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Negative LDO for -100V to -90V

Sheng-wei Wang
Prodigy 70 points
Other Parts Discussed in Thread: TPS40210, TL783, TL431

Hi,

I used TPS40210 to generate +100V and -100V outputs in my circuit, it works fine but switching noise on output is as high as 1V~2V, which is not acceptable for my application. 

I had tried to add RC filter on both outputs, switching noise can be reduced a little bit but still not acceptable.

Then I add a positive LDO(TL783) on +100V output and reduce output voltage to -90V, the switching noise on +90V is much more reduced(about 300mV), so I think a suitable LDO can help me to overcome switching noise problem.

However, I cannot find a LDO which can accept -100V input and output -90V. Is there any way to use existing LDOs with some modifications(cascading LDOs?) to achieve this application ?

P.S. output loading is about 100mA for both +90V and -90V

Thanks a lot.

  • 0
    TI__Guru*** 147046 points

    Sheng,

    For the linear regulators, a shunt regulator controlling a pass transistor and protected from high voltage by a common base amplifier could work for the positive and negative regulator. The attached (untested) circuit regulates 140V to 125V. The values can be changed for 100V to 90V operation. The C1 capacitor will help phase margin when a output capacitor is used. The transistors need to be rated for the input voltage and there is no current limit or temperature shutdown.

    For the -90V, change the NPN transistors to PNP and change TL431 to TL4051 (with cathode to ground) The Vref is lower so the Vout feedback will need to change value.