Suggestions for power supply modifications

[Johan Wagener]

I just finished a PCB layout of a project we have to do. It is a variable 3A
DC power supply. I uses a L200 and a LM358 to control 2 2N3055 transistors.
The transistors limit the current. We have to make modifications (fans,
thermal protection, ect.)to the circuit to achieve good marks. I would
appreaciate any suggestions of modifications I can make to this circuit.

 

[Ghost Chip]

I just finished a PCB layout of a project we have to do. It is a variable 3A
DC power supply. I uses a L200 and a LM358 to control 2 2N3055 transistors.
The transistors limit the current. We have to make modifications (fans,
thermal protection, ect.)to the circuit to achieve good marks. I would
appreaciate any suggestions of modifications I can make to this circuit.

You might add an over-current crowbar circuit or at least an LED indicating
it's in the current-limit condition. Todays cpu fans make real nice power
supply coolers. It's cheaper to add one than a much larger heat sink.
Ghost

 

[Mjolinor]

variable
You might add an over-current crowbar circuit or at least an LED indicating
it's in the current-limit condition. Todays cpu fans make real nice power
supply coolers. It's cheaper to add one than a much larger heat sink.
Ghost

Thermistor in series with the fan supply is the first mod I do on all PC
PSUs I buy. It makes them quiet when they are not needed, RS sell suitable
ones

 

[Watson A.Name - Watt Sun]

You might add an over-current crowbar circuit or at least an LED indicating
it's in the current-limit condition. Todays cpu fans make real nice power
supply coolers. It's cheaper to add one than a much larger heat sink.
Ghost

CPU fans work great - until they sieze up and quit cooling. Then it's
just a matter of time until the whole thing quits. How do you think I
make a living as a tech at work? It's like job security!


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[Watson A.Name - Watt Sun]

Thermistor in series with the fan supply is the first mod I do on all PC
PSUs I buy. It makes them quiet when they are not needed, RS sell suitable
ones

Well, one question is what value do you use? And how do you keep the
PSU from overheating, if the fan doesn't work when the thermistor is
cool. I've seen the thermistors mounted right next to the CPU
heatsink, so I guess it senses the temp. But how does one do it for a
PSU fan.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[DarkMatter]

I just finished a PCB layout of a project we have to do. It is a variable 3A
DC power supply. I uses a L200 and a LM358 to control 2 2N3055 transistors.
The transistors limit the current. We have to make modifications (fans,
thermal protection, ect.)to the circuit to achieve good marks. I would
appreaciate any suggestions of modifications I can make to this circuit.

I would make the circuit function, fans and all, at rated load,
without significant or what you would deem excessive heating.

THEN, make sure that placing a dead short or zero ohm load on it
causes it to "fold back", which means that it (the drivers) still
exhibit some heat, but not more than when operating. That is a sort
of thermal protection built into it you limit the max current in the
design itself. Usually, one can facilitate this by using a "base
resistor" in the transistor leg, but I do not know what type of design
you are using, so I'll just say that the key to limiting the supply in
an overloaded condition is in limiting the maximum output of the
transistors, regardless of the feedback loop signal. That insures
that it will perform at the rated load, but not much (there has to be
some headroom) more than that. You should incorporate some sort of
user setable output current limit capability You really didn't give
much info about the actual design, so it is hard to suggest solutions.

 

[DarkMatter]

CPU fans work great - until they sieze up and quit cooling. Then it's
just a matter of time until the whole thing quits. How do you think I
make a living as a tech at work? It's like job security!

Bah! Some fans are good, some fans are bad. If it's cheap chinese,
it probably doesn't have a very long lifespan, I put better brand PSUs
in my PCs.

Industrial surplus and liquidators have american made (or designed
at least), ball bearing (really!) fans which are what any long life
term product should have incorporated into it.

When are you going to seize up?

The e is before the i in this one. Doh!

Ha! A mere PC tech.

 

[LASERandDVDfan]

Todays cpu fans make real nice power

supply coolers. It's cheaper to add one than a much larger heat sink.
Ghost

Or use a combination of both. - Reinhart

 

[Nico Coesel]

Thermistor in series with the fan supply is the first mod I do on all PC
PSUs I buy. It makes them quiet when they are not needed, RS sell suitable
ones

And probably makes you wonder why your PC's crashes all the time
during a hot day... Every year it's fun to notice most messages with
the subject 'Help, my computer crashes when I.....' are posted during
the summer.

 

[Mjolinor]

Well, one question is what value do you use? And how do you keep the
PSU from overheating, if the fan doesn't work when the thermistor is
cool. I've seen the thermistors mounted right next to the CPU
heatsink, so I guess it senses the temp. But how does one do it for a
PSU fan.

I knew that was coming, I have searched the RS site and can't find it. The
fan rotates slowly all the time so there is air flow over the device. They
really do work well, I got the part number from an article in a PC magazine
about 8 years ago. I know that I saved the RS packaging in case I needed to
order any more but can't find it now. If it turns up I will post again.

 

[Mjolinor]

And probably makes you wonder why your PC's crashes all the time
during a hot day... Every year it's fun to notice most messages with
the subject 'Help, my computer crashes when I.....' are posted during
the summer.

In fact this PC doesn't crash (over much ). It actually runs in a hotter
environment than most as it is in the loft and for example, the max and min
internal temp on this little theremometer here read 49.8 and 15.5. Not that
I am up here during the hot times, you can't walk more than half way up the
stairs without breaking into serious sweats and taking clothes off but the
computer works fine.