LM7824CT replacement
I need to replace this TO220 regulator in a power supply I'm working
on. The original is a "CT" suffix however looking through the books I see that there are several other versions of this part. The original seems to be a 1.0 amp device while several others appear to be able to handle 1.50 amps. I would like to buy a few extras to have on hand. Aside from any appreciable price difference, would it make sense to buy a bunch of "CT's" that will only handle 1.0 amp when there are1.50 amp parts available that will do the equivalent job? Thanks, Lenny |
LM7824CT replacement
klem kedidelhopper wrote:
I need to replace this TO220 regulator in a power supply I'm working on. The original is a "CT" suffix however looking through the books I see that there are several other versions of this part. The original seems to be a 1.0 amp device while several others appear to be able to handle 1.50 amps. I would like to buy a few extras to have on hand. Aside from any appreciable price difference, would it make sense to buy a bunch of "CT's" that will only handle 1.0 amp when there are1.50 amp parts available that will do the equivalent job? Thanks, Lenny It makes sense to get a larger unit if it's not going to put you in the poor house. Jamie |
LM7824CT replacement
klem kedidelhopper wrote:
I need to replace this TO220 regulator in a power supply I'm working on. The original is a "CT" suffix however looking through the books I see that there are several other versions of this part. The original seems to be a 1.0 amp device while several others appear to be able to handle 1.50 amps. I would like to buy a few extras to have on hand. Aside from any appreciable price difference, would it make sense to buy a bunch of "CT's" that will only handle 1.0 amp when there are1.50 amp parts available that will do the equivalent job? Thanks, Lenny We used to use that LM78xx family in the 80's, a lot of them. The 05, 08, 12, 18 and 24's. I don't remember a 1.5A version in the TO220 case, but technology marches on as they say. One hint, they aren't rocket science. It's a cheap regulator that does the job simply, but I'm unsure if better ratings would give better results. The main problem we found with those is the source voltage, I think they are all rated with Vcc max at 36v, even the 5v ones. There is a min of something like 3v over the regulation voltage (7805 needs min 8v in, the 7812, 15v and so forth). The closer you can get to that, the better the life span. The heat sink is also important, it needs one. I think the data sheets from National said something about 100ma-250ma "free air", and the full 1A draw with some minimum postage-stamp sink, but don't beleive it. They are/were supposed to be over-current and short circuit proof, but they do pop like firecrackers when they let loose. One handy trick with them, if you lift the ground pin and insert a pot or some diodes, you can make it regulate at different voltages, keeping all the ripple rejection and other specs within specs. So a 7805 with a 30v source, a few caps and like a 500 ohm pot makes a quick and dirty 5v-24v variable regulated power supply, 1A max as usual. I don't know what you found with the 1.5A rating but it would just be cost considerations, if there is a 10 cent difference, fine, if it's $10, forget it. This is a 30 year old comment that probably doesn't apply but we did find differences depending who made them. Both the National and Motorola versions were fine, the ones by SGS stunk. There was another by Fairchild but I think they were SGS's with a re-ink job on them. -bruce |
LM7824CT replacement
On Dec 1, 7:01*am, Bruce Esquibel wrote:
klem kedidelhopper wrote: I need to replace this TO220 regulator in a power supply I'm working on. The original is a "CT" suffix however looking through the books I see that there are several other versions of this part. The original seems to be a 1.0 amp device while several others appear to be able to handle 1.50 amps. I would like to buy a few extras to have on hand. Aside from any appreciable price difference, would it make sense to buy a bunch of "CT's" that will only handle 1.0 amp when there are1.50 amp parts available that will do the equivalent job? * Thanks, Lenny We used to use that LM78xx family in the 80's, a lot of them. The 05, 08, 12, 18 and 24's. I don't remember a 1.5A version in the TO220 case, but technology marches on as they say. One hint, they aren't rocket science. It's a cheap regulator that does the job simply, but I'm unsure if better ratings would give better results. The main problem we found with those is the source voltage, I think they are all rated with Vcc max at 36v, even the 5v ones. There is a min of something like 3v over the regulation voltage (7805 needs min 8v in, the 7812, 15v and so forth). The closer you can get to that, the better the life span. The heat sink is also important, it needs one. I think the data sheets from National said something about 100ma-250ma "free air", and the full 1A draw with some minimum postage-stamp sink, but don't beleive it. They are/were supposed to be over-current and short circuit proof, but they do pop like firecrackers when they let loose. One handy trick with them, if you lift the ground pin and insert a pot or some diodes, you can make it regulate at different voltages, keeping all the ripple rejection and other specs within specs. So a 7805 with a 30v source, a few caps and like a 500 ohm pot makes a quick and dirty 5v-24v variable regulated power supply, 1A max as usual. I don't know what you found with the 1.5A rating but it would just be cost considerations, if there is a 10 cent difference, fine, if it's $10, forget it. This is a 30 year old comment that probably doesn't apply but we did find differences depending who made them. Both the National and Motorola versions were fine, the ones by SGS stunk. There was another by Fairchild but I think they were SGS's with a re-ink job on them. -bruce That's very interesting about the 500 ohm pot. I've never heard of doing that before. I would have thought that the regulated voltage would have been dictated by some internal zener diode or something. But in any case I have a bag of 7805's and I'm going to experiment with them. As far as the capacitors go are you talking about using any additional from the usual input and output caps? Lenny. |
LM7824CT replacement
klem kedidelhopper wrote: That's very interesting about the 500 ohm pot. I've never heard of doing that before. I would have thought that the regulated voltage would have been dictated by some internal zener diode or something. But in any case I have a bag of 7805's and I'm going to experiment with them. As far as the capacitors go are you talking about using any additional from the usual input and output caps? Lenny. Here is the datasheet on that family of regulators. the first page shows 'Adjustable Output Regulator' and that you need a fixed resistor from output to common, along with the pot from common to ground. http://www.national.com/ds/LM/LM340.pdf Texas Instruments UA7824CKC is 1.5A Mouser has several 1.5A types in stock: http://www.mouser.com/Semiconductors/Integrated-Circuits-ICs/_/N-6j73k?Keyword=7824&FS=True starting at 47 cents each, which is only seven cents more than the 1A types. They are $4.56 for ten or $43.70 per hundred. this is for the 511-L7824ACV made by STMicroelectronics. The right part is cheaper than screwing around with extra resistors & pots that can go open. http://www.mouser.com/ProductDetail/STMicroelectronics/L7824ACV/?qs=sGAEpiMZZMtOXy69nW9rM5taedogOtNRM5vVsMlyJSo%3d The description column list the output of each part. -- You can't have a sense of humor, if you have no sense. |
LM7824CT replacement
Michael A. Terrell wrote:
Here is the datasheet on that family of regulators. the first page shows 'Adjustable Output Regulator' and that you need a fixed resistor from output to common, along with the pot from common to ground. http://www.national.com/ds/LM/LM340.pdf Yeah but I think that is specific to the LM340, on the 78xx series you just need a resistor in the path to ground. This is more what I was talking about: http://www.fairchildsemi.com/ds/LM/LM7805.pdf It's a bit messy with the 741 in circuit (fig 13), but allows you to use higher value pots. The single resistor method works but may require a multi-turn pot to dial it in with precision or a need for odd values to hit the target. Just play around with it, use a 7805 and Vcc around 24-28v for the best range and just experiment with different values to ground. Just tie the wiper to one of the ends, one end to ground and the other to pin 2. You need that cap on the output to ground to snuff oscillation and something on the input for ripple but thats about it. That 78xx family is forgiving but if it's too hot to touch, you are doing something wrong. -bruce |
LM7824CT replacement
Bruce Esquibel wrote: Michael A. Terrell wrote: Here is the datasheet on that family of regulators. the first page shows 'Adjustable Output Regulator' and that you need a fixed resistor from output to common, along with the pot from common to ground. http://www.national.com/ds/LM/LM340.pdf Yeah but I think that is specific to the LM340, on the 78xx series you just need a resistor in the path to ground. This is more what I was talking about: http://www.fairchildsemi.com/ds/LM/LM7805.pdf It's a bit messy with the 741 in circuit (fig 13), but allows you to use higher value pots. The single resistor method works but may require a multi-turn pot to dial it in with precision or a need for odd values to hit the target. Just play around with it, use a 7805 and Vcc around 24-28v for the best range and just experiment with different values to ground. Just tie the wiper to one of the ends, one end to ground and the other to pin 2. You need that cap on the output to ground to snuff oscillation and something on the input for ripple but thats about it. That 78xx family is forgiving but if it's too hot to touch, you are doing something wrong. I did it over 30 years ago for a high current bench power supply to service business radios. It provided 5.5 V to 16 V at up to 90 amps, and was used once to test a car starter I'd rebuilt for one of my service trucks. If you read the datasheet, LM340 is the National Semiconductor name for the 78** family. It is followed by a dash & the output voltage. The reason for the second resistor is to make the output voltage more stable. The current consumed by the regulator varies with temperature, so the lower value fixed resistor across the output to the common terminal makes it a lot stiffer. WTH would you spend money on a precision variable resistor just to let it drift, as the die temperature changes with the output current? A pair of resistors is a better choice for a fixed output, since no one can screw with it and the output won't go high if the rheostat opens. It's still cheaper to buy the common values 10 or more at a time and use the right part. You waste time & parts to kluge the wrong part into the circuit, and both cost you money. In some types of repairs, you are not allowed to kluge in the wrong part without a huge pipe of paperwork, and I did a lot of that kind of work, from '72 until I was sidelined by my health a few years ago. I keep 5, 8,9,12,15 & 24 positive regulators and 5,12,15 V negative regulators in stock. Most TO-220 are under 25 cents each, in single quantities. I still have some TO-3 metal cans in stock, along with some long obsolete Motorola ten pin regulators that were common in early external 300 baud modems. There was an early EPROM programmer project in BYTE magazine that used separate transistors to ground different resistors to set the programming voltage on various pins, since there were so many combinations used in the '70s. -- You can't have a sense of humor, if you have no sense. |
LM7824CT replacement
In article ,
Bruce Esquibel wrote: Michael A. Terrell wrote: Here is the datasheet on that family of regulators. the first page shows 'Adjustable Output Regulator' and that you need a fixed resistor from output to common, along with the pot from common to ground. http://www.national.com/ds/LM/LM340.pdf Yeah but I think that is specific to the LM340, on the 78xx series you just need a resistor in the path to ground. This is more what I was talking about: http://www.fairchildsemi.com/ds/LM/LM7805.pdf It's a bit messy with the 741 in circuit (fig 13), but allows you to use higher value pots. The single resistor method works but may require a multi-turn pot to dial it in with precision or a need for odd values to hit the target. Just play around with it, use a 7805 and Vcc around 24-28v for the best range and just experiment with different values to ground. Just tie the wiper to one of the ends, one end to ground and the other to pin 2. You need that cap on the output to ground to snuff oscillation and something on the input for ripple but thats about it. That 78xx family is forgiving but if it's too hot to touch, you are doing something wrong. Maybe not. The temperature where most folks say "too hot to touch" (too hot to keep your finger on) is around 130 F; the maximum junction temperature rating for those regulators is around 300 F. Isaac |
LM7824CT replacement
On Dec 3, 1:08*am, isw wrote:
In article , *Bruce Esquibel wrote: Michael A. Terrell wrote: * *Here is the datasheet on that family of regulators. the first page shows 'Adjustable Output Regulator' and that you need a fixed resistor from output to common, along with the pot from common to ground. http://www.national.com/ds/LM/LM340.pdf Yeah but I think that is specific to the LM340, on the 78xx series you just need a resistor in the path to ground. This is more what I was talking about: http://www.fairchildsemi.com/ds/LM/LM7805.pdf It's a bit messy with the 741 in circuit (fig 13), but allows you to use higher value pots. The single resistor method works but may require a multi-turn pot to dial it in with precision or a need for odd values to hit the target. Just play around with it, use a 7805 and Vcc around 24-28v for the best range and just experiment with different values to ground. Just tie the wiper to one of the ends, one end to ground and the other to pin 2. You need that cap on the output to ground to snuff oscillation and something on the input for ripple but thats about it. That 78xx family is forgiving but if it's too hot to touch, you are doing something wrong. Maybe not. The temperature where most folks say "too hot to touch" (too hot to keep your finger on) is around 130 F; the maximum junction temperature rating for those regulators is around 300 F. Isaac Thanks for all the replies guys. While I can certainly appreciate not having to screw around klugeing a circuit it is interesting to know that I can play with this basic design as it was suggested if I should ever need to. And many times over the years I've had to do things like this to get the job done. When you're 75 miles from home on a Friday afternoon and "Miller time" is fast approaching it's nice to be able to make something work that otherwise might require another service call on Monday. Not to mention the added inconvenience this saves the customer. BTW, I was always taught that good design practice dictates that if a semiconductor is too hot to keep your finger on, (greater than around 55.0 degrees C), then it's running too hot. However I remember some military aircraft power supplies I worked on in the 70's that ran a lot hotter then that on a regular basis. It always seemed like poor practice to me but I never heard of an F15 going down because of one, so I guess it was OK. Lenny |
LM7824CT replacement
Michael A. Terrell wrote:
If you read the datasheet, LM340 is the National Semiconductor name for the 78** family. It is followed by a dash & the output voltage. Yeah, for some reason I had the LM317 stuck in my head which was some kind of variable regulator. It wasn't very good of a device, but was common. It's still cheaper to buy the common values 10 or more at a time and use the right part. You waste time & parts to kluge the wrong part into the circuit, and both cost you money. In some types of repairs, you are not allowed to kluge in the wrong part without a huge pipe of paperwork, and I did a lot of that kind of work, from '72 until I was sidelined by my health a few years ago. The above comment depends on the situation. Of course it's better to use the exact part and do the repair properly, but that doesn't hold true of all circumstances. Back in the 80's I was involved with a wholesale guy here in Illinois out near Rockford, he used to buy semi-trailers of returned merchandise and closeouts, anything from clock radios, multi-band radios, cable converters and some stuff I couldn't figure out its use. At best, and I do mean at best, it was $2 a repair. Most of the time it was 50 cents, but parts were billed separate. On first thought, most people would just laugh getting paid that little, but when you are looking at 3000, 4000 or 5000 peices with one group exceeding 20,000 items, it makes you think. Basically if you spent more than 5 minutes to repair it, you were doing charity work. So it comes down to meatball surgury, cut out the bad part, get a new fix in, button it up and move on to the next. The majority of that crap had power supply problems, I'm talking the old, linear device type, some kind of transformer, a couple diodes (if you were lucky) and maybe 1 filter cap. After that it was transistor de'jour to feed the device. Some of these had PNP where it was supposed to be NPN (I guess 2SB is close enough to 2SD), or on some, they were missing altogether. Identifying a zener diode, ha, didn't have the luxury. Most of those were probably some pin diode from the 60's that looked close enough. Point was, I made a lot of money doing the kludge, paying someone to tack solder a couple parts to a 7805, pay someone else to clip here, clip there then solder in the kludge to these points, instant 9v regulation. Plug it in, if it works, on to the next. Was easier using the mess soldered onto the 78xx than getting the right one because you had leads to work with, not jumpers, which attaching them would of slowed things down. It wasn't rocket science, wasn't elegant and in some respects, was kind of embarassing. But it was work, paid well if you could figure out the routine and overall made everyone happy. The only major botch job I did where nearly everything came back to be reworked was these goofy modulators, which I can't even imagine to this day what they were being used for. They wanted to retune them from a channel 2 output to channel 4, which after playing with a couple, seemed to be a simply coil retuning, but turned out they weren't 75 ohm "things" but 50 ohm, so they didn't work wherever they ended up. I hated that, not only because of doing it twice, but the chamber that the coils were in was sealed via a half dozen sheet metal screws that were like 1/8", tiny ****ers. I had to have custom made hardened steel bits made because any socket or hand tool would simply wear out after a days use. And of course, the heads to them mostly didn't like being untighten and tighten twice. Anyway, getting back to the subject, I understand what you are saying but I wasn't employed by NASA here. That guy was trying to make a dollar on something that probably cost him 25 cents. Here in Chicago there was a lot of opportunities like him. We used to have these places that sold "hotel tv's", cheap 19" RCA sets (usually) for half or less what they were going for retail. In the early 80's, most video stores that did tape rentals also did machine rentals, they were still too expensive for everyone to own one. All of the above didn't care about the quality of repair, just the costs. Even if up front you told them that on the cheap it may only last 3 months, if it was a lot less than doing it the right way, cheap it was. Just saying that LM78xx series is a versatile little device that can be used in a far wider arena than what the spec sheets say. -bruce |
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