Re: Capacitor-selection
- From: John Popelish <jpopelish@xxxxxxxx>
- Date: Sat, 31 Mar 2007 12:41:24 -0400
Rikard Bosnjakovic wrote:
For my next project I've just built a PSU using a small 9V-transformer. Hooking it up to a Graetz-bridge for rectification, I measure 9.5 volts over Vcc/GND (i.e. over "+" and "-" on the bridge) using my DMM.
Now I'm going to add filter caps. What I'm unsure of here is if 10v-ratings will work, or if 0.5 volts is a way too small safety margin. I have big (~4000uF) 10v-caps in my junkbox, and since the junkbox serve a purpose (using older but working components) I feel that I want to pick those instead of new 16v-rated caps instead.
So, will 10v-ratings work or will it be a too narrow margin?
A 9 volt AC sine wave swings from +1.414*9 to -1.414*9 or +-12.7 volts. A 9 volt transformer under no load may produce something like 110% of 9 volts (the rated voltage is produced at full rated current load), so those peaks might by more than a volt higher than that, approaching 14 volts. And sometimes the line voltage will be a bit higher than normal. The rectifier will waste somewhere between a volt and 2 volts of the transformer output, and the capacitor will tend to charge up to the peak of the rectified output, under light load. I would go with at least a 15 or 16 volt capacitor (little cost or size penalty for using a 25 volt unit), at about 4000 uF per ampere of expected output current. Expect to get a DC output current of only about 50 to 60% of the AC current rating of the transformer secondary.
.
- References:
- Capacitor-selection
- From: Rikard Bosnjakovic
- Capacitor-selection
- Prev by Date: Re: Volt-amps BS
- Next by Date: Re: Volt-amps BS
- Previous by thread: Re: Capacitor-selection
- Next by thread: Counting the number of banknotes in a stack using the optical technology
- Index(es):
Relevant Pages
|
|
