7805 regulator substitute

moxhamj

New Member
Sometimes you come across a circuit that is just cool. This is a switching regulator for a 7805 that uses components that cost not much more than a 7805. But allow for the fact that it doesn't get hot and so doesn't need a heatsink, and it costs less.

All credit to the author Roman Black http://www.romanblack.com/smps/smps.htm

It is so simple I just had to build one. In fact, I needed something like this anyway because solar power is expensive and it seems crazy to throw it away as heat. SMPS are great - feed in 18V at 20mA and you magically get 5V at 60mA.

I have just completed one on the protoboard and it works just as described. Regulation varied about 0.2V depending on the load. There is no ripple at all I could see on the scope trace.

This could be perfect with a 5V supercap because the solar volts are not critical and can vary over a wide range. The quiescent current is going to be at least the current drain through the 8k2 but there might be scope to use a 78L05 equivalent for the reference.

I'm still working through Mr Black's website but he has some other nifty circuits, including a self turn off circuit for a pic/picaxe.
 
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hippy

Technical Support
Staff member
Looks interesting. The graphs on the sub-page(s) seem to indicate a preferred range of load currents it is best suited to so perhaps not good for a PICAXE just by itself or with lots of additional components but I'm no expert. I'm sure you'll keep us informed of your experiments and experience.
 

Michael 2727

Senior Member
If you are going to build the circuit above, check the data sheet on the SCR you
intend to use as some may need more than 5mA MIN as the latching (hold) current.

Doc, did you find the one where they use a 7805 as a 1.8MHz transmitter ;)
There are some very clever circuits hidden away on the net, you just have to look.
 

Michael 2727

Senior Member
On purpose?
Yes ! That was the design.

But I know of another instance where a Plugpack Supply almost shut down
an entire TV Network in Melbourne. A faulty unit introduced so much RF and
noise into the 240V grid that Comms between the Media Storage, Editing and
Broadcasting sections were tripping out and resetting.
They had to systematically unplug every device in the entire building
until the culprit was found. (about an hour later)
 

BeanieBots

Moderator
That ciruit has be admired for its simplicity.:cool:
I'd question the efficiency figures though.:confused:
(especially at anything much below its max current)
 

westaust55

Moderator
Irrespective of whether the efficiency is as high as stated, it will be far better than a 7805 over the range 3mA to 800mA. And . . . . yes I am using a 7805 with small heatsink at the moment.

With a 7805 and delivering say 800mA delivered and using ~5mA quiescent current:
15V dc input --> best efficiency = ~33%
9V dc input ---> best efficiency = ~55%
7V dc input ---> best efficiency = ~71%

These figures also droop way down at lower output currents.

The 7805 however does have a few "protection features" built in but there have also been posts in the past suggesting these are not perfect.
 

stocky

Senior Member
Yes ! That was the design.

But I know of another instance where a Plugpack Supply almost shut down
an entire TV Network in Melbourne. A faulty unit introduced so much RF and
noise into the 240V grid that Comms between the Media Storage, Editing and
Broadcasting sections were tripping out and resetting.
They had to systematically unplug every device in the entire building
until the culprit was found. (about an hour later)
Similar experience with a "generic" 56k modem - original models had 9vac plugpack and linear PSU on board - later model had same plugpack but SMPS on board. In this case one cap went leaky in the smps and it generated a carrier on CDMA wiping out a local cell! Modem worked fine and the first the owner new of it was when a guy from the ACA walked in with a spectrum analyser and a yagi and pointed it at the modem!

:)
 

hmose

New Member
Sometimes you come across a circuit that is just cool. This is a switching regulator for a 7805 that uses components that cost not much more than a 7805. But allow for the fact that it doesn't get hot and so doesn't need a heatsink, and it costs less.

All credit to the author Roman Black http://www.romanblack.com/smps/smps.htm

It is so simple I just had to build one. In fact, I needed something like this anyway because solar power is expensive and it seems crazy to throw it away as heat. SMPS are great - feed in 18V at 20mA and you magically get 5V at 60mA.




How does one get ahold of Mr Black? Do you suppose he has this or other regulator kits for sale?? Email or telephone available?? Thanks
 

moxhamj

New Member
I'd like to contact him too, but couldn't find any links. Re kits, I managed to find all the bits in my parts cabinet, but they are common parts anyway. The transistors are generic switching transistors rated up to 800mA. The inductor takes a bit more searching.

? it needs a PCB?
 

westaust55

Moderator
I'd like to contact him too, but couldn't find any links. Re kits, I managed to find all the bits in my parts cabinet, but they are common parts anyway. The transistors are generic switching transistors rated up to 800mA. The inductor takes a bit more searching.

? it needs a PCB?
From his website: roman@romanFROGblack.com
witht he note: (Just remove the ANIMAL from my email address!)

He seeminging does sell some kits but mainly a clock from what I can see.
 
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