Output taking time to go to 0V

[FreshmanNewbie]

I am using this AC-DC Module - LS01-K3B05SS (https://www.mornsun-power.com/html/pdf/LS01-K3B05SS.html)

which converts 230V AC mains to 5V. When I turn off the 230V mains AC, the 5V takes around 10seconds to go to 0V.

This 5V from the AC-DC module has a 220uF cap alone. Why does it take 10s for the 5V to go to 0V?

 

[danadakk]

Depends on load current draw from cap :

Q = C x V
dQ/dt = I = C x dV/dt

So lower load current being taken out of C longer its takes to
do the dV or drop in voltage. Compounding problem is if load
itself is not linear in current draw, not atypical that its current draw
at lower V much lower hence even longer for C to decay.


Regards, Dana.

 

[FreshmanNewbie]

Depends on load current draw from cap :

Q = C x V
dQ/dt = I = C x dV/dt

So lower load current being taken out of C longer its takes to
do the dV or drop in voltage. Compounding problem is if load
itself is not linear in current draw, not atypical that its current draw
at lower V much lower hence even longer for C to decay.


Regards, Dana.

I have removed the capacitors at the output of the AC-DC module. Still the output takes a lot of time (10 seconds) to go to 0V.

 

[barry]

Then there’s some capacitance elsewhere in the circuit.

 

[D.A.(Tony)Stewart]

I am using this AC-DC Module - LS01-K3B05SS (https://www.mornsun-power.com/html/pdf/LS01-K3B05SS.html)

which converts 230V AC mains to 5V. When I turn off the 230V mains AC, the 5V takes around 10seconds to go to 0V.

This 5V from the AC-DC module has a 220uF cap alone. Why does it take 10s for the 5V to go to 0V?

Perhaps you ignored the 10% minimum preload but both C1 and C2 are necessary to store energy during a 1 cycle dropout which is often a std. design feature at full load.

Consequently, your 10 s result is an excellent figure of merit for no load time constant for low leakage. A 1 s decay would be acceptable, but 10 s decay indicates an excellent result.

 

[KlausST]

Hi,

what´s the problem at all?
Many power supplies keep the voltage for 10s on no load when powered off.
Laptop supplies, 5V USB supplies, 24V industrial supplies ....

I mean: When I switch my hand held light off (no load) the battery keeps the voltage for years... and I see no problem with it.

--> do a test with useful load current

****
As Tony wrote The input capacitor needs to keep the energy for a one cycle power out at full load.
Now at no load the capacitor energy needs to be dissipated somewhere .. since it is a "green" power supply it is designed for low power dissipation ... especially at no load.
Additionally the power supply is designed for a wide input voltage range. This means the input capacitor needs to work even at minimum specified input voltage.
Like 85V AC. capacitor stored energy rises with square of voltage. 85V --> 230V means more than 7 times the stored energy.
And if you consider a minimum "operable" capacitor voltage (maybe 50V DC) then the ratio of the "usable" energy is even a bigger factor.

So the behaviour is quite expectable - surely nothing special.

Klaus