Hi All, I need to build a PIC18F4550 based circuit powered from the 4 NiMH batteries. The problem is that the power supply voltage for fully charged batteries is equal to 5.6V which is above acceptable limit for PIC18F4550. On the othe hand The fully discharged batteries provide only 4.4V (while PIC needs at least 4.2V). It seems that I need either a swicthing DC/DC converter (which I'd like to avoid, because the design is price sensitive), or a LDO stabilizer... Certainly I can build a dedicated LDO stabilizer (sample circuit fot LT-Spice is provided at the end of the message), or use e.g. LP2951 (http://www.national.com/ds/LP/LP2950.pdf or http://www.fairchildsemi.com/ds/LP/LP2951.pdf) set at 4,2V. However a have also a very simple, but a little crazy idea - to use a LP2950-5.0V as a "voltage limitter". If you look at the http://www.national.com/ds.cgi/LP/LP2950.pdf datasheet, at the page 9 "Dropout characteristics", you can see that for input voltages above ca. 5.5V the LP2950-5.0V provides the output voltage limiting at the level of 5.0V, and at lower input voltages it provides almost constant dropout of ca. 0.4V. Or maybe I should use just a Schottky diode with forward voltage of c.a. 0.4V? -- Thank you in advance for any suggestions, Wojtek PS. - Own LDO stabilizer simulation for LT-Spice Version 4 SHEET 1 1300 680 WIRE 64 16 -128 16 WIRE 160 16 64 16 WIRE 384 16 256 16 WIRE 480 16 384 16 WIRE 576 16 576 0 WIRE 576 16 480 16 WIRE -128 48 -128 16 WIRE 64 80 64 16 WIRE 208 80 144 80 WIRE 576 80 576 16 WIRE 832 80 576 80 WIRE 384 112 384 16 WIRE 832 128 832 80 WIRE 208 144 208 80 WIRE 208 144 128 144 WIRE 64 176 64 80 WIRE 288 176 64 176 WIRE 480 192 480 16 WIRE 576 192 576 80 WIRE 128 208 128 144 WIRE 288 208 288 176 WIRE 64 256 -32 256 WIRE 384 256 384 192 WIRE 384 256 352 256 WIRE -32 272 -32 256 WIRE 208 304 128 304 WIRE 288 304 208 304 WIRE 384 304 384 256 WIRE 480 304 480 256 WIRE 576 320 576 272 WIRE 832 320 832 208 WIRE 832 320 576 320 WIRE -32 384 -32 352 WIRE 576 384 576 320 FLAG 208 384 0 FLAG -32 384 0 FLAG -128 128 0 FLAG 384 384 0 FLAG 576 384 0 FLAG 576 0 Uwy FLAG 480 304 0 SYMBOL npn 64 208 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL npn 352 208 M0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL pnp 256 80 M270 SYMATTR InstName Q3 SYMATTR Value BCW68F SYMBOL res 160 64 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 2k SYMBOL res 192 288 R0 SYMATTR InstName R2 SYMATTR Value 1.5k SYMBOL voltage -32 256 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 2.5 SYMBOL voltage -128 32 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 5 SYMBOL res 368 96 R0 SYMATTR InstName R3 SYMATTR Value 1.8k SYMBOL res 368 288 R0 SYMATTR InstName R4 SYMATTR Value 2.5k SYMBOL res 560 176 R0 SYMATTR InstName R5 SYMATTR Value {Robc} SYMBOL current 832 128 R0 WINDOW 3 -294 319 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 10mA 1m 1n 1n 10m 20m) SYMATTR InstName I1 SYMBOL cap 464 192 R0 SYMATTR InstName C1 SYMATTR Value 100n TEXT -168 424 Left 0 !;dc V2 5.6 4.4 TEXT -120 -176 Left 0 !.STEP PARAM Robc LIST 45, 70, 100 TEXT -168 448 Left 0 !.tran 1s -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist