JSR03, 7.5 volts out instead of 5 V

[peranders]

Which voltage reference do you use, LM431?

Voltage at pin 2, 3, 6 and 7 of the opamp?

DZ1 is a LED? Is it lit?

[Bradley Kindell]

Hi P-A,

I am using a TS431 voltage reference.

the OP-AMP has the following voltages on its pins

2 = 2.55v
3 = 2.55v
6 = 5.71v
7 = 7.31v

Brad

[Bradley Kindell]

i forgot I am using a red 140mcd led for DZ1 and both leds are lit.

[peranders]

The sense connections are connected?

The pin 2 should have the output voltage divided by 2. Have you checked this voltage divider carefully? 1 k+ 1k

R12 mounted, R11 not mounted?

[Bradley Kindell]

R1 and R2 are both 1k

I have installed R11 as shown on the 5v parts list, although I thought that R12 would be needed on lower output voltage versions.........


Brad

[peranders]

Try to remove R11 and use only R12.

[Bradley Kindell]

no good.

just removed R11 and put R12 in place. Output still the same. Only difference now is that the Opamp is getting 10.5 volts via R12.

any other ideas?

the main LED is not as bright as the one used in the DZ1 position.

everything else is as per the BOM for the 5v output.

R10 is shown as a wire jumper in the BOM and also 470 ohms - I have fitted the wire jumper - is this correct?

Brad

[Bradley Kindell]

the sense inputs are shorted to the corresponding outputs - is this correct?

[peranders]

Since you have exactly the same voltage on pin 2 and 3, no short there? A close up photo could help me.