the boy who had two fathers , and could not read datasheets ...

[petey twofinger]

i am trying to power a camcorder that uses a 5 volt 1.5 amp ac adapter  by using a 5 amp non-adjustable  lm1084-5 with a 12 volt 7 mah  sla battery . looking at the data sheet the example circuit for the adjustable model shows a 10uf electro on the in side and a 10 uf tantalum on the out . but i am not using the adjustable model .

i am hoping some of the experts here would help me out , as it isnt that complicated but i am a total dolt who can not comprehend datasheets .

http://www.ti.com/litv/pdf/snvs037f

below is what i am confused about in the datasheets , at the very bottom is what i think MIGHT work , but could be improved perhaps quite a bit ,

now there is this :

http://www.ti.com/litv/pdf/snvs037f

?

then there is this :



this above figure three shows two tantalums , i only ordered one ... and is that a fixed model 1084 ? it doesn't specify ... the comment states the capacitor on the left " may be omitted if the input supply is well bypassed within 2'' of the lm1085 ' .... hmmm i ordered a 1084 but the 1085 is almost the same thing so ... i was planning on keeping the box on a 6 inch length of larger gauge wire but in the same bag , fairly close to the battery . do i need this tantalum cap ? i only ordered one and was planning on a ten uf electro there on the left in place of where the ten tant is with the cryptic note ... ?

lastly :



what i have in mind is this ,,,



is this ok ? by no means is that what i have my heart set on ... the main limit is the fact i only have one 10 uf tant cap coming , i would like it to work as best i could make it , but ... oh yeah , i am gonna fuse the input , and i do have a lge heat sink .

i am concerned about noise ... i really am shooting in the dark here , but i would like to figure it out as the parts are arriving the day before i need to shoot with the cam .

thanks  

http://www.ti.com/litv/pdf/snvs037f

[gjcamann]

I think you're going to be OK. Use the last circuit in your post and omit the input cap (that's only there for input power noise filtering, but coming from a battery you should be OK, try to keep the leads from the battery as short as possible and maybe shield them if you can). Watch the polarity on the input cap.

You probably don't need the fuse, this chip can handle short circuits.

[Govmnt_Lacky]

I think you might be stuck in a stompbox state-of-mind Petey! 

You are trying to power a camcorder. Not a stompbox. I really dont think you would need to worry so much about the power filtering as you would need to worry about the proper voltage and current getting to the camcorder.

You want it to be as close to the needed voltage and current as possible AND you want it to be a reliable supply. Since the original calls for a 5V/1.5A supply, I think it is safe to say that as long as you can supply a good 5-5.5V at about 1 amp you should be OK 

Is the camcorder power connection proprietary? Do you have any equivalent power adapters on hand? Cell phone adapters usually run at about 5V/1A 

[markeebee]

How about a 6v sla?

[R.G.]

i am trying to power a camcorder that uses a 5 volt 1.5 amp ac adapter  by using a 5 amp non-adjustable  lm1084-5 with a 12 volt 7 mah  sla battery .

GL is correct - think about getting the voltages and currents right.

You say the camcorder uses a 5V 1.5A AC ADAPTER? Is this a simple transformer that puts out 5Vac and the camcorder makes what it needs from that?

5Vac is a sine wave which alternates with peaks of 5*1.414 = 7.07V. If you rectify that with a diode bridge, you get 7.07V minus two diode drops, 5.67Vdc peak, and you lose some from that by the ripple on any filter cap.  If you use one diode to half wave rectify it, you get only one diode drop loss and about 6.3Vpeak, plus twice the ripple for the same cap size.

If you stick 5VDC into the same input, it's rectified, too, although it doesn't need it. It drops to 3.6V or 4.2V respectively. That may not be enough to run whatever is inside the camcorder.

There is a possibility that the adapter is already rectified, but not filtered, as well. In that case, it's not clear what the camcorder would do. Probably a big filter cap. But the DC level from a "5V" output is still subject to some question.

IMHO, you're playing "You Bet Your Camcorder" if you don't know more about what's coming out of the adapter and/or what the camcorder needs.

[artifus]

how about... *warning idiot thinking ahead*

ignore cams dc input jack. make nice power supply. connect to cams battery terminals instead of dc jack. i can't afford to replace your camcorder if you follow this wonky thinking.

*also* 10uf either side? i'm used to seeing decades, ie 10u in 100n out. what is the reasoning behind the tant? (please educate me!)

*my wonky thinking being that an unknown battery input maybe slightly more inviting than an unknown power jack input in terms of what follows circuitry wise. is a battery more predictable than a power supply? can we mimic that input? known knowns, known unknowns, and unknown unknowns. i've done this with cheap cams but nothing i'd cry about had it gone wrong. time forbid - taxi for art!*

night night x

[petey twofinger]

oops , that was me not being clear , it is an ac adapter in the sense that it adapts ac to dc so i totally typed that wrong , sorry . 


the output of the adapter is dc , the camera takes dc . there is a yt video , a guy did this same idea and it works , but he used the adjustable lm1084 and the circuit that i build with the 1084-5 is going to be different . i can not make head nor tale of the data sheet so i was hoping some folks could clarify exactly what i need to do . but now i am confused about using the 1084-5 vs something with less amps

artifus , i did that on our last cam corder , ran it that way for many many years ... i may end up doing the same , i would love to get ahold of a dead battery for this unit as they are $$$ . the stock battery life isnt good but i sill dont want to hack it till its dead .

so the 5 amp voltage regulator is overkill ? i do have some 7805's here and those are one amp , the lm317 i have here are 1.5 amp , hmmm . the guy on youtube ran his with a lm1084 non adjustable , and he said the heat sink was HOT . would using one of these lower amp vregs reduce that heat effect ? ythe 6 volt battery is a good idea but i have 8 or 9 12 volt sla's and no 6 volts plus , we are broke .


i suppose i could test the cam when it arrives , see what its drawing actually somehow ... then go from there , i was just thinking that if the ac to dc adapter was rated at 1.5 amp , using a one amp vreg or 1.5 would be cutting it too close for comfort ... if i built the circuit with the 1084-5 i would just use one tantalum 10 uf on the output , with a fuse and a giant heat sink , test it out and it should work fine is what i am thinking , but ... then there are those other lower amp vregs i have here . i did do a tes with a vreg vs a phone charger , the phone chargers use more current so i would like to avoid using those but they may be cleaner / less ripple and stuff . in the past i have messed with this stuff a bit and at times it does get noisy depending on how many things are running on the sla .

thanks yall !

[R.G.]

Ah. That's a horse of a different color.

I would not be worried with a 1.5A regulator, although a 5A regulator will probably be loafing more, and may be easier to heatsink. The physical setup is a big issue. Good to see a big heatsink worried about already! That Ic is going to be generating (12V-5V)*`1.5A = 10.5W of heat, and that's not a trivial amount.

this above figure three shows two tantalums , i only ordered one ...

Put a tantalum cap wherever they tell you to. What's going on there is that a voltage regulator is a medium-power feedback amplifier set up to amplify only one output voltage. If it has the wrong conditions, it will oscillate, and that's generally what they use tantalums for.

and is that a fixed model 1084 ? it doesn't specify ...

Probably. In general, the application info would apply. Although I agree with you, it isn't a model of clarity. But you can assume that the application info on a datasheet refers to one of the models being specified.

the comment states the capacitor on the left " may be omitted if the input supply is well bypassed within 2'' of the lm1085 ' .... hmmm i ordered a 1084 but the 1085 is almost the same thing so ... i was planning on keeping the box on a 6 inch length of larger gauge wire but in the same bag , fairly close to the battery . do i need this tantalum cap ? i only ordered one and was planning on a ten uf electro there on the left in place of where the ten tant is with the cryptic note ... ?

Here's what they're trying to tell you, but don't. Tantalum caps have a high capacitance per volume, and they also have low internal resistances and inductance. The oscillation quirks I mentioned above get worse if there is a long run of wire between the IC pin and the next nearest low-impedance filter cap. They're trying to say "It may - and probably will! - oscillate if you don't get a low-ESR cap within 6" total wiring from the IC pins."

A better answer is to put the tantalum cap as near the IC pins as you can put it and have it survive mechanically.

lastly :
...
what i have in mind is this ,,,
...
is this ok ? by no means is that what i have my heart set on ... the main limit is the fact i only have one 10 uf tant cap coming , i would like it to work as best i could make it , but ... oh yeah , i am gonna fuse the input , and i do have a lge heat sink .

It's probably OK. If you only have one tantalum, put it on the INPUT side of the IC, the ... er, 12V side. The output caps can be ordinary aluminum electros. Be really, really, really sure you get the polarity correct, because tantalum can go off like a shot if it's backwards and there's a lot of current available, like from a SLA battery.

Shoot, while you're at it, stick several 22uF, 47uF, 100uF, etc. aluminum caps as you want on the input and output sides. It won't hurt. The caps on the output "serve to improve transient response" as many app notes say for these things, but are not critical for stabilty **except** for LDO style regulators.

i am concerned about noise ... i really am shooting in the dark here , but i would like to figure it out as the parts are arriving the day before i need to shoot with the cam

Probably will not be an issue.

[markeebee]

How about a 6v sla?

I may be missing something here.  Can you not buy a 6v sla for about ten dollars, and connect it directly to the cam's DC socket or battery terminals?  Granted, we won't learn much about regulators, but it seems more practical to me.

[markeebee]

Sorry, think I just broke the DIY rules.

[Jdansti]

Sorry, think I just broke the DIY rules.

Not really.  You have to still rig the connections from the SLA to the camera, and you could build an SLA charger.

Heck, if you don't mind using non-rechargeable batteries, just go get one of those big lantern batteries or connect 4 D cells in series (or 4 in series in parallel with another 4 in series for extra capacity).

[petey twofinger]

markbee , i have eight 12 volt sla's , i am planing to build this device as the permanent replacement for the factory battery . indoors i would use the supplied wall adapter , bu the cam is going to mostly be used to shoot us making music outdoors . i would think that the 12 volt set up would last a lot longer than the 6 but i may be incorrect . generally i like to use massive batteries , i ran four deep cells on my peddle boat . i had 8 so at the half day point i would meet up with my wife by the river bank , bbq ,  swap the dead four out , then go on . the boat had a lot of unnecessary electronics but it was also a ton of fun . http://www.youtube.com/watch?v=i9hEr38yboY ask me about the time i capsized ...

it just makes more sense to me as i already have chargers and a bunch of 12 volt sla's than to purchase a 6 volt model , but yes it certainly would be more simple .

going to pick up the cam tonight but the parts are coming on the 15th , thanks so much every one . i understood all of that R.G. which is no small accomplishment on your part , it was a great help , your willingness to help is truly admirable / inspirational . a huge thank you to you for your time and efforts , you have helped perhaps thousands of folks , i would think that if their is any cosmic justice in order , you have a giant gold star next to your name on the chart .