5 Operation Description

VIPer50A-E/ASP-E

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As soon as the power goes below this limit, the auxiliary secondary voltage starts to increase

above the 13V regulation level, forcing the output voltage of the transconductance amplifier to

switch is maintained in the Off state, resulting in missing cycles and zero duty cycle. As soon as

operates again. The above cycle repeats indefinitely, providing a burst mode of which the

effective duty cycle is much lower than the minimum one when in normal operation. The

equivalent switching frequency is also lower than the normal one, leading to a reduced

consumption on the input main supply lines. This mode of operation allows the VIPer50A-E/

ASP-E to meet the new German "Blue Angel" Norm with less than 1W total power consumption

for the system when working in stand-by mode. The output voltage remains regulated around

the normal level, with a low frequency ripple corresponding to the burst mode. The amplitude of

this ripple is low, because of the output capacitors and low output current drawn in such

conditions.The normal operation resumes automatically when the power gets back to higher

5.3

High Voltage Start-up Current Source

An integrated high voltage current source provides a bias current from the DRAIN pin during

the start-up phase. This current is partially absorbed by internal control circuits which are

placed into a standby mode with reduced consumption and also provided to the external

start-up current generator is switched off, and the converter should normally provide the

(see Figure 11).

In case there are abnormal conditions where the auxiliary winding is unable to provide the low

device goes back to the inactive state where the internal circuits are in standby mode and the

start-up current source is activated. The converter enters a endless start-up cycle, with a start-

up duty cycle defined by the ratio of charging current towards discharging when the device tries

to start. This ratio is fixed by design to 2A to 15A, which gives a 12% start-up duty cycle while

the power dissipation at start-up is approximately 0.6W, for a 230Vrms input voltage.

This low value start-up duty cycle prevents the application of stress to the output rectifiers as

well as the transformer when a short circuit occurs.

parameters, among which transformer design, output capacitors, soft start feature, and

compensation network implemented on the COMP pin. The following formula can be used for

defining the minimum capacitor needed:

where:

values.

generally at full load.

C

VD D

I

DD

t

SS

V

DD hys t

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