# Current regulation by way of reducing voltage, when is it ok?

#### jlawley1969

Joined Feb 22, 2021
15
Hi, me again,
where I am inverting 160VDC to 110VAC by way of an H bridge with modified sine wave. It will basically be mains power but the main purpose will be to charge laptops and similar devices. I have been given the design restraint of 3A output max and I have developed a way latching the circuit to shut down when it goes above 3A. But after posting here yesterday I was wondering if regulating the current would be a better solution. The best way I have seen this done is by reducing the voltage.

So my main question is would this method of current regulation work for my situation? from what I have seen laptop chargers are generally rated to accept a minimum VAC of 100 so that would give me about 10Vrms to play with. Would I be able to reducing the voltage more? Is there a better DC current regulating methods? (one that doesnt involve switching)
thank!

#### Papabravo

Joined Feb 24, 2006
16,103
It sounds like pure nonsense. Devices that you plug into the mains don't require current limitation, why would they need an inverter to do something that the mains won't do for them? Loads take the power they require -- no more, and no less.

#### ronsimpson

Joined Oct 7, 2019
1,227
It is common for a load to pull extra power at first turn on. Heating element, motor, TV, Computer .......
I would build the circuit to drop the voltage back for a while before "latching off".
In power there are two types of regulation CV and CC. Constant Voltage and Constant Current.
Normally you will run in CV and regulate at 110V. When the current reaches 3A you can drop the voltage and run in "not more that 3A" mode. (CC) Then if the voltage is less than 50V for more than 0.5 seconds latch off. (or turn off wait 3 seconds and try again).
What ever you do you need to save the half bridge from shorts and too much current.

#### Ian0

Joined Aug 7, 2020
2,189
If you connect a switched-mode power supply to it, the power supply will regulate its output, so if the input voltage reduces it will take more current not less, in order to keep the output the same.
The result of that is that the switching devices in the power supply will run warmer, and it will probably fail sooner.