0-30V Stabilized Power Supply

[denci]

So, what heatsink do you suggest, how much should be a thermal resistance, i have one heatsink with 5°C/W at home, which I intend to fix on housing of BD139.
I think that it is enought for condition in this stabilized power supply with max 5A current or not??

 

[audioguru2]

If three 2N3055 output transistors share the 5A of current then each has 1.7A and its minimum current gain is 40. Then the current in the BD139 is a max of 125mA. Its max voltage is 36.2V so its max power dissipation is 125mA x 36.2V= 4.5W.

The max allowed chip temperature of a BD139 is 150 degrees C but 130 degrees is safer. Your ambient might be 30 degrees. The thermal resistance from chip to case is 10 degrees/W and for thermal grease is about 0.3 degrees/W. Then with a perfect heatsink the case will be at 30 degrees C and the chip will be (4.5W x 10.3) + 30= 76.4 degrees C.

Your heatsink must have a thermal resistance of (100 degrees - 76.4 degrees)/4.5W= 5.2 degrees C/W or less.   

 

[denci]

I usually use this way to calculate the heatsink, it is wrong that way:
(130°C-30°C)/4.5W - (10C/W+0.3C/W) = 11,9°C/W

 

[denci]

http://www.changpuak.ch/electronics/calc_23.php

With this online claculator i have got the same results ??? ???

 

[madafakamw]

Hi everyone,
I've made an online order for TLE2141 and i forgot to ask what package is build in. So i'm stuck with these.

Will my psu work?

 

[audioguru2]

I've made an online order for TLE2141 and i forgot to ask what package is build in. So i'm stuck with these.
Will my psu work?

When the output current is 3A check that opamp U2 is not too hot.

 

[madafakamw]

Thank you for your quick reply. I will keep in touch.

 

[denci]

What is wrong with my heatsink calculation in 5 post ago??

 

[LEECH666]

I usually use this way to calculate the heatsink, it is wrong that way:
(130°C-30°C)/4.5W - (10C/W+0.3C/W) = 11,9°C/W

What is wrong with my heatsink calculation in 5 post ago??

Nothing wrong really.

Audioguru either made a small typo and actually wanted to type

(130°C - 76.4°C)/4.5W = 11.91K/W

or he substracted another 30°C of safety margin from the maximum junction temperature value of 130°C.

(130°C - 30°C - 76.4°C)/4.5W = 5.24K/W

Florian

 

[denci]

Tnx a lot!

 

[LEECH666]

In any case a smaller Kelvin per Watt value is always safer.
A heat sink with 5.24 K/W is most likely more expensive than one with 11.9 K/W.

Florian

 

[denci]

Where should i place the 1kohm pot3 for fine voltage regulation?

 

[xristost]

I finalized my second power supply unit. Now I may combine two voltages up to 60V or use them as dual voltage PS.
Pictures, details, schematic and PCB here.

 

[LEECH666]

Very nice. Is this the latest REV2 version of the PSU or the original version? The shematic seems to be different, and you're only using one output power transistor.

 

[audioguru2]

Very nice. Is this the latest REV2 version of the PSU or the original version? The shematic seems to be different, and you're only using one output power transistor.

It is a combination of the original schematic and the latest schematic:
1) It uses Q2 to solve the "Opamp Phase Inversion" problem with the TL081 opamps used in the original project but the MC34071 opamps do not have that probem.
2) The value of R15 is much too high.
3) Its single 2N3055 output transistor will get extremely hot (maybe hot enough to fail) when the output is set for 3A and it is shorted or has a low voltage. Its max dissipation is about 90W.
It has a huge heatsink and a fan so maybe it will survive.

 

[xristost]

It is a combination of the original schematic and the latest schematic:
1) It uses Q2 to solve the "Opamp Phase Inversion" problem with the TL081 opamps used in the original project but the MC34071 opamps do not have that probem.
2) The value of R15 is much too high.
3) Its single 2N3055 output transistor will get extremely hot (maybe hot enough to fail) when the output is set for 3A and it is shorted or has a low voltage. Its max dissipation is about 90W.
It has a huge heatsink and a fan so maybe it will survive.

1) I deliberately kept Q2 because with it output voltage drop more quickly after power off.
2) R15 is 1k in original schematic and I don't know what will change if I replace it with lower value resistor since everything is working OK.
3) I decided to use only one output transistor, because the PS would rarely be used at low voltage and high amperage. With this heatsink and the fan running it manage to dissipate 60-70 W for a long periods without problem. For a couple of minutes it survived shorting at 3A.

BTW, for the second unit I put 2SC5589 instead of 2N3055, because it was ease to mount

 

[LEECH666]

I've got four TIP3055 (TO-218 / SOT 93) here, and two 2N3055 (TO-3). I've decided to use silent CPU coolers. I am uncertain if a single BD139 will be enough to drive four TIP3055s. I am only aiming for 30V / 3A output, so the additional TIP3055s would just be there to compensate for the lower power rating and to dissipate the heat more easily.

I have two options now ... (see attached pics):

View attachment 41715

View attachment 41716

View attachment 41717

 

[LEECH666]

More pictures.
Not quite sure which variant I want to use.
2N3055 on a L-profle mounted on the heat sinks or TIP3055 mounted flat on the heat sinks.

View attachment 41718

View attachment 41719

View attachment 41720

 

[audioguru2]

R15 wastes supply voltage. 1k is too high but 100 ohms is fine.

When output transistors are connected in parallel so they share the heat then each one needs a 0.33 ohm emitter resistor so that their base-emitter voltage differences do not cause the one with the lowest Vbe to hog all the current.

The minimum current gain of one 2N3055 with a current of 3A is about 27. Then the max current in the BD139 is 3A/27= 111mA.
Two 2N3055 transistors each have a max current of 1.5A then their minimum current gain is about 42. Then the max current in the BD139 is 3A/42= 71mA.
You can calculate the current in the BD139 if there are 3 and 4 output transistors.

 

[denci]

As we know power dissipation of one of three 2N3055 output transistor is aprox. 65W and recommended thermal resistance for heatsink for one transistor is (200-35)/65 - (1.5 + 0.2) = 0,84 °C/W, but how can i calculate the required thermal resistance of heatsnik for three same transistor with the same power dissipation?
Is ther any equation for this or is eought that i get the heatsnik with thermal resistance three times smaller than thermal resistance for one of each used transistor??...sorry for my english!!
TNX