What is it?

This board includes the rectifier, reservoir capacitors and inrush limiter for positive and negative rails. Combine with a suitable transformer, fuse and regulation circuitry to make a nice DC power supply. I created this board for use in my DIY bench supply, but this style of linear power supply is particularly prized for use in audio equipment due to the lack of high frequency switching noise.

Features

• Inrush limiting NTC thermistors protect your fuse from high currents
• Thermistors can be bypassed with a solder jumper on the back if not needed
• Can be used with a single winding transformer or center-tap, see the wiring diagram above (note single winding will increase ripple and voltage drop)
• Mounting holes sized for m3 machine screws
• Keeps your power supply looking neat and tidy compared to point-to-point construction
• Comes assembled as shown in the photos, but you have to supply your own transformer and regulation circuitry

Specifications

• Maximum output: +-25V (AC-in peak voltage must not exceed this)
• Maximum average current (per AC input): 3A
• Reservoir capacitance (per rail): 8800uF nominal
• Ripple @ 15v, 1.5A: about 0.5VPP (measured)
• Voltage drop @ 15v, 1.5A: about 3.5v (after warming up, measured)
• Distance between mounting holes: 1.4" x 2.7" on center

Notes on Voltage

Transformers are typically rated in RMS voltage, but peak voltage determines the rectified voltage. You must make sure your transformer's peak output does not exceed the 25V limit. Take the rated voltage and multiply by 1.414 to approximate the peak voltage, then add some safety margin. I recommend using a 14v single winding or 28v (14-0-14) center tapped or smaller transformer. That corresponds with about +-19v output with no load. Using a center tapped transformer will reduce ripple on the output. If you need higher voltage than that, use the contact seller link and tell me your requirements - I may be able to swap out some components to accommodate.

When choosing your other components, be sure to take the diode, protection and regulator drops into account. For example, if you are using LM317+LM337 regulator and need +-12v, 1.5A output, first calculate the voltage you need to account for the drop. LM317 has about 3v dropout voltage and this board drops about 3.5v at 1.5A, so you need 12+3.5+3=18.5VPP input. 18.5/1.414 ≈ 13v RMS. Finally, make sure that your no-load voltage does not exceed the maximum for the transformer you select. If you select a 14v transformer for this, check that 14*1.414=19.8 is less than 25v.