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TDA16846

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

Infineon Technologies 

TDA 16846

TDA 16846-2

Figure 5 Startup Voltage Diagram

Primary Current Simulation PCS (Pin 2) / Current Limiting

A voltage proportional to the current of the power transistor is generated at Pin 2 by the

RC-combination R2, C2 (Figure 4). The voltage at Pin 2 is forced to 1.5 V when the

power transistor is switched off and during its switch on time C2 is charged by R2 from

the rectified mains. The equation of V2 and the current in the power transistor (Iprimary) is

:

V2

=

1,5 V +

L---p--r--i-m--a--r-y---×----I-p--r--i-m--a--r-y

R2 × C2

Lprimary: Primary inductance of the transformer

The voltage V2 is applied to one input of the On Time Comparator ONTC (see Figure 2).

The other input is the control voltage. If V2 exceeds the control voltage, the driver

switches off (current limiting). The maximum value of the control voltage is the internal

reference voltage 5 V, so the maximum current in the power transistor (IMprimary) is

:

IMprimary

= 3--,--5-----V------×-----R----2----×----C-----2-

Lprimary

The control voltage can be reduced by either the Error Amplifier EA (current mode

regulation), or by an opto coupler at Pin 5 (regulation with opto coupler isolation) or by

the voltage V11 at Pin 11 (Fold Back Point Correction).

Data Sheet

9

2003-07-31

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