Data Sheet

8

Rev. 2.1, 2004-01-01

TLE 4305

Application Information

The TLE 4305 is a voltage and current regulator for Switch Mode Power Supply (SMPS)

applications.

It controls the output voltage and the maximum output current of a power supply unit. It

is located on the secondary side of the SMPS.

The TLE 4305 consists of a output voltage control loop and a current control loop. The

driver is especially designed to drive the opto-isolator. The current controls the PWM

duty cycle of the primary regulator.

Isolated SMPS

Switch mode power supply (SMPS) systems generate a regulated DC voltage

V

isolated from the primary side. A maximum output current

I

system in any load failures.

Figure 3

Isolated SMPS Principle

The principle of an isolated SMPS is shown in Figure 3. The primary side of the SMPS

is supplied by the line. The secondary side supplies a regulated voltage to the load.

Primary and secondary side are isolated from each other by the transformer and an opto

isolator.

A SMPS controller such as the Infineon TDA1683x controls the PWM duty cycle of the

output voltage signal. The signal is transmitted by a Transformer with n1:n2 (n: number

of windings). On the secondary side a load capacitor is charged. The secondary

regulator controls the output voltage

V

analog control signal to the primary side through an opto isolator to regulate the PWM

duty cycle of the primary signal. The loop is closed through the primary SMPS regulator

and the transformer.

Simple SMPS defines the output voltage by a voltage divider and a transistor. This

requires very precise resistor values and due to the nature of the transistor the control

signal is dependent on temperature and device variation. The current limitation has to be

done on the primary side with elements suitable for high voltages.

AES02888

SMPS

with

Cool Set

Secondary

Regulator

with

TLE 4305

Opto

Isolator

Line

Precise Output Voltage

Output Current precise limited

Short circuit protected