TIP35C as Pass Transistor Thermal Loss 50%

[asking]

Hello,

I have designed simple circuit of Pass Transistor with 2X TIP35C along with LM317 Because i need to control huge current. As Per Data Sheet TIP35C can easily handle around 25A each TIP35C Transistor. I have paralleled the 2X TIP35C and using 24Volt 15Amp power supply. While giving output its 50% of total power. Input SMPS AC Line shows 115 Watt and output Generated on the Controlled DC Side is just 55 Watt... ? 50% Energy loss ?

what should i do to reduce the losses ?

Circuit diagram link:-
https://www.pocketmagic.net/wp-content/uploads/2010/02/PSUs.jpg

Please tell me...why 50% loss ? Does it depends on wire thickness ? i have used 3 Sq MM Thick wires and not more than 30 CM long...Thanks

 

[D.A.(Tony)Stewart]

Linear regulators have low noise but poor efficiency unless Vdrop is held to a minimum.
50% is normal. when input is twice adjusted output.

You mention SMPS design but this is not SMPS , which can do 80~90 efficiency. This is a LINEAR regulator.

1st define your acceptable requirements for input and output power, voltage, current

 

[asking]

Hello,

I want to make Adjustable Power Supply 0-24Volt. Input is 24V 15AMP and using 2x TIP35C along with LM317 with Pass Transistor configuration. I just want to find the losses and efficiency of circuit. According to my analysis its 50% loss in thermal heat. What if i put 4X TIP35C thermal loss would be less ? Single TIP35C is capable of handling 25AMP but why not in this case ?

 

[D.A.(Tony)Stewart]

If you put in 24V 15A and set output to say 0.001V 15A ( 15mW) You still are putting in 24Vx15A=360W and your efficiency is near 0% OK. This is the extreme.

Another problem is with Vout is you get extra Vdrop from 0.1R resistors ( 0.5V drop) and bypass Vbe drop of 0.8V or more you will get almost a 4V drop so you also will be able to reach 20V output maybe.

Reconsider this design and choose a SMPS Buck design instead.

 

[tpetar]

SunnySkyguy is right, you make heating device for winter and not effective power supply with regulation.


https://www.tme.eu/en/katalog/#id_c...sed_params=365:24611,24792,24849,24612,24613;

 

[crutschow]

Hello,

I want to make Adjustable Power Supply 0-24Volt. Input is 24V 15AMP and using 2x TIP35C along with LM317 with Pass Transistor configuration. I just want to find the losses and efficiency of circuit. According to my analysis its 50% loss in thermal heat. What if i put 4X TIP35C thermal loss would be less ? Single TIP35C is capable of handling 25AMP but why not in this case ?

The configuration of a linear regulator has no effect on the efficiency or power loss. It can affect where the power is dissipated. The efficiency is always Vout divided by Vin, with a dissipation of (Vin - Vout) x I(current).

 

[asking]

If you put in 24V 15A and set output to say 0.001V 15A ( 15mW) You still are putting in 24Vx15A=360W and your efficiency is near 0% OK. This is the extreme.

Another problem is with Vout is you get extra Vdrop from 0.1R resistors ( 0.5V drop) and bypass Vbe drop of 0.8V or more you will get almost a 4V drop so you also will be able to reach 20V output maybe.

Reconsider this design and choose a SMPS Buck design instead.

Thanks...i will try for Buck Converter which would be more efficient..