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Need Explanation: Motor's Power Supply

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Don_dody

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I build 5V power supply using 1A transformer and 7805 regulator. I want to drive 4 Motors. Each of the motor require 500mA to operate.

My question, If all the motors should operate together at the same time, is my power supply enough or I need to build a new one with higher current rating?
I'm asking because my 7805 regulator is very hot even using heat sink.
 

manishanand14

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Hello Don_dody !

Your power supply 7805 based is not capable of delivering that much current.7805 can deliver max 1A current.

Make a 5V power supply using LM350.It can deliver upto 3A. Also increase your transformer current rating to 3A minimum.
 
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Don_dody

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Hi too,

1. So you mean if all the four motors operate together, they will need (500 mA x 4) = 2A ??
2. What about my transformer, diode, and capacitors ? I use 1A transformer, 1N4001 diode, and 25V capacitors. Should I replace them too ?
3. Is there any other FIXED regulator that result 5V with high current rating other than LM350?
 

manishanand14

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Yes obviously if your motors are drawing 500mA at 5V, then total they will be drawing 2A.If you are not selecting a proper current rating linear regulator then output voltage will drop i.e less than 5V.

You can't use an 1A transformer.You have to use 3A transformer or higher for LM350. Also you can use LM2576 switching regulator IC to make yourself a switching type power supply capable of handling upto 3A.

You can use 1N5408 diode[3A current rating].

25V Capacitors are Ok but If you can use 1000uF/50V filter caps when you are using a 12-0-12 or 18-0-18 stepdown transformer, it would be better.
 
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Don_dody

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Thank you for your very clear explanation.

I want to ask one more thing. What about my minimum system, LCD, and the other that required 5V but not so high current ? Can I take the power from this also or make separated power supply for them?
 

manishanand14

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I think you can extract power for your LCD also if you use LM2576 with proper heatsink because it can deliver max 3A.

Read LM2576 datasheet in detail.It has the complete design.Do use the filter circuit [given in the datasheet]to filter out the output ripples.

For very faithful operation use very high value filter capacitor in the output of LM2576 i.e 2000uF/50V or higher because I guess your motors will be switching on/off frequently.While switching on they draw more current.
 
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Don_dody

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Look at this picture:
ps.png

I decide to make two power supplies.

1. Can I connected the ground of both power supply as shown by that picture?
2. I use step down transformer 220 to 7-9 V. Is this (7-9) too small/big ?
 

manishanand14

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I think you should not connect both the grounds together.

Use stepdown transformer rated 12-0-12 with 3A or higher like 5A because you can always extract more power for future add ons. Also even though you get 3A rated transformer it is usually practically not possible to extract 3A current in real situations due to transformer quality.You can eliminate D2.

If you use 12-0-12 output stepdown transformer then you can construct a full wave rectifier using only 2 diodes.Parallel the diodes for better safety margin to increase the current handling.

Better build a separate 12V unregulated power supply using 12-0-12 V/5A output transformer 1N5408[2 or 3 in parallel ] and 4700uF/50V filter capacitor,then you can use it to connect other things in modular form like LM2576 based supply and LM7805 based supply.

It is always good to have a general purpose high current power supply for your future projects.It will be like one time investment for many projects.


If you are using 7805 for powering microcontrollers and other logic circuits,it is better because it is a linear voltage regulator.Hence output ripple will be less.
 
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manishanand14

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Please get some help from other board members regarding L293D motor driver.


I don't want to give you wrong suggestion.I am not very sure about connecting both the grounds.
 
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Don_dody

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Hi, Ive built the LM2576 based supply.

First: When I tested it, there is smoke coming from the 1N5822 diode. Did you know why this could happen?

Second: I decide to built the new one, then the 100uF capacitor is blown after a while. How can it happen?

Third: I'm not giving up, I tried to built the new one (the third), and the same problem occur, there is smoke near to the diode, and after that power gone.

Any suggestions?
 

manishanand14

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What voltage rating transformer you have used?

You must use 1N5408 diode[2 in parallel].1N5822 is a schottky diode with 40V PIV rating[not enough].Don't use schottky.

What is the voltage rating of the cap you used.Use 50V or higher.

Give your schematic.
 
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Don_dody

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220 - 12V Zero transformer.

You must use 1N5408 diode[2 in parallel]
As the bridge or to replace the 1N5822 ? Maybe with picture is clearer.

Why schottky diode cannot be used?

This is the schematic:
sch.png
 

manishanand14

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How much current you are drawing from the power supply.

As the bridge or to replace the 1N5822
.As per the diagram it is OK.

I am presently using the LM2576 based power supply and it is working fine.

The 100uH inductor should be rated for much higher than 3A i.e. 6A or higher.

Are you sure you have done the circuit as per the diagram given in the datasheet.

First try for smaller load say which draw 1A current, to make sure that your circuit is working fine.


Try to use a freewheeling diode with the motor load.
 
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Don_dody

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I use 4 motors, each of them requires 500 mA. Plus micro-controller and LCD.

- - - Updated - - -

Is there any explanation of my question above?
 

manishanand14

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I thought you are using schottky for the bridge rectifier.

Since you are using motor load there are other issues as well.A motor draws more than rated current during turing ON.SO if all your motors are turning ON at the same time they will collectively draw much more than the supply is rated for.
 

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