Hi Salas, I've just completed another pair of your BIB regulators but have a problem with one and would welcome a steer from you.
I've built pos and neg modules, target voltage is +/-14.75V. Each module has a separate (25VA) transformer winding at 15V AC. All LEDs light up and nothing smoked. Target load current is 350mA plus 135mA shunt current. I have a suitable load resistor installed across the outputs. Mosfets are bolted to thick aluminium chassis for heatsinking.
The two modules use identical passive components. Output voltage setting chains consist of 2* red LEDs, 2.2K resistor and 500R multi-turn preset.
On the positive module I have dialled in to 14V output for testing (I can set a max output voltage of 15.8V). Measured voltages are;
AC in = 17.2V
DC after R101 = 17.99V
For output voltage of 14V the measured resistance between the D101 link and SO3 = 2.3K
On the negative module the maximum output voltage I can set is 12.11V. Measured voltages are;
AC in = 17.2V
DC after R101 = 19.1V
For output voltage of 12.11V the measured resistance between the D201 link and SO3 = 2.7K (as one might expect!).
I can adjust the output voltage to some on both modules so I'm assuming the sensing circuit and shunt mosfet are OK on both. I'm thinking the problem is with the constant current circuit on the negative module, Q201. Q202? What should I measure to narrow it down more?
Any advice gratefully received.
Cheers
Ray
I've built pos and neg modules, target voltage is +/-14.75V. Each module has a separate (25VA) transformer winding at 15V AC. All LEDs light up and nothing smoked. Target load current is 350mA plus 135mA shunt current. I have a suitable load resistor installed across the outputs. Mosfets are bolted to thick aluminium chassis for heatsinking.
The two modules use identical passive components. Output voltage setting chains consist of 2* red LEDs, 2.2K resistor and 500R multi-turn preset.
On the positive module I have dialled in to 14V output for testing (I can set a max output voltage of 15.8V). Measured voltages are;
AC in = 17.2V
DC after R101 = 17.99V
For output voltage of 14V the measured resistance between the D101 link and SO3 = 2.3K
On the negative module the maximum output voltage I can set is 12.11V. Measured voltages are;
AC in = 17.2V
DC after R101 = 19.1V
For output voltage of 12.11V the measured resistance between the D201 link and SO3 = 2.7K (as one might expect!).
I can adjust the output voltage to some on both modules so I'm assuming the sensing circuit and shunt mosfet are OK on both. I'm thinking the problem is with the constant current circuit on the negative module, Q201. Q202? What should I measure to narrow it down more?
Any advice gratefully received.
Cheers
Ray
Thanks.
No problem with rectifiers or smoothing caps as DC voltages are fine; I see 21.4V DC before R101/R201
Ray
R101/201 = 6R8. Value derived using the Salas calculator spreadsheet.
On the negative supply the voltage drop across R201 = 2.3V
On the positive supply the voltage drop across R101 = 3.4V
Thanks
Ray
OK, thanks. First I'll look through my spares box for a resistor in the range of 10-20ohms and parallel that across R201. Will report back.
I'm using the same dummy load resistor for both modules, switching back and forwards between them with consistent results.
Ray
Last edited:
Just to clarify what I'm aiming for with the negative regulator, I've just adjusted the positive regulator to deliver its target output of 14.75V and measured it again;
AC in = 17.3V
DC before R101 = 21.2V
DC after R101 = 18.3V
Voltage across R101 = 2.9V
Current across R101 = 430mA
That all looks good to me.
Now to the spares box.
Ray
AC in = 17.3V
DC before R101 = 21.2V
DC after R101 = 18.3V
Voltage across R101 = 2.9V
Current across R101 = 430mA
That all looks good to me.
Now to the spares box.
Ray
Unusually, the first resistor I looked at was a 5W 15R8!
Anyway, I hooked that up with croc leads in parallel with R101, giving 4R5.
The results are strange though;
AC in = 17.3V
DC before R101 = 21.2V
DC after R101 = 19.9V
Voltage across R101 = 1.3V
Current across R101 = 288mA
So, less voltage drop and less current?
Anyway, I hooked that up with croc leads in parallel with R101, giving 4R5.
The results are strange though;
AC in = 17.3V
DC before R101 = 21.2V
DC after R101 = 19.9V
Voltage across R101 = 1.3V
Current across R101 = 288mA
So, less voltage drop and less current?