Curious about a regulator configuration

[lilimike]

Hi,

In the following schematic, I don't understand what D2 and D3 are there for.
It is the first time I see a regulator configured like this and the data sheet doesn't indicate anything about this. Could some one please explain?
This is from a PIC programmer **broken link removed**.

Thanks

Mike

 

[ericgibbs]

Hi,

In the following schematic, I don't understand what D2 and D3 are there for.
It is the first time I see a regulator configured like this and the data sheet doesn't indicate anything about this. Could some one please explain?
This is from a PIC programmer **broken link removed**.
View attachment 42416
Thanks

Mike

Hi,
By adding the 2 diodes in the 12V reg ground line, it raises the 12V out to approx 13.4V, due to the 0.7Vdrop across each diode.
For programming the Vpp needs to be about 13.3V

 

[lilimike]

Eric,

This makes a lot of sens, I didn't think we could raise the output voltage like this but its a great new thing I learned today.

Thank you Eric

Mike

 

[ericgibbs]

Eric,

This makes a lot of sens, I didn't think we could raise the output voltage like this but its a great new thing I learned today.

Thank you Eric

Mike

hi Mike,
For future reference when using 'fixed' voltage regulators, the diodes can be replaced with a fixed or variable resistor/s and set to give higher voltages than stated on the reg.
The modified regulator does not meet the ideal specification but for most applications it dosn't matter.

 

[lilimike]

Great information,
thank you again,

Mike