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Control IC for Switched-Mode Power Supplies using MOS-Transistors TDA 4605-2 Bipolar IC Features q Fold-back characteristics provides overload protection for q q q q q q q external components Burst operation under secondary short-circuit condition implemented Protection against open or a short of the control loop Switch-off if line voltage is too low (undervoltage switch-off) Line voltage depending compensation of fold-back point Soft-start for quiet start-up without noise generated by the transformer Chip-over temperature protection implemented (thermal shutdown) On-chip ringing suppression circuit against parasitic oscillations of the transformer P-DIP-8-1 Type TDA 4605-2 Ordering Code Q67000-A5020 Package P-DIP-8-1 The IC TDA 4605-2 controls the MOS-power transistor and performs all necessary regulation and monitoring functions in free running flyback converters. Because of the fact that a wide load range is achieved, this IC is applicable for consumer as well as industrial power supplies. The serial circuit and primary winding of the flyback transformer are connected in series to the input voltage. During the switch-on period of the transistor, energy is stored in the transformer. During the switch-off period the energy is fed to the load via the secondary winding. By varying 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 independent 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 will start if the transformer has transferred the stored energy completely into the load. Semiconductor Group 54 06.94 TDA 4605-2 In the different load ranges the switched-mode power supply (SMPS) behaves as follow: No load operation The power supply is operating in the burst mode at typical 20 to 40 kHz. The output voltage can be a little bit higher or lower than the nominal value depending of the design of the transformer and the resistors of the control voltage divider. Nominal operation The switching frequency is reduced with increasing load and decreasing AC-voltage. The duty factor primarily depends on the AC-voltage. The output voltage is only dependent on the load. Overload point Maximal output power is available at this point of the output characteristic. Overload The energy transferred per operation cycle is limited at the top. Therefore the output voltages declines by secondary overloading. Semiconductor Group 55 TDA 4605-2 Pin Definitions and Functions Pin No. 1 Function Information Input Concerning Secondary Voltage. By comparing the regulating voltage - obtained from the regulating winding of the transformer - with the internal reference voltage, the output impulse width on pin 5 is adjusted to the load of the secondary side (normal load, overload, short-circuit, no load). Information Input R