Help with Voltage regulator

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AThayer said:
can you explain your circuit a little more?
Click to expand...
So the top picture is from you.
The bottom circuit is from you but upside down.
Bottom left is connected to ground.
Top is connected to +90V.
The motor will see 65V.
Exact same circuit, just turned over.
 
OK, Mostly working. My goal is Vin=90V Vout = 65V (motor is R5, 10 ohms, 6.5A)
L2 is 100uH 20A coil or transformer.
L1 is a secondary winding to get power to run the IC. (UC3842)
IC running in constant off time mode.
Feedback: IC wants to get 2.5 volts on "FB", R4&R9 10V>2.5V, so 10 V across R11, so 64V across R6.
Right now current limit at 9 to 10A.
It takes about 6mS to get up and running. (in spice) it will take longer in real life. (0.75s)

Here is the start up voltage across the motor.

It wants a current of 1A or more.
 

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AThayer said:
The power supply puts out 85-90 volts dc. I am looking to reduce that voltage to 65-75vdc.
Click to expand...
AThayer said:
What do you guys think about this design?
Click to expand...
This is not what you asked for.
This is 220 V AC input. The output is pulsed.
This 2uF cap on the input gives me the idea it is very low power. Can not run even a small motor. Go back to where you got this and find out what it does.
 
A 555 monostable makes a pulse and is not a voltage regulator. When the AC voltage becomes too low then the SCR turns on and stays turned on until the power is turned off.
 
ronsimpson said:
This is not what you asked for.
This is 220 V AC input. The output is pulsed.
This 2uF cap on the input gives me the idea it is very low power. Can not run even a small motor. Go back to where you got this and find out what it does.
Click to expand...
I was just trying to look outside the box.
 
So what would the circuit in #25 output? Again I am just trying to learn about electronic and options. Also couldn't some circuitry be added to provide feedback?
 
Be aware that the post #25 circuit is dangerous, because it doesn't provide mains isolation. Any part of it could be LIVE!
 
Ron's circuit of post #24 is a professional design.

Why consider anything else?

spec
 
AThayer said:
So what would the circuit in #25 output?
Click to expand...
Input is 220V 60hz from the wall.
The 2uF cap has an impedance (like a resistor) 1/2 pi F C So in your head replace the cap with a resistor.
After the 4 diodes you have half sign wave bumps at 120hz. (full wave rectification)
I don't know the voltage because it is very dependent on the load. (2uF and load makes a voltage divider)
The SCR turns on at some point set by the time of the IC 555. The SCR turn off at 0 voltage. (same as zero crossing)
Output voltage is in red.
 
Added RC on emitter of Q3. Fixed over shoot. (needs more work but OK for now)
Did much testing for short and over load.
Short circuit current is about 10A.
Under short circuit or heavy load the IC will run for a short time then wait for a while to let Q1 & D5 cool off.
Added .IC command to make start up work faster.

Power up with out overshoot.
 
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