Hi All,

The attached part circuit shows the power input to a DC Xenon beacon circuit. A customer is asking what is the capacitance of the device/unit. I am guessing they want that to possibly figure out inrush, also these beacons can sit at the end of a long cable run when installed.

I am trying to figure out how to do a rough-only calculation, would I be way off if I just say around 100uF based on the largest cap C1 on the power in section? The rest of the circuit U1 is a PWM generator for the step-up but.

Your input is appreciated.

 

What value and type is F1? Is it fast blow or slow blow? How many amps is it rated at? I have to guess that the input voltage is somewhere around 18 volts DC; probably less. How much less is yet unknown to us.

 

Thanks, @Tonyr1084 F1 is a slow 850mA, input range 20-28VDC.

 

The time constant R15.C16 will give it a bit of a soft-start, by taking 50ms or so to switch the MOSFET fully on.

 

The total input capacitance appears to be 300 MFD as there are three 100 MFD capacitors across the input, one immediately and two more with only a common mode choke in series.

 

@Ian0 Thanks, that section is the inrush controller part, but I was after the rough total circuit capacitance.
@MisterBill2 Thanks, did you mean just over 100uF plus including a couple of 100nF (C4 & C6)? So roughly just over 100uF?

If someone is asking about the capacitance of a circuit, I would automatically think they are indirectly referring to the inrush of the unit, I can't think of what else they are after.

 

The total input capacitance appears to be 300 MFD as there are three 100 MFD capacitors across the input, one immediately and two more with only a common mode choke in series.

C1 looks like 100µ
C4 & C6 look like 100n

 

C1 looks like 100µ
C4 & C6 look like 100n

C4 and C6 looked like "m" at the time. You are correct, though. Sorry about the misreading.

 

Thank you all. I guess we conclude that the input capacitance is roughly just over 100uF.