Based on tracking pre-regulator circuit form National and this link I expect to achieve 1A regulated current. But in reality ripple voltage is around 0.2V RMS.
The voltage across second reg is around 2V and does not change if one or two red LEDs are connected between Vout2 and Vadj1.
Sims in LTspice are ok.
The voltage across second reg is around 2V and does not change if one or two red LEDs are connected between Vout2 and Vadj1.
Sims in LTspice are ok.
Are you sure about that?The voltage across second reg is around 2V and does not change if one or two red LEDs are connected between Vout2 and Vadj1.
When 4,7mF caps were in the doubler - 100%. And it was odd. Changing R7 did not help.Are you sure about that?
Two setups were tested - same result.
I recently built one of these tracking preregs and it works fine.
Looking at your circuits, the values look a bit odd. Here are some specific comments.
1) The 1000uf cap at the output of the 1st regulator isn't needed although it shouldn't cause any problems.
2) The resistors around the 2nd regulator look odd. What voltage are you trying to regulate? Compare your circuit to the referenced circuit. They don't look the same.
3) The value of R6 (top circuit) or R2 (bottom circuit) = 6.3ohms is much too low. Typical values should be 100 - 240 ohms. Similar comment for R7 in the top circuit.
--Gary
I didn't notice that. The cap on the reg2 adjust pin has got to go. Or at least shunted with a resistor.
Why remove? It improves ripple rejection by 20 dB according to datasheets. What shunt resistor value?
So now we learn it is a current regulator you want to build. Carry on.
Er, I wrote it in the subject. Too much or too little alcohol
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