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 Reverse recovery of a diode

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wasssup1990 Posted - Sep 25 2010 : 11:43:55 PM
For anyone interested, I made a simple boost converter that boosts 14V up to 60V to power a 100W light bulb. The reason why I am posting this is to show what the reverse recovery time (trr) of a silicon diode looks like on a DSO. I used a FR304 (Fast Recovery Diode) found in a modern SMPS from a kitchen refrigerator.

Channel 1 (yellow trace) is the ripple voltage across the output capacitor. Channel 2 (blue trace) is the positive going edge of the gate voltage on a RFP50N06 MOSFET. You can see as the MOSFET tries to turn on the diode needs roughly 152nS to be able to block the change in polarity across it.

Download Attachment: fr304_trr.png
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deltaX is the time period between the two cursor positions. deltaX is shown to be 152nS which is almost spot on with what the data sheet says.


Download Attachment: FR304_DSheet.png
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wasssup1990 Posted - Sep 26 2010 : 02:39:37 AM
If you are wondering how I made the inductor take a look at this collage. I removed the ferrite core from an unused T.V.'s HV flyback transformer. The winding itself had its original iron core removed - it was from a model train power supply.

Download Attachment: BoostSMPS_resize.jpg
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wasssup1990 Posted - Sep 26 2010 : 01:59:12 AM
FYI,
Boost converter SMPS experiment measurements:


V(in) = 24.1V
I(in) = 470mA
V(out) = 59.2V
I(out) = 184.4mA

Efficiency = 96.38%

T(ambient) = 21.1C
T(ferrite) = 24.2C
T(winding) = 26.3C
T(heat-sink MOSFET) = 23.3C
T(MOSFET) = 23.5C
T(output capacitor) = 21.8C
Tmax(load light bulb glass) = 128C aprox

The light bulb is a 100W 240V type operating at 24.67% rated voltage. I cannot produce 240V out of my boost converter due to the 60V reversed biased Zener diode from Drain to Source in the MOSFET.

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