AN2755

Test results and significant waveforms

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To maximally benefit from the THD optimizer circuit, the high-frequency filter capacitors after

the bridge rectifier should be minimized, compatibly with EMI filtering needs. A large

capacitance, in fact, introduces a conduction dead-angle of the AC input current in itself thus

reducing the effectiveness of the optimizer circuit.

2.3

Overvoltage protection and disable function

The L6562A is equipped by an OVP, monitoring the current flowing through the

compensation network and entering in the error amplifier (pin COMP, #2). When this current

reaches about 24 µA the output voltage of the multiplier is forced to decrease, thus reducing

the energy drawn from the mains. If the current exceeds 27 µA, the OVP is triggered

(dynamic OVP), and the external power transistor is switched off until the current falls

approximately below 7 µA. However, if the overvoltage persists (e.g. in case the load is

completely disconnected), the error amplifier eventually saturates low hence triggering an

internal comparator (static OVP) that keeps the external power switch turned off until the

output voltage comes back close to the regulated value.

The OVP function described above is able to handle abnormal overload conditions, i.e.

those resulting from an abrupt load/line change or occurring at startup.

The INV pin doubles its function as a non-latched IC disable. A voltage below 0.2 V shuts

down the IC and reduces its consumption to a lower value. To restart the IC, the voltage on

the pin must exceed 0.45 V. The main usage of this function is a remote ON/OFF control

input that can be driven by a PWM controller for power management purposes. However it

also offers a certain degree of additional safety since it causes the IC to shut down in case

the lower resistor of the output divider is shorted to ground or if the upper resistor is missing

or fails to open.

Figure 19.

EVL6562A-400W inductor current

ripple envelope at 230 Vac - 50 Hz -

full load

Figure 20.

EVL6562A-400W Inductor current

ripple (detail) at 230 Vac-50 Hz -

full load

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CH1: Q1/Q2 drain voltage

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CH2: I L inductor current ripple envelope

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CH3: MULT voltage - pin #3

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CH1: Q1/Q2 drain voltage

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CH2: I L inductor current ripple envelope

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CH3: MULT voltage - pin #3