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Old 3rd December 2012, 01:06 AM   #1
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Default modifying number of turns on trafo

good day to everyone.herewith is the schematic of the project ive done.
everything is good until now.
i just want to ask if is it possible to add turns on the secondary of the trafo.i used ei-33 trafo from old atx psu.i want to add turn up to let say 50+v.am i going to change the irfz44 or the tl494?
need some experts regarding this.i just want to try it but parts of that project are hard to find here in my place.i ordered them from ebay so i want to ask first to avoid expensive mistakes.
tia
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Old 3rd December 2012, 03:44 AM   #2
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If you are just raising the output voltage (and lowering output current in proportion) I don't think you need to change anything. Except for output diode PIV if required.

If you are raising the output voltage and output power then you may have to change the transformer, the FETs, the Fet's drive.

But I'm not sure why you would need to change the 494.
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Old 3rd December 2012, 04:59 AM   #3
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thank's dug
fets are hard to find here in my place.ive search the web about smps with higher voltage output and found that parts are hard to avail so i just thought that what if i'll just modify what ive done but i have to ask experts first.
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Old 3rd December 2012, 03:12 PM   #4
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I do not understand your question. Are you saying you have already built this smps with an EI33 core and it is working. And now you want to modify it for more voltage on the secondary.
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Old 5th December 2012, 01:04 AM   #5
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Quote:
Originally Posted by powerbob View Post
I do not understand your question. Are you saying you have already built this smps with an EI33 core and it is working. And now you want to modify it for more voltage on the secondary.

sorry for the late reply so much bz.
yeah i built this one and im asking if it is possible or safe to turn up/add more voltage to secondary.
thank's for the time
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Old 5th December 2012, 03:22 AM   #6
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“i want to add turn up to let say 50+v"

After 30V you need to be a little more careful with isolation of the primary and secondary. As a minimum use 3 wraps of a high temperature high voltage tape between the 2 winding’s, and also each secondary. You can add more secondary turns, if you have room for them? What is the winding width of your bobbin? I will try to run some numbers.

The primary side is OK with the TL494 and the irfz44 fet’s.
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Old 5th December 2012, 08:02 AM   #7
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Yes u can wind more on the secondary. More windings may give you more ringing. As long as the MOSFETs can handle the voltage spikes, no prob with them. But increasing the voltage by 20% may also increase the current output and thus the power? Will the devices and transformer handle that?

Quote:
Originally Posted by powerbob View Post
“i want to add turn up to let say 50+v"

After 30V you need to be a little more careful with isolation of the primary and secondary. As a minimum use 3 wraps of a high temperature high voltage tape between the 2 winding’s, and also each secondary. You can add more secondary turns, if you have room for them? What is the winding width of your bobbin? I will try to run some numbers.

The primary side is OK with the TL494 and the irfz44 fet’s.
30V? I've done flyback transformers up to 350V without any tape at all for experimentation. I dunno how high a voltage transformer wire handles, but it surely is >30V. If you have high leakeage inductance it may be good to try without tape and interleave as much as possible. If you have too much leakeage capacitance tape between layers will help. It's all trade offs and experimentation is neccesary to find the optimum combination.
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Old 5th December 2012, 12:19 PM   #8
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Quote:
Originally Posted by blakdrag View Post
good day to everyone.herewith is the schematic of the project ive done.
everything is good until now.
i just want to ask if is it possible to add turns on the secondary of the trafo.i used ei-33 trafo from old atx psu.i want to add turn up to let say 50+v.am i going to change the irfz44 or the tl494?
need some experts regarding this.i just want to try it but parts of that project are hard to find here in my place.i ordered them from ebay so i want to ask first to avoid expensive mistakes.
tia
To produce 50V You need 17 windings in each secondary. (Will give 48V)
Remember that the bobbin used limits the power, so even if You have more voltage on the secondary, You will get less Amps.
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Old 5th December 2012, 12:30 PM   #9
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Quote:
Originally Posted by TANDBERGEREN View Post
To produce 50V You need 17 windings in each secondary. (Will give 48V)
Remember that the bobbin used limits the power, so even if You have more voltage on the secondary, You will get less Amps.

WRONG

You need to know the V/T ratio of the transformer before you can make such wildly innaccurate statements.
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Old 5th December 2012, 12:59 PM   #10
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Quote:
Originally Posted by KatieandDad View Post
WRONG

You need to know the V/T ratio of the transformer before you can make such wildly innaccurate statements.
I don't thing his statement innaccurate. This is switching power supply, so if V/T ratio got wrong, PWM ratio still can be change.

Didiet
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