I need help with developing a control loop for a SCR controlled power supply. My circuit is based on a construction article published in Poplar Electronics written in the 80’s by G.R. Baumgras. I use a series of one shot timers to control the firing of the SCR where the original circuit used uA 723. The purpose for the design is to provide a pre-regulated voltage source for a precision voltage power supply. The pre-regulator greatly reduces the power waste of the precision regulator voltage drop when supplying low voltage at a high current level. I need help with developing the control loop. As the power supply output capacitor is loaded the operating point need to shift to keep the pre-regulator around 5 to 6 volts higher than the precision voltage level. The set point is dynamic and varies from 1 to 5 volts. I need help with developing a circuit that will offset the set point to maintain the desired pre-regulator voltage under varying load conditions.
Present circuit functionality: Vp= pre-regulator voltage, Vo = Precision Voltage Out, Vc = Voltage control to SCR trigger circuit.
Vo Vp Vc
0 10 4.20
7.5 14.6 3.94
13.7 20.6 3.582
20 25.6 3.204
25 28.62 2.91
The above chart is for a 130 ohm load.
When operating the pre-regulator set for 12 volts and 130 ohm load the required Vc is 4.00 volts. When loaded to 18 ohms, Vp drops from 12 volts to 10.65 volts. Changing Vc from 4.00 to 3.733 to bring Vp back to 12 volts. Using an differential amp will work to detect voltage unbalance between Vp – Vo, however this output is zero when balanced. How can I use this error to sum with the set point (Vc) to offset the Vc?
I just need ideas, I can/will do the research.
I have schematic for SCR trigger and general Block Diagram both in pdf format. Neither will upload to this forum, error message is " The upload is empty ... file name". Both file open with Adobe reader XI, file size is 88K and 13K. This is a common problem/issue for me, what am I doing wrong?
Present circuit functionality: Vp= pre-regulator voltage, Vo = Precision Voltage Out, Vc = Voltage control to SCR trigger circuit.
Vo Vp Vc
0 10 4.20
7.5 14.6 3.94
13.7 20.6 3.582
20 25.6 3.204
25 28.62 2.91
The above chart is for a 130 ohm load.
When operating the pre-regulator set for 12 volts and 130 ohm load the required Vc is 4.00 volts. When loaded to 18 ohms, Vp drops from 12 volts to 10.65 volts. Changing Vc from 4.00 to 3.733 to bring Vp back to 12 volts. Using an differential amp will work to detect voltage unbalance between Vp – Vo, however this output is zero when balanced. How can I use this error to sum with the set point (Vc) to offset the Vc?
I just need ideas, I can/will do the research.
I have schematic for SCR trigger and general Block Diagram both in pdf format. Neither will upload to this forum, error message is " The upload is empty ... file name". Both file open with Adobe reader XI, file size is 88K and 13K. This is a common problem/issue for me, what am I doing wrong?