LT3999 light load operation

Hello,

please check page 11. If you need a more stable Vout the use of a LDO might be necessary.

br

Markus

Hello Markus-san

Thank you for your quick reply.

I understand your answer but please let me know about the output voltage at light load.

I evaluated with almost the same circuit as datasheet sheet1 and found the following result.

Vin:12V

Vout：35V

Iout：no load

Fsw：500kHz

Turns ratio　 Np：Ns=1：1.08

The output of this circuit is calculated to be about 13V so this result is very high.

Are there any way to get an output voltage about 13V at no load condition?

Best Regards,

Hgtk

I would like to know the 

Is there a way to  regulate the output voltage at light loads?

Hello,

the LT3999 is a push-pull stage where the Dutycycle is fixed and can only be modified with the RDC pin from the primary side. There is no feedback loop to accomodate for load/line variations from the output.

So you might 'attach' either a reistive load for operating at a default load as minimum load or use a zener on the output to limit the possible Vout increase.

The intended low noise applications are mainly Signalchains consisting of several opamps/ADCs which offer a decent amount of power consumption, hence your problem will not occur.

kind regards

Markus

Hello 

Thank you for your reply.

I will try it.

Best Regards,

Hgtk

Hello Markus-san

I have an additional question about LT3999.

I am evaluating a ± output circuit and found a following large ringing waveform at SW pin.

CH1：10V/div

Fsw：500kHz

output current：50mA

I use almost the same circuit as below.

Would you please tell me the how to reduce this ringing? 

Best Regards,

Hgtk