Single control PSU able to output all the way from +15V to -15V

Thread Starter

atferrari

Joined Jan 6, 2004
3,916
I recall building long ago, a PSU with a unique output able to go up and down between -15V to +15V with a single control. It was used to control a small DC motor.

Recently I tried something but my flawed design, caused excessive heating and I desisted.

What is the right name for it? Adjustable...what? I discard "dual" because that identifies PSUs with coexisting negative and positive rails.

Could anyone lead me to a simple design? Regulated but little power would be OK.

Gracias for any help.
 
Last edited:

nsaspook

Joined Aug 27, 2009
7,179
Search for bipolar (four quadrant power supply) power supply.

A pre-regulated ±17V bulk power source and a analog bipolar power opamp circuit can be used for a simple inefficient linear dissipative circuit. The voltage adjust input can be a simple balance pot between the two rail opamp rail voltages with the wiper as the output to the opamp circuit.

https://cds.cern.ch/record/987553/files/p209.pdf

3.2 Linear dissipative stage
 

Thread Starter

atferrari

Joined Jan 6, 2004
3,916
Search for bipolar (four quadrant power supply) power supply.

A pre-regulated ±17V bulk power source and a analog bipolar power opamp circuit can be used for a simple efficient circuit. The voltage adjust input can be a simple balance pot between the two rail opamp rail voltages with the wiper as the output to the opamp circuit.

https://cds.cern.ch/record/987553/files/p209.pdf
Yes BIPOLAR! That was the expression @nsaspook ! Gracias.

Reading now.
 

dl324

Joined Mar 30, 2015
10,480
Yes BIPOLAR!
In it's most general definition, bipolar refers to two power supplies; a positive voltage and a negative voltage. They're sometimes in the same power supply and sometimes offer tracking or independent voltages. An example is Tektronix PS 503A; a triple output supply.
 

nsaspook

Joined Aug 27, 2009
7,179
In it's most general definition, bipolar refers to two power supplies; a positive voltage and a negative voltage. They're sometimes in the same power supply and sometimes offer tracking or independent voltages. An example is Tektronix PS 503A; a triple output supply.
In this instance we are talking about the single terminal output to a common/return.
 

dendad

Joined Feb 20, 2016
3,426
If you are still going to drive a motor, I would look at a controller, like an Arduino, driving an H bridge with PWM.
A lot more efficient.
But, what current are you talking about for you supply?
 

crutschow

Joined Mar 14, 2008
24,709
In it's most general definition, bipolar refers to two power supplies; a positive voltage and a negative voltage.
According to Google:
A bipolar power supply is a four-quadrant tool that operates in quadrants one, two, three, and four of the Cartesian coordinate system. This means it provides positive and negative voltages across its output terminals without needing to switch any external wiring.
 

Thread Starter

atferrari

Joined Jan 6, 2004
3,916
Is kind of a personal debt to myself for something I did not know how to solve some time ago. Nothing that should take more than one day to assemble.

The eventual use would be to drive a small hobby DC motor at the first stage of a simple design. Later a PIC will take charge.

Buying any power opamp is impossible here (corona or not) but I recalled having built a buffer stage for an opamp in a function generator, following a design by member Dick Cappels. (Look here).

A quick revision via LTSpice says I need to revise how to set gain in a long tail pair. That pretty much covers it.

Thanks for your interest and disposition.
 

crutschow

Joined Mar 14, 2008
24,709
To drive a motor the simplest way would likely be to use a rail-rail op amp with a complementary pair of emitter followers.
This has some crossover distortion but that is not likely a problem when driving a motor.
If a signal emitter follower does not have enough gain, then you could use a Sziklai pair (complementary Darlington) since they have a lower drop than a standard darlington (one Vbe drop instead of two).

Do you know how much current the motor takes?
 

Thread Starter

atferrari

Joined Jan 6, 2004
3,916
To drive a motor the simplest way would likely be to use a rail-rail op amp with a complementary pair of emitter followers.
This has some crossover distortion but that is not likely a problem when driving a motor.
If a signal emitter follower does not have enough gain, then you could use a Sziklai pair (complementary Darlington) since they have a lower drop than a standard darlington (one Vbe drop instead of two).

Do you know how much current the motor takes?
Not yet Carl. Selecting one is next step, but all I got are really small.

I will revert as soon as I choose one.
 

dl324

Joined Mar 30, 2015
10,480
A bipolar power supply is a four-quadrant tool that operates in quadrants one, two, three, and four of the Cartesian coordinate system. This means it provides positive and negative voltages across its output terminals without needing to switch any external wiring.
A bipolar power supply only operates in 4 quadrants if it can sink and source current. Most are going to be 2 quadrant.
 

nsaspook

Joined Aug 27, 2009
7,179
A bipolar power supply only operates in 4 quadrants if it can sink and source current. Most are going to be 2 quadrant.
A two-quadrant power supply is more common but it's still not what most people use for circuits, a one-quadrant supply that can only source power. A common use for a two-quadrant power supply is for something that emulates a rechargeable battery as it can both source and sink power at the same voltage polarity.

I've seen and used several types of bipolar power supplies for magnetic field control using quadapoles and solenoids.
2016-04-19_07-17-45.jpg
 

bassbindevil

Joined Jan 23, 2014
86
For a DC motor, the easiest solution is pwm control of an h-bridge, like an R/C car's ESC (electronic speed control). Doing it linearly sounds like a servo motor amplifier.
 

Thread Starter

atferrari

Joined Jan 6, 2004
3,916
For a DC motor, the easiest solution is pwm control of an h-bridge, like an R/C car's ESC (electronic speed control). Doing it linearly sounds like a servo motor amplifier.
I implemented PWM control with PIC micros, many times in the last 10 or 12 years. Do not worry. As I said, the focus is on the PSU.
 
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crutschow

Joined Mar 14, 2008
24,709
Here's the LTspice simulation of the circuit I mentioned for 0 to 100% U2 pot rotation.
The Sziklai pair output gives a 3A maximum current.

The op amp can be just about any rail-rail output type.

If the load current is less than 200mA, then you only need Q1 and Q3.

1585952407083.png
 
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