TDA 4916 GG

Version 2.0

8

1 May 1996

Comparator K1 (duty factor setting for voltage mode control)

The two plus inputs of the comparator are so connected that the lower plus level is

always compared with the minus input level. As soon as the voltage of the rising edge of

the sawtooth (minus input) exceeds the lower of the two plus input levels, the output is

inhibited via the turn-OFF Flip-Flop, that is to say the High time of the output can be

continuously varied. Since the frequency remains constant, this corresponds to a duty

factor change.

Comparator K2

The comparator has a switching threshold at 1.5 V. Its output sets the fault Flip-Flop

when the voltage on capacitor

C

the setting pulse only if no reset pulse (fault) is applied. This prevents resetting of the

output as long as a fault signal is present.

Comparators K3 (overvoltage), K4 (undervoltage),

V

Overcurrent

These are fault detectors which cause the output to be inhibited immediately by the fault

Flip-Flop when faults occur. When faults are no longer present, the duty factor is

reestablished via the soft start

C

the input of K4 with the aid of which an adjustable hysteresis or latching is made

possible. The value of the hysteresis is determined by the internal resistance of the

external drive source and the current injected internally at the input of K4. In the event

of undervoltage at K4, the injected current flows into the device.

Comparator K5 (duty factor setting for current mode control)

K5 is used to sense the source current at the switching transistor. The plus input of the

comparator is fed out. Enabling of output Q SIP after cessation of the fault is effected

with an H signal at the turn-OFF Flip-Flop output.

Comparator K6 (overcurrent turn-OFF)

The turn-OFF Flip-Flop is reset when overcurrent is detected by K6. In combination with

the pulse-omission facility, individual pulses can then be omitted. This then results in a

limited rise in the output current with a rising overload at the output.