Help : power supply- voltage regulator

[ade77]

Thank you for all those that have replied me towards this power supply.  In particular Lacy and Kittmaster.

I have developed a basic voltage regulator . However, I want to get a power supply that can deliver like 60V, and take about 10A current, because that what the load will require.

The regulator I have developed only delivers about 20V, I use the formula Vo = (R2/R3 + 1) * Vref. where my Vref is now 10V ( 2 zener diode). Even when I tried to decrease the resistance of R3, it does not make a difference.

Any help will be appreciated.

[lacy]

I can't be sure as to why you are not getting your output voltage. I have tried various different configurations and part values and all I am getting is 20V. Your configuration looks correct, but there is something just not right about the voltages I am seeing and I can't put my finger on at this time.

I will continue examining it to see what I can find. It may take a while so be patient and if I do find soemthing I will be sure to let you know.

[lacy]

O.K. I believe I have got it. There was a 2 fold problem with your regualtor and I will outline them below.

1) For some reason I could not get the 3-terminal Virtual Op Amps to work in this circuit. I traded that out for the 5 Terminal one. It is the very last one in the list of the Virtual category.

2) You are comparing your voltage from the bridge to your output voltage. If you have your input referenced to 10V and your output dviding this by a factor of 2 then once the voltage at the divider junction reaches 10V then the op amp will stop driving the transistor. Therefore you are only going to get 20V Out (ref*2 since both resitors are equal in value)). Therefore, you have to have your input reference to what you want the output to be. In this case 60V is what you want so you have 30V at the divider junction (Vo/2 since both resitors are equal value) your input reference would have to be 30V. I have never heard of a 30V Zener (they may exist, but it seems to me tha they would have to be quite large). so you may have to use a voltage divider on the input side instead.

It is my opinion that the design of this regulator is not going to work for you in reality if you decide to build it. The 2N2904 I I know is not going to handle 10A in reality. Based upon my findings I don't even know if you are going to be able to use an op-amp as the error amp due to the amount of voltage that has to be tied into it.You may be able to find such an op-amp but you will have to do some research to find one. I think most of the op amps in Multisim are low voltage in the range of 5VDC-22VDC. I would suggest looking  on the internet and see if I could find a better alternative that uses more robust components or if you definitely want to design this on your own, reasearching the components in Multisim to see if any of them can handle the voltage and current requirements.

I hope this helps and I haven't confused you in any way

Message Edited by lacy on 10-06-2007 02:24 PM

[lacy]

I want to clarfy one thing about my previous message. You probably can find a 30V zener because the largest value I have ever dealt with is 24V which is not that far off and they probably won't be much larger than a standard value. When I made the post I had an error in my thinking and was thinking about the 60V output. So I apologize for my mental slip there and hope this straightens that out. The rest of my message hopefully is on the spot.

[ade77]

Thank you very much Lacy. However, I noticed that the Op-amp has a setting that needs to be changed in the properties. The default voltage swing is +- 20V. so in reality if I changed my R3, it will still not go more than 20V at the output.

So when I change the Opamp settings to like +-60V, I can now use the formula Vo = Vref(R2/R3 +1), then change my R2 and R3 to get my desired voltage, but it would not exceed 60V.

However, like you pointed out clearly; that in reality it would be difficult to find the components that will withstand such current. 

Thank you for your time and support.

[lacy]

You must have read my mind. I was just about to make a post about the voltage swing being limited to 22V +/- as far as the 3 terminal amp was concerned. Nice catch. Correct me if I am wrong but  your Vref, as I see, it  going to be your input to the op-amp with the zener. With the current configuration your Vo is going to be 10V(10K/10K+1) or 10*2 and that equals 20. So you are still going to have to change the reference on the input side to match. otherwise you will still have only 20V output..

Message Edited by lacy on 10-06-2007 05:39 PM

[kittmaster]

The problem is your using a real world model the 3904. Your completely forgetting the fact that this transistor can only handle MAYBE 1/2 to 1 watt at its maximum and your trying to push 10 amps through it......never gonna happen.

try using an ideal transistor component for the regulation model.

[lacy]

It may be better in the long run if he could find real world modeled components in Multisim that can accomplish this.This way he will know what components to get before he goes to build it  As far as the series transistor regualtor there is one that I found that can handle the current requirements of 10A and that is the 2N3055A.

In my opinion Multisim doesn't seem to care about current or voltage limits In other words, you can't blow a transistor by exceeding any maximums. I simulated this with the 2n3904 and it worked. I know that in the real world that  60V at 10A through a 3904 would result in a fried transistor in a matter of milliseconds. There is a "Rated Virtual" category in my version that does take voltage and current limits into account. If he has these he might want to consider using these to test with.

This is my observations and I could be wrong, but I have yet to fry a component with the models in Multisim with the exception of the "Rated Virtual" Category.

[wlyuen2000]

hi, your circuit is correct. the only problem is that your measuring scope B terminal is not grounded. I think the wire is missing there.

[lacy]

Thank you for pointing that out. This still did not correct what his problem was. The problem was that the op amp was voltage limited to +22V and -22V and he was wanting 60V on his output.

We thank you for you reply and catching the ground not being hooked up.It is always good to make sure your grounds are hooked up in real life and in the simulator.