Did i kill my 7805? - Electronic Circuits Projects Diagrams Free

Marks256 · 24th August 2006, 04:26 AM

I have a neat little power supply that i made up. Here is the link to the schematics; Power Supply

I have a 9Vdc @ 500mA power supply running into it. I just turned it on, and my z80 circuit booted, i then went to turn the manual clock on, and everything just, shut off? I immediately turned off the power switch. Now, when i try to turn it on, the 7805 gets REALLY hot REALLY fast. I did have a heat sink on it, too. What is the deal? I am guessing i blew it out.

eblc1388 · 24th August 2006, 04:35 AM

Test the 7805 alone without the Z80 connected.

A good 7805 will gives close to 5V at its output and remains cold without load.

RadioRon · 24th August 2006, 04:38 AM

7805 is hard to blow out due to load problems because it has a thermal limiter built in. If it is getting hot with a load attached, there is probably a bad load, like a short circuit.

Marks256 · 24th August 2006, 05:25 AM

Oh my God! I feal soooo embarrassed! I found a short circuit! :embarrassed: My bad.

One of my CAPS were shorting on one of my resistors.

Sorry for starting a full thread about this? Oh well, i am going to put a fan on the heat sink tomorrow. :cool:

Dr.EM · 24th August 2006, 10:06 AM

Once you have eliminated the short, you probably won't need the fan? What is the proper current drain of the circuit, got to keep it under 1A for the 7805.

**Nigel Goodwin** · 24th August 2006, 10:29 AM

Quote:

Originally Posted by Dr.EM

Once you have eliminated the short, you probably won't need the fan? What is the proper current drain of the circuit, got to keep it under 1A for the 7805.

And WELL under 1A if you don't want to make toast on the 7805!

JimB · 24th August 2006, 02:12 PM

Quote:

Originally Posted by Marks256

I have a 9Vdc @ 500mA power supply running into it.

Less than 500mA would be better!

JimB

Marks256 · 24th August 2006, 04:03 PM

No. The thing gets very hot as it is. I know i am sucking A LOT of power from this baby. Soon, i am going to pull the power supply out of an old Apple 2e. I have the connector all soldered together, but i am just to lazy to pop the thing out.

I rigged up a nice i686 fan onto it. I just have to figure out how to mount it? I am thinking Twist-Ties, or maybe cable ties? I don't know right now. I think i will go get that power supply! :cool:

AllVol · 24th August 2006, 05:39 PM

For what it is worth, I recently built a little 7805-regulated psu that I have successfully used for several projects. The attached shows it powering a two-digit counter that has been in continuous operation for a couple of months.

I am using a Hewett-Packard wall-wart that is labeled 9 vdc @1000 mA.
I have not had any heat problems. As can be seen, I do not have to use a heat sink.

AllVol

Marks256 · 24th August 2006, 05:44 PM

Then why on earth does mine get so HOT? I have literally burned my finger on the thing!

AllVol · 24th August 2006, 05:57 PM

I dunnough.... I have goofed up a few times and got things backwards. They got hot in a hurry, sometimes even to the point of extinction. Carefully check everything. Sometimes an error can be so obvious it looks correct.

Allvol

**Nigel Goodwin** · 24th August 2006, 06:19 PM

Quote:

Originally Posted by Marks256

Then why on earth does mine get so HOT? I have literally burned my finger on the thing!

For a start, do you have capacitors on the input and output, with short leads as close as possible to the 7805? - if not it's probably oscillating?.

Assuming you do, then measure the current it's taking from the supply, and also measure the input voltage (don't beleive the spec on the PSU).

Marks256 · 24th August 2006, 08:23 PM

Yes, i have got the filter caps on the input, and on the output. I don't have anything to test it with, but the fan keeps it nice and cool now.

**Nigel Goodwin** · 24th August 2006, 09:21 PM

Quote:

Originally Posted by Marks256

Yes, i have got the filter caps on the input, and on the output. I don't have anything to test it with, but the fan keeps it nice and cool now.

A Z80 is a fairly hungry chip - I would still suggest you measure the current though. If you haven't got a multimeter I suggest you go out and buy one!, you can't do anything without one, you've got a breadboard - you should have bought a meter first!.

Marks256 · 24th August 2006, 09:49 PM

I now, but i only have $5us right now. I used to have one, but i blew it out(long story). I know that the Z80 is a HUGE power hog. I am just going to connect a new power supply to it.

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24th August 2006, 04:26 AM	(permalink)
Marks256	Did i kill my 7805? I have a neat little power supply that i made up. Here is the link to the schematics; Power Supply I have a 9Vdc @ 500mA power supply running into it. I just turned it on, and my z80 circuit booted, i then went to turn the manual clock on, and everything just, shut off? I immediately turned off the power switch. Now, when i try to turn it on, the 7805 gets REALLY hot REALLY fast. I did have a heat sink on it, too. What is the deal? I am guessing i blew it out. __________________ There is no "I" in "team", unless Apple makes it... Then it would be iTeam.

24th August 2006, 04:35 AM	(permalink)
eblc1388	Test the 7805 alone without the Z80 connected. A good 7805 will gives close to 5V at its output and remains cold without load. __________________ L.Chung

24th August 2006, 04:38 AM	(permalink)
RadioRon	7805 is hard to blow out due to load problems because it has a thermal limiter built in. If it is getting hot with a load attached, there is probably a bad load, like a short circuit. __________________ RadioRon

24th August 2006, 05:25 AM	(permalink)
Marks256	Oh my God! I feal soooo embarrassed! I found a short circuit! :embarrassed: My bad. One of my CAPS were shorting on one of my resistors. Sorry for starting a full thread about this? Oh well, i am going to put a fan on the heat sink tomorrow. :cool: __________________ There is no "I" in "team", unless Apple makes it... Then it would be iTeam.

24th August 2006, 10:06 AM	(permalink)
Dr.EM	Once you have eliminated the short, you probably won't need the fan? What is the proper current drain of the circuit, got to keep it under 1A for the 7805. __________________ Angry!? I'm absolutely electrolytic! Will have to make do with myspace now I guess...

24th August 2006, 04:03 PM	(permalink)
Marks256	No. The thing gets very hot as it is. I know i am sucking A LOT of power from this baby. Soon, i am going to pull the power supply out of an old Apple 2e. I have the connector all soldered together, but i am just to lazy to pop the thing out. I rigged up a nice i686 fan onto it. I just have to figure out how to mount it? I am thinking Twist-Ties, or maybe cable ties? I don't know right now. I think i will go get that power supply! :cool: __________________ There is no "I" in "team", unless Apple makes it... Then it would be iTeam.

24th August 2006, 05:39 PM	(permalink)
AllVol	For what it is worth, I recently built a little 7805-regulated psu that I have successfully used for several projects. The attached shows it powering a two-digit counter that has been in continuous operation for a couple of months. I am using a Hewett-Packard wall-wart that is labeled 9 vdc @1000 mA. I have not had any heat problems. As can be seen, I do not have to use a heat sink. AllVol __________________ All those who believe in psycho kinesis, raise my hand. Last edited by AllVol; 6th February 2007 at 01:49 AM.

24th August 2006, 05:44 PM	(permalink)
Marks256	Then why on earth does mine get so HOT? I have literally burned my finger on the thing! __________________ There is no "I" in "team", unless Apple makes it... Then it would be iTeam.

24th August 2006, 05:57 PM	(permalink)
AllVol	I dunnough.... I have goofed up a few times and got things backwards. They got hot in a hurry, sometimes even to the point of extinction. Carefully check everything. Sometimes an error can be so obvious it looks correct. Allvol __________________ All those who believe in psycho kinesis, raise my hand.

24th August 2006, 08:23 PM	(permalink)
Marks256	Yes, i have got the filter caps on the input, and on the output. I don't have anything to test it with, but the fan keeps it nice and cool now. __________________ There is no "I" in "team", unless Apple makes it... Then it would be iTeam.

24th August 2006, 09:49 PM	(permalink)
Marks256	I now, but i only have $5us right now. I used to have one, but i blew it out(long story). I know that the Z80 is a HUGE power hog. I am just going to connect a new power supply to it. __________________ There is no "I" in "team", unless Apple makes it... Then it would be iTeam.