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Author Topic: DC Variable Voltage source for a 24-V Lamp  (Read 954 times)
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techneo
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« on: August 10, 2019, 09:01:10 09:01 »

Hi,

 I want to design a DC variable voltage source from 0-24VDC. The input DC available to me is +24VDC. I have a single turn potentio-meter used by the operator to select the lamp brightness level.

 Initially i used an atmega328 micro-controller to sense the user input from the potentio-meter and then change PWM of the control signal to the P channel mosfet IRF4905 . The problem in this approach was a 24-V switching signal at the output which was not visible at the lamp but was disturbing other circuits in the close vicinity. Switching frequency for the circuit was 2 Khz. I tried to design a low pass LC filter but since the input voltage changes regularly, i was not able to get a pure DC-varying output signal.

 I am also considering other options including an LM317 regulator based design but since i want to have extended control of the input signal sensing in digital domain, i don't want to go that way.


-techNeo
« Last Edit: August 10, 2019, 09:11:49 09:11 by techneo » Logged
pickit2
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« Reply #1 on: August 10, 2019, 12:28:25 12:28 »

I would use a LM2596 converter.
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Old_but_Alive
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« Reply #2 on: August 10, 2019, 01:26:18 13:26 »

obtaining 0-24 volts will be difficult.

how do you produce a 0.3v output ?

1-24v no problem

why use a micro ?, its a linear/switch mode solution.

have a look at the LT3080 family

particularly   the app bit on high efficiency regulator
« Last Edit: August 10, 2019, 01:34:46 13:34 by Old_but_Alive » Logged

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kreutz
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« Reply #3 on: August 10, 2019, 02:37:46 14:37 »

LM2596 buck converter modules are available for a few dollars (I agree with Pickit2). Maximum current about 3 Amps, minimum output regulated voltage will be over 1.25Vdc so you need a compromise solution, maybe using a potentiometer with switch (using the switch contacts in series with the 24Vdc input).
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bobcat1
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« Reply #4 on: August 11, 2019, 01:50:29 01:50 »

HI
Using linear power supply will dissipate lot of heat specially when input is 24V and output is 2 or more voltage in difference , Therefor I recommend using switching PSU or just use PWM and high power switch

All the best

Bobi
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Old_but_Alive
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« Reply #5 on: August 11, 2019, 02:29:56 02:29 »


I bought 10 of these for$20

https://www.ebay.co.uk/itm/2-5-10PCS-5A-Lithium-Charger-CV-CC-buck-Step-down-Power-Supply-Module-LED-Driver/172825888360?hash=item283d39c668:m:m7pK-R1ma5a8jpQpbn33rXA

the modules schematic can be found if you google

« Last Edit: August 11, 2019, 02:33:43 02:33 by Old_but_Alive » Logged

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techneo
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« Reply #6 on: August 11, 2019, 04:21:36 04:21 »

@Old_but_Alive

1. I think i have found a very elegant option for variable output voltages using XL4015. As far as voltages less than 1.25 are concerned, my atmega controller will sense the it and simply cutt-off the output once i reach this lower limit for output voltage.

2. So as given in the datasheet of XL4015, i am thinking of replacing R2 with either a digital pot from AD which i have used quite often or i can straight away replace it with the operator adjusting resistor. This will give me a voltage output from 1.25 upto 36V (as per datasheet)....

3. I assume that a fixed value inductor of 47uH will suffice for the entire range from 1.25 to 36 V ? right?

4. Do you foresee any problems with this approach?


This seems quite good an alternative.... Kiss

-techNeo

Posted on: August 11, 2019, 03:43:12 03:43 - Automerged

I would use a LM2596 converter.

Yes it is also a good option specially with a current output of 3A but the minimum output voltage is a bit high i.e 4.5V . Compared to this product, the LT family (LT3085) offers a minimum voltage output of 1.2V with a current output of 0.5A. Since LT LDOs can be used in parallel, the overall current output can be increased manifold.

-techNeo

Posted on: August 11, 2019, 04:18:21 04:18 - Automerged

LM2596 buck converter modules are available for a few dollars (I agree with Pickit2). Maximum current about 3 Amps, minimum output regulated voltage will be over 1.25Vdc so you need a compromise solution, maybe using a potentiometer with switch (using the switch contacts in series with the 24Vdc input).

I think my first option is to go for XL4015 based module because of its easy availability. Then i will order LT comps from digikey and hopefully will get what i want..

-techNeo
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