LT3012

Thread Starter

Martino Chiro

Joined May 1, 2015
102
The specs of the LT3012 shown a 250mA max output current.
There is a solution to get more current from this device ?
It is possible to parallel more LT3012 ? Or, put some power transistor in the basic configuration
shown in the data shhet that boost the 250mA limit ?

Thank You
 

crutschow

Joined Mar 14, 2008
24,079
Why not just use a regulator that has a higher current capability?
How much current do you need?
What is the input and output voltage?
 

Alec_t

Joined Sep 17, 2013
10,712
An external transistor could be used, but would have to dissipate, for example, (80-5)*1 = 75W for an 80V input and 1A output at 5V :eek:.
 

Alec_t

Joined Sep 17, 2013
10,712
So power dissipation by the outboard transistor would be 24W +/- 10%. Still a lot to handle!
A switch-mode converter would be a lot more efficient.
 

Thread Starter

Martino Chiro

Joined May 1, 2015
102
Interesting the use of he LM2596. But again i need to put a transistor to get a drop of at least 8 - 10V.
It is not possible to parallel more LT3012 ?
 

Alec_t

Joined Sep 17, 2013
10,712
It is not possible to parallel more LT3012 ?
In theory you could, but in practice the ICs will not be exactly matched (even if from the same batch) so they won't share the current equally. One will be taking more than its fair share of the load. You will have to ensure that this share does not cause the IC to go into thermal shut-down. The total power dissipated will still be 24W, which is going to need very effective heat-sinking. As mcgyvr asked, how are you going to handle that? Unless you have a sackful of 3012's looking for a use it will be cheaper and more efficient by far to use a switched-mode supply.
 

Thread Starter

Martino Chiro

Joined May 1, 2015
102
Both the L4978 and the LM317HV are good solutions for me.
When Vin - Vout = 24V the L4978 seems can deliver 2A of output current max.
When Vin - Vout = 24V the LM317HV seems can deliver 1A of output current max
from the Figure 17 "Current Limit" for T and K package type, in the TI data sheet.
 

benta

Joined Dec 7, 2015
101
I don't know the L4978, but I've worked a lot with the LM317/317HV.
Your main concern is thermal management = cooling, and this is true for both devices.
You'll need to dissipate ~24 W to the surrounding air, and that means a relatively large heatsink.
Thermal resistance junction-case is 0.9 K/W for the "T" version, you need to add insulation (mica or silicone) which is around 1 K/W (worst case), let's say 2 K/W from junction to heatsink. This means a temperature rise of 48 Celsius.
Say your maximum surrounding temperature is 35 C (I'm guessing here).
To keep the junction temperature below 125 C, your heatsink needs to have a thermal resistance of:

125 - 35 - 48 = 42, meaning your heatsink must have a thermal resistance of no more than 42/24 = 1.75 K/W

That is quite a big chunk of aluminium, please check the heatsink suppliers' websites for example products.

A solution with a switching regulator or a DC/DC-converter module might be better.

Best Regards,

Benta.
 
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