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ArcticMyst Security by Avery

2 Amp+ driver circuit needed.

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I'm trying to rebuild a green module pointer.  The driver has problems and I'm looking for a 2 Amp+ driver circuit.  I don't want to re-invent the wheel here unless I have to.  The present circuit has a bank of MosFets but the remaining driver circuit is crapped out.

Mike

Balancing 50 LM317's should be a trick.
 





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Apparently the LM317T is capable of "excess of 1.5A" at 37V, so it stands to reason it can handle much more than 1.5A at whatever 2V or so you're going to be using it at, especially with good heatsinking... Don't quote me on that though, I'm pulling this directly out of my ass.
 
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Pseudo -- you are sorta right about the LM317 but even eliminating heatsinking as a consideration, a device has its current limits. I'm looking for a driver circuit which controlls several small Mosfets. This is from an unknown crap China builder.
I may have to design my own but I was hoping for a similar circut.

Mike
 
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Jamlin --- thanks but there's no schematic. Those waveforms look like pulsed or analog power control for a show. I just need a driver for a pointer.

Mike
 
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Hemlock Mike said:
Jamlin --- thanks but there's no schematic.  Those waveforms look like pulsed or analog power control for a show.  I just need a driver for a pointer.

Mike

Well, for $35 you can't really complain that it has more features than you need.. That's still a really good price for that caliber of driver. For comparison, Merideth makes a 1.5A driver for fifty bucks. Looks like the drlava driver will work fine for pointer use, so long as your host can fit it.
 
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Thanks for the searches but space in this is limited. I will look at these and see if one will fit and can be controled by a feedback resistor. This is a large pointer I'm working to rebuild.

Mike
 
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You can use an LM350 in place of the LM317, for up to 3A. If you switch to an LM338, you can go up to 5 or 6A. Resistor is calculated the same as with the LM317.
 
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You could use a power transistor with a pot and a cap and some resistors for max allowable level.

This would allow you to go as high as the transistor is rated for (usually much more than the regulators) and would be adjustable via the pot.

The problem is that this would fade with the batteries, but you could pump a lot of power.

The flexmod uses a big transistor this same way, but also uses another component that allows a constant current.

My circuit design experience is limited... but a transistor would be super simple and work like a champ.

Might even be able to put a simple voltage regulator on the gate leg of the transistor to get rid of the sagging battery problem.
 
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WOW -- Now I have to digest this info provided ...... The space for the driver is limited but I'm looking at that 350.
My present supplied circuit is a small board driving 3 Mosfets on another board.
Thanks for the ideas guys.

Mike
 
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Mike,

The LM1587 is a good choice as well. The circuit is identical to the DDL. It's available in SMT and TO-220 package. So for 2A you'd use a 3W, 0.62 Ohm resistor... (The entire driver costs about $5 to throw together.)

cheers,
kernelpanic
 

Benm

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Hemlock Mike said:
WOW -- Now I have to digest this info provided ......  The space for the driver is limited but I'm looking at that 350.  
My present supplied circuit is a small board driving 3 Mosfets on another board.  

I doubt the LM350 is the best approach here. It works exactly like the 317, but at these current levels you will burn a lot of power in both the lm350 and the resistor. To operate within spec, it needs 3 volts between input and output, and another 1.2 between output and adjust, resulting in a total of over 8 watts electrical use by the driver alone (!).

I would recommend using a battery/supply voltage closer to the LD voltage, and a circuit like this:
http://www.instructables.com/files/deriv/FTF/KKU6/Z2HEWIFNTP5/FTFKKU6Z2HEWIFNTP5.MEDIUM.jpg (R3 has ~0.7 volts over it, current calculation works like the LM317 circuit). The total drop for these doesnt need to be more than about 1 volt.

Depending on whats currently in the circuit, you might be able to use he existing mosfets as well. Also, if you need your diode case grounded, you can build a mirror image (using pnp instead of npn etc.) of the circuit.
 
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In the line of Benm's post, the original driver is probably using a current multiplier circuit, which you could try as well, recycling or just replacing the components in there with that. You can use a circuit like this one, or even this as a basis, and then just have it control more than one mosfet to multiply the current.
 




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