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Help me reduce 230V rectified DC voltage to 30V DC voltage without using transformer

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aruna1

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Hi, I want to make a power supply that will reduce 230V AC voltage to 5V DC voltage. Do do this I want to use a buck converter. Easiest buck converter I can get is MC34063. it has input up to 40V.
what I want to know is how to reduce 230V rectified DC voltage to 30V DC voltage so I can use MC34063 to drop 30V to 5V.
I have added a diagram below. my question is to solve the middle box named as "voltage dropper". I'm looking for a simple circuit for this. since i dont know current requirement of the load I guess i cant use a resistive dropper. any idea would be great.

EDIT: cant use a transformer due to space constraints.

thank you
 

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Re: voltage dropper help

The normal solution would be to use a transformer. Don't wire it as shown though, it goes between the AC input and the rectifiers. Select a transformer with a voltage just a little higher than the voltage you want out and with a current rating no lower than the load current at 5V.

Brian.
 

Re: voltage dropper help

Hi
I forgot to mention. I dont want to use a transformer due to space constraints.
any other solutions?
 

Re: voltage dropper help

My suggestion would be to buy a cheap 5v mobile charger (assuming that the current you need is about 500mA), the price is a few $ in ebay.
Making the circuit yourself wouldn't be very easy because you need a proper driver with a transformer as a DC-DC converter.

Alex
 

Re: voltage dropper help

hi
yes that is an option but limited to 5v. unless I can figure out a way to adjust output voltage on charger it is limited only for 5v.
I didnt use it coz in future i might have to increase supply voltage to the load up to 12 v. so if i use mc34063 i can do it with ease.
 

Re: voltage dropper help

Buy a 12 volts SMPS plug pack power supply and use a 317 to regulate the output as you need in future. By the way your requirements are increased in every post. Any other points pending? Too your current requirement is not mentioned in any of your previous posts.
Cheers
 

Re: voltage dropper help

I was running some simulations and thought this could do some thing. see below circuit.

230v to 7.5V transformer less. any ideas on this method? zener use is a 8.2V one.
you can see the voltage values on multimeters attached
 

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Re: voltage dropper help

pranam77 said:
Buy a 12 volts SMPS plug pack power supply and use a 317 to regulate the output as you need in future. By the way your requirements are increased in every post. Any other points pending? Too your current requirement is not mentioned in any of your previous posts.
Cheers
Click to expand...

I'm not sure about the current exact requirement but will be below 500mA
 

Re: voltage dropper help

The transistor in your circuit would have a voltage drop of about 300v.
You transistor can only work with 1.25W but suppose that you use a different transistor that can work with many watts, then for 100mA output you will have 300v*0.1A=30W as heat.

Alex
 

Re: voltage dropper help

And consider that the most common mode of failure in transistors is to go short circuit!

Brian.
 

Re: voltage dropper help

Yes, and when that transistor fails you may get 300v in the output.
It is not a good idea to use a circuit that doesn't have an isolation from the mains power, it is not safe.
Your circuit should be isolated and have protection mechanisms for over current, over voltage, overheat etc.

Alex
 

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Re: voltage dropper help

alexan_e said:
Yes, and when that transistor fails you may get 300v in the output.
It is not a good idea to use a circuit that doesn't have an isolation from the mains power, it is not safe.
Your circuit should be isolated and have protection mechanisms for over current, over voltage, overheat etc.

Alex
Click to expand...

yep I totally forgot about heat dissipation. how stupid of me.
 

You may use a high value of capacitor (with a 1ME of parallel resistor) in series with the 230V supply line, it will reduce your 230V supply to 40V!
But you have to increase capacitance value to get a affordable current level.
 
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