- #1
DragonPetter
- 830
- 1
If I consider a simple example of charging a capacitive load with a low impedance source, and charge the capacitor through a diode, I will have a very high current spike through the diode while the capacitor charges to the supplied voltage.
When I look for diodes and see their peak pulse current, most of them are quite small compared to the "theoretical" infinite current you would have into a capacitor to charge it.
Say the ESR of a capacitor is 100 mOhms, and you charge it with a 20V source through the diode, the current spike in the diode will be about (20-.7)/.1 = 199 amps, and I have not found a normal diode that has this spec.
Yet I have seen, for example, a car battery with a diode after its positive terminal, to protect a reverse voltage connection, and then feed into a capacitive load (ceramic capacitors in front of a SMPS) and these diodes are fine.
Why do these diodes have small peak pulse currents, but can handle surge currents?
When I look for diodes and see their peak pulse current, most of them are quite small compared to the "theoretical" infinite current you would have into a capacitor to charge it.
Say the ESR of a capacitor is 100 mOhms, and you charge it with a 20V source through the diode, the current spike in the diode will be about (20-.7)/.1 = 199 amps, and I have not found a normal diode that has this spec.
Yet I have seen, for example, a car battery with a diode after its positive terminal, to protect a reverse voltage connection, and then feed into a capacitive load (ceramic capacitors in front of a SMPS) and these diodes are fine.
Why do these diodes have small peak pulse currents, but can handle surge currents?