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How does LNK306 work at 24 ~ 150VDC

Posted by: moha+1s on Fri, 08/13/2021

Dear support team

I need to design a non isolated power supply, Input 24 ~ 150VDC, output 12V 300mA, I want to use lnk306, according to the datasheet, the minimum drain supply voltage is 50V. If the input is lower than 50V and the external power supply is added in the bypass pin, can lnk306 work? How does this external power supply need to be designed? If this solution does not work, please recommend an appropriate solution.

Thank and Best Regard.

 

Comments

Submitted by PI-Hiro on Wed, 08/25/2021

Hello moha+1s,

The minimum drain supply voltage of 50V guarantees the operation of the power supply in your intended application up to the full load condition. We cannot guarantee that the power supply can operate up to the full load condition with a lower input voltage. 

As the input voltage decreases, there will be an increase in the duty cycle and this will be capped at DCmax as given in the datasheet. Once it reaches DCmax, the power supply output may not operate at full load condition. Another factor is that at start-up, the power supply may operate at the maximum duty cycle, but if it does not start-up properly within 50ms, the IC will enter auto-restart. 

You can try to build the power supply, but if the power supply does regulate at a lower input voltage, it may be only at low load condition.

Thank you.

 

Dear PI-Hiro

According to the datasheet, the maximum duty cycle of lnk306 is 66%. After calculation, when the input is 24V and the output is 12V, the duty cycle is lower than 66%.

In my practical application, the input is not lower than 40V, the output is fixed 12V, and the power is within 2W.

After testing, the output power can reach 3.6W when the output is 48V. Lnk306 seems to work very well, Does this mean that the lnk306 can work continuously, even if the datasheet says the minimum drain supply voltage is 50V?

Thank and Best Regard.

 

Submitted by PI-Hiro on Tue, 09/07/2021

Hello moha+1s,

LNK306 uses ON/OFF control and not PWM control (where the duty cycle is the ratio of the output to the input voltage). In ON/OFF control, the duty cycle will increase as the load demand on the output also increases while still maintaining output regulation. 

When operating at a lower voltage input and a full load output condition, the energy may not be enough to power both the IC and the load. This may cause a slow start-up for the
IC and when it does not start-up properly within 50ms, the IC will enter auto restart. That is maybe why when you tested at 40V input, the power supply reaches regulation, but not at full load condition of 3.6W output. 

As stated earlier, the minimum drain supply voltage of 50V in the datasheet only guarantees the operation of the power supply up to the full load condition. Although it may operate at lower input voltage, performance may vary as the datasheet only guarantees full load output operation at a minimum of 50V drain supply voltage. 

Thank you.

Regards,

PI-Hiro