Toe Cutter
New Member
Hello. I am interested in building a regulated laboratory-type power supply with variable voltage and variable current limiting. I've been looking around the net for schematics and ideas. I would like to avoid the LM317/ua723 style supplies and just use transistors and op-amps.
I found the schematics for the old HP linear supplies and I think they have some good ideas, but I can't quite understand one aspect of this design. I've attached images for the HP 6502B schematic and a simplified drawing from the HP app note 90B.
Most of it I can follow. What they do with this supply is have a floating reference/bias supply with a precision +/- 6.2 volts. The common of this floating supply is tied to the (+) output and one input of a differential amplifier. The output of the diff amp eventually drives the series regulator.
The +6.2 volt, regulated supply and a precision resistor (R12/R13) form a precision current source. This is tied to the other input of the differential amplifier and shunted by the voltage setting potentiometer.
I can sort-of, almost see how this scheme works to regulate the voltage, but I am missing something. Where does the reference current through R12/R13 go? It has to return to the reference regulator somehow. Does it flow through the R10 setting potentiometer? This is the part I am getting stuck at. Could someone help me better understand how the voltage setting and feedback works? Also, I found an IC, the MC1466, which uses a very similar concept. But this IC is long obsolete.
I find this idea, with the floating reference and auxillary supply appealing because it eliminates the requirement to use components rated for higher voltages. For example, I have a transformer that outputs 60VDC (rectified and filtered). Without an auxillary supply, I might need op-amps that have a > 60V rating. Thanks!
I found the schematics for the old HP linear supplies and I think they have some good ideas, but I can't quite understand one aspect of this design. I've attached images for the HP 6502B schematic and a simplified drawing from the HP app note 90B.
Most of it I can follow. What they do with this supply is have a floating reference/bias supply with a precision +/- 6.2 volts. The common of this floating supply is tied to the (+) output and one input of a differential amplifier. The output of the diff amp eventually drives the series regulator.
The +6.2 volt, regulated supply and a precision resistor (R12/R13) form a precision current source. This is tied to the other input of the differential amplifier and shunted by the voltage setting potentiometer.
I can sort-of, almost see how this scheme works to regulate the voltage, but I am missing something. Where does the reference current through R12/R13 go? It has to return to the reference regulator somehow. Does it flow through the R10 setting potentiometer? This is the part I am getting stuck at. Could someone help me better understand how the voltage setting and feedback works? Also, I found an IC, the MC1466, which uses a very similar concept. But this IC is long obsolete.
I find this idea, with the floating reference and auxillary supply appealing because it eliminates the requirement to use components rated for higher voltages. For example, I have a transformer that outputs 60VDC (rectified and filtered). Without an auxillary supply, I might need op-amps that have a > 60V rating. Thanks!