DC to DC doubler, 500mA & and fan regulator

Thread Starter

Johnny Lai-Kristiansen

Joined Jul 14, 2018
5
Hello,

I look for a DC to DC doubler that can make 12V DC to 24 DC and deliver up to 0.5A. At the same time i also need the 24V output to be adjustable from 0-24V

I have attached two diagrams that i'm currently looking at, but first off the DC 2 DC doubler cannot deliver 0.5A and second, i'm not sure the diagram from the regulator can take 24V in. To me it seems like 2 x 9V(18V) batteries that is connected to that circuit.

What do i need to change for this to work and deliever enough current to my 3 fans?
(1 fan use 100mA)

If you have other diagram that can do the same i'm of course open for that.
 

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Sensacell

Joined Jun 19, 2012
2,456
Buy an off-the-shelf DC-DC 12 to 24 V converter module.

The charge-pump circuit is not going to produce enough output current to drive fans.
Remember that the fans probably draw more when they start up, you should over-specify the converter.

Then perhaps look into PWM to control the fan speed.
 

Thread Starter

Johnny Lai-Kristiansen

Joined Jul 14, 2018
5
I don't have time to wait for a module to arrive, it takes 10-30 days to arrive from most places outside my location.

That's why i want 500ma at least.

Isn't is a PWM control in diagram 2?
 

Thread Starter

Johnny Lai-Kristiansen

Joined Jul 14, 2018
5
What do you have to work with?

You need a boost regulator (also called switching regulator or SMPS). Having it adjustable to 0V may be difficult. Why do you want that?
What do you have to work with? Not sure what you mean by that, but i have access to the components and a testboard

Adjust from 5-10 volt to 24 volt is fine too
 

dl324

Joined Mar 30, 2015
9,155
What do you have to work with? Not sure what you mean by that, but i have access to the components and a testboard
You seem to be implying that getting parts takes too long and you don't want to wait.

What electronic components do you have to make a switching regulator?

Why do you want a variable voltage? If it's to adjust fan speed, the generally accepted method is to use PWM; not varying voltage.
 

AnalogKid

Joined Aug 1, 2013
8,157
Circuit #2 is an opamp voltage follower connected with the pot wiper as the input. See a 741 datasheet to confirm the pinout. It is not a PWM anything. The 3904 is acting as an emitter follower; the 3906 is ... not. Even if the circuit worked as intended, the transistors would burn up almost immediately when the motor starts running in either direction.

About that - even if the circuit worked, it is intended to make the motor run both forwards and backwards. You can *not* run a small DC cooling fan backwards. The motors do not have brushes, they use an electronic control circuit. Connecting the motor to reversed DC kills the internal circuit.

Given your experience level, you can't design a switching boost regulator, purchase the parts, build it, and debug it in fewer than 30 days. I recommend buying a "boost regulator" module on ebay. Conceptually, a charge pump voltage doubler followed by a linear voltage regulator is a good plan. But the 555 circuit will make less than 100 mA output current, and the regulator circuit will not work at all.

ak
 

DickCappels

Joined Aug 21, 2008
5,952
This is a good starting point.

upload_2018-7-15_22-2-32.png
Build this. Leave out the 7805, LED, Q10, R60, R61, and R62, and replace R44 with a jumper. Change R45 to 5.1k.
 
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