Power supply problem for isolation amplifier?

乱世煮酒论天下

Power supply problem for isolation amplifier? [Copy link]

When the potential of the signal to be tested is very high, an isolation amplifier is needed to achieve high-voltage detection. The isolation amplifier is divided into two circuits on the left and right in the schematic diagram. The left side represents the high-voltage input circuit, which also needs power supply, so the power supply and ground on the left are also high voltage. The back-stage circuit on the right is a low-voltage detection circuit, which also needs a separate power supply. The power supply for low-voltage detection and the power supply for high-voltage detection are completely isolated.

1. This kind of high-voltage detection is most commonly used in the inverter drive circuit. The switching power supply of the small and medium-power inverter provides 4 drive power supplies, three power supplies for the upper bridge drive and one power supply for the lower bridge (because the lower bridge is in common ground). I think the principle is like this. These four drive power supplies are provided by the switching power supply and are isolated from each other. Therefore, the front stage of the drive circuit isolation amplifier is also isolated from each other, but the back stage of these four drive isolation amplifiers is in common ground. Only low-voltage weak electricity is needed to detect the signal on the high-voltage side. Why can the small isolation chip withstand the isolation of thousands of volts in structure, and what technology is used?

2. To achieve isolation between the high-voltage side and the low-voltage side, the isolation amplifier has no feedback, and generally uses optical isolation or magnetic isolation technology. Usually, the optical isolation solution is used, but how does the optical isolation solution amplify the analog signal? How does the optical receiving end of the subsequent detection determine the strength of the optical signal emitted by the previous stage and then output a linear signal?

maychang

[Why can the isolation chip withstand thousands of volts in terms of structure? What technology is used? ]

Some use magnetic coupling, some use capacitive coupling, and some use optical coupling.

In the past, an isolation amplifier AD210 was used, which used magnetic coupling (transformer) for isolation.

maychang

[How does the optical isolation solution achieve the amplification of analog signals? 】

Look up "linear optocoupler". For example, the datasheet of HCNR200 201. It has a light-emitting diode and two photoelectric tubes inside.

maychang

[In order to achieve isolation between the high voltage side and the low voltage side, the isolation amplifier has no feedback]

The linear optocoupler has two identical phototubes inside, the purpose of which is to achieve negative feedback of the amplifier, thereby ensuring that the nonlinearity of the linear optocoupler is very small.

大智若愚123

I have benefited a lot and learned a lot. There are many posts like this where people help each other.

beyond_笑谈

Why can a small isolation chip withstand thousands of volts of isolation in terms of structure? What technology is used?
// Mainly divided into capacitive isolation and transformer isolation, there is also high-speed optocoupler isolation

beyond_笑谈

How does the optical isolation solution achieve the amplification of analog signals?

//You can understand the CTR of the optocoupler