0-30V Stabilized Power Supply

[red baron]

About a month ago I asked if anyone could explain why my 30V 5A (with 3 x TIP3055 output transistors) suddenly failed at 45V and no current.  Both Audioguru and Redwire (I think) suggested a short in one of the 3055s.  Finally I have isolated the fault to a 'popped' 3055.
At the time that the PS failed, I was trying to charge a 'golf cart' battery which was nearly fully charged so no significant current.  I set the volts on 14.1V and current limit at 1A.  When touching the PS leads to the battery there were a few sparks (possibly back to front polarity), and maybe not, but PS popped the 3055.
Has anyone had experience with the PS and 'active' loads like batteries, as opposed to passive loads like resistors?

 

[liquibyte]

About a month ago I asked if anyone could explain why my 30V 5A (with 3 x TIP3055 output transistors) suddenly failed at 45V and no current.  Both Audioguru and Redwire (I think) suggested a short in one of the 3055s.  Finally I have isolated the fault to a 'popped' 3055.
At the time that the PS failed, I was trying to charge a 'golf cart' battery which was nearly fully charged so no significant current.  I set the volts on 14.1V and current limit at 1A.  When touching the PS leads to the battery there were a few sparks (possibly back to front polarity), and maybe not, but PS popped the 3055.
Has anyone had experience with the PS and 'active' loads like batteries, as opposed to passive loads like resistors?

I've never tried anything like that but I'd think that this particular power supply wouldn't want to be used like that.  If I were to try and charge a battery, I'd research a specific charging circuit or at least protection circuitry to add to the output of a power supply to allow this.

On an unrelated note, I've been playing with the simulation and found that if I change the value of C6 in the sim schematic (C4 in the original schematic) to a larger value I can get the output to slowly ramp up.  I tried introducing the spike like I had it in the mosfet circuit but it doesn't really affect the output so it's as if the circuit doesn't suffer from the problem.  But, if we reduce the time the output can rise with a larger value here wouldn't the issue be solved for the most part?

 

[audioguru2]

I've been playing with the simulation and found that if I change the value of C6 in the sim schematic (C4 in the original schematic) to a larger value I can get the output to slowly ramp up.  I tried introducing the spike like I had it in the mosfet circuit but it doesn't really affect the output so it's as if the circuit doesn't suffer from the problem.  But, if we reduce the time the output can rise with a larger value here wouldn't the issue be solved for the most part?

C6 in the latest SIM circuit prevents the current regulator from quickly cutting back or quickly allowing more current. Then if the output is suddenly shorted the current in the circuit will skyrocket until the slowly ramping opamp can catch up which is very bad.
Maybe the current sensing resistor should be non-inductive (not wire-wound).

 

[deepak.roy.alchemist]

plz clarify if we keep the value of C6 at moderately small measure than on the voltage regulating opamp, would the current regulator work satisfactorily?

 

[liquibyte]

C6 in the latest SIM circuit prevents the current regulator from quickly cutting back or quickly allowing more current. Then if the output is suddenly shorted the current in the circuit will skyrocket until the slowly ramping opamp can catch up which is very bad.
Maybe the current sensing resistor should be non-inductive (not wire-wound).

What about the sims C9 (orig C6)?  I can get the same results there as well.

 

[audioguru2]

What about the sims C9 (orig C6)?  I can get the same results there as well.

It slows down changes in the voltage regulation. Add a load then the voltage suddenly drops and when this capacitor charges then the voltage slowly comes up to normal. Disconnect a load and the voltage suddenly increases and when this capacitor charges then the voltage slowly comes down to normal.
It prevents high frequency oscillation, maybe because the output transistors are very slow.

 

[liquibyte]

Well, up until I can get my hands on a couple of 0.47R non inductive resistors to test I'll keep playing with the simulation and trying to find a way around this.  When you get down to it, non-inductive resistors at this resistance and power rating end up costing half as much each as the 10-turn pots I used.  Is there no way to minimize or mitigate this with a wirewound resistor?

 

[Ronaldinie]

Hello guys. Since i'm new to electronics, may I know what are the function of the op-amps in this circuit?

Thank you.

 

[audioguru2]

Hello guys. Since i'm new to electronics, may I know what are the function of the op-amps in this circuit?

We cannot teach the basics of opamps in one post but here goes:
1) Everyone who modifies this circuit uses a different parts numbering system so I will describe the three opamps as the voltage reference circuit, the voltage amplifier and the current regulator.

1) The voltage reference opamp provides a constant current to the 5.6V reference zener diode and has a gain of 2 times so the reference voltage is 11.2V.

2) The voltage amplifier opamp drives the BD139 driver transistor which drives the two 2N3055 output transistors. Two resistors in the amplifier allow the amplifier to have a gain of 2.68 times so that the 11.2V reference is amplified up to 30.0V at a high current.

3) The current regulator opamp compares the voltage produced by the load current in the 0.47 ohms current sensing resistor with the voiltage of the current setting potentiometer. If the sensed voltage is too high then this opamp reduces the voltage from the voltage setting potentiometer through a diode until the load current is the same as is set. If the output is shorted then the current regulator opamp causes the output voltage setting to drop to almost zero so the current is not higher than the setting of the current setting pot. 

 

[liquibyte]

Here's a pic showing what audioguru is referring to.

 

[liquibyte]

Maybe the current sensing resistor should be non-inductive (not wire-wound).

On some advice, I shorted across the resistor and I'm still getting the same results so I don't think that's what is causing this.

 

[liquibyte]

Here's a corrected and slightly modified version of the simulation.  There were a few errors in the original and I've rearranged things to more closely resemble the original schematic.  I didn't renumber the parts because it's a pain to do.  It's easy to renumber them top to bottom, left to right which is why my Eagle schematics are renumbered the way they are but to do this based off of the original would take quite awhile and if you add or remove something it just screws up the flow.  I've been trying to get a decent spike simulated but it's not going very well so far.  I have noticed that the output of the current control op amp oscillates where the other two don't.  Anyone else have any experience with LTSpice IV?

See this post for the latest simulations.

 

[audioguru2]

The current regulator opamp is not oscillating. Its output is saturated as high as it can go which is about +28V because it is not regulating the current so of course it shows the 120Hz ripple from the unregulated +39V, which is reduced to +29V by the 10V zener diode.
The moment the current regulator opamp begins to work then its output will have no ripple.

 

[liquibyte]

The current regulator opamp is not oscillating. Its output is saturated as high as it can go which is about +28V because it is not regulating the current so of course it shows the 120Hz ripple from the unregulated +39V, which is reduced to +29V by the 10V zener diode.
The moment the current regulator opamp begins to work then its output will have no ripple.

Yep, you're right, as I lower the current pot to about .48 it starts to kick in and smooth out the output.  It's neat to be able to simulate this in a somewhat accurate way.  I've got the trimmer on the voltage set so it outputs right at 30V when the voltage pot is set at 1 (.7025) but I haven't messed with the current side of things yet.  I'm still trying to figure out how to emulate a voltage spike on the input without drawing the time frame out with the soft start mosfet circuit.  For some reason when I change the time to ramp the voltage up, the spike stretches out along with it instead of firing and just shutting off.  It's kind of frustrating really.

Edit: Here's a nice plot showing that if anyone's interested.

 

[liquibyte]

I finally got the spike to behave.  I've put U1, U2, and U3 behind the mosfet soft-start circuit and left the pass transistors outside of that.  Here's the results and the simulation so that you can run it for yourselves.

Edit:  I was just browsing around TI's site and came accross Taming linear regulator inrush currents.  ;D  Figure 2 shows I was on the right track here.  I think we may have a workable solution with this.

2nd edit:  I'm attaching a separate simulation that injects noise into the input in addition to the spike.  This one takes awhile to run but the results are fantastic in my opinion.  The output of the supply is very smooth even though the input is rough as hell.

 

[liquibyte]

Last one, I promise.  I finally got my hands on the TLE2141 models from TI and found out how to use them.  I'm not sure if these will show up right or not.  If they don't work as expected, let me know and I'll walk you through how to do it.  I'm also going to delete my previous model zips so as to avoid confusion.

Edit: I made this in the real world and ran into a problem.  If the 10uF cap has no charge then the circuit works beautifully but if the cap has a charge it holds the gate open and allows the transient to pass to the output if you turn off the power and then turn it on again right away.  I think I've come up with a way to bleed the cap but have only done this in simulation so if those that know could have a look and tell me if I'm on the right track I'd appreciate it.

 

[Ronaldinie]

We cannot teach the basics of opamps in one post but here goes:
1) Everyone who modifies this circuit uses a different parts numbering system so I will describe the three opamps as the voltage reference circuit, the voltage amplifier and the current regulator.

1) The voltage reference opamp provides a constant current to the 5.6V reference zener diode and has a gain of 2 times so the reference voltage is 11.2V.

2) The voltage amplifier opamp drives the BD139 driver transistor which drives the two 2N3055 output transistors. Two resistors in the amplifier allow the amplifier to have a gain of 2.68 times so that the 11.2V reference is amplified up to 30.0V at a high current.

3) The current regulator opamp compares the voltage produced by the load current in the 0.47 ohms current sensing resistor with the voiltage of the current setting potentiometer. If the sensed voltage is too high then this opamp reduces the voltage from the voltage setting potentiometer through a diode until the load current is the same as is set. If the output is shorted then the current regulator opamp causes the output voltage setting to drop to almost zero so the current is not higher than the setting of the current setting pot.

Thank you very much. This really help me a lot.

 

[liquibyte]

See my last post above for an issue that I ran into and a possible solution.  I'm not sure if this will work or not and if I'm overloading things with the voltage divider circuit to the base of the PNP transistor.  The thing simulates rather well for all that but I'd like some opinions.

One thing I'm worried about is power dissipation in the base resistors and the transistor itself.  There's a fine line between the three values of resistors in the soft start circuit and the actual ability to shunt to ground after power off.  If I use bigger resistors, similar to the overcurrent shunt, I end up with a 4V spike as the transistor turns off and, what I believe is the mosfet turning back on due to residual energy in the cap.  Am I going about this all wrong?

Edit again:  I think this might work as far as power dissipation goes.  I kept trying to think in terms of input to ground so I think that's where I was running into trouble.  I'm going to try this out tomorrow and see what kind of results I get.

2nd edit:  It won't work in this configuration.  I'm working on another version but I'm having trouble with Vgs voltages and fall off times.  Stay tuned.

 

[liquibyte]

I think I may be on to something finally.  I've checked the power across the soft start components and things seem to be within tolerances there.  You can replace the TLE2141's if you want but they work fine if you keep the TLE2141.301.sub file in the same folder as the 0-30V-0-3A.asc file.  I got this circuit out of some research I was doing on soft starts to the primaries of the transformers and modified it for my purposes.  The original circuit had a pot in series with R13 to adjust the delay but it didn't want to work in this context so I deleted it.  I'm still not sure why it wasn't adjusting the time delay but I'll keep playing with it until I figure it out.  I'll admit that the mosfet and pnp might not be ideal but I used the ones that were standard to LTSpice and had the kinds of specs I wanted.  I did check the datasheets on them and, to my newbie mind, they seemed fine for this instance.  Please give criticism and suggestions if you have them.

I posted this over at EEVBlog as well to get more opinions.

 

[liquibyte]

This works really well until you start to play around with the current regulation side.  The transistor and mosfet in the soft start needs more work I'm thinking because it's not quite stable as current goes down.  This is a shot of the final schematic I'm working with.  The current and voltage trimmers are as accurate as I can get them and still have this simulate in a relatively fast manner.  If you load the output with R=limit(3000,V(n002)**2/.3,3000) and set the current pot to 0.01 and voltage to 1, you'll get what you see in this plot.  If you set the current pot to one and leave the voltage pot at 1, you'll have to set the Rload to R=limit(10,V(n002)**2/90,10) to see the nice plot above.  I'm still working on it but I'd say for the most part that this is done enough to try out and test in the real world.  If anyone does, could you report back your findings?  I can't build one of these right now due to other obligations at the moment.  This thing is better than a video game.  ;D