If input voltage is less than Vuv then what will be converter state?

Hi Mayur@111,

Thank you for reaching out to Power Integrations and for your interest in our devices.

Addressing the first question, kindly take note that the TopSwitch-JX undervoltage response is different during power up and normal operation.

At power-up, UV keeps TOP264-271 off until the input line voltage reaches the undervoltage threshold. A single resistor connected from the VOLTAGE-MONITOR pin to the rectified DC high-voltage bus sets UV threshold during power-up. Once the power supply is successfully turned on, the UV threshold is lowered to 44% of the initial UV threshold to allow extended input voltage operating range (UV low threshold). 

If the UV low threshold is reached during operation without the power supply losing regulation, the device will turn off and stay off until UV (high threshold) has been reached again. 

If the power supply loses regulation before reaching the UV low threshold, the device will enter auto-restart. If the UV high threshold is not exceeded, the MOSFET will be disabled during the next cycle. 

Addressing the second question,

Upon computation, the theoretical Vuv of your circuit is indeed 15V, which is computed using the formula Vuv = Rtotal*Iuv(25uA) + Vv (2.8V). Kindly take note that the configuration disables the line overvoltage features due to the added Zener Diode which keeps the Vpin current from exceeding the Iov which is around 112uA. No auto-restart should happen when the input of the converter is below 15V as the primary MOSFET will not be switching in this state.

You can also check the typical waveforms in regard to the Vpin in page 7 of the TopSwitch-JX datasheet. You can use the link below.

topswitch-jx_family_datasheet.pdf (power.com)

Thank you.

Regards

Thanks for detail explanation. 

In second question I have one doubt. 

During power up Vuv threshold is 15V.  If converter is properly on, then Vuv low voltage threshold comes into picture which is 44% of 15V = 6.6V

When converter input voltage is decreasing below 15V & if converter is able to provide power to load. Is there possibility that (6.6- 15)V DC input converter is on or it can be in auto restart mode?

My requirement is converter must be completely off below 15V dc input, for this can you suggest anything?

Hi Mayur@111,

In that scenario wherein the converter is properly on. When we decreased the input voltage below Vuv  but still above the 44% of Vuv , the converter is still in operation. The causes that will put the converter in auto-restart are output short, output overload, output overcurrent, control pin voltage going below 4.85V, and if the circuit have an external output overvoltage protection.

However, kindly take note that the 15V of input voltage is too low and will not exceed the required drain to source voltage of the primary MOSFET for it to turn on. Even if your input voltage is above Vuv but still below the required drain to source DC voltage (18V), the converter will not operate.

Kindly see the attached image for the details.

Thank you.

Thank for your quick response. 

My requirement is converter must be completely off below 15V dc input, for this can you suggest anything different than Under voltage feature?

Hi Mayur@111,

The simplest way that won't need additional external components is only by utilizing the undervoltage feature. You can still set the Vuv at 15Vdc, this means that the converter won't operate below this Vuv during power up. 

But as mentioned, the drain to source voltage of the primary MOSFET should be above 18Vdc for it to start switching. This means that whenever your input voltage is lower than 18Vdc, the converter won't turn on or operate. Even if you have undervoltage resistors that sets the Vuv at 15V, the drain to source voltage requirement of 18V is the first condition that must be met for the converter to operate. 

Such condition is true during power up, when the voltage reduced to below 18Vdc during normal operation, or power down. The device won't attempt to switch and is completely off during such condition in the input voltage where it is below 18Vdc.

Thank you.

Regards