VIPer20A-E

Operation description

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5

Operation description

5.1

Current mode topology:

The current mode control method, like the one integrated in the devices, uses two control loops

- an inner current control loop and an outer loop for voltage control. When the Power MOSFET

output transistor is on, the inductor current (primary side of the transformer) is monitored with a

outer voltage control loop defines the level at which the inner loop regulates peak current

through the power switch and the primary winding of the transformer.

Excellent open loop D.C. and dynamic line regulation is ensured due to the inherent input

voltage feedforward characteristic of the current mode control. This results in improved line

regulation, instantaneous correction to line changes, and better stability for the voltage

regulation loop.

Current mode topology also ensures good limitation in case there is a short circuit. During the

first phase the output current increases slowly following the dynamic of the regulation loop.

Then it reaches the maximum limitation current internally set and finally stops because the

internally set can be overridden by externally limiting the voltage excursion on the COMP pin.

An integrated blanking filter inhibits the PWM comparator output for a short time after the

integrated Power MOSFET is switched on. This function prevents anomalous or premature

termination of the switching pulse in case there are current spikes caused by primary side

capacitance or secondary side rectifier reverse recovery time.

5.2

Stand-by mode

Stand-by operation in nearly open load conditions automatically leads to a burst mode

operation allowing voltage regulation on the secondary side. The transition from normal

Where:

device is able to provide in normal operation. This current can be computed as :

may be affected by the efficiency of the converter at low load, and must include the power

drawn on the primary auxiliary voltage.

1

2

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+

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