Discussion in 'General Electronics Chat' started by nahlaelazab, Jun 18, 2014.

1. ### nahlaelazab Thread Starter New Member

Jun 18, 2014
1
0
for simple peak detector of diode and series capacitor, i 'd like to know why the capacitor reaches the peak after some cycles. i think the charged voltage level in 1st cycle is vp-vdiode and it is the max value can be reached using this circuit

2. ### crutschow Expert

Mar 14, 2008
13,505
3,379

The charging time is determined by the value of the capacitor and the available charging current from the source (or the source resistance). So if it doesn't charge to the peak in one cycle then you need more charging current or a smaller capacitor.

3. ### AnalogKid Distinguished Member

Aug 1, 2013
4,702
1,300
In most offline power supply circuits, either linear or switching, the bulk capacitor charges up to Vpeak in one or two cycles of input AC. But the current surge is huge. It is typical for the 200 W switchers in pc chassis to have an inrush current of 40A - and that is with inrush current limiting. Without limiting it can hit 100 A.

So it really is all about the current sourcing capability of the circuit feeding the peak detector. e x c = i x t. If you know the frequency of interest and the available current, you can calculate how much voltage will build up in the cap in the first cycle.

ak