TEA1622P 查看數據表（PDF） - Philips Electronics

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TEA1622P

STARplug™

Philips Electronics 

Philips Semiconductors

TEA1622P

STARplugTM

7.2 Pin description

Table 3: Pin description

Symbol

Pin Description

VCC

GND

1

supply voltage

2

ground

RC

3

frequency setting

REG

4

regulation input

AUX

5

input for voltage from auxiliary winding for timing (demagnetization)

SOURCE 6

source of internal MOS switch

n.c.

7

not connected

DRAIN

8

drain of internal MOS switch; input for start-up current and valley sensing

8. Functional description

The TEA1622P is the heart of a compact flyback converter, with the IC placed at the

primary side. The auxiliary winding of the transformer can be used for indirect feedback to

control the isolated output. This additional winding also powers the IC. A more accurate

control of the output voltage and/or current can be implemented with an additional

secondary sensing circuit and optocoupler feedback.

The TEA1622P uses voltage mode control. The frequency is determined by the maximum

transformer demagnetizing time and the time of the oscillator. In the first case, the

converter operates in the Self Oscillating Power Supply (SOPS) mode. In the latter case, it

operates at a constant frequency, which can be adjusted with external components RRC

and CRC. This mode is called Pulse Width Modulation (PWM). Furthermore, a primary

stroke is started only in a valley of the secondary ringing. This valley switching principle

minimizes capacitive switch-on losses.

8.1 Start-up and undervoltage lock-out

Initially, the IC is self supplying from the rectified mains voltage. The IC starts switching as

soon as the voltage on pin VCC passes the VCC(start) level. The supply is taken over by the

auxiliary winding of the transformer as soon as VCC is high enough and the supply from

the line is stopped for high efficiency operation.

As soon as the voltage on pin VCC drops below the VCC(stop) level, the IC stops switching

and restarts from the rectified mains voltage.

8.2 Oscillator

The frequency of the oscillator is set by the external resistor and capacitor on pin RC. The

external capacitor is charged rapidly to the VRC(max) level and, starting from a new primary

stroke, it discharges to the VRC(min) level. Because the discharge is exponential, the

relative sensitivity of the duty factor to the regulation voltage at low duty factor is almost

equal to the sensitivity at high duty factors. This results in a more constant gain over the

duty factor range compared to PWM systems with a linear sawtooth oscillator. Stable

operation at low duty factors is easily realized. For high efficiency, the frequency is

reduced as soon as the duty factor drops below a certain value. This is accomplished by

increasing the oscillator charge time.

9397 750 12578

Product data sheet

Rev. 01 — 17 March 2004

© Koninklijke Philips Electronics N.V. 2004. All rights reserved.

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