TDA 16846/16846-2

TDA 16847/16847-2

Version 2.0

10

31 Jul 2003

Fold Back Point Correction PVC (Pin 11)

V

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 (

I

:

Off-Time Circuit OTC (Pin 1)

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

curve. When the driver switches off (Figure 7) the capacitor

C

I

pin 3 reaches the level

V

I

capacitor’s voltage reaches 3.5 V. The charge time TC1 is

:

For proper operation of the special internal anti- jitter circuit, TC1 (rising time for

I

should have the same value as the resonance time “tR” of the power circuit (Figure 7).

After charging

C

resistor

R

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

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

V

OFTCD). As long as

V

suppress wrong zero crossings of

V

after switch-off. The discharge time of

C

1)

i.e.

V

.

Control Voltage

Output Power

Off-time TD1

1.5 - 2 V

Low

Constant (TD1

2 - 3.5 V

Medium

Decreasing

3.5 - 5 V

High

Free running, switch-on at first minimum

4V

V

11

3

⁄

–

2

C

2

×

×

------------------------------------------------------------

=

TC1

×

1mA

-------------------------

≈