Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

problem in power supply

Not open for further replies.


Full Member level 4
Oct 27, 2005
Reaction score
Trophy points
Activity points
dear frnzs
me sending this figure of two power supplies.please any one can tell me that what is the difference between the two and how much voltage at the output does each ckt provide. i m feeding this output voltage to a microcontroller 8051 along with eeprom and ds1820. what effect will either have on the ckt.


Looks like one of the circuits is a full wave rectifier and the other a half wave rectifier. Definately a FWR is more power efficient

These boxes labelled "230Vac" are in fact transformers that produce 1 x 9Vac (top) and 2 x 9Vac center-tap (bottom) ..
Both circuits are full-wave rectifiers; see:
**broken link removed**

From the 7805 side there is no difference at all; both will give you 9Vpp voltage which before being delivered to 7805 voltage regulator has to be smoothed by a capacitor to produce unregulated ≈12Vdc. The capacitance depends on the current you are going to draw from 5V output, and if you assume that this regulator is capable of 1A output current you should use at least 1000µF capacitor ..

thnx for replying ianp .u said "that produce 1 x 9Vac (top) and 2 x 9Vac center-tap (bottom)" but i think the top one is giving 18 v ac .m i right and if so wil that effect .and one thing more im using 1000u f cap but i just not mention that in the diagram

The top one delivers 9Vpp and the bottom one, the "center tap" configuration, delivers the same --> 9Vpp, that is ..
And, it is good to hear that you have already included 1000µF smoothing cap, however, another good idea would be to add 0.1µF caps at both sides of the 7805 regulator ..

thnx a lot for this Ianp but i have one more doubt i have interfaced 24c02 with 89c51 what pull resistors should i use 4.7k or 10k, on SCL and SDA line, will the difference cause any problem.should there be any capacitor on SCL and SDA line with ground, if then please suggest me which one should i use.

If you don't use PORT0 pins, you don't need them at all ..
If you do, both values will do the job..

thnx. please have a look on diagram below it's from AT24c02 datasheet. they have used 5.1k resistors on port P1, what should i do. Actually sometimes the eeprom is missing to right correct values when i use 10k. and should there be any capacitor on SCL and SDA line with ground, if then please suggest me which one should i use.

This digram describes connection of up to 7 of 24CXX devices on the same SCK and SDA lines ..
Try to connect 4k7 resistors, it wouldn't heart, but if you connect only one EEPROM to PORT1 pins, I am pretty sure you don't need any pullups at all ..
I don't think "missing bits" issue is related to pullups ..

thnx once again, then what can be the reason behind "missing Bits" i have checked the eeprom routine and the delays are proper too.if u want i can send the code also.

Not open for further replies.

Part and Inventory Search

Welcome to