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Registered Member #308
Joined: Sun Mar 12 2006, 03:30PM
Location: Denmark
Posts: 7
1: in my efforts to improve my coilgun-boost converter im starting to wonder if the diode i have used is fast enough, im sitting here with a 2-page datasheet on it, it doesnt say much, how do i determine how fast a diode is?
2: that whining that comes when you use a camera with blitz, how does that happen?, what kind of component(s) do that?, and would it be fairly accurate to use it as a voltage "indicator"?
Registered Member #85
Joined: Thu Feb 09 2006, 01:22PM
Location:
Posts: 21
1) Normally the diode datasheet should state the "reverse recovery time" which describes the time it takes for a diode to stop conducting upon voltage reversal. To measure this time you could monitor the current flowing through your diode with an ossciloscope and watch, how long reverse current is flowing.
2) The whining comes from the transformer that is driven in the upper end of the audible range (or hormonics of those?) and hence vibrates at those frequencys. The frequency varies with the voltage of the charged capacitor because the duty cycle and therefore the frequency rises, as the voltage rises. You can use it as a voltage indicator when you mesure which frequency the inverter puts out at which voltage, but there are better, simpler, more accurate and more reliable approaches. I could imagine, that the frequency is also dependant on the input voltage or the temperature.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
When we talk of how 'fast' a diode is, we are reffering to how quickly it turns OFF. So if this diode (1N54xx are slow) is used to 'catch' the excess energy in the coil - it's ok If this diode is subjected to frequent high-frequency reversals (such as a xwitching power supply / boost convertor) use UF54xx or other 'fast' diodes.
If a diode data sheet doesn't give reverse recovery time you can assume it's a standard (slow) diode typ. several us recovery, dc to audio frequencies only.
When I come across cheap fast diodes on eBay I buy a bunch so most of my circuits use fast diodes whether they're needed or not.
P.S. The pitch of the "whining' sound as the capacitor is charging is related to power/battery voltage and capacitor charging voltage so you can use it as a rough guide to charging voltage but a meter is much better.
Although moving coil panel meters are cute/stylish/retro I advise using those very cheap supermarket digital multimeters as they are cheaper, more accurate, and overall more versatile.
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2 quick questions: diode speed?, camera blitz-whining?
