EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: KBJ on May 18, 2019, 10:54:38 am
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I am currently designing a power supply system where i need 3 voltages i.e 3.3v,2.5v and -2.5v. for 3.3v i'm using a MIC5504-3.3YM5-TR. For the bipolar voltages i have planned to use a charge pump of 5v and use a split rail power supply. The entire system uses a 3.7v lipo battery. The problem i'm facing is ground reference. There is a virtual ground from the split rail power supply and 3.3v LDO has a ground. Is implementing such a system is possible if so how to connect the ground and virtual ground?
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Many linear amplifiers that use a split supply can be biased at half the supply voltage and use coupling capacitors to work perfectly with a single supply.
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Awhile ago, Audioguru did schematic showing the inverting and non-inverting op-amp configurations: both DC and AC coupled. Here's my version, showing the differential configuration too. The recommended resistor values are selected to ensure the DC impedance seen by the inputs are virtually equal and is important for a bipolar op-amp, with high bias currents.
(https://www.eevblog.com/forum/beginners/tl072-microphone-preamp-(differential)/?action=dlattach;attach=388679;image)
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How much current on each rail ?
How accurate must the 2.5v and -2.5v be?
If the current is low on 2.5v, you could get that simply by adding a diode after the 3.3v ... a basic `1n4001..1n4007 will have a forward drop of 0.7v..0.8v at even 50-100mA ... so 3.3v - 0.7v = ~ 2.6v
You could get a basic charge pump regulator like MAX1720 to invert the 2.5v and you get -2.5v if you only need up to 50mA or so : https://www.onsemi.com/pub/Collateral/MAX1720-D.PDF (https://www.onsemi.com/pub/Collateral/MAX1720-D.PDF)
There's also regulators like AP3427 which have 2 outputs, so you can use one chip to create both 3.3v and 2.5v with higher efficiency: https://www.diodes.com/assets/Datasheets/AP3427M.pdf (https://www.diodes.com/assets/Datasheets/AP3427M.pdf)
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For the bipolar voltages i have planned to use a charge pump of 5v and use a split rail power supply. The entire system uses a 3.7v lipo battery. The problem i'm facing is ground reference. There is a virtual ground from the split rail power supply and 3.3v LDO has a ground. Is implementing such a system is possible if so how to connect the ground and virtual ground?
no, it is not possible to mix a 0V with virtual ground/0V.
ALL voltages are with reference to a 0V !
As Mariush has suggested there are special ASICs that convert a positive voltage to a negative voltage.
I was going to suggest the old classic 7660, which converts a positive toltage to a negative voltage.
Hope that helps.