Negative 1V5 at 100mA is so expensive?

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cupoftea

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Hi,
Just looking for the cheapest, fairly well regulated NEG1V5 supply from a 10V source. Load from 0 to 100mA.
The attached is the cheapest i can get so far.
Any cheaper ideas?
Charge pumps are not regulated (not the cheapos) and so cant really do it even though cheap.

Its just a NEG1V5 rail which acts as a turn off voltage for NPN's....due to the sheer expanse of the circuit, and wiring etc, the grounds may not be the same everywhere, so we want a slight negativised turn-off voltage to assure we deffo turn off when we want to.

LTspice and PNG attached.

BTW we would use the cheaper UCC28C43 rather than the pin4pin LT1243.
 

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  • CUK NEG 1V5.png
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  • cuk.zip
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The LM555 ( non cmos ) has an inherent flaw - in that the shoot thru current in the output stage at every transition is significant - this is why if you run them at 50 - 100mA and say 100kHz for too long - they simply die - whereas the TLC 555 will drive an emitter follower for ever @ 100kHz.

For increased efficiency - the skilled engineer can choose L1 shown above and the caps to operate near resonance - where the switching currents are near zero at every transition - pulling down on pin 5 reduces the pwm and gives a reg -Vout.

Smaller cap sizes are inherently current limiting to the load.
 
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Thanks,
The attached LTspice and PNG, shows the reg'd 555. We would use
the 7555 as it avoids the output stage problem that Easy Peasy
kindly spoke of.
It needs the filter inductor or else the di/dt in the ground
tracks will be large and create possible noise issues.
--- Updated ---

So its 555 vs Cuk
 

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  • 555 regd.zip
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  • 555 regd.png
    54.3 KB · Views: 16
  • 555 regd_common base.png
    53.3 KB · Views: 12
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