DC power supply without transformer

Thread Starter

Peter Pan

Joined Mar 24, 2005
122
Hi,

I am interested whether it's safe to use home made DC power supply which does not have a transformer. This supply consists of rectifier and simple filter (to smooth voltage pulsations) only and can be connected to 230V AC mains (which is its input) and provides about 200V DC output.
 

bertus

Joined Apr 5, 2008
19,944
Hello,

It is never safe without a transformer.
The transformer gives isolation from the mains.

Greetings,
Bertus
 

b.shahvir

Joined Jan 6, 2009
444
DC power supplies without transformers are available (actually they contain small HF Xmer but it does not provide electrical isolation) and are used in modern electronic appliances like computers & TV sets. They are widely known as 'Switched Mode Power Supplies' (SMPS).

However, they should never be opened with power ON as the chassis of SMPS unit carries line voltage (120VAC or 220VAC) depending on rating and can deliver nasty electrical shocks if tempered to with mains on.
 

Thread Starter

Peter Pan

Joined Mar 24, 2005
122
Hello,

It is never safe without a transformer.
The transformer gives isolation from the mains.

Greetings,
Bertus
Hi Bertus,

Thank you. This power supply is supposed to be used with the 60 Watts linear RF amplifier using IRF840 which we talked about on the week - I wonder how much current it will need if it is supposed to be powered by DC voltage about 100-120V? I will need to figure out what transformer to look for.
 

bertus

Joined Apr 5, 2008
19,944
Hello,

When you look at the site it says 700 mA @ 60 Volts.

The 60 Watt linear amplifier is simple all solid state circuit using power mosfet IRF840. The IRF series of power transistors are available in various voltage and power ratings. A single IRF840 can handle maximum power output of 125 watts. Since these transistors are used in inverters and smps they are easily available for around Rs: 20/-.
The IRF linear amplifier can be connected to the out put of popular VWN-QRP to get an output of 60 Watts. The circuit draws 700 ma at 60 Volt Vcc. Good heat sink is a must for the power transistor.

Greetings,
Bertus
 

mik3

Joined Feb 4, 2008
4,846
What type of amplifier is it? class A, AB, B?

What is its efficiency?
 

Thread Starter

Peter Pan

Joined Mar 24, 2005
122
Hello,

When you look at the site it says 700 mA @ 60 Volts.

Greetings,
Bertus
Whether it's possible that an amplifier which takes 42W DC (P=I*U, so here P=0.7A*60V=42W) from power supply will amplify a signal to 60W?
 

bertus

Joined Apr 5, 2008
19,944
Hello,

You are right.
I think you should take 125 Watts for the powersupply, if you want 60 watts output.
(I think you can sometimes have your doubts about what they write on the net).

Greetings,
Bertus
 

Thread Starter

Peter Pan

Joined Mar 24, 2005
122
Hello,

You are right.
I think you should take 125 Watts for the powersupply, if you want 60 watts output.
(I think you can sometimes have your doubts about what they write on the net).

Greetings,
Bertus
Agh, that was not actually wrong (just an understatement) when they say that "The circuit draws 700 ma at 60 Volt Vcc" as then author says that "my IRF840 power amplifier working at 120Volts". But one who wants to construct the amplifier has to think for himself.
 

bertus

Joined Apr 5, 2008
19,944
Hello,

Yes, those things happen, some misreading.
Take care of cooling the FET well. (it has to dissipate some watts).

Succes,
Bertus
 

Thread Starter

Peter Pan

Joined Mar 24, 2005
122
Hello,

Yes, those things happen, some misreading.
Take care of cooling the FET well. (it has to dissipate some watts).

Succes,
Bertus
There will be big enough radiator (maybe even fan). Thanks for advising this design - LTspice shows that it works nicely!:)
 
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