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AN1902 - APPLICATION NOTE

Figure 15: Operation during the EoL phase

3.5.2 OVERTEMPERATURE

A thermal protection is activated when the junction temperature exceeds ~150°C. Its effect is the same of

the EoL detection. For the timing definition it must be considered that the current generator on CapEOL

where:

∆v

3.5.3 OVERCURRENT

The network D1, Dz1 and R6 connected between SEC and CAP1 pins realizes the overcurrent

protection limiting the maximum accepted peak current. This function is very useful during the ignition

and the EoL, where the converter, working very close to the resonance frequency (f1), can reach very

high current levels (possibility of saturation of the transformer). This circuit is applied only on the low side

VK06. It works anticipating the device switch OFF when a defined current level is reached, in other words

the working frequency is increased. The modality is the following: an increasing in the current value

causes an increase of the secondary winding voltage (we are working at the resonance frequency). As

soon as this voltage exceeds the zener Dz1 + diode D1 breakdown, an amount of current will flow into

Choke Current

LS CapEOL pin Voltage

C

8

v

EOL

∆

I

EOL

2

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