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Can you uprate 7805 voltage regulators?

Doomguy42

Member
Hi there.
I've replaced a late 1980's L7805cv 5v voltage regulator with what I think is a slightly higher rated modern version: 78M05. I've not powered my board up yet as I've been hit by a wave of doubt. I figured it would be fine if it's higher rated as it's more up to the job. However if it's supplying too much current to my board that could be a problem? I just do hobby repairs so figured I better check with a pro and see if my selection is ok?
Thanks
 
Last edited:

rjenkinsgb

Well-Known Member
Most Helpful Member
A higher current or power rated one is fine, as long as it's the same output voltage, which that is.

Things just take the current they need as long as the voltage is correct; a somewhat higher current rating in a power supply does no harm.

However, an L7805CV is rated at one amp. A 78M05 is a lower rated part so not suitable for that application.
(An L in the middle of the part number means a low rated one, eg. 78L05).
 

Doomguy42

Member
Thanks... i was hoping for that although I can see I've made the mistake on the L prefix thinking it was meaning Low so and M would be ok.
 

unclejed613

Well-Known Member
Most Helpful Member
a 78M05 is rated at 500mA, not 1 amp. if you want a higher current rating look for a manufacturer that rates their 7805 at 1.5A and get one of those. if you want a 5A regulator look for a 78H05 (but it will not fit in the same place since it's in a larger package like TO-3 or TO-3P)
 

tomizett

Active Member
In addition to the maximum rated current, what generally limits the capacity of these regulators is the power that they can dissipate - they won't do full current at maximum dropout voltage (for long) without overheating and shutting down. So a 1.5A regulator won't necessarily be more capable in your application than a 1A regulator if it's the same size (and so has the same capacity for dispersing heat). They will both shut down at the same time because they will both reach the same temperature.
 

cpprioli

New Member
Unclejed613 is right on the money regarding rated current. The standard LM7805 is either 1.0A or 1.5A, depending upon manufacturer and/or suffix. Any letters in the middle of the v/reg number tells the story about current ratings. A 78L05 is a low-current model, a 78M05 is a medium-current model, and a 78H05 is a high-current version. Generally, the L version is in a TO-92 package while the H version is in a TO-3 package. Shop and choose carefully to maintain correct operation. Also, if your v/reg is operating at or near its current capacity, heatsink it to help get rid of the heat generated. Also, the greater the difference between input and output voltage, the hotter the v/reg will run.
 

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