Q67000-A2379 データシートの表示（PDF） - Siemens AG

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Q67000-A2379

Control ICs for Switched-Mode Power Supplies

Siemens AG 

TDA 4601

Circuit Description

The TDA 4601 is designed for driving, controlling and protecting the switching transistor in flyback

converter power supplies during start-up, normal and overload operations as well as during

disturbed operation. In case of disturbance the drive of the switching transistor is inhibited and a

secondary voltage rise is prevented.

Start-Up

The start-up procedures (on-mode) include three consecutive operating phases as follows:

1. Build-Up of Internal Reference Voltage

The internal reference voltage supplies the voltage regulator and effects charging of the coupling

electrolytic capacitor connected to the switching transistor. Current consumption will remain at

I9 < 3.2 mA with a supply voltage up to V9 approx. 12 V.

2. Enabling of Internal Voltage - Reference Voltage V1 = 4 V

Simultaneously with V9 reaching approx. 12 V, an internal voltage becomes available, providing

all component elements, with the exception of the control logic, with a thermally stable and

overload-resistant current supply.

3. Enabling of Control Logic

In conjunction with the generation of the reference voltage, the current supply for the control logic

is activated by means of an additional stabilization circuit. The integrated circuit is then ready for

operation.

The start-up phase above described are necessary for ensuring the charging of the coupling

electrolytic capacitor, which in turn supplies the switching transistor. Only then is it possible to

ensure that the transistor switches accurately.

Normal Operating Mode / Control Operating Mode

At the input of pin 2 the zero passages of the frequency provided by the feedback coil are registered

and forwarded to the control logic. Pin 3 (control input, overload and standby identification) receives

the rectified amplitude fluctuations of the feedback coil. The control amplifier operates with an input

voltage of approx. 2 V and a current of approx. 1.4 mA. Depending on the internal voltage reference,

the overload identification limits inconjunction with collector current simulator pin 4 the operating

range of the control amplifier. The collector current is simulated by an external RC-combination

present at pin 4 and internally set threshold voltages. The largest possible collector current

applicable to the switching transistor (point of return) increases in proportion to the increased

capacitance (10 nF). Thus the required operating range of the control amplifier is established. The

range of control lies between a DC-voltage clamped at 2 V and a sawtooth - shaped rising AC-

voltage, which can vary up to a max. amplitude of 4 V (reference voltage). During secondary load

reduction to approx. 20 W, the switching frequency is increased (approx. 50 kHz) at an almost

constant pulse duty factor (1:3). During additional secondary load decreases to approx. 1 W, the

switching frequency increases to approx. 70 kHz and pulse duty factor to approx. 1:11. At the same

time collector peak current is reduced to < 1 A.

Semiconductor Group

9

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