Hello,
I'm trying to make a small power supply using a common schematic found on the web which has been around for many years. For comparison, it is the smaller diagram in the blue box at the link below.
Due to availability issues, I had to use 2 transformers in series to get the voltage I wanted. I had to substitute 68 uF, 200 V caps for the 4700 uF caps, and use LM317 and 337 voltage regulators with their associated circuitry for adjusting the voltage (highlighted in purple.)
I'm trying to get +15 and -15 V, and only need <100 mA. The circuit is supposed to be good for up to 1.5 A. The expected voltages are shown. The actual measured, open circuit, voltages are in red, in parentheses.
I can't find anything wrong, or any bad parts, but when I put the voltage regulators in the circuit, the maximum voltages I get are +8.7 V and -7.0 V, when the regulators should be good to +/- 37 V.
I tried different, also new, regulators, and changed R1 from 240 ohms to 120 ohms (what it should be depends on where you look.) I still get the same output.
All parts are brand new except the 68 uF caps which I scrounged from a fluorescent light circuit. I tried 4700 uF, 35 V caps temporarily (the voltage they see is about 38 V) but that didn't make any difference either.
Does anyone see anything I'm missing?
Thanks in advance.
P.S. I want to power a INA121 instrumentation amp, and small FET circuit.
I'm trying to make a small power supply using a common schematic found on the web which has been around for many years. For comparison, it is the smaller diagram in the blue box at the link below.
Due to availability issues, I had to use 2 transformers in series to get the voltage I wanted. I had to substitute 68 uF, 200 V caps for the 4700 uF caps, and use LM317 and 337 voltage regulators with their associated circuitry for adjusting the voltage (highlighted in purple.)
I'm trying to get +15 and -15 V, and only need <100 mA. The circuit is supposed to be good for up to 1.5 A. The expected voltages are shown. The actual measured, open circuit, voltages are in red, in parentheses.
I can't find anything wrong, or any bad parts, but when I put the voltage regulators in the circuit, the maximum voltages I get are +8.7 V and -7.0 V, when the regulators should be good to +/- 37 V.
I tried different, also new, regulators, and changed R1 from 240 ohms to 120 ohms (what it should be depends on where you look.) I still get the same output.
All parts are brand new except the 68 uF caps which I scrounged from a fluorescent light circuit. I tried 4700 uF, 35 V caps temporarily (the voltage they see is about 38 V) but that didn't make any difference either.
Does anyone see anything I'm missing?
Thanks in advance.
P.S. I want to power a INA121 instrumentation amp, and small FET circuit.
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