Author Topic: Low power, low quiescent step-down from 65V to 40V?  (Read 644 times)

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Offline asymconTopic starter

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Low power, low quiescent step-down from 65V to 40V?
« on: May 07, 2020, 03:04:21 pm »
Hi there,
I need to work around a 53V limit of a LDO on a specific board by injecting it 40-ish volts, while the rest of the circuit gets full 65V.
And I'm a bit struggling to get 40V out of 65V in (somewhat) simple design.

Project requirements are these:
  • sub 1mA quiescent current, ideally zero (this preregulator will be always connected to battery)
  • at least 50mA output current (30mA expected maximum, with some reserves)
  • stable output at 40V, regardless of what is the input voltage (always above 40V, but discharged battery will be 45V)

With such small currents, both LDO and switching regulators are good, but getting the quiescent current below 1mA is crucial.
I tried to play with TL783, but couldn't get anywhere, based on R2 value, it sucks up to 5mA from the source.

Is there a simple or ready-made solution for this?

Thanks!
« Last Edit: May 07, 2020, 03:10:53 pm by asymcon »
 

Offline pardo-bsso

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Re: Low power, low quiescent step-down from 65V to 40V?
« Reply #1 on: May 07, 2020, 03:07:30 pm »
Series string of zeners?
 

Offline asymconTopic starter

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Re: Low power, low quiescent step-down from 65V to 40V?
« Reply #2 on: May 07, 2020, 03:12:11 pm »
Series string of zeners?
Might work, but I forgot to mention, that the 40V out should be if possible, stable, regardless of input.
 

Offline unitedatoms

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Re: Low power, low quiescent step-down from 65V to 40V?
« Reply #3 on: May 07, 2020, 03:18:16 pm »
Consider following shunt regulator like classic Zener, but with current limiter instead.
+60V->LT3092(tuned to 0.5mA, bypassed by 20-30V Zener to protect it)->reference resistor bypassed with capacitor->ground.

At top of reference resistor you get exactly say 41V (by choosing a resistor). Tap this point with base of Darlington emitter follower, with say 10k resistor at base.

Edit: or shunt regulator with pair of LT431 20V each and emitter follower.
« Last Edit: May 07, 2020, 03:23:32 pm by unitedatoms »
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Offline eliocor

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Re: Low power, low quiescent step-down from 65V to 40V?
« Reply #4 on: May 07, 2020, 04:24:03 pm »
I never had problems with the LM5165 (11µA no load quiescent current).
Unluckily its max input voltage is just 65V.... :(
 

Offline asymconTopic starter

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Re: Low power, low quiescent step-down from 65V to 40V?
« Reply #5 on: May 07, 2020, 05:03:55 pm »
Found possibly best solution for this -> TPS7A4001
100V, ultra low IQ (just few uA) and 50mA max output.
But I miscalculated and it turns out I'll need close to 100mA.

Would enhancing the heat dissipation abilities of TPS7A4001 would allow it to operate at 100mA (typ. current limit kicks in at 117mA)?
http://www.ti.com/lit/ds/symlink/tps7a4001.pdf
« Last Edit: May 07, 2020, 05:06:30 pm by asymcon »
 


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