LT1054 Simple Question

[lkm32]

Hello all,

I've been working on a small project that needs a negative voltage rail and after trying out a whole lot of different options (virtual ground, two batteries, etc.) and decided on using a dedicated IC (LT1054IP in this case to give me a simple unregulated negative voltage).  I am basing this on a circuit in the LT1054 datasheet.

In simulation, the circuit works well but breadboarding it resulted in me only getting a positive 5 Volts at the output.

Any advice as to what I might be doing wrong?

[rxxbxyhxxb]

Did you use the LT1054L which is 3.5V~7V Absolute operating.

[lkm32]

Did you use the LT1054L which is 3.5V~7V Absolute operating.

No, I am using the LT1054IP from TI. Also, I am not even getting a negative voltage at the output.

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[theatrus]

Did you build it as documented?

What capacitors? Do you have a scope you can use to check if the unit is actually switching or attempting to?

[lkm32]

Did you build it as documented?

What capacitors? Do you have a scope you can use to check if the unit is actually switching or attempting to?

[emoji21] whelp I found out what the issue was. I feel stupid.

I hooked up the cap + side to a scope and noticed that other than an initial poweron rise it would stay stable at around VCC.

I then had the common sense to do continuity tests on the various jumpers and lo and behold the jumper from ground to the breadboard rail was broken.

Replaced that and everything is fine now.  I will get some tantalum capacitors tomorrow though to get less of a voltage drop at higher currents.

Thanks for the patience and sorry for my stupid mistake.

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[theatrus]

It happens to the best of us

I'd recommend MLCC ceramics for the most part, though tantalums are ok.

[John Coloccia]

Depending what you're doing, you may want to protect the power input with a zener.  I forget the spec off the top of my head, but if the absolute max rating is 12V, for example, I promise you that 12.0001V will blow it up.  It's a common issue with these kinds of charge pumps.

[lkm32]

Yup, abs max is 16V for unregulated so I have a 15.1V zener on the input.

This may be out of scope, but is is possible to make an unregulated inverter using a MC34063 or the like?  While not super necessary, it would be nice to have a greater input voltage range.

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