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TOP Switch OVP |
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| 2017年11月20日 | |||||||
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Output overvoltage protection (OVP) - User programmable for Hysteresis / Latching shutdown- Primary or secondary sensed VOLTAGE MONITOR (V) Pin - The detection of the hysteretic or latching output over-voltage protection (OVP) is through the trigger of the line over-voltage threshold. - If IV exceeds IOV(LS) (336 μA typical) longer than 100 μs, TOP264-271 will latch into a permanent off state for the latching OVP. - If IV does not exceed IOV(LS) or exceeds no longer than 100 μs, TOP264-271 will initiate the line overvoltage and the hysteretic OVP. Primary-side OVP protection During a fault condition resulting from loss of feedback, output voltage will rapidly rise above the nominal voltage. The increase in output voltage will also result in an increase in the voltage at the output of the bias winding. A voltage at the output of the bias winding that exceeds of the sum of the voltage rating of the Zener diode connected from the bias winding output to the V pin and V pin voltage, will cause a current in excess of IV to be injected into the V pin, which will trigger the OVP feature.
Secondary-side Accurate OVP If greater accuracy is required, a secondary sensed OVP circuit is recommended. In OVP testing, the output voltage will be increased . When reverse biased voltage applied to the Zener diode reaches Zener breakdown (ZOV), it starts allowing large amount of electric current. This current will go through opto-coupler (UOV) . This current will be impacted by output voltage. The opto-coupler (UOV) go through this current , transfer an electrical signal to primary side and current begins to flow into the V-pin. When this current exceeds IOV(LS) (336 μA typical) longer than 100 μs, the internal latching shutdown circuit in TOP Switch is activated. Base on Zener breakdown characteristic, this current is also impacted by output voltage.
Latching or Hysteresis OVP R9 controls the IV - 0 ~20 ohm for latching OVP - 5.1k ohm for hysteresis OVP (Auto Restart) COVP - Select to deliver OVP trigger current - 100μs with 100nF typical RX - Prevents false OVP triggering due to leakage current - Start from 100 kohm |
