I know a virtual ground will never be as good as proper bipolar supply, but there is a lot to be said for the convenience of only needing one DC source for circuits that need a split supply.
After searching the forums I've read that if the virtual ground supply is floating (for example, two batteries), it's all right to connect the virtual ground to the main system ground. But what if the virtual ground supply has an earth reference as well? An example would be a laptop power brick with a 3 pin mains plug - live, neutral and ground. The virtual ground used could be a simple resistor divider, TLE2426, or BUF634 rail splitter. Is it safe to use such a virtual ground supply with a "normal" ground in a non-floating circuit?
I'm trying to get my head around the current flow but I keep confusing myself. Things could go wrong. With a resistor divider on a 24V supply, you actually have 24V, 12V and 0V, not a true +12V, -12V, 0V, right? This means the virtual ground is actually 12V above system ground, yes? Does the same apply with the TLE2426 / BUF634 setup?
Any advice would be great before I fry something...
After searching the forums I've read that if the virtual ground supply is floating (for example, two batteries), it's all right to connect the virtual ground to the main system ground. But what if the virtual ground supply has an earth reference as well? An example would be a laptop power brick with a 3 pin mains plug - live, neutral and ground. The virtual ground used could be a simple resistor divider, TLE2426, or BUF634 rail splitter. Is it safe to use such a virtual ground supply with a "normal" ground in a non-floating circuit?
I'm trying to get my head around the current flow but I keep confusing myself. Things could go wrong. With a resistor divider on a 24V supply, you actually have 24V, 12V and 0V, not a true +12V, -12V, 0V, right? This means the virtual ground is actually 12V above system ground, yes? Does the same apply with the TLE2426 / BUF634 setup?
Any advice would be great before I fry something...
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Really? Why is that?
How can a "virtual" ground system also have a ground connection? It would no longer be "virtual" (I prefer the term floating ground) in that case.
You might think about what is happening when you connect a floating ground system to one that has an earth ground reference.
Remember that the magnetic circuit in a transformer cannot pass DC and decouples the absolute voltage levels on the primary and secondary. This is the same whether the PS is linear or switching - both use a transformer. It's only when you tie one point in the system to a fixed voltage "reference" that you really establish the voltages WRT that reference. For example, you claim "0V, 12V, 24V" but the actual voltages could be anything unless one of those is tied to a reference voltage. The PS is only generating the RELATIVE VOLTAGE DIFFERENCES of 12V (between 0V and 12V, and again between 12V and 24V). This is why you can connect two floating supplies, like two 12V batteries with + and - tied together , and the voltage can add to produce 0V, 12V (at the +/- tie point), and 24V. The same is true for any floating supplies.
Thank you for the reply Charlie.
I've just measured a TLE2426 with a 12V supply, and sure enough the virtual ground output is at 6V in relation to the supply's ground. If I used it in a circuit and connected that virtual ground to the ground of a CD player, via an RCA cable, there would be a 6V difference and current would flow, yes? This would surely burn out the TLE2426 with the short circuit?
Does this mean that a TLE2426 is only useful when the entire system (source, amp, etc) is floating and not tied to mains earth anywhere, since they all share the same ground via interconnects?
I've just measured a TLE2426 with a 12V supply, and sure enough the virtual ground output is at 6V in relation to the supply's ground. If I used it in a circuit and connected that virtual ground to the ground of a CD player, via an RCA cable, there would be a 6V difference and current would flow, yes? This would surely burn out the TLE2426 with the short circuit?
Does this mean that a TLE2426 is only useful when the entire system (source, amp, etc) is floating and not tied to mains earth anywhere, since they all share the same ground via interconnects?
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Apologies for my noobishness - that's exactly what I'm trying to understand. The vast majority of the reading I've done uses term like signal ground, power ground, and chassis ground.
Let me try another approach. Let's say that ground is exactly that - a spike driven into the earth. This is connected via the third pin to Class I equipment, and omitted in Class II double insulated equipment. Most of the builds I've seen on the DIYAudio forums have their signal 0V reference connected to the chassis at some point, and the chassis in turn is connected to the ground pin of the IEC inlet. Likewise, the power supply 0V reference is also connected to the chassis. This means that ground, signal 0V, power 0V and the chassis should all be at the same potential. Am I right so far?
The virtual (floating) center reference created by something like a TLE2426 or resistor divider is actually just half the supply voltage (eg. 6V from a 12V supply). This gives is a point around which we can now define a new schema of +6V, 0V at the floating center, and -6V. This is fine when the whole system is based around that floating center. Am I still on track?
My question is this: how does this floating center behave when some part of the system (such as the CD player mentioned in my previous post) has its 0v reference at the same potential as ground due to chassis connection, which is what the floating center sees as -6V?
I hope that clears things up. Please help with simple explanations if possible
Only if there are no currents flowing in any of the ground wires. You may be confusing safety ground (which forms a current loop to blow a fuse or breaker when something goes wrong with mains wiring) with signal ground (which establishes a voltage reference point for music signals).BuckarooBanzai said:
I suspect you need to understand voltage. All voltages (yes, every one everywhere in the entire universe) is the difference in potential between two points; there is no such thing as 'a voltage'. When you say something is at +6V you and the person you are talking to must agree on what the second point is; often some agreed 'ground'. If something is floating then by definition it is not referenced to a ground so therefore cannot have a voltage. A +6-0--6V supply which is floating may have 12V between its two outputs, but is does not have a voltage with respect to ground. I don't mean zero volts (which is a voltage), but no voltage at all - undefined, non-existent.
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