Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: loogie on February 10, 2009, 05:56:36 am

Title: Need some help. Having chip failures
Post by: loogie on February 10, 2009, 05:56:36 am

I have a friend whose been working on this simple LED pulsing curcuit:

http://www.electronics-lab.com/projects/motor_light/020/

When he uses a battery as the power source it works ok.  When he substitues a 4.5v wall wart it goes for a while and then the chip fails.  He's tried adding some resistance to the power supply and that seems to help, but it still eventually fails.  He needs it for a display he's working on that will be running for hours at a time.

Do any of you have any ideas on how this could be improved or how he might be able to save the chip?  I know I'm not giving much info, but he's in England, I'm in Akron and neither of us knows too much about this stuff.

Thanks

Title: Re: Need some help. Having chip failures
Post by: sluckey on February 10, 2009, 06:23:10 am

Be sure the wallwart is DC. Then put a 7805 5 volt regulator (with cap on input and cap on output) between the wallwart output and the circuit.

Title: Re: Need some help. Having chip failures
Post by: loogie on February 10, 2009, 09:33:47 pm

Thanks!  I'll pass that along.

Title: Re: Need some help. Having chip failures
Post by: PRR on February 11, 2009, 09:01:29 pm

Try TL072 chip.

Try 100K resistor so that huge cap doesn't blast the chip's input.

But circuits like this DO usually work, without special care. You are nowhere near the chip's 32V supply voltage limit, output current, etc. And a circuit very much like this is on the first page of the '358 datasheet (http://www.national.com/ds/LM/LM158.pdf).

Title: Re: Need some help. Having chip failures
Post by: PRR on February 11, 2009, 09:08:06 pm

I'm now thinking: bad connection, makes contact at first, then fails; the act of swearing and replacing the chp "fixes" it, at first, then fails again.

Stuff like that makes us crazy.

Title: Re: Need some help. Having chip failures
Post by: loogie on February 12, 2009, 05:06:07 pm

Try TL072 chip.

Wll do, guv'.  Thanks.

Title: Re: Need some help. Having chip failures
Post by: sluckey on February 12, 2009, 05:16:20 pm

If all you want to do is flash a LED and you're not locked in on any particular circuit, you should look at the 555 timer. Very simple, cheap, minimum components, and rugged.

Title: Re: Need some help. Having chip failures
Post by: loogie on February 13, 2009, 01:15:59 pm

Is the 555 capable of a ramp wave?  Thats what we need.

Title: Re: Need some help. Having chip failures
Post by: sluckey on February 13, 2009, 02:53:11 pm

no.

Title: Re: Need some help. Having chip failures
Post by: loogie on February 19, 2009, 08:19:09 pm

This is an international project.  My good buddy, Heywood, down in Tejas had success with an LM324.  I'm guessing he used that because that's what he had.

I'm going for the TL072 this weekend.

Title: Re: Need some help. Having chip failures
Post by: DummyLoad on February 19, 2009, 11:57:43 pm

Quote from: sluckey on February 13, 2009, 02:53:11 pm

no.

yes.

http://www.allaboutcircuits.com/vol_6/chpt_6/8.html

Title: Re: Need some help. Having chip failures
Post by: loogie on February 20, 2009, 03:49:47 pm

Ok, looks like another option.  Thanks!