DER-60
Adapter – TNY268
May 27, 2005
4.5 OTP, OVP and LPS Protection Circuit
Q1, Q3, R11 and R21 from a SCR to pull BP pin act as a latch circuit. R8 is a thermal
resistor of a NTC type. R8 and R9 from an OTP’s trigger circuit of the SCR. The SCR
will be triggered when temperature raise to OTP setting point.
D21, R27, R44, U23 and R1 form an OVP trigger circuit of the SCR. When output
voltage raise to let D21 conducted, it will trigger the SCR for protection.
R33, C36, D24 and R36 form a LPS trigger circuit of the SCR. R33 and C36 set at about
300ms delay time for peak 4A output current testing. (The peak current testing is
4A/200ms/ 1A/us and 0.25A/ 1800ms/ 1A/us, and then the output voltage can’t be less
than 3V.) If the output load is increased, the bias voltage will be increased too. When
the bias voltage increased to LPS setting point, it will let D24 conducted to trigger the
SCR for protection.
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