Guru
Joined: 02/02/2017
Location: AustraliaPosts: 1424
| Posted: 11:22am 19 Mar 2018 |
I just tried this with a 60W Apple "magsafe" macbook powersupply.
This is an offline switching PS.
Light blue is the current transformer, 10V/div and 0.095 V/Amp
The negative going peak is 30V which is 315 Amps.
The DC bulk capacitor on the HV side of this PS seems to appear
as a short circuit during the initial stage of charging.
The Purple trace is as always the 50 Amp LEM current sensor.
Blue is AC output voltage.
These short lived high current events show how important it is to over build
the mosfets. This inverter under test uses 4 x IRF3808 on each leg of the bridge
These are rated at 140A each at 25 Deg C for continuous load.
Pulse current rating is 550 A and I guess this is the max current you can put through
the device while being careful not to let the chip get "too hot"
wronger than a phone book full of wrong phone numbers