Author Topic: variable power supply circuit  (Read 5202 times)

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Offline xavier60

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Re: variable power supply circuit
« Reply #25 on: June 18, 2020, 09:45:31 am »
yes thats what the circuit i attached above is similar, it also works in switching mode. its not on continuously . it switches the comparator checks the voltage and switches off till the output is stable.
dps 3005 also works the same way
You have forgotten to include your age in your profile.

The hand drawn design in the first post will operate as a linear regulator and likely an unstable one.
If you  want  to make a switch mode regulator, the best chance of success is with a self contained Buck IC like the LM2596.
Without an oscilloscope you will be working in the dark were SMPS is involved.
« Last Edit: June 18, 2020, 09:48:11 am by xavier60 »
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Offline aneeshTopic starter

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Re: variable power supply circuit
« Reply #26 on: June 18, 2020, 12:03:17 pm »
yes i want to build linear supply which works with power transistors but why does it become very hot with mosfet.
some manufacturers have achieved good results with mosfet.
let me be clear is it because of high freq, duty cycle or turn on or off cycle because of gate source resistor
 

Offline mikerj

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Re: variable power supply circuit
« Reply #27 on: June 18, 2020, 12:15:20 pm »
yes thats what the circuit i attached above is similar, it also works in switching mode. its not on continuously . it switches the comparator checks the voltage and switches off till the output is stable.
dps 3005 also works the same way

Your circuit is a linear regulator, NOT a switching regulator.  Which part of your circuit do you think provides the PWM waveform for driving the MOSFET?  Where is your inductor and freewheel diode?
 

Offline aneeshTopic starter

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Re: variable power supply circuit
« Reply #28 on: June 18, 2020, 12:28:26 pm »
yes linear regulator but if you see its the opto pulses which switches the transistor on/off but i think am i not switching it on and off properly.
i have attached a ref circuit of another manufacturer.
 

Offline kallek

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Re: variable power supply circuit
« Reply #29 on: June 18, 2020, 12:58:11 pm »
You can't beat Ohm's law! Unregulated voltage minus output voltage is turned heat in mosfet! Mosfet is doing it's stuff to work as resistor!
 

Offline ArthurDent

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Re: variable power supply circuit
« Reply #30 on: June 18, 2020, 02:24:00 pm »
“…i am replacing the power transitor with pmos but it becomes very hot and temp goes on increasing.”
“…i completely understand the working but because i want to use single tap which is cheaper and for that reason i wanted to modify the circuit using mosfet.”

Whether you use bipolar or mosfets for the pass elements of a power supply, with the same design and same load you will be dissipating the same amount of heat.

You aren't understanding what everyone is explaining to you. Until you're willing to read and understand what they are saying, you will continue to have these overheating problems. There is a big difference between linear and SMPS topologies and once you understand that and design your power supply accordingly, it will work much better. Perhaps you should read some of the references suggested above to understand the basics before you try to build a power supply beyond your current understanding.
 

Offline exe

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Re: variable power supply circuit
« Reply #31 on: June 18, 2020, 04:45:29 pm »
Peeps, I think this is a buck converter. Look at the diode, inductor and capacitor. Or at least the intent was to build one. I don't see any feedback.
 

Offline mikerj

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Re: variable power supply circuit
« Reply #32 on: June 18, 2020, 05:03:05 pm »
yes linear regulator but if you see its the opto pulses which switches the transistor on/off but i think am i not switching it on and off properly.
i have attached a ref circuit of another manufacturer.

That circuit appears to be part of a buck converter, it has the inductor, the diode and the output capacitor which are all required for a switching regulator.  Where are these parts in your design?
 

Offline aneeshTopic starter

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Re: variable power supply circuit
« Reply #33 on: June 18, 2020, 06:38:55 pm »
ok i understand ...so i have to use some kind of pre regulator instead of multiple taps .. as transformer becomes expensive.
any reference of pre regulator
« Last Edit: June 18, 2020, 06:42:53 pm by aneesh »
 

Offline kallek

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Re: variable power supply circuit
« Reply #34 on: June 18, 2020, 08:18:12 pm »
Do you know what you are going to use your power supply for?
Because many times for example 20V/3A or even 1 amp is more than enough for bench power supply. And when you have working design you can modify it for higher current.
 

Offline aneeshTopic starter

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Re: variable power supply circuit
« Reply #35 on: June 19, 2020, 02:07:32 am »
yes i have the design working with me using transistor but i wanted to make it more compact. I wanted to remove such big heatsinks as they are custom made and transformers that are single tap.
 


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