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Old 17th January 2009, 01:12 PM   #81
L700 is offline L700  Malaysia
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thanks .... i dunno y after the bridge it soo high voltage

can i use LM338 to lower down the voltage
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Old 17th January 2009, 05:18 PM   #82
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A transformer converts AC to a different voltage AC. The bridge converts AC to DC. To calculate the DC after the bridge (assuming there are smoothing capacitors), multiply the transformer secondary voltage by 1.4. So for a 30V transformer, you'll get 42V. BUT, that is at full transformer load. At no load, your voltage will be higher. 46V is not abnormal.
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Old 17th January 2009, 07:39 PM   #83
Nuuk is offline Nuuk  United Kingdom
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Quote:
can i use LM338 to lower down the voltage
Yes, in which case you will have a regulated supply as described here . But I suggest you do plenty of reading before you build it.
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Old 18th January 2009, 05:43 AM   #84
L700 is offline L700  Malaysia
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Quote:
Originally posted by Redshift187
A transformer converts AC to a different voltage AC. The bridge converts AC to DC. To calculate the DC after the bridge (assuming there are smoothing capacitors), multiply the transformer secondary voltage by 1.4. So for a 30V transformer, you'll get 42V. BUT, that is at full transformer load. At no load, your voltage will be higher. 46V is not abnormal.

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Originally posted by Nuuk


Yes, in which case you will have a regulated supply as described here . But I suggest you do plenty of reading before you build it.
thanks man .... i been reading i need to put in trimmer to adjust the output voltage
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Old 18th January 2009, 01:14 PM   #85
Stream is offline Stream  Russian Federation
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Hello. I'm newbie DIYer , so have many qestions

My next (and first "serious" at the same time) project will be simple Headphone amp (CMOY and the second one is class A on IRF510).

I read some begginer guides and draw this scheme (see attach).
Tranformer has two secondaryes (4 wires) . I wonder if I need two rectifier-bridges or only one is necessary?

I'd like You to check this, and tell, if it has any mistakes, please

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File Type: png psu01.png (11.9 KB, 1391 views)
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Old 19th January 2009, 08:03 PM   #86
jockwe is offline jockwe  Sweden
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humm, i have a problem with my psu. i have a dual secondary 31Vdc. but if i am trying to get ground between the two secondarys, but if i connect the two to use a single rectifier the whole transformator gets really hot, and if i use 2 rectifiers and try to get a ground between + and - it also gets really hot. i can get power from it but simply not when i try to get a ground too. what could i possibly be dooing wrong?
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Old 19th January 2009, 08:42 PM   #87
AndrewT is offline AndrewT  Scotland
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you forgot to use a light bulb tester for first power up of any project.
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Old 19th January 2009, 09:01 PM   #88
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Quote:
Originally posted by jockwe
humm, i have a problem with my psu. i have a dual secondary 31Vdc. but if i am trying to get ground between the two secondarys, but if i connect the two to use a single rectifier the whole transformator gets really hot, and if i use 2 rectifiers and try to get a ground between + and - it also gets really hot. i can get power from it but simply not when i try to get a ground too. what could i possibly be dooing wrong?
Sounds like your secondary wires are mixed up?
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Old 19th January 2009, 11:23 PM   #89
jockwe is offline jockwe  Sweden
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turns out my transformer was broken in some way, there was connectivity between the two secondarys. damn, now i have to get another one.
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Old 25th January 2009, 05:51 AM   #90
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I throw myself at your mercy nuuk.


My ps is developing altogether far too much power. I'm getting about 82v dc out of it per secondary. I have an amveco xformer rated at 140VA, 24v secondary vac, 2.8aac. At first I had no juice atall. I tore down, re-filed the secondaries and built a new rectifier on the spare audiosector board. Now I have too much power!
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