Can anybody explain me?

[bomba]

The 330Ohms Ressitor and the potentiometer (both can disipate 2W) burn, when the circuit needs to deliver more than 1 Amp.
I don't understand why. I would like to know a solution to avoid this problem.

Thanks in advance

 

[jetset]

maybe you're exceding the load current of the voltage regulator. the maximun load current of this one is 0.7 A, and your circuit is requesting 1A, maybe there's some problem with that.

 

[IanP]

I think the problem lays in TIP30C.
It is rated to 100V (max) so at high voltages it "gives up" allowing the high voltage to go through TIP152 to the output, and if the potentiometer is in its lower region to much current will go through 82Ω resistor, potentiometer and 300Ω, and they will just burn ..
Try to address this issue by finding HV PNP transistors rated to at least 200V ..
Regards,
IanP

 

[bomba]

Jetset

The Tip30c and Tip152 form a current booster, in order to permit that the regulator can deliver more than 0.700mA.

thanks

 

[SkyHigh]

Remove R6P. It is so small, only 82Ω, passing huge amplified current from your cascaded darlington pairs and sziklai pairs. No wonder anything down under that regulator burnt.

 

[bomba]

skyhigh

R6p is necessary to set the regulator voltage. I think that the problem is in the resistor of the transistor tip30c and tip152.

Thanks

 

[throwaway18]

Re: problem with high voltage regulator

Please give your threads meaningfull subject eg "Can anybody explain me?" is bad, "problem with high voltage regulator" would be ok

If the input voltage is unregulated it might be higher than you expect.

>The 330Ohms Resistor and the potentiometer (both can disipate 2W) burn, when the circuit needs to deliver more than 1 Amp.

The regulator works correctly at currents below 1A?
What output voltage are you testing at?
What is the input voltage when it fails?

In this regulator circuit you have nearly the full ouput voltage across R6P R10P

125V * 125V / (82 + 10000 + 330)= 1.5watts

Which suggests that it should be possible to put the resistors across the unregulated supply without them burning.

The transistors will be getting hot at 1A output. Is the variable resistor close to the transistors and being made hot?

Check the manufacturers datasheet for the variable resistors you are using.
The variable resistor may be rated less than 2W at higher temperatures.
For example the vishay model 534 wirewound pots are nominally rated 2W
but must be derated to under 1W at 100degrees centigrade.

>I think the problem lays in TIP30C.
>It is rated to 100V (max)

True and that should be corrected but there is only over 100V across those transistors at startup, if the output is shorted or if the regulator is adjusted to give under 25V out.