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### Topic: How to get a 3.6V supply from 5V? (Read 18201 times)previous topic - next topic

#### fungus

#15
##### Apr 28, 2013, 11:17 pm

So, my suggestion (reply #2) is just a bridge too far then?

No, it works...I even tried it (see reply #7). The only thing I didn't like is that the Zener gets very hot when the sound module is idle (Not drawing current).

If the current draw was constant and I could fine-tune the resistor then I'd probably use that method - simplicity is good.

#### fungus

#16
##### Apr 28, 2013, 11:21 pm

use 2 pcs  IN4001 will give you ~3.4V output at current 80-100mA.

Yep. The thing is that the module current is variable and the voltage goes up to about 5V when it's drawing no current. 5V is beyond the chip specs. 5V might not damage that chip when there's no current passing but it means I can't put in a decoupling capacitor. A big capacitor would supply 5V for a while when the chip powers up - risky for both the chip and the SD card!

#### fungus

#17
##### Apr 28, 2013, 11:23 pmLast Edit: Apr 28, 2013, 11:26 pm by fungus Reason: 1

I've always been curious what would happen if you switched (for the constant voltage circuit, 1st one of the 3) the zener diode for
a resistor/voltage divider?  would the transistor hold the voltage? i'll try that out tomorrow.

The Zener is there to allow for variable input voltages (eg. batteries). If the input voltage is constant then it should work.

I might give it a try tomorrow, too. Any voltage from 3.5-3.6V should work so I ought to be able to find a pair of resistors that works (I'll start with a pot attached to the transistor base and see if I can 'dial' an output voltage).

#### runaway_pancake

#18
##### Apr 29, 2013, 01:39 am

OK
I thought in Reply #7 that you'd breadboarded strykeroz's zener circuit with the 15?.  That circuit will blow 100mA all the time, some of the current will be diverted to the circuit placed in parallel with the zener (the "output").

When using a zener to establish VB in the transistor voltage regulator, nothing like 15? would be necessary, maybe 5mA (IB) at most for 100mA (max) out.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#### fungus

#19
##### Apr 29, 2013, 12:13 pm
I went to the local shop and they had LM317s and a 4.3V Zener diode. It's the first time they had everything on my list. I'll have a play later.

I just wanted to post this:

It's the inside of an LM317. How on earth does anybody design something like that?

#### MarkT

#20
##### Apr 29, 2013, 01:29 pm

It's the inside of an LM317. How on earth does anybody design something like that?

Modularly - the overall circuit is a few submodules connected tegether, and each submodule
has several parts (typically amplifier section, current- and bias-setting components, protection
components).  One module will be a voltage reference in a regulator.  Most of the rest is
an op-amp (itself several differential amplifier stages), and then there will be a high-current output section.

When presented as one big schematic like this you need to be able to read circuit diagrams
to interpret it
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

#### cjdelphi

#21
##### Apr 29, 2013, 02:11 pm
After spending a few days building a circuit which works, draw it all out....   and it quickly gets complicated

Just try building a flip flop out of transistors and resistors, 2 transistors, 4 resistors, 2 capacitors + wire, 1 flip flop will give you 1 stored bit, the circuit is easy enough to build 1, now take a shift
register, 8 flip flops, hook them up, then read the circuit!

What i'm trying to say is, Robert Noyce, THANK YOU!!!! THANK YOU!!! THANK YOU!!!!!!!

Thank you for being everything William Shockley was not! and coming up with the Intergrated Circuit... I wish so wish I could of got to meet him, but sadly he died doing what he loved to do, after a few lengths of the pool which he did very often, he suffered a heart attack.. thanks to Bob Noyce, we had the IC, thanks to Bob Noyce, he had the intelligence to let engineers get on with discoveries and ideas of their own, letting them follow up on their own work which ultimately lead to the first microcontroller ever made!

William Shockley, Guglielmo Marconi, and others (however clever they were) got in the way of progress, be arrogance "do it my way or get on the high way" or "i'm going to patent everything even if i never made it!" money grabbing, power hungry!!!! UGHHHH

Circuits could only really become this complex because of the integrated circuit

#### runaway_pancake

#22
##### Apr 30, 2013, 12:33 am
OK.
I made the circuit, two variations with resistors and one using a zener.

The transistor is a 2N3904.
The circuit on the right has better regulation, benefiting from more base current.
Not stellar performance, admittedly, but not too bad for some parts from the stock of stuff.

I used a 1N750A, a "4.7V" zener, in place of R2, and 55? for R1.  In circuit it measured 4.55V
It did slightly better than the "all resistor" version.

Code: [Select]
`Vo      R_L    mA3.9     22K     --3.77    300    12.63.68     59    61.33.63     40    903.77 - 3.63 = ? 0.14V `
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#### fungus

#23
##### Apr 30, 2013, 09:11 amLast Edit: Apr 30, 2013, 02:06 pm by fungus Reason: 1

I made the circuit, two variations with resistors and one using a zener.

Yep, after a bit of playing around that's is the circuit I"m going to use, but with a 4.3V Zener instead of R2 and R1=100 ohm.

The LM317 didn't work too well. I think it's a combination of being right on the limit for dropout voltage and my limited collection of resistors for setting the voltage. I'm sure if I'd had a 6V input it would have worked out much better. I could have looked for better resistors, too, or even a trimmer pot but the transistor circuit was working well so I didn't bother.

#### sonnyyu

#24
##### Apr 30, 2013, 09:17 pm
my 2 cents;-

1. Positive saturated Op-Amp

The LM358 has a positive saturation drop of about 1.4V. Let's say you supply LM358 with +5V and GND for its positive and negative supply.
Now when you saturate LM358 to the positive side, you won't get 5V at the output. The output will come out to be about 1.4V less than 5V, which is around 3.6V. LM358 is dirty cheap, \$0.95 at sparkfun. It is belong to device could sold by weight not by pieces, say 0.5 kg of LM358, 0.25 kg of 555, 1 kg of LM317 ...

LM358 will give max 40 mA, if more current is required, read and understand Op-Amp internal diagram,  to substitute bigger  output Op-Amp.

Deriving 3.6V from 5V