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Can I create a micropower regulator out of discreet parts?

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rx5

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Regulators help pls

Hi all!

im gonna use a 7805 as a 5volt reg... but is not efficient enough?? gonna use it in low current apps.... (<5mA at most)....

ive heard of micropower or microwatt regulators(+5V and 3.3V) i just forgot the specific part number though... im having a hard time sourcing those.... but i could easily get 7805 or 78L05 here....

so is it possible to create one out of discreet parts? (transistors,resistors, diode etc etc) ??

any help is really apreciated :)
 

Re: Regulators help pls

You can go to **broken link removed**
They have range of switching/linear regulators and they also have "free samples" service.
 

Re: Regulators help pls

IanP

hi!

tnx but i preffer REALLY discrete parts... :) i would stay clear from those MAXIMs...

that is, IF a micropower regulator can be done with discretes.....

btw, input is in the range of a max +10V @50mA , actually im planning to build a wind-up torch.....
i just BUSTED my white LED when i charged the .22uF cap (using a steper motor as the source) and quickly DUMPED the charge to the LED...... *dang* it went DEAD..!! so i would really have to put an EFFICIENT voltage regulator...!! :)
 

Re: Regulators help pls

You can have a look at this:
"This
application note will describe some different
switched capacitor methods of driving white-LEDs.."
**broken link removed**

or you can build very efficient voltage regulator based on 3524, (pulse width modulator) without external transistor...
 

Re: Regulators help pls

(I am not sure realy about this but) I am afraid you cannot use discrete elements for such low currents because you will face serious problems with noise.
 

Re: Regulators help pls

rx5 said:
Hi all!

im gonna use a 7805 as a 5volt reg... but is not efficient enough?? gonna use it in low current apps.... (<5mA at most)....

ive heard of micropower or microwatt regulators(+5V and 3.3V) i just forgot the specific part number though... im having a hard time sourcing those.... but i could easily get 7805 or 78L05 here....

so is it possible to create one out of discreet parts? (transistors,resistors, diode etc etc) ??

any help is really apreciated :)
Click to expand...

First you need switching power regulator if you want efficiency.

I was just wondering why you would insist on building using discrete components? Is this a required project?

Otherwise in term of cost-effectiveness, performance, using IC offer way more advantages than discrete component. Some of them costing only a few cents.
 

Re: Regulators help pls

can i ask,
based on what condition do we rate the efficiency of the regulator?
is it the current requirement of the circuit?
 

Re: Regulators help pls

banh said:
can i ask,
based on what condition do we rate the efficiency of the regulator?
is it the current requirement of the circuit?
Click to expand...
I think datasheet usually states the efficiency at rated load. Pls correct me if I'm wrong.
 

Re: Regulators help pls

banh said:
can i ask,
based on what condition do we rate the efficiency of the regulator?
is it the current requirement of the circuit?
Click to expand...

Usually at different load current and voltage.

For example, efficiency at 1A, 3V load given an input voltage of 5V ...

But there are different load vs. input conditions ...
 

Re: Regulators help pls

It isn't that complicated to build a voltage regulator using discrete parts.
But I don't think it's easy to reduce the quiescent current that much as to compete very favourably with a 7805. I am thinking only about the required reference current.

And simplicity is also an issue; you will not get the performance of a 7805 using just a few components.
You may be better off using a switching regulator; it's somewhat more complicated, but more efficient, too.

If you're still interested I can suggest a thing or two.
 

Re: Regulators help pls

Try this

h**p://www.torex-usa.com/product/pro02/pdf/XC6202(E).pdf
 

Re: Regulators help pls

There are several low Iq parts available from different manufacturers.
But, since you wanted a "discrete" one, try this.
It should have a quiescent current of about 200µA at the minimum input voltage of 7V. That compares favorably with the 3.8mA for the LM78L05. The current limit should kick in at about 15mA.

Q4, R4 provide overcurrent protection. D2 is there to compensate the variations of Q3 Vbe with temperature. The LM385-2.5 is available from National. It is important to use a low current Zener diode, such as the LM385, or you will have poor regulation. If you cannot get this part, then I will post another circuit, using a transistor array to build it.

If hope this circuit is "discrete" enough.
 

Regulators help pls

VVV,
yah THAT is descete enough.. hehe ... yah, its the "standby" quiescent current im after.. since you say its 200uA, IT IS good enough... compared to the 3.8mA of 78L05.... ill try breadboarding it....

only one more prob, WHAT part can i substitute for that LM385 2.5V zener??? i ithink i cant find those in our area... :(
 

Re: Regulators help pls

Current limiter Q4 in the above circuit will not work because short circuit current will flow through Q2 and Q4 to the output with no limit. Q2 will burn.
Collector of Q4 must be connected to collector of Q3.
 

Re: Regulators help pls

Good point there, Borber.
Sorry about that, rx5. Connect the collector of Q4 to base of Q2.

As for the reference, try to look for a micropower shunt reference. It has to be lower than 5V, of course, but around 2-2.5V is preferred over 1.2V. Minimum current will influence the value of the 6.8k resistor and the overall quiescent current. When you find something, please post.
Try Linear Technology, ST, National.
 

Regulators help pls

VVV,
ok.. :) btw you said in your earlier post you could replace the 2.5V zener with descrete transistors... :) care to show how??
 

Re: Regulators help pls

Actually, I said replace them with a transistor array. That will be complicated, not so accurate and requires a chip like the CA3046. Can you get that?

Can you find an LT1004-2.5 or LT1034-2.5 or LT4040-2.5 from Linear Technology, or TL4431-2.5 from National? Also, the 4040 is made by National (LM4040) Micrel and Texas Instruments. Can you get any of these parts?
As a matter of fact, many companies make the LM385, too.

I know the TL431 is a very popular chip (almost every manufacturer makes it) and would make things very easy, but, unlike the TL4431 I suggested above, requires at least 0.6mA to operate. Is that going to be acceptable?
Can you get a TL431? Almost any power supply uses one of these, even power supplies in computer monitors.
 

Regulators help pls

VVV,

i will post ASAP for the parts that are available in our area.....

btw, can that zener be replaced with ordinary diodes in series???
like is it/does it use the voltage drop of diodes?? or should it be a ZENER? :)
 

Re: Regulators help pls

You can use 3 x 1N4148 for roughly 2.1V and calculate new value for resistor between output and the base of Q3.
 

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