Hi,
Not sure if best to post in general chat or power electronics, but:
I am having some significant issues when measuring my power converter capacitances with a hand-held LCR meter than I expect from the specification. I have a series-parallel combination of capacitors that should give an effective capacitance of 30nF. I have attached a schematic.
However, when the components are placed on the board, they are each reading a capacitance of approximately 17.5nF. I was confused because this significantly higher value isn't just one component, but all of them. I also have a 330uF electrolytic capacitor at my power converter input alongside some 0.1uF and 1uF decoupling capacitors, but the total input capacitance when measured with the LCR meter is about 20uF. It is a combination of electrolytic and smaller MLCC capacitors, but no more than 20% tolerance from the specification.
I also have a 120R resistor, which is 1% tolerance, showing up as 98R. Some more 1nF capacitors, 5 in parallel, which is reading a capacitance of >8nF. I have tested a different set of capacitors, also C0G from KEMET with an impedance tester, which confirms a capacitance of 10nF. I have not tested the ones soldered on my board yet, but plan to do so next week when I am back at work.
Can anyone suggest any reasons why a hand-held LCR meter could give such wildly different readings when components are soldered to the PCB? Some kind of layout issue, perhaps? Any suggestions are welcomed.
Note: I tested the 10nF C0G capacitor with the hand-held LCR, it is showing 10nF as expected, and agrees with the impedance tester, when not soldered to the PCB. So this leads me to believe that there is something else going on "inside the bonnet" when they are soldered which starts to effect their effective capacitance?
Thanks,
SiC
Not sure if best to post in general chat or power electronics, but:
I am having some significant issues when measuring my power converter capacitances with a hand-held LCR meter than I expect from the specification. I have a series-parallel combination of capacitors that should give an effective capacitance of 30nF. I have attached a schematic.
However, when the components are placed on the board, they are each reading a capacitance of approximately 17.5nF. I was confused because this significantly higher value isn't just one component, but all of them. I also have a 330uF electrolytic capacitor at my power converter input alongside some 0.1uF and 1uF decoupling capacitors, but the total input capacitance when measured with the LCR meter is about 20uF. It is a combination of electrolytic and smaller MLCC capacitors, but no more than 20% tolerance from the specification.
I also have a 120R resistor, which is 1% tolerance, showing up as 98R. Some more 1nF capacitors, 5 in parallel, which is reading a capacitance of >8nF. I have tested a different set of capacitors, also C0G from KEMET with an impedance tester, which confirms a capacitance of 10nF. I have not tested the ones soldered on my board yet, but plan to do so next week when I am back at work.
Can anyone suggest any reasons why a hand-held LCR meter could give such wildly different readings when components are soldered to the PCB? Some kind of layout issue, perhaps? Any suggestions are welcomed.
Note: I tested the 10nF C0G capacitor with the hand-held LCR, it is showing 10nF as expected, and agrees with the impedance tester, when not soldered to the PCB. So this leads me to believe that there is something else going on "inside the bonnet" when they are soldered which starts to effect their effective capacitance?
Thanks,
SiC