Power supply help....

[JRGarcia13]

Hello Everyone. Best forum by far!
I'm buliding a variable power supply but I'm not sure of what is the purpose of two componets, perhaps one of you can clear this up for me.

http://www.electronics-tutorials.com/basics/power-supp-variable.htm

Figure 1 - variable bench power supply schematic
My question is:
What is the function od D5 and D6???


Thanks in advance.
JRGarcia13

 

[jimkirk]

On the page you refer to, there's a link to the National Semiconductor spec sheet for the regulator. Download that, it will tell you what need to know. Short answer: protection against shorts.

 

[melone]

According to that website....


5. Diodes D5 and D6 are for protection in the event either the input or output are shorted. The resistor R1 connects across the anodes of both D5 and D6 and nowhere else. Look closely at diagram. R1 does NOT connect to the "out" line. Similarly C4 connects from "output" to ground and NOWHERE else.

 

[itsmoked]

melone; Why do you say this? [red]"The resistor R1 connects across the anodes of both D5 and D6 and nowhere else. Look closely at diagram. R1 does NOT connect to the "out" line."[/red]

Looks like it connects to the output to me... How else does the LM317 get output feedback if it doesn't?


Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[OperaHouse]

Protection against input or output shorts does not mean short protection in the conventional sense. These diodes prevent a negative voltage being created in a short condition that could destroy the regulator IC. Primary problem is the stored energy in the caps. You wouldn't see these diodes in most regulator circuits that didn't have the creative input of a neophite producing interesting wiring situations. Shorts can still produce likely damage although the regulator should thermally limit.

 

[melone]

I just copied it directly from the website in the OP question......

 

[JRGarcia13]

Thank you all for your responses. They were very helpful.
JRGarcia.

 

[IRstuff]

Figure 2 of that webpage shows

Vout=1.25V*(1+R2/R1)

TTFN

 

[john111smith]

If you need a power supply with 2A or more output, it is better to use a Bulk Swich Mode ones. search LM2576 documents. Also, It may have a variable example circuit.