power supply

[Adam2014]

Hi
i want to design a dual power supply as this the simulation i have done .
Q1) at the beginning of simulation the positive voltage start at 5 volt then decrease to 3 volt and still fixed at 3 volt
while the negative voltage start and still fixed at -5 volt
Q2) what the ripple value ?

 

[tronitech]

Doesn't your ground need to be connected to a centre tapped transformer?

All your capacitors are shown as polarised? Only the electrolytics are polarised (C1, C10) and C1 is shown the wrong way round.

 

[crutschow]

Yes, you need a transformer with a center-tapped secondary for that circuit to work.
Note that in your circuit both the plus and minus output currents have to be identical. Any load imbalance causes ground current which has no circuit path back to the transformer output. Remember, all currents must always have a return path.

 

[Adam2014]

thanks i rebuild my work and it works well ...
what the ripple value of my circuit ? i need it about 10%

 

[audioguru]

Your transformer has no voltage rating so we do not know if the regulators have enough input voltage to work properly.
Your circuit has no load so if the regulators have enough input voltage then the ripple will be extremely low.

For ripple as high as 10% then you do not need the voltage regulators.

 

[Adam2014]

this power supply for another circuit ,, i can propose the other circuit is a load ?
i need a max ripple 10% if i can reduce it i will do it

 

[audioguru]

The 470uF main filter capacitors have a fairly low value so they will produce plenty of ripple if the load current is more than a few hundred milliamps. The datasheets for the voltage regulator ICs show that they reduce ripple at least 1000 times so that 2V of ripple at their input results in 0.002V at their output.
If the voltage regulator ICs do not have a minimum input voltage (including the reduction in voltage caused by ripple) of about 7V then the ripple is passed to their outputs.