12V Power outlet -> argghhhhh!

[Rob Farmer]

Those values are ok(ish) if you're running straight from a full wave rectifier at mains voltage but are way too high for DC circuits.

Whats the Diode for? It will give a voltage drop of around .63V across it but unless it's a higher current device may give you some problems. If it's an IN4007 or In4002 then it will only be rated at 1A - too low for what you are running. You shouldn't need the diode so I'd bin it.

The voltage should drop if you dump those hugh capacitors.

If you go for the smaller caps I mentioned above don't use Electrolytics.

 

[snoopy]

Of course the bloody diode is a 1A type - I thought it was 2A Curses!!!

So it's no wonder with the 1000uF capacitor it was cycling on/off.

I'll short that and drop in some smaller caps too and see how it goes tomorrow.

Cheers!

Andy

 

[Engineer]

I'm confused also - I have designed countless circuits over more than 25 years with these type of regulators and they are normally dead easy to use. As said above you don't need huge capacitors. The 0C temperature range will not stop it working - it might not meet the full performance specification but it will still operate. I can't help thinking that there is a simple explanation for this. When you find it you will kick yourself!

 

[snoopy]

All done and its still cycling on/off. I'm 99% the chip is cutting power thinking there's a short (IPAQ must take the full 2A when charging).

It's new chip time!

 

[snoopy]

Ok it's affirmative. Though IPAQ's are rated at 2A@5V adapter wise if given more they'll take it to fast charge the battery. So my next step is to limit the amount of current that can be drawn to the IPAQ. If I'm right a 2.5ohm (2.2 actual) resistor in series with the output should limit the current to 2A?

 

[ianf]

What's the rating of the regulator? We sort of went through this a while ago with homebrew 5v quest psus. I seem to remember that getting a regulator that can lose 7+v and sink >1A is fairly rare.

It's been a long while since I dabbled in this stuff but you'd need a resistor that would limit the current to the level that the reg is rated at rather than the end device.

 

[Rob Farmer]

It sounds like theres an in-rush current when you switch the Ipaq on. You will need something a bit more sophisticated than a resistor to control the current.

You need a current limiting voltage regulator. The easiest way to get that is to use the LM317 voltage regulator I mentioned before and use it to control a power resistor. The voltage regulator will handle upto 1.5Amps but the transistor could be set to handle any current greater than that. That current could also be limited by the circuit but could easily handle currents of double the regulators.

It's called a pass transistor circuit but it's starting to get a bit more sophisticated than just a simple voltage reg.

Good Luck

 

[snoopy]

And so it's fixed...


The IPAQ takes the whole 2A and was tripping the regulator. I stuck a second one in parallel (naughty I know) and this sorted it but since one came in ever-so before the second it would trip. I've slowed down the initial burst by using another 1000uF capacitor on the output. All was good after I added two large heatsinks.

The circuit the GPS came with was a switching power supply. The chip didn't have a number on it so I couldn't get it replaced. I identified it today as being able to supply upto 3A.

The powers fixed but my GPS mouse isn't coming on. A little more debugging and I'll have this wrapped up.

Cheers and happy new year!

 

[Engineer]

And so it's fixed...


The IPAQ takes the whole 2A and was tripping the regulator. I stuck a second one in parallel (naughty I know) and this sorted it but since one came in ever-so before the second it would trip. I've slowed down the initial burst by using another 1000uF capacitor on the output. All was good after I added two large heatsinks.

The circuit the GPS came with was a switching power supply. The chip didn't have a number on it so I couldn't get it replaced. I identified it today as being able to supply upto 3A.

The powers fixed but my GPS mouse isn't coming on. A little more debugging and I'll have this wrapped up.

Cheers and happy new year!

Well that would explain it - I guess what you really need is a higer rated regulator, 3A 5V regulators are available e.g. National semiconductor LM123/232/323 in a T03 package.

Running two regulators in parallel isn't ideal as they will never share the current equally due to small but finite differences in their output voltages. If you are drawing the full 2A then you will need a sizeable heatsink as the power dissipation will be (12V-5V)x2A = 14W!!

If you wanted to get a little more sophisticated and reduce the heatsink size then you could use a switchmode power supply - but thats another story!! I'll design you one for a small fee ))

Here is the link to the data sheet of the 3A regulator.
http://www.national.com/pf/LM/LM323A.html#datasheet

 

[Engineer]

Ok it's affirmative. Though IPAQ's are rated at 2A@5V adapter wise if given more they'll take it to fast charge the battery. So my next step is to limit the amount of current that can be drawn to the IPAQ. If I'm right a 2.5ohm (2.2 actual) resistor in series with the output should limit the current to 2A?

Ohms Law says that 2A flowing through a 2.5Ohms resistor will drop 5V!!!!

 

[snoopy]

All should be working well but looks like my GPS mouse if buggered now, no light is going on on the unit. I've checked the power is going into the unit

Polstar PGM-111.

Bastard. Bastard. Bastard.

 

[_monkey_]

I am trying to solve a similar problem now. i would like to bike power a HP Ipaq. It requires 5V 2A and also has fast and slow charge modes.

Would two of these in parallel fit the bill 1A Switching voltage regulator series ?