TheBackShed.com

Forum Index : Electronics : finally got it working

Author

Message

irishron40
Senior Member

Joined: 22/09/2014
Location: Ireland
Posts: 251

Posted: 02:04pm 19 Jul 2016

Copy link to clipboard

Print this post

It took a bit of time, but got it finished.

Thanks for the help and advise I have received.

Its a combined psu power supply and a variable 10A 2.5-28volt power supply

casing was from an old videotape player , and I put on a aluminium Front panel.

ron

Gizmo

Admin Group

Joined: 05/06/2004
Location: Australia
Posts: 5078

Posted: 02:14pm 19 Jul 2016

Copy link to clipboard

Print this post

Nice work Ron

Bet you learned a lot along the way.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

irishron40
Senior Member

Joined: 22/09/2014
Location: Ireland
Posts: 251

Posted: 02:17pm 19 Jul 2016

Copy link to clipboard

Print this post

I Did Glenn. especialy to use a magnifying glass. the problem was very tiny solder bridges.

all worked out in the end.

ron

oztules

Guru

Joined: 26/07/2007
Location: Australia
Posts: 1686

Posted: 07:03pm 19 Jul 2016

Copy link to clipboard

Print this post

Knowing what not to do is half the battle

Good that you persisted.

.........oztules

Village idiot...or... just another hack out of his depth

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 01:30am 20 Jul 2016

Copy link to clipboard

Print this post

Nice work, its been a long time comming and you have now got there.

Have you been game enough to short the output leads and dial the current up for a brief moment, to see if all works as intended.

How many more are you going to build now you have several made boards kicking around and all you need is to find the solder bridges on them.

Pete.

Sometimes it just works

Pete Locke
Senior Member

Joined: 26/06/2013
Location: New Zealand
Posts: 181

Posted: 08:42pm 20 Jul 2016

Copy link to clipboard

Print this post

Well done Ron. Yep, them wee small solder whiskers can cause clever bits to let the smoke out, and they wont tell you why

irishron40
Senior Member

Joined: 22/09/2014
Location: Ireland
Posts: 251

Posted: 11:22am 21 Jul 2016

Copy link to clipboard

Print this post

Thx Pete Locke. I learned the hardway , and will never forget that

Quote Have you been game enough to short the output leads and dial the current up for a brief moment, to see if all works as intended

Yes I did that and it worked Pete.

Can you just explane what stops this circuit from braking after shorting it?

I know it works , but love to know is it the lm723 that protects this circuit?

Thanks everyone.

ron

larny
Guru

Joined: 31/10/2011
Location: Australia
Posts: 346

Posted: 12:48pm 24 Aug 2016

Copy link to clipboard

Print this post

If you look at the data sheet for the LM723, I expect it will mention current limiting.

When the current reaches the level set by the Pot, the LM733 changes from a voltage source to a current source. Thus the current will not rise further.

I don't have the data sheet for the LM733 so here is an example from the 78L05 data sheet.

LM78L05
Output voltage tolerances of �5% over the temperature range
Output current of 100mA this limit is automatic. It is not set by a Pot.
Internal thermal overload protection
Output transistor safe area protection
Internal short circuit current limit

The items I've coloured are the internal protection features.

Note that the 78L05 is much simpler than the LM733.
Hope this helps, Len

Print this page

To reply to this topic, you need to log in.