[SOLVED] designing power supply

[JUBAYER]

I was designing a power supply for my personal use with L7805CV, L7809CV,L7812cv for fixed supply and LM317T for variable supply. The problem is, can i use a single heat sink for all those ICs? or it will short all the output of the Ics to a single node. Also i am using TIP 42 for high current supply. Now if i use one heat sink for all 7800`s and another for all the TIP42`s, is that OK? and also i need suggestion for 1W 0.3Ω 1% resistance?

 

[sivamani]

You can use common heat sink,if the heat sink area is touching to single node or net..

 

[kam1787]

also i need suggestion for 1W 0.3Ω 1% resistance?

use 3 1ohm 1% in parallel, with ..............3,3 ohm

 

[nilses]

You can use a common heatsink without problems.
Just remember to use a "TO220 mounting kit". This kit contains , a mica plate,bolt, nut etc to mount the Volt.Reg.

Also add some "heattransfer paste" between the VoltReg and the heatsink.

 

[JUBAYER]

thanks..... but i actually need model number of powerful heat sustainable resistors...not a parallel combination....

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Thanks for the reply...............But interface area of the IC is noted as output on the datasheet. My question is, if i use common heat sink for all those regulator IC`s mounting on TO220 kit ,all the outputs will not get shorted? sorry if i am wrong,i have not used this heat sink before. .

 

[kam1787]

thanks..... but i actually need model number of powerful heat sustainable resistors...not a parallel combination....
.

even 3 1/2 watt resistors in parallel will handle 1.5W - - you had asked for only 1 W

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. My question is, if i use common heat sink for all those regulator IC`s mounting on TO220 kit ,all the outputs will not get shorted? s .

..........the heat sink of those ICs is the ground, so it is alright to mount to the same heat sink - if all have the same ground. No need for a mica insulator. The insulator is only needed to isolate them electrically.

 

[albbg]

There are many suppliers and brokers. Have a look to:

**broken link removed**
https://www.newark.com/ohmite/41fr30e/resistor-wirewound-0-3-ohm-1w-1/dp/64K8657
https://canada.newark.com/vishay-dale/wsl2512r3000fea/resistor-metal-strip-0-3-ohm-1w/dp/60K8449

About the heatsink, all the 78xx have the tab of the TO220 can connected to ground, then if the ground of all the circuit they will supply can be the same, you can use the same heatsink and no mica insulator is required (improving the thermal performances). I mean the ground of the 5V will be the same of that of 9V taht will be the same of the 12V. Take into account that LM317, instead, has the tab connected to Vout, then to share the same heatsink of the 78xx you must use an insulator.

 

[Electro nS]

use the multimeter to beep (short test) the reulaotor tab with the pin and check wether this pin is GND or Vout etc . if in all ICs the tab is GND then yes you can use the same heatsink , other wise you cannot ,unless you use some kind of thermally conductive electric isolated material ( MICA for example ) . one last test before running the system check if there is a short between any pins !

cheers