AN8037 Panasonic Semiconductor, AN8037 Datasheet - Page 16

• Manufacturer Part Number: AN8037
• Description: AC-DC switching power supply control IC with standby mode
• Manufacturer: Panasonic Semiconductor

AN8027, AN8037
16
[1] Operation descriptions (continued)
7. Local resonance operation (power MOSFET turn-on delay circuit)
Application Notes (continued)
Notes on the feedback control (continued)
[Countermeasures]
barrier diode between V
a power supply system. It is also not possible to prevent levels from being pulled down to negative voltages in the
control IC itself. Therefore, the most important point in designing countermeasures is to prevent such negative
voltages from reaching the parasitic device conductance voltage.
Note) If a Schottky barrier diode is added to the circuit and the condition improves initially but the symptoms reappear when
(Reference)
The following our Schottky diodes are available.
Note) * : Former part number
through R9 and C9. The power MOSFET will be held in the off state while a high level (a level higher than the
threshold voltage, which is 0.25 V typical) is input to the TR pin.
at 0.7 V (typical) (sink current: 3 mA), and the lower limit voltage is clamped at about 0.15 V typical (source
current: 3 mA). (Refer to figure 11.)
until the TR pin input voltage becomes lower than the threshold voltage as the bias winding voltage falls after the
transformer discharges its energy, and the minimum off-period (T
(Refer to the "Setting the off-period" section in the "Operating descriptions, 2. Oscillation circuit.") As a result,
ringing in the bias winding does not be regarded as a turn on signal during the minimum off-period.
MA2C700A (MA700A*)
MA2C723 (MA723*)
MA2C719 (MA719*)
If an application exhibits the symptoms of the case described above, or similar symptoms, first insert a Schottky
Local resonance operation by using the AN8027 or AN8037 is possible with circuits as shown in figure 13.
C7 is the resonance capacitor, and R9 and C9 form a delay circuit for adjusting the power MOSFET turn on time.
When the power MOSFET is off, the voltage that occurs in the drive winding is input to the TR pin (pin 1)
The TR pin also has a clamping capability for upper and lower limit voltages. The upper limit voltage is clamped
The power MOSFET off-period is determined by the longer period of the following two periods: the period
the input voltage or other parameter is increased, try replacing the Schottky barrier diode with one that has a larger
forward current (both peak and average values). The current capacity of the Schottky barrier diode is sometime
insufficient.
Part No.
OUT
and GND. It is not possible to completely remove the mechanism described above from
Reverse voltage
30 V
30 V
40 V
Forward current (average)
200 mA
500 mA
30 mA
OFF(min)
) stipulated by the internal oscillator.
Voltage Regulators
Forward current (peak)
150 mA
300 mA
1 A