TEA1501 Philips Semiconductors, TEA1501 Datasheet - Page 5

• Manufacturer Part Number: TEA1501
• Description: Greeny; GreenChip
• Manufacturer: Philips Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The TEA1501 contains a high voltage power switch, a high
voltage startup circuit and low voltage control circuitry on
the same IC. Together with a transformer and a few
external components a low power, isolated, flyback
converter can be built. The Greeny system operates in a
burst mode. During each burst period the output voltage is
regulated to a desired voltage level.
System operation
O
The Greeny system can be switched on and off by means
of a low cost, low voltage switch. In the Off mode the
startup current source and power switch are disabled. In
the On mode, Greeny delivers the startup current for the
supply capacitor and after the supply voltage reaches the
startup level Greeny activates the power switch.
S
The startup is realized with a high voltage startup current
source instead of a dissipative bleeder resistor which is
commonly used by low voltage control ICs. When Greeny
is switched on, the startup current source is enabled and
starts charging the Vaux capacitor. The startup current
level is high and accurate (typical 1.8 mA) which results in
a well-defined and short startup time, within 0.25 s. After
the supply voltage reaches the startup level the current
source is switched off and the Vaux capacitor supplies the
chip. Reducing the power dissipation in the current source
to zero after startup is one of the green features of Greeny.
O
After startup the flyback converter starts delivering energy
to the secondary and auxiliary winding. The Greeny
system works with fixed switching frequency and fixed
peak current.
1998 Aug 19
TARTUP
N
PERATION
Greeny; GreenChip
/O
FF
5
As all the windings of the flyback transformer have the
same flux variation, the secondary voltage and the
auxiliary voltage are related via the turns-ratio (n
Therefore, the isolated secondary voltage is controlled by
the non-isolated auxiliary voltage.
The burst mode operates by switching at high frequency
until the Vaux voltage reaches its regulation level of 20 V.
Greeny stops switching until the time period set by the
burst oscillator has expired. At the start of the next burst
period Greeny starts switching at high frequency and
repeats the cycle again.
To guarantee a stable operation in a burst mode controlled
system a Vaux slope compensation circuit is integrated in
Greeny. The Greeny system delivers a constant voltage to
the secondary load until a burst duty cycle of 40%.
D
The TEA1501 has a data transfer function which makes
communication from the isolated secondary side to the
non-isolated primary side of the transformer possible,
without using an opto-coupler. This communication
function is activated by increasing the secondary load.
With this data transfer function a main power supply can
be switched on and off by the Greeny system.
The power delivered to the secondary and auxiliary
winding is proportional to the number of primary current
pulses per burst period, provided that the converter
operates in discontinuous conduction mode. During each
burst period the number of primary current pulses is
counted. A threshold (N
clamp level on the OOD pin is set to data-on level from
data-off level in case the N
data-on clamp level can be sensed by the on/off input of a
main supply control IC of the GreenChip
data-on clamp level is maintained until a burst appears
with a number of pulses below the N
ATA TRANSFER
data
) of 56 pulses is integrated. The
data
threshold is passed. This
Preliminary specification
data
threshold.
TEA1501
family. The
s
/n
a
).