Likriktning och "switching transients"
Valve Wizard nämner 3 olika sätt för att tämja det han kallar för <i>switching transients"] från likriktningen. Har någon här på bojen trixat med dessa? Vilket sätt rekommenderas och hur stor skillnad gör de?
1. Kondingar parallelt med dioderna.
<i>Values of 10nF to 47nF are common, and they will also act as snubbing capacitors to supress the voltage transients produced by the diodes switching."]
2. Litet motstånd i serie efter likriktaren.
<i>Whenever the diodes switch on and off, as they deliver large pulses of current to the reservoir capacitor, they tend to produce a voltage spike known as a 'switching transient'. This can introduce high-frequency 'hash' noise into the power supply. This can be alleviated to some extent by placing a small resistor in series with the rectifier before the reservoir capacitor. This effectively 'slows down' the rate at whch the diodes switch on and off, smearing the transistion and reducing the switching transient."]
3. En mindre konding parallelt med första glättningskondensatorn.
Quote:
The reservoir capacitor needs to have a low reactance at frequencies up to 40kHz, because the HT at this point will contain high frequency harmonics caused by rectification. Its performance at these frequencies can be greatly improved by adding a capacitor in parallel with it, ten times smaller in value. (Another can also be added, ten times smaller than the second, but this would be usually be considered an extravogance.)
Själv anger han alltså en kapacitans på en tiondel av glättningskondensatorn, medan man i denna tråd även nämner värden på ca. en hundradel som tillräckliga:
http://ampgarage.com/forum/viewtopic.php?t=12166Vad anser bojen-juryn om dessa knep?
/Stefan
