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Project Notes

#511 Bridge Doubler Split Supply

An AC-powered bridge doubler supply with DC output governed by 7815/7915 ±15V DC linear regulation.



Learnelectronics recently had a good video on Youtube covering the Delon/full-wave bridge doubler circuit, which prompted me to take a closer look at this classic circuit.


I’ve taken some measurements of the basic circuit powered by a 12VAC adapter, and then added ±15V linear (7815/7915) regulation for a handle split-supply unit that could be quite handy on the bench.

The Basic Bridge Doubler

The “Delon” voltage doubler topology comprises two half-wave peak detectors, so the DC output is twice the peak input voltage. This can be used as a single-sided DC supply, or by using the centre tap, as ± split supply.

In my build, I’m using an isolated 12AVC power adapter. If mains supply is used for the circuit, tapping the centre connector can be very unsafe unless care is taken to ensure this is wired to the neutral mains wire.

Any sufficiently-rated rectifier would do for the bridge, however I’m using 1N5819 for low forward voltage to minimise loss. For testing, a 10kΩ resistor is in-circuit as a representative load.



With a couple of LED voltage meters attached, we can see about ±19.5V on the output:


The scope trace below shows the capacitors doing their job as peak detectors, sagging a bit due to the load. In the trace:

  • CH1 (yellow) - AC input
  • CH2 (blue) - positive DC output
  • CH3 (red) - negative DC output


Adding ±15V Regulation

With ±19.5V, that’s just enough headroom for a ±15V regulated supply, so I added regulation with 7815/7915 positive and negative regulators in a standard configuration. I bumped up the output capacitors to 2.2µF to eliminate noise I was seeing on the negative rail.

Since Fritzing lacks good 7815/7915 parts, I redrew the schematic in EasyEDA:

I’m using a couple of nice little 24V Edison indicator lamps on the output as a test load.



The scope trace below shows the capacitors doing their job as peak detectors, sagging a bit due to the load. It’s apparent this is operating pretty much at the load limit before regulation would start to break down. In the trace:

  • CH1 (yellow) - AC input
  • CH2 (blue) - negative DC output before regulation
  • CH3 (red) - negative regulated DC output
  • CH4 (green) - positive regulated DC output


Transferred to protoboard with the following layout. I’ve included some gratuitous LEDs on each side of the supply - a pair of 5mm strawhat LEDs with 4.7kΩ current-limiting resistors. Green for the +15V rail, red for the -15V rail:


Under test with some 24V edison lamps:


Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.