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120VDC to 12VDC and 5DC without using any converters?

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darla1

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120VDC to 12VDC and 5DC

dear all

can anybody tell me how to step down 120VDC to 12DC and 5DC to supply microcontroller and mosfet driver circuit. without using any converters.

thanks in advance
 

Re: 120VDC to 12VDC and 5DC

Maybe a HV linear regulator like this will help. It depends on your current consumption.
 

Re: 120VDC to 12VDC and 5DC

A typical microcontroller and driver circuit shouldn't draw more than 20mA.
To drop voltage from 120Vdc to 12V(or5V) you may use 4.7k@4W resistor and a 12V (or 4.7V) Zener diode.
 

Re: 120VDC to 12VDC and 5DC

thank you mr maggot and Drwhof

my micro and driver circuit is taking alomost 60ma of current,


thanks

ramesh
 

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    darla1

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Re: 120VDC to 12VDC and 5DC

This method is not efficient, as most of the power is lost in the series resistor (P=R*I²) .. but it's simple ..
So, pay attention on the wattage of the resistor ..

On the other hand, there are switching power supplies that can easily take 100Vdc/ac input and convert it to 5Vdc/100-500mA; they are of the size of a mach-box (not much bigger than a high-wattage resistor) and also they are efficient and don’t generate much heat ..
Maybe that’s the way to go ..

Rgds,
IanP
 

Re: 120VDC to 12VDC and 5DC

IanP said:
This method is not efficient, as most of the power is lost in the series resistor (P=R*I²) .. but it's simple ..
So, pay attention on the wattage of the resistor ..

On the other hand, there are switching power supplies that can easily take 100Vdc/ac input and convert it to 5Vdc/100-500mA; they are of the size of a mach-box (not much bigger than a high-wattage resistor) and also they are efficient and don’t generate much heat ..
Maybe that’s the way to go ..

Rgds,
IanP
Click to expand...

yes i ll agree with this but i dont want to use this type..i need simple and efficiant technique.

thank you very much

ramesh
 

Re: 120VDC to 12VDC and 5DC

dear all

can anybody suggest better supply to get my requirement..

darla
 

Re: 120VDC to 12VDC and 5DC

darla,

you can replace the resistor by a capacitor using the formula:

Xc = 2 x PI x F x C

C = 1 / (2xPIxFxXc)
 

Re: 120VDC to 12VDC and 5DC

hi all

plz find attached document which i am using for power supply design...here i am using second circuit diagram which is including transistor and diodes....

in th document they are getting Vaux 14V but when i am testing this i am getting only 2V.

all values are same as shown in the diagram.....

can anybody help...

darla
 

Re: 120VDC to 12VDC and 5DC

You can do a circuit like this. I just simulated it with microcap. Not tested.
Transistor I suggest use MPSA42. C1 must be 3uF 450v. In the simulation is for a load of 60mA. Input is 220v 50h.
R2 is just for simulation. Don't use in the final circuit!!
D1 is a 13V zenner diode
 

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    darla1

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Re: 120VDC to 12VDC and 5DC

thanks Mr penrico

this is transformer less power supply from mains.....(i dont want to use the circuits which is shown by you)

please note that i have regulated 120DC, i need to step down this to 12V and 5VDC to power up microcontroller and driver circuit. total current reuired is 50mA maximum.

thanks
darla
 

Re: 120VDC to 12VDC and 5DC

I'm not sure if it would work, but why not tie some resistors in series and pull your voltages of them, assuming you don't need much current.
 

Re: 120VDC to 12VDC and 5DC

If you don't want to use a Buck or a discrete linear regulator you could use this.

TL783C HV three terminal regulator.

http://focus.ti.com/lit/ds/symlink/tl783.pdf

These are under two bucks.

Digikey has them

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-20687-5-ND

I would recommend you use a resistor at the input of the regulator to drop some voltage and spread out the power dissipation.You will have to dissipate 5.4W divide it up between power resistors and the TO pack regulator use a proper heatsink on the regulator!! Then just use a 7805 off the TL783 for your 5V.

[edit] Sorry t_maggot didn't notice you already suggested the 783.
 

120VDC to 12VDC and 5DC

Get a computer power supply! +5 -5 +12 -12
all at your fingertips
 

Re: 120VDC to 12VDC and 5DC

think about it... you cannot reduce volts without dissipating all of them away.. there are a million ways to do this, but they all burn off the same amount and are by definition inefficient since your goal is TO REMOVE ENERGY. and all the easy ways to remove energy is heat..
OR
you can use a dc-dc converter.. transformer will convert v to i
you know.. there are tiny .5"x.5" dc-dc like this:
https://www.murata-ps.com/cgi-bin/c...0e99d5f6271d0c9f8942071a/Product/View/8904409

it can only take 70v in, but stepping down to 70v, and then using this would double efficiency.. plus it would isolate everything from the powerside

i am in this same boat, i just used a mosfet turned on partially to get down to 70v, and then a different model dc-dc converter that has completely floating +15v and -10v outputs... since im driving a 600amp igbt and need the negative voltage to turn off the igbt well.
 

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