AN3407

Main characteristics and circuit description

Doc ID 018857 Rev 1

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Figure 4.

Oscillator characteristics

Pin #14 (HBCS) of the L6585DE is equipped with a current sensing and a dedicated

overcurrent management system. When the EOI voltage reaches 1.9 V, the IC enters run

mode and the switching frequency is set only by R17 (RRUN). In Figure 5 the protection

thresholds are shown. They are sensed by the circuit C18, R26, D8, D9, R27, and C19 and

are fed into the L6585DE pin#14 (HBCS).

Figure 5.

Half-bridge protection thresholds during run mode

2.4

Output voltage feedback loop

The output voltage is kept stable by means of a feedback loop implementing a typical circuit

using U3 (TS2431) modulating the current in the optocoupler diode. On the primary side,

R34 connecting pin#2 (RF) of the L6585DE to the optocoupler's phototransistor allows

modulating the L6585DE oscillator frequency, thus keeping the output voltage regulated.

R17 connects the same pin to ground and sets the minimum switching frequency.