Products > Test Equipment
An investigation about ripple current of Kunkin KP184
atarian:
Here are some more grabs. Probe connected onto the VIN+ and VIN- screw terminals on top board this time. Scope set to DC coupling now to be see if any DC voltage is present. Like this, I have seen massive swing down to -3VDC with rise time about 0,8s and drop time about 5s. Just like coil kick back, only there is no coil anywhere as far as I can see? Except for the transformer...
Anyway, here you are:
DC coupling, 1V and 200us /div
atarian:
In greater details:
DC coupling, 200mV and 400ns /div
atarian:
AC mains switch state change events:
atarian:
AC output on transformer looks good enough tho. Almost perfect 50Hz sine, no oscillations. Something must have been feeding this 5MHz noise into the 16V DC power rail then. As far as I can see there is only 7805 linear 5V regulator and some SOT23-6 packaging chip hooked up there (U24). I think I have my suspect.
EDIT: U24 seems to be some kind of switched mode power/PWM fan speed controller. With U24 temporarily removed from PCB, all ripple on DC power rails and output is gone.
G.O.N.E.
All I am seeing is just white noise with amplitude of around 15mV (my oscilloscope/probes can not do any better anyway). Naturally, heatsink cooling fan is out of order now and the question is how to hook it up again. Does anyone see any better solution then to move it entirely onto separate board with separate power supply?
Can anyone please identify the chip so that we get at least a datasheet with design recommendations? Maybe Kunkin just fed up something in its implementation.
atarian:
After all, it will not be that hard task: U24 is simple switching mode regulator with very poor parameters. Yes, it cripples input "by design":
http://aosmd.com/res/data_sheets/AOZ1282CI.pdf
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