I'm looking for a voltage regulator

I\'m looking for a voltage regulator

Hello,

I have bought an small Isun solar panel and when there's enough sunlight I can easilly run a small radio on it but only because the Solar panel delivers around 7 volts at 240 mA (max) and my little radio runs on 6 Volt and does just fine on the 6 Volt setting of the solar panel.

However I also have electronic devices running on 4.5 and 3 Volts and I'm looking for a small voltage regulator that will take up to 7.6 Volts input and can switch to either 3 Volt or 4.5 Volt output (constant).

Because the Solar panel is small I'm looking for an as small as possible Voltage regulator.
If anybody knows where I could get such a device for not to much money I would appreciate if he/she could let me know.

Best Scouting wishes from Holland,

Bagheera

Re: I\'m looking for a voltage regulator

Small world...my best friend moved to your town a few years ago! Beautiful town. Here, in the US, Radio shack sells a small 5 volt regulator. I believe it can handle up to 12 volt input. It's inexpensive, too.

Re: I\'m looking for a voltage regulator

Use an LM117 or LM317.

By a careful selection of resistors you can make the output voltage switchable to whatever you wish it to be.

Re: I\'m looking for a voltage regulator

[ QUOTE ]
UK Owl said:
Use an LM117 or LM317.

By a careful selection of resistors you can make the output voltage switchable to whatever you wish it to be.

[/ QUOTE ]

There's probably a problem with using the 317 in this type application, drop out (of regulation) due to lack of 'headroom'. This is the minimum voltage that the input must be higher that the output by. Typically this is about 3 Volts for the 317. This means you cannot use this part for a 5 Volt supply, since the solar panel would need to put out 8 Volts, any less and you can't make 5 Volts.

A partial solution is to use National's "Low Drop Out" positive regulator, the LM1086. This is a 317 type part (although 1.5 Amps) built to have under 1.5 Volts as a minimum headroom. Under a Volt at lower current levels. Otherwise you pick a pair of resistors (in fact the same values) to determine output voltage.

Still better is a purpose built regulator using a low voltage op amp, voltage reference, and pass transistor (much like the 1086 in fact). It should be fairly easy to lower this requirement to a few tenths of a Volt. So, Bagheera, how's your soldering?

Doug Owen

Re: I\'m looking for a voltage regulator

That depends....
if you need maximum efficiency, you'll have to build or buy a switching regulator (if you really want max. efficiency, a maximum power point tracker, but with a small panel the electronics probably would eat more than you gain...).
For everything else, i.e. for everything where the current you need doesn't exceeed the current the panel will deliver under load, a zener diode across the panel is sufficient. This is also known as 'shunt' regulation. Just take care that you get a zener diode that can handle the panel's power (or build one with a power transistor).

Bye
Markus

Re: I\'m looking for a voltage regulator

Doug, are there any example schematics available for the
device you describe?

Re: I\'m looking for a voltage regulator

I think Marcus has the best advice. Shunt regulators work well with solar panels, due to the panel's high internal resistance. The big advantage is that they don't require any headroom at all. A simple zener diode, rated for the appropriate power, is painfully simple, and very cheap!

If you want better precision and adjustability, then it's not too complicated to design a linear shunt regulator.

best wishes,
Steve K.

Re: I\'m looking for a voltage regulator

Paul, look on National Semiconductor's site (or any IC manf., nearly) for 'application notes' for the LM317 or LM1086. A Google search will turn up lots of schematics as well.

Re: I\'m looking for a voltage regulator

Hello Guys,

Thanks for the 'tips', to answer Doug's question I can solder but Í would need a detailed list and schema in order to start building something.

I guess that I would only need to regulate to one Voltage and would settle on 2.9-3 Volt output, this should be perfect for my Garmin Vista but also feed my little Sony Shortwave radio.

Best Scouting wishes,

Bagheera

Re: I\'m looking for a voltage regulator

Ok, if you only need 3 Volts and the panel is rated for less than 300 mA, a simple 3V/1W Zener Diode will fit the bill. Trouble is, Conrad doesn't have them, they start off at 3.9V for the 1.3W diodes :-(.
Another (not so good, but probably good enough) possibility would be to use 4..5 standard diodes (e.g. 1N400x, 1 <= x <= 7) in series.
Wire the diodes in series, then connect the cathode to the - and the anode to the + (i.e. effectively short-circuit the panel with the diodes - but since each diode drops about 700 mV, you'll see 4..5 * 700 mV across the diodes).

Bye
Markus

Re: I\'m looking for a voltage regulator

[ QUOTE ]
Bagheera said:

Thanks for the 'tips', to answer Doug's question I can solder but Í would need a detailed list and schema in order to start building something.

I guess that I would only need to regulate to one Voltage and would settle on 2.9-3 Volt output, this should be perfect for my Garmin Vista but also feed my little Sony Shortwave radio.



[/ QUOTE ]

Howdy,

If you're up to the assembly, I suggest a reference (say LM385), op amp (LM358?), a small signal NPN driver (say 2N3904) and low Vsat PNP pass transistor in a TO-220 package ('power tab'). Plus a couple of resistors, maybe a pot to make it variable. The lot should fit in a match box. Let me cobble something together (and be sure it works....), I'm not sure what PNP to use and how if/how much heat sink may be needed (as well as wanting to be sure I have the other details right.....).

I haven't sorted out posting photos, let alone scanned schematics here, PM me your address, I'll mail you the details.

Doug Owen