Lowish DO regulator

How much current?

Leon

Sorry, I didn't see the 200 mA. 8-)

I like the D-PAK LM1117.

Leon

On a sunny day (Wed, 8 Oct 2008 06:41:16 -0700 (PDT)) it happened MooseFET wrote in :

If you have 12V, even if it drops to 10.7, then a simple diode for reverse protection would do. Below that you better disconnect that battery anyways to protect it.

In cases like this I would use the MOSFET as low dropout pass, or a nomal BJT,

As you are not playing switchmode, then a simple discrete stabilizer would work, get a cheap reference fro ma low power LM317, let's see:

PNP power

+10 to + 35 V ---- a diode k ------------------------e c---------------- + 8.3 | | b T1 | | === | | | | 10u --- | | | R3 5k9 tant. | | | | | /// | about +2.4 c c | LM317L-------------- b b----| | | | e e | | R1 150 | | T2 | T3 | | | | |_______| R4 2k4 |---- | | | | === 10u R2 /// R2 150 --- tant. | 150 | | /// /// /// 2 x NPN

No, you forgot to specify how accurate the 8.3V needs to be :-)

Maybe the above circuit, something I solder together on the desk when I need a voltage, will work for you. All component values are guessed. Use a trimpot for R4.

The way it works: The LM317L creates a reference voltage, very stable, of about 2.4xx volt. When output voltage is low, T2 conducts, and base current of T1 is limited by (2.4 - 0.7) / R2. Then when the output voltage rises, T3 starts conducting when its base get to

2.4 V, and lifts the emitter of T2, decreasing drive currrent in T1.

The circuit has a low dropout of .2 V, the saturation voltage of T1.

I'd consider a switcher here. 35V minus 8.3V at 200mA is over 5W. Personally I stay away from LDOs, seen too many not so well or not at all documented instabilities. The topper was one that began rather wild oscillations once the battery impedance rose above a certain level. Of course none of this was mentioned in the datasheet. I did not like that LDO in the circuit but a client's engineer wanted it. Call to the mfg, more and more guys came into the office over there, lots of mumbling, shoveling of papers, schematics etc. Suddenly someone at the mfg exclaimed "Oh drat!". Then I knew we were in hot water.

I'd vote for Prop 8888: A ban on LDOs :-)

--
Regards, Joerg

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Why not roll your own LDO out of discrete components?

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
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My thoughts exactly. Some switchers stop switching and act as a pass element when the input is equal or less than the desired output.

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Sure. But then I might as well roll my own switcher out of jelly bean parts. Which I usually do :-)

I just did two more of those, neither one will make any PWM chip vendor happy because there ain't none in there. Ok, one contains a PLL but I could only bring myself to using a 15c logic part.

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That, and then the SEPIC has been invented a long, long time ago.

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The nice thing about rolling your own LDO is that you can properly compensate the loop instead of "relying" on getting the right dissipation factor in a capacitor.

I'm sure it was marketing guys who conjured up that crap in the first place. Now everyone is stuck with it.

I have a nice LDO in a recent (2007) chip design... it's only 1.8V out at 15mA, but stable as a rock with ON-CHIP compensation.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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 I love to cook with wine     Sometimes I even put it in the food

Probably the only way to get it would be to buy some big GPS device manufacturer or something like that ;-)

Usually I need more than 15mA. But bottomline I do not trust these things anymore unless you, I or someone I trust has designed it. Especially since manufacturers have fallen into the habit of not disclosing circuit innards anymore. My "consumption" of ICs in designs has actually dropped since that started. The design I am wrapping up this week would drive tears into the eyes of semiconductor execs. Almost

600 parts, except for two chips all jelly bean stuff. Dirt cheap.

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e f d

It doesn't withstand the 35V max. Bummer.

e f

I want nice quiet non-EMI making linear.

10.2 - 8.3 - 0.5 =3D 1.4V so this really isn't LDO land. d

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For less parts, I can use a non-LDO if I use a P-MOSFET for the inverse voltage protection.

That is LDO land, or at least pretty darn close. But I'd roll my own and not trust chip manufacturers.

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[snip]

I presume the "10.2" is your nearly dead 12V battery?

But what's the "0.5"... your disconnect device shouldn't be dropping that much... unless you're just using a diode???

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

e f d

There is a lot more that can go wrong in a DC/DC than a LDO. [I've designed both. In fact, most switcher chips have an intergrated LDO for internal use, but I've done stand alone LDOs as well.] I think you are in the minority on this one, er, not that there is anything wrong with that. ;-)

My voters guide is just slightly less in weight than a National semi catalog. Oh wait, do they still publish catalogs?

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I find it hard to believe once you integrate all the start-up and protection circuits that this is cost effective.

Same here... national, state, county and city offices, EIGHT nasty propositions, unification of school districts, plus bond issues, and judge retentions (I always vote to NOT retain any of them ;-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

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I would like to use a diode for the inverse protection and not the P channel MOSFET circuit.