# How does this work

Discussion in 'General Electronics Chat' started by Humanityrulz, Jul 23, 2009.

1. ### Humanityrulz Thread Starter Active Member

Jul 21, 2009
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CAN U EXPLAIN about DUAL diodes functioning in the above circuit please...

Apr 20, 2004
15,808
295
3. ### Humanityrulz Thread Starter Active Member

Jul 21, 2009
60
0
Sorry abt that ,, i am new tho this blog.. i am getting confused , i don't understand where to post my Querry..?

Two DUAL DIODS IN THE LOOP (TOTAL 4 DIODES) in upper right hand side.. functioning..

4. ### Humanityrulz Thread Starter Active Member

Jul 21, 2009
60
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Hi ,i am using KA78l05A Voltage regulator (Vin 15V , Vo=5V)in my PCB board, it's showing 5v reading b4 connected in PCB board, and in PCB board it shows output voltage 7V instead of 5V.. why? I am connected one capcitor parllel at input and one capacitor at output in parllel... do u have any idea..?
Interesting point is, I replaced LM340T5 7805(5V output ) it's working fine in that PCB circuit...giving 5v o/p.
KA78L05A regulator giving strange reading when vary the voltage...(O/P voltage proportional to I/P voltage.... regulator o/p must 5V eventhough changes in the input voltage I believe..!)

I know these are very basics Querrys... but theoritically i am ok.. but when comes to this practical sessions .. i don't understand .. ..... Thankq for your relpy
....

Last edited: Jul 23, 2009
5. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
The circuit you're asking about is a snippet of a larger oner intended to generate sine waves. Follow the link - http://www.national.com/an/AN/AN-263.pdf - and go to page 11 of the PDF. Those diodes are the logarithmic elements in the feedback path.

As far as the regulator goes - a 78L05 is in a T-92 package and rated for 100 ma out. The dissipation caused by the 15 volt input may be overheating the poor thing. It would be much happier with a 7 volt input, but also with current under 100 ma.

6. ### Humanityrulz Thread Starter Active Member

Jul 21, 2009
60
0
Thankyou for your reply with fine solutions.... i will check this today ... as far as, while I building circuit.... MOSFET chip is failing after the continuous running at 60 degrees.. in circuit it's not well designed as per the datasheet.. (with out connecting CAP's in i/p and o/p..Is there any problem with out CAPACITORS... ) http://www.onsemi.com/pub_link/Collateral/MC34151-D.PDF datasheet of MC33151 operating temp upto 85....but particular component not working properly at above 60deg... in my circuit i/p for this mosfet driver comes from multivibrators... o/p indicates (two leds..LED) in my circuit i skipped the resistor and capacitors as per the datasheet.. what is the function of the resistor and CAPACITORS at i/0 and o/p(PAGE 3 in given PDF link) Please clear my doubt in this circuit(page3) about resistor and capacitors..