AN8021L データシートの表示（PDF） - Panasonic Corporation

部品番号

コンポーネント説明

メーカー

AN8021L

AC-DC switching power supply control IC

Panasonic Corporation 

Voltage Regulators

AN8021L, AN8021SB

s Application Notes (continued)

[2] Operation descriptions (continued)

3. Overvoltage protection circuit (OVP)

OVP is an abbreviation of Over Voltage Protection. It refers to a self-diagnosis function, which stops the power

supply to protect the load when the power supply output generates abnormal voltage higher than the normal

output voltage due to failure of the control system or an abnormal voltage applied from the outside (figure 2 and

figure 3).

Basically, it is set to monitor the voltage of supply voltage VCC terminal of the IC. Normally, the VCC voltage

is supplied from the transformer drive coil. Since this voltage is proportional to the secondary side output voltage,

it still operates even when the secondary side output has overvoltage.

1) When the voltage input to the OVP terminal exceeds the threshold voltage (6.0 V typical) as the result of power

supply output abnormality, the protective circuit shuts down the internal reference voltage of the IC to stop all

of the controls and keeps this stop condition.

2) The OVP is released (reset) under the following conditions:

• Decreasing the supply voltage (VCC < 8.4 V typical: OVP release supply voltage)

The discharge circuit is incorporated so that the electric charge which is charged in the capacitor

connected to the OVP terminal can be discharged with the constant current of 5 µA (typical) for the next re-start.

Vth(OUT) =

Secondary side output voltage under normal operation VOUT

VCC terminal voltage under normal operation

× V7

V7 = Vth(OVP) + VZ

Vth(OUT): Secondary side output overvoltage threshold

Vth(OVP): OVP operation threshold

VZ : Zener voltage (external parts of OVP terminal)

TIM/OVP terminal voltage

0V

VTH OVP

(to 6 V)

Time

Internal reference voltage

0V

(to 7.1 V)

(to 5 V)

(IC stop state)

Time

Triangular wave oscillation

0V

(to 2 V)

(to VCC)

(IC stop state)

Time

IC output

0V

(IC stop state)

Figure 2. Explanation of OVP operation

Time

9

Share Link: