DF06M View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'DF06M' PDF : 42 Pages View PDF
AN1262 APPLICATION NOTE
Figure 15. Secondary feedback: TL431 + optocoupler circuit (IV)
Vcc
IC
Vout
L6590
L6590D
RH2
VFB
Rc
Cs 470 nF
RL2
Naux
IF
RB
RH1
COMP
RF2
CF1 RF1
VK
TL431
RL1
CF2
Table 20. G1(jω) Implementation: secondary feedback (IV)
Symbol
Definition
RL2; RH2 RL2 > V-1---5-C---V-C- [kΩ] ; RH2 = V-----C---C-2---.-–-5----2---.--5-- ⋅ RL2
RF2 RF2 > 0.4 · RH2
RL1
RL1 ≈ 0.27 to 2.7 [kΩ]; RH1 = V-----o--u--2-t---.–-5----2---.--5-- ⋅ RL1
RB
RB < CTRmin ⋅ V--I--Q-o---u-+--t--–-R--2------3-.-L--5---.-2--5--
RC
RC = -2----⋅---π-----⋅--1-f--Z----⋅---C-----S--
CF1
CF1 = -CR----BT----R-⋅---R-m---H-a---1x----⋅⋅---RG-----F1---02-
RF1
RF1 = -(--R----H----2----+-C----R-F---1-C----)---⋅---C-----S- – RH1
CF2
CF2 = -2----⋅---π-----⋅---R-1----F---2----⋅---f--P--
this network can be designed). The bias resistor of the photodiode will be selected so as to sustain the quiescent
current of the L6590 and the current through the divider RH2+RL2. Please note that the steady state supply volt-
age Vcc (used in table 20 to choose RL2 and RH2) has to be sufficiently higher than the UVLO threshold (say 3-
4 V, depending on CS). In fact, the PWM starts only when the Vcc voltage has decayed from the start-up thresh-
old to the neighborhood of the steady state value. During this time the PWM is inhibited by the error amplifier,
saturated low because the voltage at the pin VFB is higher than 2.5V.
The turn number of the auxiliary winding will be such that the VCE across the phototransistor never falls below
1-2 V, to let it work in its active region. In case of constant current regulation, the variation of the output voltage
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