Diodes in series

[MrBugs]

Can someone tell what the current handling characteristics are when using diodes in series?

Thank you
Brent

 

[Styx]

The current handling on diodes in series is no different than if ONLY one was used or tow in series or thre or...

In series the potential blocking voltage is the sum of all the blocking voltages


If you want to increase the current handling, then parallel diodes.



However, in upping the current handling of diodes by putting them in parallel you MUST ensure that they share current (not easy).

Equally by increasing blocking voltage by putting a load in series you must be careful of sharing the voltage (during switching)

 

[k7elp60]

For diodes in series, the forward current is for the lowest rated current diode. If the diodes have the same forward current then it is that rating.
When diodes are placed in series the current rating does not change, but the PIV does, and it = the addition of the individual diode PIV. When diodes are placed in series to increase the PIV rating it is highly recommended to parallel each diode with a high value of resistor to equalize the PIV across each diode.

 

[Dean Huster]

To elaborate a bit more on that PIV problem, I might add that the reason for swamping the series diodes with a high value resistor is because the reverse resistance of diodes of the same type number can vary radically. Three diodes of a four-diode series string may have a reverse resistance of 10M ohms at 500v while the fourth diode has an "even better" reverse resistance of 1G ohm. The diodes in the reverse direction will act as a voltage divider and the majority of the voltage will be across that one diode and easily blow it. The resistors equalize that voltage by bringing down the reverse resistance enough to protect them without introducing a significant amount of ripple into the supply.

Dean