DC to DC Power Supply Design

[paul_g_787]

HI. I am wondering if anyone can shed some light on this DC to DC power supply design? (see attached image).
I am not sure exactly what is going on here as I have never dealt with this type of power supply before.

I can see that it outputs +5V (VCC)
and ground is AG
so I am assuming VEE is -5V? But it is not labelled.

I may be missing something obvious but can anyone explain what is going on with this circuit and how it is generating a negative voltage from the +5VDC?

I am working on a little project which requires both a +5V and -5V supply, and I am looking at powering it from USB, which of course is only +5V.

Any alternative designs or suggestions are welcome.

Thank you.

[Mark]

Depending on your current requirements, what about the LTC1044?  5Vin, -5Vout. 

The LTC®1044 is a monolithic CMOS switched capacitor
voltage converter which is manufactured using Analog
Devices’ enhanced LTCMOS™ silicon gate process. The
LTC1044 provides several voltage conversion functions:
the input voltage can be inverted (VOUT = –VIN), doubled
(VOUT = 2VIN), divided (VOUT = VIN/2) or multiplied (VOUT
= ± nVIN).

[Mark]

Another option for a possibly cleaner supply: LTC3265, so this part takes 5V from USB, boosts the voltage and uses LDO for lower noise +/- outputs. 

Boost Charge Pump Generates 2 • VIN_P
(VIN_P Range: 4.5V to 16V)
Inverting Charge Pump Generates –VIN_N
(VIN_N Range: 4.5V to 32V)
Low Noise Positive LDO Post Regulator Up to 50mA
Low Noise Negative LDO Post Regulator Up to 50mA

[T3sl4co1l]

It's a blocking oscillator, though not a great one I think.  Would be okay for low to modest currents, where efficiency and ripple don't matter.  The transformer could be a small pulse transformer, coupled inductor, or even some common mode chokes.

Tim

[paul_g_787]

Thanks everyone! Using the information you all have provided I think the simplest solution for me is to use an ICL7660 (because they are cheap and easy to get). I found that it is a compatible IC for the aforementioned LTC1044.

Additionally, the output current of the 7660 far exceeds what my circuit needs on the -5V rail.

After reading the data-sheet for the ICL7660 and looking up some example circuits, I have come up with the attached schematic. Anyone have any opinions on this design or suggestions for improvement?

[tooki]

For what it's worth, in a project I'm working on, we are using the TI TPS65133 to get ±5V rails from a single Li-Ion battery (3.7V). I simply duplicated the layout and component choices from the datasheet and it works perfectly, being clean enough for audio.

[eplpwr]

Anyone have any opinions on this design or suggestions for improvement?

C2 has the polarity wrong.

[LaryPant]

Anyone have any opinions on this design or suggestions for improvement?

C2 has the polarity wrong.

Edit: I was looking at the wrong schematic. Disregard everything down below.

No it does not.

C2 is connected between Vee and ground. Vee is at -5 V and ground is zero. So the positive terminal should be connected to ground, as is shown in the circuit diagram. Ground is at a higher potential than Vee.

By your logic C3 would have no polarity wrong as well, but it is correct AFAIK.
The positive terminal of a capacitor goes to the highest potential, and in this case it is ground and not Vee.

Lary

[T3sl4co1l]

Are you looking at the wrong one?



C2 positive goes to "-5V", pretty obvious typo, just flip it around.

Tim

[LaryPant]

Are you looking at the wrong one?



C2 positive goes to "-5V", pretty obvious typo, just flip it around.

Tim

Oh dammit, I looked at the original schematic.

Sorry!

I will update my other post.

[paul_g_787]

C2 has the polarity wrong.

Yes indeed!. I did notice that too and have corrected it but thanks for pointing it out