Linear Power Supply Circuit [LM317, LM337, Adjustable & Low Noise]

Linear Power Supply Circuit [LM317, LM337, Adjustable & Low Noise]
A single-output transformer

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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

[bobshifimods]

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.

[SebastianScholle]

Nice way to get also negative voltage! But with this design you need that extra filtering caps, which you have. Good job.

[frontier]

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.

[FileFixer]

Adding 10μF bypass capacitor from ADJ pin to GND can improve PSRR for additional -7dB.

[BruceMardle]

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!

[ovi_]

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.

[gino]

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

[CHRlSTlAN]

Could you test the output voltage at maximal und medium current. With no load is every linear controlled power supply fine.

[mahlonkarpaiya]

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

[zahiddogan]

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%?

[radionicapcelica]

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

[samhsavdr]

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

[lillyreyes]

have you ever used a digital potentiometer ?

[ohmware]

does it have a short circuit protection???

[miguelaraujo]

Nice but, ripple needs to be tested at maximum load condition and usable frequency but yeah I liked it.