energypower
Looking at the Microchip Energy Chip reference design
I noticed that the power is being sampled from neutral. My first reaction to this was this is backwards, that the power should be sampled from the live. however, the guide talks about the concept of a live or hot ground. what is the advantage of using a hot or live ground as the ground reference in such a design as opposed to sampling from live?
The rate at which these gates are turned on and off seems to have no relation to the power used.
This is where you are wrong. Basically, each gate is a capacitor with an incredibly tiny capacitance. Switching it on and off by "connecting" and "disconnecting" the voltage moves an incredibly tiny electrical charge into or out of the gate - that's what makes it act differently.
And a moving electrical charge is a current, which uses power. All those tiny currents from billions of gates being switched billions of times per second add up quite a bit.
From the datasheet:
This is saying the junction temperature will rise 100 K per watt dissipated. The case temperature will be somewhat less than this, but this datasheet doesn't break out the junction-to-case thermal resistance separately, only the junction-to-ambient.
A change of one K is the same as one degree C, so you will see both units used for this spec.
When you are dissipating that 0.42 W at room temperature, the junction is about 25 + (100 * 0.42) = 67 C. If we guess that the case temperature is halfway between junction and ambient, that would be about 46 C, or 115 degrees Fahrenheit. Does that sound about right?
Best Answer
The current shunt of an electricity meter is in the live conductor. This means the low voltage circuit reference is the live conductor.
The voltage circuit of the meter is as you explain connected between the live and neutral circuits, with the volt drop resistor connected to the neutral circuit.
All shunt electricity meters use this principal. They are safe because the are double insulated as indicated by the \$\ {\LARGE\square}\hspace -2.2ex {^\square}\ \ \$ symbol on the faceplate.