One for the electronics buffs…seemingly obscure 5v voltage regulators

[Johnnybravo]

Looking for two 5v regulators….but here’s the rub…Whilst they look the same as the normal 7805 type regulators, they are not. The pin allocation in them in different. So, where can I find some 78dl05p regulators in the U.K.? RS does not stock them…
Or an alternative part number for a low drop out 5v regulator with the same pin allocations.
Thanks in advance

 

[sako243]

Where are you sourcing your data for the pinout from?

The only data sheets I can find show it as having the same pinout as the LM7805 series.

 

[Neilj]

From what I can find that's still input, common, output (left to right) like a normal 7805 as @sako243 says?

 

[pawsnizzy]

Same as 7805

 

[Seadog]

Agreed, same pinout.

 

[awemawson]

Johnny you should be able to bell out the connections on the PCB to confirm what is what on that regulator.

 

[Johnnybravo]

L

Where are you sourcing your data for the pinout from?

The only data sheets I can find show it as having the same pinout as the LM7805 series.

I looked at the pc board. Pin on the left when the heat sink is away from you is 1. Middle pin marked 3 and pin on the right marked 2.

Normally in that orientation pin 1input on the left
Middle pin 2 common
Right pin 3 output.

I assumed with pins 2 and 3 marked the other way round, the input and output were swopped.

If that’s not the case, what would a suitable voltage regulator be? It’s for the memory on a cnc lathe. Initial search shows it as low drop out and if memory serves correctly, something like 250ma output

 

[Johnnybravo]

Having looked at the traces on the board, middle pin is definitely common

 

[ajlelectronics]

Initial search shows it as low drop out and if memory serves correctly, something like 250ma output.

That would be a 78L05 in a TO-92 package, that one is a 78D. It will be around about 800mA output capability in TO-220.
They are also largely bulletproof, so why do you think it is faulty?

 

[Johnnybravo]

That would be a 78L05 in a To-92 package, that one is a 78D. It will be round about 800mA output capability in TO-220.
They are also largely bulletproof, so why do you think it is faulty?

Machine not booting up. This is a power distribution board. It has a 7,5v rail incoming that gets regulated down to 5v for two of the computer boards in the machine. It was a know weak link. Having spoken to the technician who has serviced this since new, he knows the symptoms. Apparently they changed this on the later models. Cannot find another replacement board. He suggested changing the two regulators and the 4 capacitors.

They power the two big memory capacitors. So when it boots up it’s throwing checksum errors, which, according to him, stems from these not charging the capacitors . He’s worked on these machines 20 years, so trust his experience

 

[skotl]

Machine not booting up. This is a power distribution board. It has a 7,5v rail incoming that gets regulated down to 5v for two of the computer boards in the machine. It was a know weak link. Having spoken to the technician who has serviced this since new, he knows the symptoms. Apparently they changed this on the later models. Cannot find another replacement board. He suggested changing the two regulators and the 4 capacitors.

Have you tried the most basic (without wanting to appear condescending) task of checking the pins for 7.5v, 0v and 5v?

That will tell you whether the regulator is working and, if it’s not, which pins are vIN and COMMON.

 

[skotl]

Also, even if the pins are different (which seems unlikely) I’d get the most available in spec 7805 and just put short solid core insulated jumpers between it and the board.

*if* the pinout really is different, of course.

 

[Johnnybravo]

He had a quick check and said one of them is faulty.So was trying to source some, or a viable alternative whist still making enquiries about a complete board.

 

[ajlelectronics]

He had a quick check and said one of them is faulty.So was trying to source some, or a viable alternative whist still making enquiries about a complete board.

With 2.5V headroom, you don't really need anything special. A conventional 7805 will do (I can send you a couple as they are getting scarce) or there are switching versions now available at a fiver each or thereabouts.
Electrolytics are always worth swapping, but the bypass capacitors should have survived. Spec for the regulator is 0.33uF on the input and 0.1uF on the output, as close to the pins as possible. Some designs don't think that they are required and so the regulator becomes an oscillator, which is a very bad thing.

 

[Johnnybravo]

With 2.5V headroom, you don't really need anything special. A conventional 7805 will do (I can send you a couple as they are getting scarce) or there are switching versions now available at a fiver each or thereabouts.
Electrolytics are always worth swapping, but the bypass capacitors should have survived. Spec for the regulator is 0.33uF on the input and 0.1uF on the output, as close to the pins as possible. Some designs don't think that they are required and so the regulator becomes an oscillator, which is a very bad thing.

Thank you. I have actually got a couple of conventional 7805’s lying around from something I built a couple of years back and I bought a couple of spares

 

[sako243]

Having looked at the traces on the board, middle pin is definitely common

So I've I've understood you correctly it is the correct pin-out for an 7805 regulator? So you're seeing 7.5V on the input, and nothing on the output?

As others have said they're normally fairly resilient little devices so either the reg is faulty or something downstream is pulling it down. Since they're pence to swap out I'd cut the output pin and disconnect it from the board and check again if you get 5V on this pin then something downstream is dragging the rail down. If that's the case check 5V to ground and see if it's low resistance / short, remove the caps - is it still short? If not problem found and can be replaced. If not then more investigation.

A conventional 7805 will do (I can send you a couple as they are getting scarce)

Really??? Thousands around - https://uk.rs-online.com/web/p/voltage-regulators/2988508

 

[Johnnybravo]

So I've I've understood you correctly it is the correct pin-out for an 7805 regulator? So you're seeing 7.5V on the input, and nothing on the output?
View attachment 480742
As others have said they're normally fairly resilient little devices so either the reg is faulty or something downstream is pulling it down. Since they're pence to swap out I'd cut the output pin and disconnect it from the board and check again if you get 5V on this pin then something downstream is dragging the rail down. If that's the case check 5V to ground and see if it's low resistance / short, remove the caps - is it still short? If not problem found and can be replaced. If not then more investigation.

Really??? Thousands around - https://uk.rs-online.com/web/p/voltage-regulators/2988508

Thanks @sako243 . Will investigate further at the weekend

 

[Johnnybravo]

Having looked into this a bit further , I am not convinced this would be a straight swap with a normal 7805 in that if you Google that part number it seems to be bipolar and able to regulate both positive and negative 5v

 

[ajlelectronics]

Having looked into this a bit further , I am not convinced this would be a straight swap with a normal 7805 in that if you Google that part number it seems to be bipolar and able to regulate both positive and negative 5v

What are your voltage readings on the input pins?

 

[ajlelectronics]

able to regulate both positive and negative 5v

Nope...

KIA78DL05PI Download

Download KIA78DL05PI Datasheet. File Size: 323.81 Kbytes. Part #: KIA78DL05PI. Description: BIPOLAR LINEAR INTEGRATED CIRCUIT (THREE TERMINAL POSITIVE LOW DROPOUT VOLTAGE REGULATOR). Manufacturer: KEC(Korea Electronics).

www.alldatasheet.com

It does seem a strange choice of component for the purpose, without being able to see your circuit diagram at least.