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PTN78000H minimum load current

Other Parts Discussed in Thread: PTN78000H

I was wondering if there was a spec for the minimum load current for the PTN78000H?

My application for the PTN is a pwm heater circuit.  The pwm frequency is 2Khz, with a duty cycle from 0-100%.

Vi=+24V, Vo=12V.  A fet will be used to switch the current, driven by the pwm.

I am not too concerned with output voltage regulation/noise, more concerned with effiency, especially at low duty cycles.

 

Any recommendations beyond careful selection of the input and output capacitors?  Concerns?

Thank you in advance for any help.

Greg

 

  • Greg:

    PTN78000H  has a minium load suggest of 100mA. The reason for the  minimum laod is prevent teh asynchronous ripple from appearing  on the out put bus. The efficiency at 100mA load is about 30% .

    The output capacitance limits are:

    Minimum 100µF polarized  with ESR minimum limit of 17m Ω.  The maximum output ceramic capacitance is limited to 200µF . The current transient will requuire additional output capacitance of about  560µF to 1000µF to holdup the 12V bus .

    The input capacitance could be increased in addition to the ceramics to at least 330µF.

    Thanks

    Tom 

  • Tom,

    Thanks for the quick feedback.  Sounds like I need to rethink the design a little.


    Greg