TEA1623PH Philips Semiconductors, TEA1623PH Datasheet - Page 6

• Manufacturer Part Number: TEA1623PH
• Description: STARplug
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 12579
Product data sheet
8.3 Duty factor control
8.4 Valley switching
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.
To ensure that the capacitor can be charged within the charge time, the value of the
oscillator capacitor should be limited to approximately 1 nF.
The duty factor is controlled by the internal regulation voltage and the oscillator signal on
pin RC. The internal regulation voltage is equal to the external regulation voltage (minus
2.5 V) multiplied by the gain of the error amplifier (typical 20 dB or 10 ).
The minimum duty factor of the switched mode power supply is 0 %. The maximum duty
factor is set to 75 % (typical value at 100 kHz oscillation frequency).
A new cycle is started at the primary stroke when the switch is switched on (see
After a certain time (determined by the RC oscillator voltage and the internal regulation
level), the switch is turned off and the secondary stroke starts. The internal regulation
level is determined by the voltage on pin REG. After the secondary stroke, the drain
voltage shows an oscillation with a frequency of approximately
Where:
As soon as the oscillator voltage is high again and the secondary stroke has ended, the
circuit waits for a low drain voltage before starting a new primary stroke.
The primary stroke starts some time before the actual valley at low ringing frequencies,
and some time after the actual valley at high ringing frequencies.
curve for a reflected voltage N
Figure
by the turns ratio of the transformer).
minimum drain voltage for ringing frequencies of 480 kHz, thus reducing the switch-on
losses to a minimum. At 200 kHz, the next primary stroke is started at 33 before the
valley. The switch-on losses are still reduced significantly.
L
C
p
p
is the primary self inductance on the drain node
is the parasitic capacitance on the drain node.
6) transferred to the primary side of the transformer with the factor N (determined
Rev. 01 — 17 March 2004
V
o
of 80 V. This voltage is the output voltage V
Figure 5
TEA1623P; TEA1623PH
shows that the system switches exactly at
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
----------------------------- -
2
Figure 5
1
L
www.DataSheet4U.com
p
C
shows a typical
p
STARplug
o
Figure
(see
6 of 18
4).
TM