Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

VOLTAGE OF THE ZERO Transition DETECTOR

Positive Clamping Voltage

0.75

V

Negative Clamping Voltage

-0.2

V

Threshold Value

40

50

mV

TUL

Suppression of Transformer Ringing

3

3.8

4.5

µs

Input Current

0

4

µV

PUSH-PULL OUTPUT STAGE

SATURATION VOLTAGES

Pin 5 Sourcing

1.5

2.0

V

Pin 5 Sinking

1.0

1.2

V

Pin 5 Sinking

1.4

1.8

V

OUTPUT SLOW RATE

Rising Edge

70

V/

µs

Falling Edge

100

V/

µs

REDUCTION OF CONTROL VOLTAGE

Current to reduce the Control Voltage

50

µA

PROTECTION CIRCUIT

7.0

7.25

7.5

V

15

16

16.5

V

970

1005

1040

mV

Oj

Over Temperature : at the given chip temperature the

150

Voltage at Pin 3 if one of the protection functions was

µA

0.4

0.8

V

Current Drain during Burst Operation

8

mA

FUNCTIONAL DESCRIPTION

In free running fly-back converters, the TDA4605

assumes control of a MOS power transistor and all

necessary regulation and monitoring functions.

The serial circuit of power transistor and primary

winding of the flyback transformer is connected to

the input voltage. During the switch-on period of the

transistor, energy is stored in the transformer and

during the switch-off period it is fed to te load via

the secondary winding. By varing the switch-on

time of the power transistor, the IC controls each

portion of energy transferred to the secondary side

such that the output voltage remains nearly inde-

pendent of load variations.

The required control information is taken from the

input voltage during the switch-on period and from

a regulation winding during the switch-off period. A

new cycle begins as soon as the energy stored in

the transformer has been totally delivered to the

secondary side.

In different load ranges, the SMPS will behave as

follows :

- No-Load Operation : The power supply unit

oscillates in non continuous mode at a typical

frequency of 20 to 40kHz. Depending upon the

transformer winding and the regulated voltage

divider, the output voltage can be slightly above

the nominal value.

- Normal Operation : Starting from typ. 200kHz,

the switching frequency falls with increasing load

and decreasing AC voltage. The duty cycle de-

pends primarily on the AC voltage. The output

voltage is only slightly load-dependen t.

- OverloadPoint : Maximum output power is avail-

able at this point of the output characteristics

- Overload : The energy transferred per operation

cycle is limited at the top. Therefore, the output

voltage will fall with secondary oveloading.

TDA4605

4/6