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I'm not asking if the iPhone 4 accepts 1A. I'm telling you that it does. Thank you for your input, but that is not the information I'm looking for. I'm simply trying to figure out the best/easiest way to get the correct voltages to the D+ and D- pins on the USB port.
The charger is set to 1A, but the phone will also accept 500mA. Ideally I want 1A and that is what this circuit is set up for, but I will settle for 500mA if that's all I can get.
I understand what they're used for, and I'm aware that different voltages give different current rates (ie: 2.0V and 2.0 volts results in 500mA and 2.8 and 2.0 results in about 1A).
I just need to know if it is possible to reduce the 5V input to 2.0V and/or 2.8V safely with one resistor on each...
I'm building a switching voltage regulator using an LM2675. I am converting 28VDC to 5VDC @ 1A. The 5V end is USB and needs to be able to charge an iPhone. The entire circuit works and I have voltage going to D+ and D- (about 1.5 and 2.0 respectively).
I used the resistor layout from Ladyada...
The 28 volts are coming from an aircraft and the gadget would be a USB device (iPod, smartphone, etc.). I believe those devices are quite capable of drawing 500mA, but I know they charge quicker while drawing 1A.
The LM2575 seems better than the LM7805.
Could I just step it down several times...
Hey guys, I just came across LM2575. The data sheet states that it requires a much smaller (or none at all) heat sink than an LM7805. Are any of you familiar with it?
Ok, thanks. I'll look into the switch mode power supplies.
So if the input amperage was higher, the temperature would be lower, correct?
I'm asking, because I have a 24v to 5v converter that has little to no heat dissipation. It is an adapter to charge a USB device from a cigarette lighter.
Thanks, Brian.
If I understand correctly, this ( Digi-Key - HS365-ND (Manufacturer - 576802B03900G) ) would rise 27.3C for every watt it had to dissipate?
Ok, thanks! 1x.75 isn't bad at all. I just need to figure out how to put this all together now and some way to encase it.
---------- Post added at 11:15 AM ---------- Previous post was at 11:13 AM ----------
While we are on the topic, would it require an even bigger heat sink to convert down...
I've looked at the data sheets, but there is so much information that I cannot decipher.
If I need to use a large heat sink, the project is pointless. How big of a heat sink are we talking? Does the LM317 lessen the need for a heat sink? I know it is a large drop in voltage, thus a bunch...
Hey, thanks for the quick reply to the thread.
I was actually just looking at some information on the LM317. I do need 1.0A along with 12 volts. The 28v are coming from a battery. It does seem that the LM317 would be a better fit.
Hello, I am new to this forum and I would appreciate any help you folks can provide.
I'd like to convert 28v to 12v, and I purchased an LM7824 and a few capacitors, but doing further research, it seems I may need to add a heat sink to this. Does anyone have any experience in this application...
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