Transformerless Power Supply

[Luciano]

Hi,

With a current of 25mA the power dissipation will be less than 1 watt.

30V AC - 1.2V (rectifier loss) = 28.8V
28.8V x 1.41 = 40.608V DC
40.608V - 5V = 35.608V
35.608V x 0.025A = 0.8902 W

* * *

Not in this project but maybe one day you will need a voltage
regulator with an input voltage up to 60V.

http://www.national.com/pf/LM/LM317HV.html

Best regards,

Luciano

[psdayama]

Well estimated 1watt loss can heat LM317HV quite a bit.
I think that in the price of that regulator U can buy 2MKT capacitors
easily (Atleast in this part of world )
Please make calculations as follows:
30V ac = 30 x 1.41 = 42.42 volts DC
- 1.2volts drop = 41.22 volts - 5volts output = 36.22V
x .025A = 0.9055 Watts.

One needs big heatsink for this.

The purpose of circuit is to get lower voltage without transformer
and not much regulated voltage is required.

When required I will certainly use HV regulator if called for.
otherwise I will use switching one to make it "cool" !

Thanks a lot for suggestion.

[Luciano]

One needs big heatsink for this.

Your statement is not accurate.

1 Watt of power dissipation without heat sink is possible with a LM317HV/TO220.
Below you can see how to calculate the maximum allowable power dissipation without heat sink.

Best regards,

Luciano

How to calculate the maximum allowable power 
dissipation without heat sink:


PD MAX = TjMAX − TaMAX
         _____________
             Rja

PD MAX = Maximum Power Dissipation (Watt)


TjMAX = maximum junction temperature (°C) 
For the LM317HV the operating junction temperature range is 0°C to +125°C.


TaMAX = maximum ambient air temperature (°C) 
Room temperature or temperature inside enclosure.


Rja= thermal resistance from junction to ambient without heat sink (°C/W) 
For the LM317HV/TO220 is 50 °C/W.


Example ambient air temperature 45°C: 

125°C − 45°C
__________    =  1.6 Watt 
   50°C/W


With an ambient temperature of 45°C, the maximum power dissipation 
of the LM317HV / TO-220 without heat sink is 1.6 Watt.

With an ambient temperature of 75°C, the maximum power dissipation 
of the LM317HV / TO-220 without heat sink is 1 Watt.