The high voltage LM317HV series of ICs will allow to go beyond the traditional voltage limits of an LM317 IC and enable controlling supplies that may be as high as 60V.
0-60V Regulation with a Single IC LM317
Therefore now you can build a universal 0-60V regulated power supply circuit loaded with all the essential features of a work bench test power supply circuit.
Normally a standard LM317 IC power supply is designed to work with inputs not exceeding over 40V, which implies that you cannot enjoy the features of this wonderful linear device for inputs that may be higher than this limit.
Probably the developers noticed this drawback of the device and decided to upgrade the same with its improved version LM317 HV which is specifically designed to handle voltages upto 60V, meaning now you can exploit all the special features of an LM317 IC even with inputs higher than its earlier specifications.
This makes the IC extremely versatile, flexible and a true friend of all electronic hobbyists who are always looking for an easy to build yet rugged and powerful workbench power supply circuit.
Let's learn how this high voltage LM317 HV design is created for the proposed 0-60V variable power supply circuit operations.
Pinout Configuration of LM317HV
The following diagram shows the pinout diagram of the device LM317HV
Image Courtesy: http://www.ti.com/lit/ds/symlink/lm117hv.pdf
LM317HV 0-60V Regulated Adjustable Variable Power Supply The Design
The next diagram shows the standard LM317HV 0-60V variable regulated power supply circuit, in fact this configuration may be universally applicable to all LM317/LM117, LM338, and LM396 IC family.
Referring to the design taken from its datasheet we can see that the variable resistor or the potentiometer is specified as a 5K pot, but actually this should be much higher than this value, may be around 22K for achieving a complete 0 to max adjustable output.
The input shows a 48V but we can go a bit higher than this and use upto 56V DC as the input, but please do not stretch it to full 60V as that would mean operating the device at the verge of its breakdown limit and this could make the IC vulnerable to damage.
In case you operate it with a 60V input or slightly above this, then short circuiting the output terminals accidentally could cause an instant damage to the IC, that's why it is not recommended to force the IC to work at its full throttle. Below this limit, the internal short circuit protection feature could be expected to work normally and safeguard the IC from any possible short circuiting at the output.
C1 may be included only if the shown circuit stage is over 6 inches away from the bridge rectifier and the associated filter capacitor network
C2 is optional and may be included only to improve performance which would help eliminating all possible spikes or transients in the DC line.
For achieving a fixed regulated voltage, R2 could be replaced with a fixed resistor with respect to R1, this may be calculated using the following formula:
Vout = 1.25(1 + R2/R1),
where 1.25 is the fixed reference voltage value generated by the ICs internal circuitry.
You can also use the following software for calculating the same:
Adding Protection Diodes and Bypass Capacitor
The next diagram shows how a couple of diodes may be added to the basic voltage regulator design for reinforcing the circuit with extra protection, although this may not be too crucial.
Here D1 protects the IC from the discharge of C1 due to an accidental short circuit of Vin with the ground line, while D2 does the same against C2 discharge.
The role of C1 is already explained in the previous paragraph, C2 is used as a bypass capacitor. C2 may be included to further improve the output DC regulation as it would help to eliminate all sorts of ripple voltages that might appear across the output.
Adding a Simple Current Limiter Stage
Although the LM317HV is internally restricted to produce not more than 1.5 amps at the output, in case the output current is required to be strictly below this limit or any other desired limit below 1.5 amp, then this feature could be achieved by adding a straightforward BC547 stage as shown below:
The diagram also shows the complete LM317HV high voltage 0-60V variable regulated power supply circuit in a pictorial format.
Here R1 refers to 240 ohm, R2 could be a 22k pot, and Rc may be calculated using the following formula for achieving the required current control feature:
Rc = 0.6/Max current limit value.
For example if the maximum value is selected to be 1 amp, then the above formula could be calculated as:
Rc = 0.6/1 = 0.6 ohms
the wattage of the resistor could be calculated as given under:
0.6 x 1= 0.6 watts
The diode in the bridge rectifier should be preferably 1N5408 diodes for ensuring a smooth rectification with no heating issues.
C1 may be anything above 2200uF/100V, although lower values will also do for lower current loads and for non critical loads which do not mind slight ripple factor in the line.
The transformer could be a 0 - 42V/220V/2amp.
The 0 - 42V is recommended because after rectification and smoothing this final DC could exceed a little over 55V.
The next article we might possibly discuss regarding the various application circuits using the LM317HV high voltage regulator IC.
PCB Layout (with reference to the second diagram)
Mr. Swagatam, last weekend I successfully built a multi-volt power supply using an LM338 regulator and a 10k ohm pot to power a mini subwoofer amp. I used the existing transformer of the non-working subwoofer(output current unknown). I set the pot to give me 24vdc out. I was getting pretty decent sound at a very low volume setting. But when I turned the volume up a few notches to test, the sound abruptly stopped. I discovered that R1 had burned up. I’m not sure if the pot was ruined or not. Instead of killing the voltage, it increased it from 24vdc to 39vdc, so I may have ruined the subwoofer amp as well. Since I have no info on the transformer’s output(it’s fairly large), I didn’t know how to determine the wattage for the resistors. Any suggestions on how I can beef things up? Thanks for any help.
Buck
Hello Buck, that looks strange, R1 is protected by the pot resistance, and if the pot resistance is reduced to zero, the output voltage would also reduce to 1.25V, so apparently there’s no chance of R1 burning, unless the IC itself is faulty or duplicate this can never happen. Please check your IC output voltage response to confirm if the IC is working.
Thank you, sir. Will check it out, and let you know.
No problem!
Mr. Swagatam, I checked the LM338, and I measured 38.9 vdc on all three legs. I had removed the burned out R1 and the pot, which was sparking when I turned it, so It looks bad too. By the way, I have the LM338 fastened to the back plate heat sink, but electrically isolated from it with insulators. I ordered a pack of five of those and they look new. FYI, the R1 I used was 1/2 watt.
Buck
Mr. Buck, 38V on all pins clearly indicates the IC is damaged, so probably the IC also needs to be changed
Wow, that’s bizarre. I’m trying to figure out what caused the failure in the first place. I turned up the volume a little, which drew more current from the power supply, which then fried R1 and apparently the pot as well, and probably the amp. You said that R1 failing should’ve only caused the IC to shut down, not open up. If the same holds true for the pot, then it looks like the IC may have been faulty to begin with. I’ve seen a few sources say there are fake LM338’s out there, so I’m wondering now if I got some. If anyone else has experienced this, I would like to hear about it. Thanks again, Mr. Swagatam. I really appreciate the guidance.
Buck
Actually I meant to say the opposite, it is the R1 and the pot which got damaged due to a faulty IC, otherwise R1 has no chance of failing.
Mr. Swagatam, I just wanted to let you know that I finally got my power supply to work. I burned up a total of three LM338’s from two different suppliers, two R1 resistors and one pot. On the fourth try, I decided to not solder the LM338 onto the board, but instead butt crimped three flying leads to it and then soldered those to the board. I was wondering if maybe I was damaging them during the soldering process. I also decreased the ac voltage of the transformer and went from 24 vdc to 15 vdc by using the center tap instead of the outer leads. Even at 15 vdc, the subwoofer puts out so much bass that I can’t turn it up very high. I just wanted to say thanks again for your help. Your website is a great resource.
That’s great Buck, however a normal soldering will not damage the IC unless the leads are continuously touched for more than 10 seconds. Also, 24 V is perfectly within the specs of the IC so again that is fine. Anyway, glad you could sort it out finally.
Hello sir, please I need a 90v high voltage regulator input to 0-24v output. Thanks
Sorry I do not have this at the moment
Hai sir…
I have few doubts in Protection diode using in LM317…
If we use protection diode D1,D2 in lm317 .it will protect the o/p short circuit…
If vout short circuit to gnd what happen to ic..ic will damage or not…
In our college lab many varaible power supply damages due to o/p short circuit…
So by using protection diode in lm317 it will help or not..
Hi Kesav,
LM317/LM338 ICs are internally protected from short circuit, overload current and from over heating (thermal protection) so it is virtually indestructible.
the indicated protection diodes are actually not required, because its job is to protect the IC if a short circuit is made from the input side of the IC with a high value charged capacitor connected at the output side.
Since the above possibility is quite unlikely, the shown protection diodes actually do not own much importance, and is not relevant to output short circuit situation….
Okay sir…
But when o/p short circuit happens the IC get more heating…
I’m so affair whether the ic will damage…
If there any protection circuit available pls share me sir…
Bcs many power supplies are got damaged..in college lab..
I’m using 18-0-18v Transformer 1Ampere…
How much size heat sink required for IC317
LM317 already has all the protections in-built so no external means are required, when it heats up beyond a certain level the IC will shut down automatically until the heat returns to lower levels.
you can use the following type of heatsink, and make sure the IC is original, duplicates may not have the above mentioned protections…
https://3.bp.blogspot.com/-C_5QfBQJ9DM/WlnIPyaVA1I/AAAAAAAARaA/kGOJApt7Uo4qU-coCYtfbJJzE5o2CevZgCLcBGAs/s1600/208265.jpg
Thank u sir….
I’m using ic company name is ST…
Is this company good sir…
yes it is good, but the problem is that duplicate companies can also put fake prints, but no problem mostly it should be original
Sir I have some led driver which input is 24 volt AC and out is 54 volt dc.i want to opret it without transformer.can it possible 220 v drop into 24 volt AC or any other ideas.please suggest me.thanks in advance.
Ashok, that may be possible only through a 24V transformer or through another 220V to 24V SMPS…..
however you can try a capacitive power supply also, using the following concept:
https://homemade-circuits.com/2016/07/scr-shunt-for-protecting-capacitive-led.html
replace the zener with a 24V zener in the design
Hello Mr. Swagatam.
Is it possible to change this circuit giving a boost in amperage?
Thanks.
Hello Amadeu, yes that may be possible by implementing the following concept in the above design
https://homemade-circuits.com/2016/10/lm317-variable-switch-mode-power-supply.html