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24

RD-0608

Fig. 30 Open Circuit Fault Signals, with Clamp

The yellow waveform shows the output voltage and the red waveform shows the VS switching waveform. In this

example there is no output capacitor. When the output goes above the over voltage threshold the VCC voltage

shown in blue is quickly pulled below VCCUV- and then gradually charges back up to VCCUV+ through RS1. If an

output capacitor is connected then VCC is pulled almost to zero by IC3 and the systems takes longer to re-start.

(

)

2

2

1

5

.

2

OV

OV

OV

out

R

R

R

V

+

⋅

=

The values of the divider resistor ROV1 and ROV2 are calculated as follows:

Let ROV2 = 10K

()

Ω

≈

Ω

=

Ω

−

Ω

⋅

=

−

=

+

⋅

=

k

R

k

k

k

V

R

R

V

R

R

R

R

V

OV

OV

OV

out

OV

OV

OV

OV

out

120

118

10

5

.

2

10

32

5

.

2

5

.

2

1

2

2

1

2

2

1