TDA16846(2000) Ver la hoja de datos (PDF) - Infineon Technologies

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Fabricante

TDA16846
(Rev.:2000)

Controller for Switch Mode Power Supplies Supporting Low Power Standby and Power Factor Correction

Infineon Technologies 

TDA 16846

TDA 16847

Fold Back Point Correction PVC (Pin 11)

V11 is deviated by a voltage divider from the rectified mains and reduces the limit of the

possible current maximum in the power transistor if the mains voltage increases. I.e. this

limit is independent of the mains (only active in free running mode). The maximum

current (IMprimary) depending on the voltage V11 at Pin 11 is

:

IMprimary

=

(--4-----V-----–-----V----1--1----⁄--3----)----×----R-----2---×-----C-----2-

Lprimary

Off-Time Circuit OTC (Pin 1)

Figure 6 shows the Off-Time Circuit which determines the load dependent frequency

course. When the driver switches off (Figure 7) the capacitor C1 is charged by current I1

(approx. 1 mA) until the capacitor’s voltage reaches 3.5 V. The charge time TC1 is

:

TC1 ≈ C-----1--1--×-m----1--A-,--5-----V-

For proper operation of the special internal anti jitter circuit, TC1 should have the same

value as the resonance time “TR” of the power circuit (Figure 7). After charging C1 up to

3.5 V the current source is disconnected and C1 is discharged by resistor R1. The voltage

V1 at Pin 1 is applied to the Off-Time Comparator (OFTC). The other input of OFTC is

the control voltage. The value of the control voltage at the input of OFTC is limited to a

minimum of 2 V (for stable frequency at very light load). The On-Time Flip Flop (ONTF)

is set, if the output of OFTC is high 1) and the voltage V3 at Pin 3 falls below 25 mV (zero

crossing signal is high). This ensures switching on of the power transistor at minimum

voltage. If no zero crossing signal is coming into pin 3, the power transistor is switched

on after an additional delay until V1 falls below 1.5 V (see Figure 6, OFTCD). As long as

V1 is higher than the limited control voltage, ONTF is disabled to suppress wrong zero

crossings of V3, due to parasitic oscillations from the transformer after switch-off. The

discharge time of C1 is a function of the control voltage.

1) i.e. V1 is less than the limited control voltage.

.

Control Voltage Output Power Off-time TD1

1.5 - 2 V

2 - 3.5 V

Low

Medium

Constant (TD1MAX.), const. frequency stand by

Decreasing

3.5 - 5 V

High

Free running, switch-on at first minimum

If the control voltage is below 2 V (at low output power) the “off-time” is maximum and

constant

TD1max ≈ 0,47 × R1 × C1

Data Sheet

10

2000-01-14

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