hi Guys
i need to power an MCU on 60v supply
unfortunately the HV version on lm317 ot 2596 is not available
a friend suggested to connect 2 lm2596 on series for 60v input & use one output
But it didnt work
as a voltage devider to read the 60v dc on analog pin i have used 100k as R1 & 9,09k as R2
using voltage devider calculator & it works But do you have any ideas if i need to use another values?
as i have tested the lm317 :
i set the output to 4.9v using 230ohm resistor & 680 & its ok for regulating 12-15v source (battery on charge)
But when testing on 2 batteries which its about 27v when charging the regulator got hot & the Mcu started to restart
& no its not cheaper than high power Zener diode its almost double the cost
What's the input voltage range of interest? 0...60V? ( Is really 0V "of interest", can it never be a tiny bit above 60.00V?)
What is the ADC's input voltage range (decodable)?
What is the ADC's offset error?
What is the ADC's gain error?
What's the ADC's input current / input impedance?
What accuracy and precision do you expect?
What is your sampling rate?
Basically you need a voltage divider to attenuate the input signal.
From your 100k/9.09k it seems you want to step down 60.00V to 5.00V.
This is the right direction .... but for my way of thinking not a good solution, because:
* it limits at (below) 60.00V, so you can never know whether your input is 60.00V, 60.5V, 63.6V.... thus I'd add some overhead
* you think that the ADC decodes up to 5V ... but it decodes always 1 LSB less than VRef. so for a 10 bit ADC it is about 4.995V (max value 1023 of 1024)
* you did not care about ADC offset error and ADC gain error
* you did not care about resistor tolerance
* you did not consider PCB layout problems like GND-bounce: microcontroller_chip_GND vs resistor_divider_GND
* it seems you use VCC as ADC_VRef .... (which I never do for absolute voltage measurements). VCC is a supply voltage, which is not reliable, it is not accurate, nor is it stable. And every error of VRef you will see as 1:1 error in the ADV result. VCC may be +/-10% off, or 5% ... maybe better. It will vary from part to part, drift with time, drift with temperature, drift with load current and it will be noisy.
Thus you need to decide the expected accuracy and precision (my question above)
For example if you want to read 60V with 0.1V (+/-0.05V) accuracy ... then it's a challenge for a 10 bit microcontroller ADC. It is a 60V/0.1V = 600 ratio....
So if your ADC has internal error of 1024LSB/600= 1.67LSB (or +/-0.8 LSB) you will be in trouble
The allowed error is 0.1V/60V = 0.17%.
So all errors in combination need to be smaller than 0.17%, VRef, resistors, ADC...
So it depends on what you need. It may be a simple solution, or it may become a challenge...
In case you are fine that you get a 60V reading with an uncertainty of +/-3V (+/- 5%) then maybe a good Vcc as Vref is suitable.
But in any other case, if you need better accuracy ... you need extra parts, better parts (tolerance) and new calculations.
Again: Thus I asked for your requirements. It's important to give values with units.
If you can't decide values ... then you don't need us .. then just do it in "trial and error" style.
Klaus
--- Updated ---
Power supply:
I don't understand the benefit of using 2 LM317 in series .... vs a voltage drop with a series zener (instead of first LM317 circuit).
Additionally I'd not use a linear supply to step down 60V to 5V with load currents above 10mA or so.
60V x 10mA = 600mW of heat. Continously wasting 11 times the power of the application
Odd its in a table prior to "normal" spec table, and not labeled as worst case. And normal
spec is input to output differential limitation. But one clearly know there has to be a max input
limitation.....
Also sim may have a crappy spice model. eg. sweep input to 100V and see what happens....
Regards, Dana.
--- Updated ---
Using a Zener as a V drop element :
Regards, Dana.
--- Updated ---
I have seen a Vref diode used as a shunt regulator for a low power micro Vdd supply to get
an accurate Vref for A/D. Obviously micro cannot have a wide variation in its load current,
but is doable in some designs. One has to pay attention to noise on supply rail as well when
using this approach. Alternatively there are also ways during production test to cal out Vdd
errors and store correction factors in EEPROM :
I'd start with "how accurate and how clean does this
kooky supply need to be?"
Like maybe a center tapped isolation transformer, a
half wave bridge and some filter caps is good enough?
60V is not a real popular input or output voltage but
you might find adjustable-output telecom-48V DC-DCs
(now 48V is also popular as server intermediate bus)
that could be "bent upward" (or ones which allow you
to use elect-resistor feedback, or kludge in a series R
to the feedback terminal that "makes it so").
my source which i have to measure & supply my board is 4x12v batteries which on charging can have up to 60v
& yes supply should be clean to power the board
So then you -don't- actually care about anything about the 60V
except surviving it. Yes?
And you have 12V, 24V taps in that battery stack, yes?
If you had told us what you actually need you'd have been done
by now. You could have told us you needed 5V clean from 60V
max rough, min ("whatever", still not stated) at (current? asked
but not answered as far as I can see).
And your 48V battery, 60V charge sure does look like a standard
"48V telecom" power system for which abound small DC-DCs.
Before you throw piece parts at it check out pricing for a done
module. Those folks make their sales by being cheaper than what
you can assemble the parts yourself, for. There's over a hundred
that look suitable (that's part -numbers-, not parts quantity!) at
But back to the battery stack. Those taps can bias a 3-NPN cascode
stack and drop moderate power apiece, 12V*I_load. Like a good ol'
dirt cheap TIP31C. Maybe a hundred ohm base limiting resistor just
for fun. Now your LM317 sits under 11.5V or so (14V charging). All
nice-nice.
Whole stack from 60V to 5V that way is a couple of bucks for TIP31Cs
and LM317. You'll want a proto board probably, 4 heat sinks good for
maybe 20C rise at 10W, and airflow to keep them there. Passives add
another buck if you want decent output ripple. And now you get to
solder and debug and solder some more.
so the expectable battery voltage range will be about:
Min: 4 x 10.5V = 42V
Max: 4 x 14.4V = 57.6V
output voltage is 5V
Max Out-In of LM317 is 40V (let´s use 35V) so IN_to_GND may be up to 40V.
The min Zener voltage needs to be 57.6V -40V = 17.6V.
Let´s say the minimum input voltage should be 10V (IN_to_GND).
Then the maximum zener voltage is 42V-10V = 32V
So 24V is a good compromise.
looking at Farnell the 1N4749A is a low cost 24V, 1W type.
1W / 24V is good for max. 40mA.
This is a single part voltage drop solution, no extra parts needed.
So you are free to choose
* a zener with 18V/20V for a bit higher load current but low cost
* two 12V 1W zeners in series for about twice load current, still low cost
* a 3W zener for higher load current
* zener, R, power-BJT solution for even higher current
Still ... I´m not friend of generating that much (useless) heat. If you consider to use a small plastics case, then you will get into trouble. Or if you consider to run the device 24/7. Or at higher ambient temperatures...
It also means reduced lifetime. Over the thumb every increase of 9°C reduces the lifetime by 50%.
increase by 18° --> 25%
increase by 27° --> 12.5%
and so on.
Thus I´d surely go with a DCDC solution. A quick farnell search gives MP4569GN-Z as low cost.
(Didn´t check any details)
so the expectable battery voltage range will be about:
Min: 4 x 10.5V = 42V
Max: 4 x 14.4V = 57.6V
output voltage is 5V
Max Out-In of LM317 is 40V (let´s use 35V) so IN_to_GND may be up to 40V.
The min Zener voltage needs to be 57.6V -40V = 17.6V.
Let´s say the minimum input voltage should be 10V (IN_to_GND).
Then the maximum zener voltage is 42V-10V = 32V
So 24V is a good compromise.
looking at Farnell the 1N4749A is a low cost 24V, 1W type.
1W / 24V is good for max. 40mA.
This is a single part voltage drop solution, no extra parts needed.
So you are free to choose
* a zener with 18V/20V for a bit higher load current but low cost
* two 12V 1W zeners in series for about twice load current, still low cost
* a 3W zener for higher load current
* zener, R, power-BJT solution for even higher current
Still ... I´m not friend of generating that much (useless) heat. If you consider to use a small plastics case, then you will get into trouble. Or if you consider to run the device 24/7. Or at higher ambient temperatures...
It also means reduced lifetime. Over the thumb every increase of 9°C reduces the lifetime by 50%.
increase by 18° --> 25%
increase by 27° --> 12.5%
and so on.
Thus I´d surely go with a DCDC solution. A quick farnell search gives MP4569GN-Z as low cost.
(Didn´t check any details)
actually i didnt use zener diode this was before & i dont know about reverse zener Diod voltage drop
i've suplllied 48v through 2x20v 1.3w Zener diode to lm2596 DCDC converter & its ok for now until i can get HV version of DCDC converter
What's the input voltage range of interest? 0...60V? ( Is really 0V "of interest", can it never be a tiny bit above 60.00V?)
What is the ADC's input voltage range (decodable)?
What is the ADC's offset error?
What is the ADC's gain error?
What's the ADC's input current / input impedance?
What accuracy and precision do you expect?
What is your sampling rate?
Basically you need a voltage divider to attenuate the input signal.
From your 100k/9.09k it seems you want to step down 60.00V to 5.00V.
This is the right direction .... but for my way of thinking not a good solution, because:
* it limits at (below) 60.00V, so you can never know whether your input is 60.00V, 60.5V, 63.6V.... thus I'd add some overhead
* you think that the ADC decodes up to 5V ... but it decodes always 1 LSB less than VRef. so for a 10 bit ADC it is about 4.995V (max value 1023 of 1024)
* you did not care about ADC offset error and ADC gain error
* you did not care about resistor tolerance
* you did not consider PCB layout problems like GND-bounce: microcontroller_chip_GND vs resistor_divider_GND
* it seems you use VCC as ADC_VRef .... (which I never do for absolute voltage measurements). VCC is a supply voltage, which is not reliable, it is not accurate, nor is it stable. And every error of VRef you will see as 1:1 error in the ADV result. VCC may be +/-10% off, or 5% ... maybe better. It will vary from part to part, drift with time, drift with temperature, drift with load current and it will be noisy.
Thus you need to decide the expected accuracy and precision (my question above)
For example if you want to read 60V with 0.1V (+/-0.05V) accuracy ... then it's a challenge for a 10 bit microcontroller ADC. It is a 60V/0.1V = 600 ratio....
So if your ADC has internal error of 1024LSB/600= 1.67LSB (or +/-0.8 LSB) you will be in trouble
The allowed error is 0.1V/60V = 0.17%.
So all errors in combination need to be smaller than 0.17%, VRef, resistors, ADC...
So it depends on what you need. It may be a simple solution, or it may become a challenge...
In case you are fine that you get a 60V reading with an uncertainty of +/-3V (+/- 5%) then maybe a good Vcc as Vref is suitable.
But in any other case, if you need better accuracy ... you need extra parts, better parts (tolerance) and new calculations.
Again: Thus I asked for your requirements. It's important to give values with units.
If you can't decide values ... then you don't need us .. then just do it in "trial and error" style.
Klaus
--- Updated ---
Power supply:
I don't understand the benefit of using 2 LM317 in series .... vs a voltage drop with a series zener (instead of first LM317 circuit).
Additionally I'd not use a linear supply to step down 60V to 5V with load currents above 10mA or so.
60V x 10mA = 600mW of heat. Continously wasting 11 times the power of the application
what do you suggest to use as Vref & what calculations do i need for measuring 0-64v?
im not intersted really of 0v lets say the measuring range is 40-64v
would you please suggest again where & how to start ?
Your project combines high and low voltage. As you experiment at getting things to work right, it's expected to burn up a few devices. I prefer to assemble simple cheap components as I develop a project. When I put together my home backup power system, I built my own 24V charge controller. Also several meters containing 3914 bargraph IC's. So that I had a notion how to fix things going wrong during pioneer living.
That's only one viewpoint. There's nothing wrong with purchasing a commercially manufactured unit. A DCDC converter will have safeguards. Nevertheless, if you buy a DCDC converter, consider buying more than one because you may need replacements.
Furthermore nowadays I need to hope they ship the correct item, and hope I chose an item compatible with my equipment, and the instructions are in clear English so I don't break it the first time I use it, and it's not a fake knock-off...etc.
Re my suggestion above, I went and drew you a map.
You may need to play with the base resistor and/or add some bleed resistors or capacitors across the NPNs if they start to sing (resistive base feeds can act like a synthetic inductor, sometimes, I would not put a bare base to the batteries although a power device ought to be rugged enough.
Part Number: LM317 I understand that the 40V rating is the maximum drop-out voltage and that the LM317 can be used at higher voltages as long as Vi-Vo is <40V.
hi Brad
i have tested this circuit on 12v & used 4.7v Zener diode with 470ohm so i get 4.9v which its what i need
but when i have supplied 60v for test the resistor & transistor got burnt
im using bd139 npn transistor which in datasheet the emmiter collector voltage is 80v
so the expectable battery voltage range will be about:
Min: 4 x 10.5V = 42V
Max: 4 x 14.4V = 57.6V
output voltage is 5V
Max Out-In of LM317 is 40V (let´s use 35V) so IN_to_GND may be up to 40V.
The min Zener voltage needs to be 57.6V -40V = 17.6V.
Let´s say the minimum input voltage should be 10V (IN_to_GND).
Then the maximum zener voltage is 42V-10V = 32V
So 24V is a good compromise.
looking at Farnell the 1N4749A is a low cost 24V, 1W type.
1W / 24V is good for max. 40mA.
This is a single part voltage drop solution, no extra parts needed.
So you are free to choose
* a zener with 18V/20V for a bit higher load current but low cost
* two 12V 1W zeners in series for about twice load current, still low cost
* a 3W zener for higher load current
* zener, R, power-BJT solution for even higher current
Still ... I´m not friend of generating that much (useless) heat. If you consider to use a small plastics case, then you will get into trouble. Or if you consider to run the device 24/7. Or at higher ambient temperatures...
It also means reduced lifetime. Over the thumb every increase of 9°C reduces the lifetime by 50%.
increase by 18° --> 25%
increase by 27° --> 12.5%
and so on.
Thus I´d surely go with a DCDC solution. A quick farnell search gives MP4569GN-Z as low cost.
(Didn´t check any details)
hi Klaus
ive tested 3x12v 1w zener diodes to reduce 36v & when i've tested this with multimeter its ok the 36v got reduced
but when i've connected an lm2595 DC DC converter the diodes got burnt & shorted & the DC DC module got burnt also even without any load
Re my suggestion above, I went and drew you a map.
You may need to play with the base resistor and/or add some bleed resistors or capacitors across the NPNs if they start to sing (resistive base feeds can act like a synthetic inductor, sometimes, I would not put a bare base to the batteries although a power device ought to be rugged enough.
hi
your suggestion is expensive one & need more wires to batteris & its not clear for me how this works
forget about the 4 batteris & lets assume i have 60 volt i want to step it down thats it
simply this is the zener diodes connection i used
but when connected an DC DC lm2596 module to the output of the diodes everything got burnt even without any load
You are a bit too economical in providing information. How can we imagine a lm2596 module? Has it a large input and output capacitor? Inrush current might overload the zener, a protective series resistor is suggested. How did you make the test, just unconnected the circuit to an unlimited 60V source?
hi
your suggestion is expensive one & need more wires to batteris & its not clear for me how this works
forget about the 4 batteris & lets assume i have 60 volt i want to step it down thats it
my source which i have to measure & supply my board is 4x12v batteries which on charging can have up to 60v
& yes supply should be clean to power the board
BOM cost for three NPNs and three resistors ought to be under $5
(heat sinks and insulators, you would need to figure). The extra wire
ought to cost you a couple of pennies.
You'd still likely be money ahead using a mini-brick DC-DC but evidently
this is not a matter of urgency or practicality.
You are a bit too economical in providing information. How can we imagine a lm2596 module? Has it a large input and output capacitor? Inrush current might overload the zener, a protective series resistor is suggested. How did you make the test, just unconnected the circuit to an unlimited 60V source?
how am i supposed to make the test ?
i have tested the 3 zeners in series without load & it reduced the voltage But when i connected ito to thw input of the module everything Burnt
also i have tested the basic NPN transistor regulator but it didnt work
BOM cost for three NPNs and three resistors ought to be under $5
(heat sinks and insulators, you would need to figure). The extra wire
ought to cost you a couple of pennies.
You'd still likely be money ahead using a mini-brick DC-DC but evidently
this is not a matter of urgency or practicality.
unfortunately wiring more cables is a big matter
if i could do this my problems is so easy so i can measure the 4 batteries & add one more wire to power my circuit from 1 battery only
Dear Johnny,
After several weeks, I hope you may have learned a valuable experience to spend more time on design specifications and less time on trial and error.
Always define your goals first for inputs, processes outputs, acceptance tolerances, sensitivity to environmental load changes, heat, noise. Then compute thermal losses, thermal resistance, heat sink to limit case rise and junction rise to 85'C max.
Also learn to test with low input voltage and increase safely so as not to explode boards.
When you do this you must estimate source impedance, load impedance @ f, surge currents.
Vin min,max=
Vout min,max =
I out min, max=
% Error budget: ADC, R tolerances, EMI =
Max Hotspot lead rise = 40'C
Max ripple /rated I ripple = 50%
Max ambient inside. = ?
Lightning protection =?
ESD protection?
etc
If time is no object, ok, otherwise get advice early and review design several times with mentors.
hi Brad
i have tested this circuit on 12v & used 4.7v Zener diode with 470ohm so i get 4.9v which its what i need
but when i have supplied 60v for test the resistor & transistor got burnt
im using bd139 npn transistor which in datasheet the emmiter collector voltage is 80v
Dear Johnny,
After several weeks, I hope you may have learned a valuable experience to spend more time on design specifications and less time on trial and error.
Always define your goals first for inputs, processes outputs, acceptance tolerances, sensitivity to environmental load changes, heat, noise. Then compute thermal losses, thermal resistance, heat sink to limit case rise and junction rise to 85'C max.
Also learn to test with low input voltage and increase safely so as not to explode boards.
an easy solution for my problem is to get an HV version of any regulator which its not available here
i was looking for other solutions for test & i've failed & i have posted here what happened exactly
so maybe one of the members who suggested another way of reducing voltage reads what im facing
& help me enhancing the solution to get it work
execuse me im not that good in english even in electronics & formulas so sometimes i need some ideas
& sometimes i have to test
Designing efficient clean SMPS power supplies is not easy without the technical details. The better choice for you is to buy a supply and learn how it works from testing. This is not a beginners project. Linear supplies on the other hand are easy to design electrically but the ratio in Vin/Vout is also the multiplier for input power which must be dumped into heatsinks. So 60/5V is 12 times the load power. This is basic thermodynamics but essential to learn.
hi
i have made the same circuit & 470ohm resistor was connected on series with 4.7v zener diode to increase the output alittle bit
as i need 4.9v & the available zener diode is 5.1v
as i think as a reference does it have to be 10w resistor ?
did it really the BD139 can handle 80v?
Designing efficient clean SMPS power supplies is not easy without the technical details. The better choice for you is to buy a supply and learn how it works from testing. This is not a beginners project. Linear supplies on the other hand are easy to design electrically but the ratio in Vin/Vout is also the multiplier for input power which must be dumped into heatsinks. So 60/5V is 12 times the load power. This is basic thermodynamics but essential to learn.
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