Isolated DC-DC power supply module, input and output common ground problem.

燕园技术宅

Isolated DC-DC power supply module, input and output common ground problem. [Copy link]

 

       The problem encountered is this: the system power supply is DC12V, and two subsystems need to be powered. One is the subsystem that generates square wave signals (here named subsystem 1), and the other is the subsystem that measures the frequency of square wave signals (here named subsystem 2). Subsystem 1 is directly powered by 12V, and subsystem 2 needs to use a DC-DC power module with isolation function to reduce 12V to 5V before powering. So if my subsystem 1 and subsystem 2 do not share the same ground, the frequency measurement cannot be achieved, right? However, the 5V power supply ground and 12V ground of subsystem 2 have been isolated by the power conversion module. If I connect the input and output grounds of the power conversion module together, the isolation function of the power module will lose its meaning. If they are not connected together, how should I achieve the common ground of subsystem 1 and subsystem 2? I hope you can give me some guidance!

maychang

The input and output of the power module do not share a common ground, but your two subsystems (generating square wave signals and measuring square wave signals) share a common ground, which is completely feasible.

燕园技术宅

maychang posted on 2019-1-13 17:15 The input and output of the power module do not share the same ground. It is completely feasible for your two subsystems (generating square wave signals and measuring square wave signals) to share the same ground.

The two subsystems have no other connection except a signal transmission line, so it is a headache to realize the common ground between the two.

qwqwqw2088

Subsystem 2 is a measurement function with isolation measures. The ground connection will not affect the overall system power supply.

maychang

Yanyuan Technology House published on 2019-1-13 19:11 It is like this. The two subsystems have no other connection except a signal transmission line, so it is difficult to realize the common ground between the two.

"The two subsystems have no other connection except a signal transmission line" That is impossible. In addition to the signal transmission line, there must be a ground wire. Or use differential signal transmission, which requires two signal lines.

maychang

Yanyuan Technology House published on 2019-1-13 19:11 That's right, the two subsystems have no other connection except a signal transmission line, so it's a headache to realize a common ground for the two.

Your two subsystems are connected with a signal line and a ground wire (so they share a common ground), which is better than connecting the input and output of your 12V to 5V module.

chunyang

If isolation is required, the signal must also be isolated. You cannot just use an isolated power supply and connect the signal directly. There must not be any electrical connection between the two systems, otherwise the isolation is meaningless. If isolation is not required, just use a normal power supply. There is no need to use an isolated power supply, which is much more expensive.

燕园技术宅

maychang posted on 2019-1-13 19:51 Your two subsystems are connected with a signal line and a ground line (so that they share the same ground), which is better than connecting the input and output of your 12V to 5V module...

I understand what you mean. It seems that you either need to replace the power module or find a way to connect a ground line.

燕园技术宅

chunyang posted on 2019-1-13 20:04 If isolation is required, the signal must also be isolated. You cannot just use an isolated power supply and connect the signal directly. There must not be any electrical connection between the two systems, otherwise the isolation will fail...

Because I bought more than a dozen power modules before, I didn't notice that they were isolated, and I only paid attention to the output power. So I plan to solve the above problems based on the use of isolated power supplies. It seems that I still have to change the power module when necessary.

maychang

Yanyuan Technology House published on 2019-1-13 20:36 I understand what you mean. It seems that either you need to change the power module or find a way to connect a ground wire

Why change the power module? Connect the input end and the output end of your isolated power module together to make it a non-isolated module. If you use non-isolated modules for your two subsystems, then the two subsystems will "share the same ground" at the power supply. If the two subsystems are connected to a ground wire in addition to the signal line, then the two subsystems will "share the same ground" by this ground wire.

燕园技术宅

maychang posted on 2019-1-13 20:48 What is the purpose of changing the power module? Connect the input end and the output end of your isolated power module together, and it is a non-isolated module. Your two...

Well, this is how it is done now. Yesterday I asked the technicians of Jinshengyang Power Supply. In addition to the isolation, the input and output common ground has no effect on the output of the module. I was worried that it would affect the output of the power supply!

chunyang

Yanyuan Technology House published on 2019-1-13 20:39 Because I bought more than a dozen power modules before, I didn’t notice that they were isolated, and I only paid attention to the output power. So I plan to use the base of isolated power supply...

If it is not a batch product, there is no change, just connect the ground on both sides of the power module. After the isolated power supply is grounded, it only loses isolation, and does not affect other things.