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- เผยแพร่เมื่อ 14 ก.ค. 2024
- Linear Power Supply Circuit [LM317, LM337, Adjustable & Low Noise]
A single-output transformer
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Article Source: www.pcbway.com/blog/technolog...
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Features:
AC - DC Conversion
Double output voltages (Positive - Ground - Negative)
Adjustable positive and negative rails
Just a Single-Output AC transformer
Output noise (20MHz-BWL, no load): Around 1.12mVpp
Low noise and stable outputs (ideal to power Opamps)
Output Voltage: +/-1.25V to +/-25V
Maximum output current: 300mA to 500mA
Cheap and easy to solder (all component packages are DIP)
A double output low noise power supply is an essential tool for any electronics enthusiast. There are many circumstances that a double-output power supply is necessary such as designing pre-amplifiers and powering OPAMPs. In this article, we are going to build a linear power supply that a user can adjust its positive and negative rails independently. Moreover, just an ordinary single-output AC transformer is used at the input.D1 and D2 are rectifier diodes.
C1 and C2 build the first noise reduction filter stage. R1, R2, C1, C2, C3, C4, C5, and C6 build a low pass RC filter which reduces noise from both positive and negative rails. The behavior of this filter can be examined both in theory and practice. An oscilloscope with a bode plot feature can perform these measurements, such as a Siglent SDS1104X-E.IC1 [1] and IC2 [2] are the main regulation components of this circuit. According to the IC1 (LM317) datasheet: “The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 37 V. It requires only two external resistors to set the output voltage. The device features a typical line regulation of 0.01% and a typical load regulation of 0.1%. It includes current limiting, thermal overload protection, and safe operating area protection. Overload protection remains functional even if the ADJUST terminal is disconnected”.As it is clear, this regulator introduces good line and load regulation figures, therefore we can expect to get a stable output rail. This is identical to the IC2 (LM337). The only difference is that this chip is used to regulate the negative voltages.D3 and D4 are used for protection. The diodes provide a low-impedance discharge path to prevent the capacitors (C9 and C10) from discharging into the output of the regulators.R4 and R5 are used to adjust the output voltages. C7, C8, C9, and C10 are used to filter the remained output noises.
#adjustable_power_supply
#LM317
#LM337 - วิทยาศาสตร์และเทคโนโลยี
Effectively this is using two halfwave rectifiers one for positive one for negative. This means each polarity isgetting supplied with intermitent pulses of power. Even with the complex input filters pulsating dc will arrive at the regulators. This maybe ok for non critical low current applications, but for things like quality audio a tranformer with two secondaries and fullwave rectification is needed.
My claim also confirms your comment. for high current applications, even a full wave rectifier is not enough and we need stronger filtering methods, in future, I will cover that
One thing I dont remember hearing being mentioned is fusing at the transformer side. Can anyone elaborate please.
Nice way to get also negative voltage! But with this design you need that extra filtering caps, which you have. Good job.
This is one of the easiest and cheapest methods
👍
Cool but no heatsink - i like to do the RC filter too ... i've designed similar but the single supply rectifier approach is very nice. I learned something from this design.
Thanks, actually what you see is not necessarily a final product to be used "as it is", so I only install heatsinks for testing purposes or no heatsink for this test, because the load is small.
Hi, really nice designg and well done PCB. I like it. Tnx. However the next step in improving the design would be the so called tracking dual power supply style where you only need 1 adjustable potentiometer to adjust 1 rail only and when you do that then the other rail will automatically self adjust the very same voltage level. There are some old IC's that do that + short circuit protection as well but they are no longer manufactured and very hard to get. So it would make sense if you could design such a circuit with individual components and perhaps add some heat sink so the circuit can be used for current values that exceed 1A per rail.
Thank you very much for you suggestion. That's interesting, however in this design I also intent to address the cases where both rail are not necessarily identical. for example positive rail could be +5V and the negative could be -12V.
Adding 10μF bypass capacitor from ADJ pin to GND can improve PSRR for additional -7dB.
Thanks
@@MyVanitar You can see in LM317/LM337 datasheet that manufacturer recommended to to add bypass capacitor between ADJ and GND pins for lowering PSSR about -7dB but with good relationship between bypass capacitor and output filter capacitor it is possible to lower much more PSSR then just add that 10μF between ADJ nd GND pins. TNT audio measure and experimeted with this relationship and conclude that is very good PSSR rejection and relationship between that two capacitors are 22μF on bypass and 220μF at output filtering capacitors (C9/C10 on your scheme). Result is additional --20dB reduced PSSR and now is under -80dB at final measurements. In case if you add bypass capacitor than you need to reconnect diodes D5/D6 directly from ADJ to OUT pins on LM317/LM337 because now that diode have this line cuted with bypass capacitor and now does not have direct connection between that pins (see LM317/LM337 datasheet). I like your schematics because does not need dual transformer output and it is simple to add another power supply in parallel with different voltage eg. 5V in parallel with same transformer. In that case we can have +/-12V and another +5V dual power supply for many different aplications eg. FY6800/6900 function generator need better power supply instead of junk inside them and I see that your scheme have realy nice perspective for that. Many thanks for your great scheme.
@@FileFixer007 Thank you very much for the information. Yes this circuit is useful in many double supply scenarios, where each supply rail can be adjusted individually.
Hi ! thank you very much for your excellent video ! i have at hand a preamp that needs +/-24V The present power supply is based on fixed voltage regulators providing negative e positive voltage. What would be your choice of circuit to get the minimum noise ? the circuit has low distortion already but noise depends a lot on the quality of the power supply of course. Kind regards, gino
Thanks Gino. In all power supplies, the output noise increases by increasing the output current, so if your load is an PreAmp, this circuit will work perfectly. However check the current consumption of your circuit for confirmation. if I remember I selected the input/output capacitors to be 35V or 50V, decide based upon your application. Since your load consumes low current, you won't need to keep the input voltage much higher than the output.
@@MyVanitar Hi thanks a lot for the kind advice. Do you sell the boards or the kit maybe ? or have a link to a seller ? as i said i would need a low ripple +/-24VDC power supply. I was thinking to buy a lap one but it is too big and the best ones are also very expensive units. The other option could be an additional regulation stage before the +/-24V stage in series. I am a quite undecided. The preamp in question is decent an old Bryston 0.5B ... it is low distortion but channels separation could be better i understand. Kind regards, gino
Since this works with only 1 transformer secondary, I wonder why 2 are used so often.
I'm planning to build a variation on this using an LM2940T-5.0 and an LM2990T-5.0 to give +/-5V outputs. Thanks for the design!
Thanks
Me again. Thanks for all the help so far.
What I need is a 1amp power suply but wanted to ask if using bigger caps and removing r1 and 2(I have noted it will be more noisy) would slow for higher currents. Alternatively could I ask your assistance in drawing up a on 317 337 power suply that would allow 1 amp. Thanks a Lot for your help
Could you test the output voltage at maximal und medium current. With no load is every linear controlled power supply fine.
The output voltage does not get affected by the load (output current increase). More output current just means more output noise and this is true for all power supplies. regulators keep the output voltage untouched, however, increasing output current causes more voltage drop on components. for example you can not get 12V output from a 12V transformer at the input. So in such cases the input voltage must be higher to compensate the drop. V=R*I, so at 500mA output, a 10R resistor will case 5V voltage drop. Therefore this circuit mainly get used in low current and noise sensitive applications such as a pre-amplifier ... etc
Good day. I have bought 5 of your boards they work great. I have a problem with one of my powersuply and wanted a little advise. R1 gets really hot on start up. I am use a 3 wqtt 10r . I just wantedto know if the power suply would work without the resistors R! and R2. Thanks
Yes, it will work, but the output noise increases. you can use resistors with lower values or short the resistor's footprint by a wire (jumper). This is actually an RC filter.
This is mainly a low current, low noise power supply for sensitive circuits (using that RC filter)
Thanks
I need help sir. I have built lm317/337 psu and i don't have oscilloscope but only dmm. My ouputs are dead locked to +/- 15VDC as per my needs. But please tell me, is it normal to get 16mV AC on those regulated ouputs? To me 16mV Ac sounds a lot? Pcb is my own design based on VRDN power supply
Did you design this circuit on your own PCB? The output should not be like the one you mentioned. if you get a high current from output, the noise level increases, but for low currents, you should not read that
How robust is the output voltage of the circuit to variations of the input voltage? For example, if the mains voltage drops from 230V to 180V, will the output voltage also drop by 20%?
No. it depends on the difference between the input/output voltage. if the input voltage does not fall off this range, nothing will happen. you as a designer should predict such situations, if they could happen
have you ever used a digital potentiometer ?
You want a digital control? yes it can be
good day i want to convert irobot roomba battery to li ion battery. This is a very common issue. How can I do charge voltage ranges from 7 to 20v .. 3200ma - 14.4v 5200ma liion battery
Replied you on another video
does it have a short circuit protection???
Yes, LM317 provides. besides output current is limited
Internal short-circuit current limiting und Thermal overload protection. www.ti.com/lit/ds/symlink/lm317.pdf?ts=1593186876030&ref_url=https%253A%252F%252Fwww.google.com%252F
Nice but, ripple needs to be tested at maximum load condition and usable frequency but yeah I liked it.
Yes, this circuit has been designed for sensitive circuits and low current applications. check my other projects as well.
HOW MANY WATTS SHOULD MULTITURN BE?
Just check what I have used. very low power potentiometers.