Hi,
Pages 11 & 12 of the NCP1203 flyback controller datasheet say that the connection of the NCP1203 to the HVDC rail via its HV pin (so that it can start itself up)
can also bring about catastrophic latch up of the NCP1203.
It says that series resistor values of >4k7 must be added in series with the HV pin to avert this danger.
One presumes the entire NCP12XX range of controllers are also susceptible to such disaster?
Though why not just insert a 400V SOD123 diode in series to the HV pin instead? The diode would stop the reversing current inherent in latch up.
Also, it would dissipate hardly anything since the startup current is a maximum of 18.5mA and diode Vf is only 1V.
So in the schem of page 2 of AND8393, why do they use D13 & R41 & R42? All they needed to do was connect D13 from the HVDC bus to the NCP1219 HV pin and its job done?
A SOD123 is only 3.85mm by 1.7mm, so its smaller than the two 0805 resistors that onsemi always recommend with the NCP12XX application schematics.
So why are they using resistors when they don't need to?
It cant be too disallow startup below X volts because 3.64kOhms x 5.5mA is only 19.8 Volts.
NCP1203
NCP1219
NCP1239
AND9296
AND8393
Pages 11 & 12 of the NCP1203 flyback controller datasheet say that the connection of the NCP1203 to the HVDC rail via its HV pin (so that it can start itself up)
can also bring about catastrophic latch up of the NCP1203.
It says that series resistor values of >4k7 must be added in series with the HV pin to avert this danger.
One presumes the entire NCP12XX range of controllers are also susceptible to such disaster?
Though why not just insert a 400V SOD123 diode in series to the HV pin instead? The diode would stop the reversing current inherent in latch up.
Also, it would dissipate hardly anything since the startup current is a maximum of 18.5mA and diode Vf is only 1V.
So in the schem of page 2 of AND8393, why do they use D13 & R41 & R42? All they needed to do was connect D13 from the HVDC bus to the NCP1219 HV pin and its job done?
A SOD123 is only 3.85mm by 1.7mm, so its smaller than the two 0805 resistors that onsemi always recommend with the NCP12XX application schematics.
So why are they using resistors when they don't need to?
It cant be too disallow startup below X volts because 3.64kOhms x 5.5mA is only 19.8 Volts.
NCP1203
NCP1219
NCP1239
AND9296
AND8393