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Power Supply with transformer 300V

D

Dotinho

Jan 1, 1970
0
Hello, i have i power supply of Siemens in one olde machine, and i
have to repair it, but i don't know how.

the essencial, the 1 step is transform 220 VAC to 315VDC and then a
MOSFET will pulse the 300VDC at 50KHz to a transformer that out 5V at
secudary, the problem is that tranformer giver out 8V and don't work..

Anyone can tell me if i change the frequency,. the output volt will
decrease?

Thanks.
 
D

Dan H

Jan 1, 1970
0
Hello, i have i power supply of Siemens in one olde machine, and i
have to repair it, but i don't know how.

the essencial, the 1 step is transform 220 VAC to 315VDC and then a
MOSFET will pulse the 300VDC at 50KHz to a transformer that out 5V at
secudary, the problem is that tranformer giver out 8V and don't work..

Anyone can tell me if i change the frequency,. the output volt will
decrease?

Thanks.

Not likely that freq is problem

More likely:

The power supply expects a load at the output that will drop the
voltage or

There is a control circuit at the output that feeds back to control
the voltage and the feedback control is not working.

Dan
 
R

Robert Baer

Jan 1, 1970
0
Dotinho said:
Hello, i have i power supply of Siemens in one olde machine, and i
have to repair it, but i don't know how.

the essencial, the 1 step is transform 220 VAC to 315VDC and then a
MOSFET will pulse the 300VDC at 50KHz to a transformer that out 5V at
secudary, the problem is that tranformer giver out 8V and don't work..

Anyone can tell me if i change the frequency,. the output volt will
decrease?

Thanks.
I have seen a few circuits that do preliminary regulation by
switching the supply voltage like that, but usually SCRs or triacs are
used, so it might be a good thing to double check not only that part but
everything around it.
Do you have a schematic; if not, scribble one up aqnd document each
part as best as you can.
Check each part to see if they are within spec, especially that "MOSFET".
I am guessing that the "MOSFET" is always on, and that the second
transformer sees the full 300V sinewave from the first one.
Then again, you did say 315VDC, which (to me) means that the circuit
may be closer to what i had seen.
First is a transformer, Primary: 220VAC,Secondary: 300VAC.
Second is most likely a bridge rectifier where at least 2 components
are SCRs that are switched, allowing the output to be adjusted from zero
to 315VDC.
Now it is possible that 4 diodes are used and a MOSFET is in the
bridge acting as a series adjustable resistor to the "load", but that
useage (as a series resistor) is extremely unlikely to say the least.
If indeed it is a MOSFET, it most likely is used as a timed and
synchronized switch to the load and there is no filtering on the 315VDC
source (might be some at thhe load).
So now one has a semi-regulated and adjustable DC to feed some kind
of a load.
It is not clear as what that load is; surly DC *cannot* be applied
directly to a transformer!
Usually, that DC is used to drive a switcher that drives the second
transformer, and the second one is dinky compared to the first
transformer. That was done in a high votage bench supply that was
precicely (via a helipot) adjustable from 0 to 3KV (i think; it has been
over 30 years).

Maybe what the layout is like the following:
First is a transformer, Primary: 220VAC,Secondary: 300VAC.
Second is most likely a bridge rectifier where at least 2 components
are SCRs that are switched, allowing the output to be adjusted from zero
to 315VDC.
Now it is possible that 4 diodes are used and a MOSFET is in the
bridge acting as a timed and synchronized switch to the load (second
transformer).
So now one has a semi-regulated and adjustable AC to feed that
transformer.

No matter what the case is, it is clear that the switching components
(SCRs, Triacs, MOSFETs) are "shorted" and thus the full sine wave is
being applied to that second transformer.
 
D

Dotinho

Jan 1, 1970
0
Robert Baer escreveu:
I have seen a few circuits that do preliminary regulation by
switching the supply voltage like that, but usually SCRs or triacs are
used, so it might be a good thing to double check not only that part but
everything around it.
Do you have a schematic; if not, scribble one up aqnd document each
part as best as you can.
Check each part to see if they are within spec, especially that "MOSFET".
I am guessing that the "MOSFET" is always on, and that the second
transformer sees the full 300V sinewave from the first one.
Then again, you did say 315VDC, which (to me) means that the circuit
may be closer to what i had seen.
First is a transformer, Primary: 220VAC,Secondary: 300VAC.
Second is most likely a bridge rectifier where at least 2 components
are SCRs that are switched, allowing the output to be adjusted from zero
to 315VDC.
Now it is possible that 4 diodes are used and a MOSFET is in the
bridge acting as a series adjustable resistor to the "load", but that
useage (as a series resistor) is extremely unlikely to say the least.
If indeed it is a MOSFET, it most likely is used as a timed and
synchronized switch to the load and there is no filtering on the 315VDC
source (might be some at thhe load).
So now one has a semi-regulated and adjustable DC to feed some kind
of a load.
It is not clear as what that load is; surly DC *cannot* be applied
directly to a transformer!
Usually, that DC is used to drive a switcher that drives the second
transformer, and the second one is dinky compared to the first
transformer. That was done in a high votage bench supply that was
precicely (via a helipot) adjustable from 0 to 3KV (i think; it has been
over 30 years).

Maybe what the layout is like the following:
First is a transformer, Primary: 220VAC,Secondary: 300VAC.
Second is most likely a bridge rectifier where at least 2 components
are SCRs that are switched, allowing the output to be adjusted from zero
to 315VDC.
Now it is possible that 4 diodes are used and a MOSFET is in the
bridge acting as a timed and synchronized switch to the load (second
transformer).
So now one has a semi-regulated and adjustable AC to feed that
transformer.

No matter what the case is, it is clear that the switching components
(SCRs, Triacs, MOSFETs) are "shorted" and thus the full sine wave is
being applied to that second transformer.


Thats true, but the transformed are mailfunction, becoused i already
tested the other part, and that tranformer don't produce anymore, and
i'm trying to get another solution, you understand?

thanks..
 
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