Post by thread:Low dropout regulators

I am constructing a battery operated PIC application where I need to be able to handle 2 Lithium cells. Since this produces up to 7.4V, this needs to be regulated down to 5V. To maximise battery life, the regulator needs low dropout (100mV) and quiescent current in the low microamps range. It should be able to supply up to 100mA peak. Maxim has regulators which are ideal, but made of unobtainium (they haven't even sent the 'free samples'). So in desperation I designed my own using two transistors and a power FET to regulate the negative side. This works fine except that I end up using a zener diode with only microamps of current through it, thus its voltage is _way_ out of spec: about 6V for a 10V zener! Does anyone know of (obtainable) zeners etc. which are rated for ultra-low bias current (say 1-5uA)? Tempco is not too much of a worry - say +/-5% over 0-40 deg C. Regards, SJH Canberra, Australia

{Quote hidden}> I am constructing a battery operated PIC application where I need to be > able to handle 2 Lithium cells. Since this produces up to 7.4V, this > needs to be regulated down to 5V. To maximise battery life, the > regulator needs low dropout (100mV) and quiescent current in the low > microamps range. It should be able to supply up to 100mA peak. > > Maxim has regulators which are ideal, but made of unobtainium (they > haven't even sent the 'free samples'). So in desperation I designed my > own using two transistors and a power FET to regulate the negative > side. This works fine except that I end up using a zener diode with > only microamps of current through it, thus its voltage is _way_ out of > spec: about 6V for a 10V zener! > > Does anyone know of (obtainable) zeners etc. which are rated for > ultra-low bias current (say 1-5uA)? Tempco is not too much of a worry - > say +/-5% over 0-40 deg C. > > Regards, > SJH > Canberra, Australia > Steve, I've been going through exactly the same problem. Have a look at the National LM2936Z5. Its a low dropout 5V regulator, supplies up to 150mA (I think), and has a quiescent current of around 15uA. Should do the trick. I think RS Components have them. Let me know how you get on. Peter. -- _______________________________________________________________________ Peter Homann email: spam_OUTpeterhTakeThisOuTadacel.com.au Work : +61 3 9596-2991 Adacel Pty Ltd Fax : +61 3 9596-2960 250 Bay St, Brighton 3186, VIC, AUSTRALIA Mobile : 014 025-925

>> I am constructing a battery operated PIC application where I need to be >> able to handle 2 Lithium cells. Since this produces up to 7.4V, this >> needs to be regulated down to 5V. To maximise battery life, the >> regulator needs low dropout (100mV) and quiescent current in the low >> microamps range. It should be able to supply up to 100mA peak. I strongly recommend the Seiko S81250 regulator to-92, sot23, or sot89 case quiescent current of 1.2 micro amps! max out 100mA about 30 cents in thousands Gary Skinner, Electronic Solutions Inc Design of custom control circuits Denver CO 303-469-9322

>I am constructing a battery operated PIC application where I need to be >able to handle 2 Lithium cells. Since this produces up to 7.4V, this >needs to be regulated down to 5V. To maximise battery life, the >regulator needs low dropout (100mV) and quiescent current in the low >microamps range. It should be able to supply up to 100mA peak. > > How about a Zetex ZM33064, TO92 package Supply Voltage Monitor designed for uP systems. Guaranteed to operate over 1V. Threshold set to 4.6V, built-in 20mV hysteresis, open col o/p sinking 10mA. Power-on reset over 4.6V. Input voltage to 10V. I have 100 in stock plus the 6 page data sheet. Let me know if you want to try one. regards peter ----------------------------------------------------------------------------- Peter J. Crowcroft PO Box 88458, Sham Shui Po, Hong Kong Voice: 852-2720 0255. Fax: 852-2725 0610 Email: .....diykitKILLspam@spam@hk.super.net Web: http://www.hk.super.net/~diykit -----------------------------------------------------------------------------

>I am constructing a battery operated PIC application where I need to be >able to handle 2 Lithium cells. Since this produces up to 7.4V, this >needs to be regulated down to 5V. To maximise battery life, the >regulator needs low dropout (100mV) and quiescent current in the low >microamps range. It should be able to supply up to 100mA peak. There is a lot of low drop-out regulator, choice depend of the total current you need and the operating range voltage and where you can find it! (often the more difficult) Output Droupout MAX Isleep Package - LP2950CZ-5.0 5V/100mA 0,6V 0,400mA TO92 - LP2950CZ-3.0 3V/100mA 0,6V 0,075mA TO92 - LP2950CZ-3.3 3.3V/100mA 0,6V 0,075mA TO92 - LM2936CZ-5.0 5V/50mA - - TO92 - LP2950CZ-ADJ Adjust/100mA - - SO8/DIP8 - MAX8863/8864 3,5V or 0,12V 0,170mA 5-SOT23 Vin MAX=5V5 Adjust/50 mA - MAX884 3,3V or Adj. 0,32V at 200mA 0,015mA SO8/DIP8 VinMax=11.5 - MAX603/604 1.3 to 11.5 0,32V at 500mA 0,035mA DO8/DIP8 VinMax=11.5 - MAX663/666 1.3 to 11.5 0,90V at 40mA 0,012mA DO8/DIP8 VinMax=16.5 - MAX667 1.3 to 11.5 0,15V at 200mA 0,025mA DO8/DIP8 VinMax=16.5 Regards, Philippe.

>>National LM2936Z5. Its a low dropout 5V regulator, supplies >up to 150mA (I think), and has a quiescent current of around >15uA. > I just tried to buy these last week from the Hong Kong NS agent & was told these are now obsolete & discontinued. Typically (for HK) they could not tell me what was the replacement part which I am sure there is because they have been very hard to get these last months due to cellular phone manufacture. ----------------------------------------------------------------------------- Peter J. Crowcroft PO Box 88458, Sham Shui Po, Hong Kong Voice: 852-2720 0255. Fax: 852-2725 0610 Email: diykitKILLspamhk.super.net Web: http://www.hk.super.net/~diykit -----------------------------------------------------------------------------