working Figure 13. Imain achieved by the proposed bipolar PFC solution
I ma i n Imain
V ce
Ic
Components values of the Feedback block have been chosen to achieve a base current modulation that allows obtaining a constant collector current in the range of VMsen t with 30 t150 . Waveforms reported in Figure 13 shows now a quasi-sinusoidal behavior of the current drawn from the main, while the blue waveform in Figure 12 shows the T1 IBON modulation performed by the negative feedback.
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AN2349
Feedback block The overall storage time modulation achieved by the Bipolar PFC working with the negative feedback network is evident in Figure 14 and Figure 15 showing real values of storage time detected on the oscilloscope at t1 and t2 instances.
Figure 14. Detail of Storage time value in t2
Figure 15. Detail of storage time value in t1
Injected Injected charges Storage time
Injected charges Storage time
Figure 16 shows the pre-heating and start-up phase waveforms. Figure 16. Pre-heating @ 220V
Vce
Ic
11/30
Selection of boost output inductor L1
AN2349
3
Selection of boost output inductor L1
The boost output inductor L1 is calculated in the peak of sinusoidal voltage at maximum instantaneous input power in order to obtain the minimum IP value assuring the discontinuous mode operation. This calculation is made considering a working operation at constant current peak IP, due to the base current modulation, and fixing a working switching frequency. Supposed a purely resistive load it is: Equation 1
( VM · IM ) P = V e f f · I e f f = -----------------------2
where VM is the maximum input main voltage and IM is the maximum input main current. Then from Equation 1, Equation 2
VM · IM = 2 P
Now considered the total energy stored by the inductor in the period at the maximum input main voltage: Equation 3
2P E T O T = 2 P T = ------fs w
where T is the period and fSW is the working switching frequency. But the total energy stored by the inductor in the period is, also, the sum of two contributes, the first LI2P/2, due to the inductor L1 charge and the other one, VMIptB/2, due to the discharge of the same via the main voltage, then equalizing the two terms we obtain: Equation 4
2 L I P VM · Ip tB 2 P-------- = ---------- + ----------------------2 2 fS W
where IP is the peak of the working switching current at maximum voltage VM and tB is the inductor discharge time that is: Equation 5
LI t B = --------------P--------Vo u t VM
with Vout imposed at 390V and it is the PFC output voltage. Substituting tB in Equation 4: Equation 6
2 Vo u t L IP VM · IP L IP LI P 2P -------- = ---------- + ------------------ · ------------------------ = ---------- ------------------------ 2 V o u t V M 2 V o u t V M 2 fS W 2
calculated in the max point of the sinusoid, in general for 30t 50 it can be can 1 written:
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AN2349 Equation 7
Selection of boost output inductor L1
2 Vo u t L IP V M s e n t · I P L IP 2---------- L I P ---P ( t ) = ---------- + ---------------------------------- · ---------------------------------------- = ---------- · ---------------------------------------- V o u t V M s e n t V o u t V M s e n t 2 2 fS W 2
2
where according to the working operation, LI2P/2 is the constant term, while the other one contains the sinusoidal modulation of the main current with 30PM = VM · IM
but IM is also the medium value of the peak of the working switching current in the period T corresponding to the max point of the Main Voltage VM. Equation 9
tA + tB I M = I P · --------------2T
where tA=LIP/VM is the L1 charge time and tB=LIP/Vout-VM is the L1 discharge time. Now from Equation 9: Equation 10
2T I P = I M · --------------tA + tB
Substituting Equation 10 in Equation 7 and resolving by L: Equation 11
P L = --- · f Vo u t VM +t 2 1 t-A----------- · ------- · ---------------------- ---- B 2 Vo u t T IM
where tA+tB/T is chosen equal to 0.70 in order to ensure that the circuit remains in the discontinuous mode leaving a dead-time of 0.3T.
3.1
Selection of boost output capacitor C4
The PFC works to obtain a sinusoidal Main Current. Therefore the capacitor C4 will charge with a rectified current at double half-wave shape, as shown in Figure 17. This current shape will generate on the electrolytic capacitor an almost continuous voltage with a ripple value depending on the same capacitor value. In order to calculate the capacitor C4, the current flowing on the electrolytic capacitor can be asssumed as thoroughly the sum of two contributions, one due to a continuous component and other one due to an alternate component, as shown in Figure 17. The alternate component will have double frequency respect to the main frequency.
13/30
Selection of boost output inductor L1 Figure 17. Current on the electrolytic capacitor
I |IM sent| IM
AN2349
IDC= 2*IM/ IAC
IM 2*IM/
2
T
T
Thus for 0I M sin t I D C + I A C
where IDC, the continuous component, is the mean value of IM sint : Equation 13
ID C =
I
2 IM --M sin t · dt = --------- 0
and IAC is the alternate component with double frequency and out of phase of /2 respect to the main one that is: Equation 14
2 IM I A C = I M -------- sin 2 t -- 2
Now substituting Equation 13 and Equation 14 into Equation 12, we have: Equation 15
2 IM 2 IM I M sin t -------- + I M -------- sin 2 t -- 2
The peak ripple voltage V M R I P P L E is: Equation 16
VM
RIPPLE
VP P = -----------R--P------E --I - P L 2
But VM R I P P L E is the alternate voltage on the capacitor due to the IAC Equation 17
VM
RIPPLE
2 IM = I M -------- · X C
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AN2349
Selection of boost output inductor L1 where from Equation 17, the IM-2IM/ is the max amplitude of the alternate current IAC on the electrolytic capacitor, while XC is the capacitive reactance XC=COUT=2f* of the electrolytic capacitor, with f*=2fmain(fmain=50/60Hz). Equalizing Equation 16 and Equation 17 you have Equation 18
VP P 2 IM -----------R--P----L-E = I M -------- · 2 f C O U T --I - P - 2
and resolving by C: Equation 19
VP P --I - P -- 1 C O U T = -----------R--P----L-E · ----4 f IM
where VP PR I P P L E = v D CO U TM A X V D Co u tM I N is the peak to peak ripple voltage and from Equation 2 IM=2*P/VM.
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PFC driving network
AN2349
4
PFC driving network
The network composed by the capacitor and resistor in series to the base of the power bipolar transistor T1 are chosen in order to fix the duty-cycle at level less than 50% in the max point of the main sinusoid and they determine the conduction time of the device, while the base-emitter resistor has the function to regulate the capacitor discharge during the off state of the device and to define the duty-cycle. The bipolar transistor used as switching is driven in a self-oscillating configuration taking the signal in order to polarize its base through an auxiliary winding on the transformer normally used in the ballast. This signal can assume three different shapes depending on the signal shape on the ballast due to the di/dt variation of the Ballast inductor current. The inductor current is the sum of the Transistor Collector Current, Diode Current and Snubber Capacitor Current. 1. End collector current with di/dt>0
Figure 18. Inductor current with di/dt>0 and transformer voltage shape
ICT1 B
+
ID2 ICT2
I T2 IL I T1
di/dt ID1
+
A VA
VB T/ 2 T
2.
End collector current with di/dt= 0
Figure 19. Inductor current with di/dt=0 and transformer voltage shape
ICT1 =0 B ID2 ICT2 di/dt ID1 A VA IT2 IL IT1
+
VB T/2
T
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AN2349
PFC driving network
3.
End collector current with di/dt < 0
Figure 20. Inductor current with di/dt<0 and transformer voltage shape
The first condition is considered for our reference design, di/dt > 0, and in particular the slope on the point A has a di/dt value four times larger than the slope of the point B. Figure 21 shows the output voltage of the transformer where the VA value is four times larger than the VB value. Figure 21. Transformer Vout shape and base current shape
17/30
PFC driving network The output voltage VT of the transformer at the initial instant is: Equation 20
VT = VC + VR + VB E = VA
0 0 2
AN2349
where 0 is the initial capacitor voltage, the T1 BE voltage.
V C = 2.5 V
VR
2
is the resistor R2 voltage and VBE is
The shape of the transformer voltage in a half period T/2 is: Equation 21
( VA VB ) · t V T ( t ) = V A -------------------------------T -2
After the initial instant, the capacitor begins to charge and, as soon as VC(t)=VT(t) the base V current IB and R 2 are equal to zero and the storage time of the device is beginning, so considering this instant t2 that is t IB O N you have: Equation 22
VT ( t2 ) = VB E + VC ( t2 ) = VB E + VC + vC ( t2 )
0
where VC(t2), voltage on the capacitor C2, is the sum of two terms VC 0, that is the initial capacitor voltage, and vc(t2) , that is the voltage variation due to the charge of the capacitor, VBE= 0.2V is base-emitter voltage when IB is equal to zero and taking in consideration that there are charges stored into the base of the transistor. Equalizing the two expressions 21 and 22 at this instant, you obtain: Equation 23
( VA VB ) · t2 V A ----------------------------------- = V B E + V C + v C ( t 2 ) 0 T -2 by considering VA=4VB 6V, VB=1.5V and t2= t IB O N .
In order to calculate t2= t IB O N you have: Equation 24
tA = tI
BON
L Ip + t S T = ----------------------V M s e n t
calculated when the collector current IC (for t=30) reaches its maximum value and the base current Ib is without modulation yet (as shown in Figure 22).
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AN2349 Figure 22. Collector current and base current shape
PFC driving network
Since vc(t2)=Q/C=Ibpeak *t2 /2C having imposed that at the instant t IB O N =tST=t2 Equation 25
I bp e a k · t C = -------------------------2 2 · vc ( t2 )
where it has been imposed Ibpeak=0.75*Ip=0.53mA. Now from Equation 20 V R2 can be calculated: Equation 26
VR = VT VC VB E
2 0
where VBE=1V is the base-emitter voltage of the device at the working current. Then, since V R2 = I bp e a k · R 2 , R2 is determined: Equation 27
VR 2 R 2 = ---------------I bp e a k
It has been said that the base-emitter resistor R1 has the function to regulate the capacitor discharge during the off state of the device and to define the duty-cycle. The mean current I R 1 M e a n on the R1 resistor during the off state of the device: Equation 28
IR V V------+------B + 0.6 · V --- A --- -C 0 2 = -------------------------------------------------------------R1 + R2
1Mean
where it has been considered a mean value of V C = 0.6 · V C 0 .
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PFC driving network
AN2349
You consider the instant of the main sinusoidal in which the collector current IC (for t=30) reaches its maximum value and the base current Ib without modulation yet (see Figure 22). Multiplying this value for T/2, the amount of charge on the capacitor C2 during the off state of the device can be calculated: Equation 29
IR
1M e a n
T · -- = Q C O F F 2 2
this value must be equal at the amount of charge on the same capacitor during the on state of the device: Equation 30
IR
1Mean
T · -- = Q C O N = Q T O T + Q T 2 T1 2 2
Substituting Equation 28 into Equation 30 you obtain: Equation 31
A VB V------+-------- + 0.6 · V --C 0 --- 2 -------------------------------------------------------------- · T = Q T O T + Q T = Q C O N -T1 2 2 2 R1 + R2
where Q T O TT 1 is the total amount of charge on T1 and Q T 2 is the amount of charge on the collector of T2. In the following picture it has been indicated with Q1 the amount of charge provided in the base during the turn-on of the device, while the Q2 is the amount of charge during the storage time, thus the total amount of charge is: Figure 23. Detail of T1 total charge during Ton
where Q2=0.6Q1 due to the recombination of some charges, so substituting in (5.13) it obtains: Equation 32
Q T O T = Q 1 0.6 Q 1 = 0.4 Q 1
T1
Equation 33 but
IB · tI Pea BO N Q 1 = ------------k----------------2
Substituting Equation 33 into Equation 32 you obtain:
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AN2349 Equation 34
IB · tI b o n Pe -Q T O T = 0.4 · ----------a-k------------------- = 0.42 C T1 2
PFC driving network
Now, the amount of charge on the collector of T2 is: Equation 35
QT = IC T · tI
2 2 BON
with Equation 36
IC T = IB p e a k IB m i n
2
Now the IBmin at the instant where the main voltage reaches its max value, v(t)=VM=310V. We consider Equation 37
di v ( t ) = L · ---dt
Equation 38
V I = I P = --- t c o n d L
Resolving Equation 38 by tcond: Equation 39
IP · L t c o n d = ------------- = 4.5 s V
but tcond= t IB O N +tST and in this instant t IB O N =tst=2.25s
1 , where T O T T 1, such to keep From Equation 32, we already know T O TT 1 IC=IP=0.7A, in this case is calculated when the base current reaches its minimum value, so knowing the hFE of the device to obtain the saturation at this current value IC, that is hFE = 19, we have:
Q
= 0.4 Q
Q
Equation 40
IC Q T O T = --------- · t c o n d 0.15 C T1 hF E
Now from
Q T O T = 0.4 Q 1
T1
, we obtain:
Equation 41
Q OT -Q 1 = -----T------0.4
But Equation 42
IB O N · tI BN Q 1 = -------------------------O--2
So
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PFC driving network Equation 43
2 · Q1 I B O N = I B M I N = ---------------tI
BON
AN2349
From Equation 36, we can obtain Equation 44
I C T = I B p e a k I B m i n = 180 m A
2
Then the amount of charge on the T2 collector is: Equation 45
QT = IC T · tI
2 2 BON
= 0.4 C
So, the total amount of charge on the capacitor C2 during the on state of the device is: Equation 46
QC
2ON
= Q T O T + Q T = 0.42 + 0.4 = 0.82 C
T1 2
Substituting Equation 46 into Equation 31 and resolving by R1, it can be calculated: Equation 47
T VA + VB 1 R 1 = -- -------------------- + 0.6 V C ------------------- R 2 0 Q 2 2 C ON
2
4.1
Feed-Back block
In order to calculate the two resistors R13 and R14 value in Figure 11 it has been imposed Vz3=200V, supposing that this feed-back block acts from this voltage value. Two instants must be considered: 1. 2. The zener diode doesn't yet conduct for t=30; The zener diode already conducts for t=90.
Therefore the two equations to be considered are: Equation 48
V D C o u t V Z 3 V i n ( t = 30 ) V Z 3 ---------------------------------- + -------------------------------------------------- = 0 R 13 R 14 V D C o u t V Z 3 V i n ( t = 90 ) V Z 3 --- ---------------------------------- + ---------------------R------------------------- = I Z 3 = I B O N T 2 R 14 13
where IBON T2 can be calculated knowing the the peak hFE of the T2 device at a minimum current value (IC=50mA ) (hFE =170). Equation 48 has to be solved by R13 and R14.
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AN2349
T Transformer and L1 inductor specifications
5
5.1
T Transformer and L1 inductor specifications
220V design
The transformer T has to be choosen as following: 1. 2. 3. The core type is N87-EFD25/13/9 by Epcos The wire gauge used to wind the transformer is 0.28 mm The number of primary winding is 150 turns, the air gap lenght has been chosen in order to obtain a saturation current of about 1.6A and an inductance value of 2.2mH 2.5% The number of secondary winding is 2 turns for each of the two secondaries The core type is N27-E20/6 (EF20) by Epcos The number of primary winding is 150 turns, the air gap length has been chosen in order to obtain a saturation current of about 1.7A and an inductance value of 1.8mH 2.5% The wire gauge to wind the transformer is 0.22 mm
4. 1. 2.
The Boost inductor L1 has to be choosen as following:
3.
5.2
120V design
The transformer T has to be choosen as following: 1. 2. 3. The core type is N87-EFD25/13/9 by Epcos The wire gauge used to wind the transformer is 0.28 mm The number of primary winding is 150 turns, the air gap lenght has been chosen in order to obtain a saturation current of about 1.7A and an inductance value of 2.1mH 2.5% The number of secondary winding is 3 turns in the PFC stage and 2 turns in the converter stage The core type is N27-E20/6 (EF20) by Epcos The number of primary winding is 150 turns, the air gap lenght has been chosen in order to obtain a saturation current of about 1.7A and an inductance value of 1.5mH 2.5% The wire gauge to wind the transformer is 0.22 mm
4.
The Boost inductor L1 has to be choosen as following: 1. 2.
3.
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T Transformer and L1 inductor specifications Figure 24. 40W demoboard electrical schematic
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T Transformer and L1 inductor specifications Figure 25. 40W demoboard PCB layout and mounting components
Table 1.
Item 1 2 3 4 Qty 5 1 5 2
40W Demoboard 220V bill of materials
Reference D1...D5 D6 1N4007 1N5818 Part Description High Voltage Low frequency Diode Power schotky diode High Voltage High Frquency diode Small signal diode
D17,D7, D9,D10,D11 BA159 D8, D13 1N4148
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T Transformer and L1 inductor specifications Table 1.
Item 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19` 20 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Qty 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 2 1 1 1 2 1 1 1 1 1 1 2 1 1 1 1 1 1 Dz2, Dz1 L1 L2 C1 C2 C3 C4 C5 C6, C7 C8 C9 C10 C11 C12 C13, C14,C15 R1 R2 R3 R5, R7 R6 R8 R9 R10 R11 R12 R13, R14 Rfuse D16 D15 L3 SCR PTC
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40W Demoboard 220V bill of materials (continued)
Reference 47V 5.6V 1.8mH 100H 220nF 400V 470nF 100V 1F 63V 22uF 450V 47nF 63V 220nF 100V 1.5nF 630V 1nF/16V 10F/35V 47nF/400V 6.8nF/1000V 100nF/400V 82 4.7 220 330K 220 1K 22K 680K 56K 39 180K 1 200V 100V 1mH X0203NA/X0202NA R(25C)=600 Part Description Glass zener diode Glass zener diode Mounting type: Through hole. Size: 14mm x 22mm. Height: < 18mm Axial inductor 0.25W Medium voltage ceramic capacitor Low voltage ceramic capacitor Low voltage Radial Electrolytic capacitor High Voltage Electrolytic capacitor Low voltage ceramic capacitor Low voltage ceramic capacitor High Voltage ceramic capacitor Low voltage ceramic capacitor Radial Electrolytic capacitor Medium Voltage ceramic capacitor High Voltage ceramic capacitor Medium Voltage ceramic capacitor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor Zener Diode Zener Diode Axial inductor 1W TO92, VDRM/VRMM=800V;IGT=200 uA, ITRMS=1.25A Type C884 PTC thermistor, 600
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Item 39 40 Qty 1 1 T D14
T Transformer and L1 inductor specifications 40W Demoboard 220V bill of materials (continued)
Reference Part Lp=2.3mH, Ns=2(PFC), Ns=2(Half Bridge) Shor t circuit Description Mounting type: Through hole. Size: Approx. 25mm x 25mm Height: 12 mm
Table 2.
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19` 20 21 22 23 24 25 26 Qty 5 1 5 2 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 2 1 1 1 1 1 2
40W Demoboard 120V bill of materials
Reference D1...D5 D6 1N4007 1N5818 Part Description High Voltage Low frequency Diode Power schotky diode High Voltage High Frquency diode Small signal diode Glass zener diode Glass zener diode Mounting type: Through hole. Size: 14mm x 22mm. Height: < 18mm Axial inductor 0.25W Medium voltage ceramic capacitor Low voltage ceramic capacitor Low Voltage Radial Electrolytic capacitor High Voltage Radial Electrolytic capacitor Low voltage ceramic capacitor Low voltage ceramic capacitor High Voltage ceramic capacitor Low voltage ceramic capacitor Low Voltage Radial Electrolytic capacitor Medium Voltage ceramic capacitor High Voltage ceramic capacitor Mediun Voltage ceramic capacitor Medium Voltage ceramic capacitor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor
D7,D9,D10,D11,D14 BA159 D8, D13 Dz2 Dz1 L1 L2 C1 C2 C3 C4 C5 C6, C7 C8 C9 C10 C11 C12 C13, C14 C15 R1 R2 R3 R4 R5, R7 1N4148 47V 7.5V 1.5mH 120H 680nF, 250V 680nF 100V 1uF 63V 22uF 400V 56nF 63V 220nF 100V 2.2nF ,630V 1nF/16V 10uF/35V 47nF/400V 6.8nF/1000V 100nF/400V 220nF/250V 22 6.8 100 8.2 330K
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T Transformer and L1 inductor specifications Table 2.
Item 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Qty 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 R6 R8 R9 R10 R11 R12 R13 R14
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40W Demoboard 120V bill of materials (continued)
Reference 220 1K 22K 680K 56K 39 220K 68K Part Description 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25W 10% Axial Resistor 0.25 W 10% Axial Resistor Axial inductor 1W 10% Zener Diode Zener Diode Axial inductor 1W TO92, VDRM/VRMM=800V;IGT=200 uA, ITRMS=1.25A Type C884 PTC thermistor, 600 Mounting type: Through hole. Size: Approx. 25mm x 25mm Height: 12mm
L ( in place of Rfuse ) 1mH D16 D15 L3 SCR PTC T D17 130V 180V 1mH X0203NA/X0202NA R(25C)=600 Lp=2.1mH, Ns=3(PFC), Ns=2(Half Bridge) Shor t circuit
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Revision history
6
Revision history
Table 3.
Date 06-Jun-2006
Document revision history
Revision 1 Initial release Changes
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