LDO regulator IC chips

 LDO (Low Drop Out) regulation has been covered a little before in previous blog posts on
 

Power Supplies https://wb9kzy.blogspot.com/2022/01/power-supplies.html
 

and
 

LED plus LDO regulator > see what happens https://wb9kzy.blogspot.com/2022/01/led-plus-ldo-regulator-see-what-happens.html
 

but I thought I'd mention two of my favorite LDO ICs:  The LM2936z-5 and the S812C50.  These are both TO-92 through-hole ICs with 5 volt outputs.  Their maximum currents are both 50 mA so they are meant for use with low power microcontroller circuits like keyers. The LM2936 is made by TI (originally from National Semi).  The S812C50 is from ABLIC which used to be known as Seiko.

As mentioned before the LDO circuit will regulate very close to the input voltage, tenths of a volt while "regular" three terminal regulators like the 78L05 will regulate with input voltages 2 volts higher than the output.  Current use is also much lower than the 78L05.  The downsides are potentially higher noise on the output, higher cost tantalum output caps needed and just higher cost of the actual regulator IC.

The LM2936 is a bipolar IC so less worries over static damage.  The LM2936 is meant for use in an automotive environment so it will withstand abuse like input voltages of 40 volts and polarity reversals of a similar magnitude.   The 78L05 will die quickly if the polarity is reversed.  The LM2936 dropout voltage is something like 0.5 volt.  The LM2936 will use about 7 uA at an input voltage of 9 volts while the 78L05 will use several mA.  The problem with the LM2936 is the price, currently $2 each plus the required tantalum output cap which will add over 30 cents more to the price.   

The S812C50 is an MOS IC so static damage is more of a concern.  The S812C50 will die above 18 volts.  The 812C50 has a reverse bias diode across the input so theoretically this would protect against reverse polarity if a series fuse is included but in reality it can be damaged by reverse polarity.  However the dropout voltage is small maybe a tenth of a volt while the current used by the regulator itself is a microscopic 1 to 2 uA at 9 volts input (usually it measures 1 uA not sure why it's 2 uA now).  The S812C50 is about 1/3 the price of the LM2936 but it also requires the tantalum output cap.

So that's the story on my favorite LDO regulators, if I want something bulletproof where cost and the lowest current aren't super important the LM2936 is used.  If the lowest current usage is necessary the S812C50 is specified.  And if all that's important is price the 78L05 conventional regulator is used.

Unfortunately the parts don't have the same pinout. Looking at the marked face, the LM2936 and the 78L05 are from left to right:  OUT - GROUND - IN.  Looking at the S812C50 is: GROUND - IN - OUT.  One thing that can be done to accommodate both pinouts (as was done with the keyer test fixture shown here) is to add another hole in line with the LM2936 and then add a trace from the additional hole to the LM2936 output.  This makes it easy to change regulators if needed (especially if pin sockets are used).

I'm sure that there are newer/better/cheaper regulator parts now but they are likely SMT only - the LM2936 and S812C50 have withstood the test of time.

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm