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Problem with high current spikes before the diode bridge

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jep_pogi

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power supply problem

hello :) im sorry this is long. please read and help me sir/mam
i am going to build an 80Vdc 2A or 3A linear regulated power supply

right now i have the following initial design.
i used simetrix to simulate the circuit.

i used a 220VAC sine wave generator as input signal (e.g.from the wall sockets) because when i use the AC signal, it has errors. so i use 220VAC 60Hz sine wave generator as input in the transformer. the 1ohm resistor in series with the input is i am not sure about it. i used 1 ohm because when i use higher value, it has a nonsense output.
the secondary side of the transformer outputs 85VAC.

here is the circuit
labgruppens3.png


Can you help me with this circuit, tell me what problems i may have.
The circuit outputs almost 80V and 3A.
it shows it here
CURRENT OUTPUT:
edaboard2.png


VOLTAGE OUTPUT:
edaboard1.png


Right now my problem is that there are very high current spikes in the input, just before the diode bridges. the spikes last for 4ms, and has a value of 200A in the beginning and 30A in steady state. I REALLY DONT KNOW IF THIS IS A PROBLEM :p but im scared to make the circuit in a box if im not really sure about it.

CURRENT SPIKES BEFORE THE DIODE BRIDGE:
edaboard3.png
 

power supply problem

I will try to have a look later - I am tied up now, but could you post you SIMetrix file?

The need for the resistor in series with the voltage source/transformer is common with simulators.

Keith
 

Re: power supply problem

I have modified your circuit slightly:

1. I have reduced the maximum time step so you get a clean sine in the simulations

2. I have added a load switch to do a stability check.

The current "spikes" are really just the top part of a sine wave when the capacitor charge is topped up. They are inevitable, but you need to make sure the capacitors can take the current, although it is RMS current that is usually important for a capacitor. Your capacitor may not need to be quite so large with such a large difference between the secondary transformer voltage and the output voltage.

You have over 100W being dissipated in your output transistor. The transistor can handle it, just make sure you heatsink it adequately.

The 200A peak start current is a bit high. The 1N5401 is rated at 200A non-repetitive peak current, 8.3ms half cycle. That specification is specifically aimed at exactly the switch on surge you are seeing, but I would recommend a larger diode or smaller capacitor, particularly because the peak current is repeated half a cycle later, although at a smaller level.

Keith.
 

    jep_pogi

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Re: power supply problem

sir,
im sorry for the late reply, i was thinking of ways for the circuit to work more.

i dont know what the maximum time step is sir :p
and its a good thing that you added a load switch to check the stability :)

here are the things i tried to do with the circuit:
first, i have replaced the filter capacitor C1, which was 6.8mF since i find it hard to find that capacitor that will handle a high voltage value. i replaced it with 2 capacitors with value of 4.7mF each and possibly 50V or 100V capacity, and added a resistor in parallel to each to ensure that they get the same voltage. is this ok?

for the current spike @ 200A, i have added a 10mH inductor after the diode bridge and before the filter capacitors. this is to reduce the current that will pass thru the capacitor. it works and reduced the current spike in the cap to 30A initial and then 5A recurring spikes. but im not sure about this idea, cause im only looking at the capacitor side, and not the diode bridge side.

i will post the simetrix file again sir. i hope you take time to look at the updated circuit design.
thanks again sir, you have helped me a lot :)
 

power supply problem

I will look at your circuit tomorrow when I am back at my computer.

Maximum timestep is the maximum time the simulator will use to go from one simulation point to the next. The default values are often too long and result in jagged sine waves. Too long a time step can cause inaccuracies and in extreme cases miss events completely.

When you set the transient analysis settings it is under the 'advanced' button, I think.

Keith
 

Re: power supply problem

jep_pogi said:
here are the things i tried to do with the circuit:
first, i have replaced the filter capacitor C1, which was 6.8mF since i find it hard to find that capacitor that will handle a high voltage value. i replaced it with 2 capacitors with value of 4.7mF each and possibly 50V or 100V capacity, and added a resistor in parallel to each to ensure that they get the same voltage. is this ok?

for the current spike @ 200A, i have added a 10mH inductor after the diode bridge and before the filter capacitors. this is to reduce the current that will pass thru the capacitor. it works and reduced the current spike in the cap to 30A initial and then 5A recurring spikes. but im not sure about this idea, cause im only looking at the capacitor side, and not the diode bridge side.

i will post the simetrix file again sir. i hope you take time to look at the updated circuit design.
thanks again sir, you have helped me a lot :)

If you put capacitors in series you will decrease the capacitance, not increase it. So, the two 4.7mF capacitors will result in 2.35mF total. The normal way of solving the problem of availability of suitable capacitors is to use multiple ones in parallel which can all tolerate the required voltage. So, two 3.3mF ones instead of your 6.8mF, for example.

I am not sure I would bother with the extra inductor to reduce the surge current. You currently have an ideal transformer with zero output resistance. If you were to use a real transformer I think you would find the current surge considerably reduced. For example, only 1 ohm of secondary resistance will reduce it to 45A.

Keith
 

Re: power supply problem

sir, here is my latest design. sorry it took me long for this one. i have removed the inductor, and i have changed the transformer ratio to a better one. 90V peak = 63VAC.
please take a look at this design again,
it has better waveform outputs, and the current surge are now only up to 70A, which i think the capacitor can handle. and i have changed the output load resistance to 33.6ohms which is the motor resistance.

if you think there will be problems with the circuit, please say sir.
thank you so much.

and also, is it a problem that i used an ideal transformer in the simulation?
because when i use the saturable transformer, the output is very very different

thanks again for your time sir
 

power supply problem

You still have capacitors in series. Please read the comments in my earlier post about that. A large part of your peak current reduction is because you have reduced the total capacitance considerably by putting them in series.

In an ideal world you would simulate with a better transformer model, but I don't think models for laminated E cores are in the library. If you use a ferrite core, you need to make sure you use the correct core type and number of turns so it doesn't saturate.

Keith.
 

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