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  • LR645 - High input voltage Linear Regulator
2016/05/01 12:00:31
CabanzoJ
I'm planning to use the Microchip LR645 linear regulator in a non-isolated power supply, datasheet ( states that LR645 is capable to deliver up to 150 mA output current using an external depletion-mode MOSFET DN2540 (
MOSFET DN2625 ( also from Microchip is another depletion-mode MOSFET with very similar characteristics but able to handle more current, can I use this FET instead to get more than 150mA from my LR645 power supply?.
2016/05/03 01:20:33
MatthewM
The internal DMOS of the LR645 is capable of supplying 30mA peak current. The LR645 can control an external DMOS so via the gate output. The suggested DN2540 DMOS in the datasheet is now the limiting factor for the current, as dictated by the saturated drain-to-source current, which (according to the datasheet I found by Supertex. Inc) it talks about a minimum 150mA drain current. 
 
If you compare the DN2625 and the DN2540, then they have similar Vgs. Looking at the saturation characteristics I can't see why you couldn't use the DN2625.
2019/05/11 15:14:56
Aville
Hello. Did you make the lr645 circuit with depletion mode mosfet?i m trying but Either mosfet is burning or lr645(8pin) is burning.
2019/05/14 11:36:07
Nikolay_Po
Have you tried to turn on the circuit at lower voltages, say, 30V, just to check is it connected properly? Also, what is a load for the regulator? May it have excessive capacitance and require long charging interval at too high current?
2020/11/09 06:05:48
Tom_Bead
Hi all,
 
Can anyone tell me if the Datasheet for the LR645 is correct?
 
We have wired it up, without the DMOSFET and this works fine for 30mA (Using the 8 pin device). This has been connected up with the trim resistors included for 9V output.
 
We however want to supply 130mA, so we have wired in the DMOSFET as per the suggested layout in the datasheet, however what we now get is that vout of the LR645 is now tracking that of Vin , i.e. if we have 20V at Vin, we get 20V vout (and not the 9V we set). Suggests that the connection of the DMOSFET to the LR645 is not correct (Tested the DMOSFET to check correct operation as well).
 
 
We are testing with DC voltage input at the moment where C1 is, bridge removed
Thoughts please?
 
Thanks

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2020/12/09 07:38:10
Tom_Bead
For everyones information, it turns out the DN2540 is extremely sensitive to Static, that is.. they can be destroyed simply by cutting the packaging 
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