EEVBlog #1116 - How to Remove Power Supply Ripple

Circuit building block time. The capacitance multiplier and how it gives almost negligible power supply ripple compared to a voltage regulator.
Whiteboard theory and then some bench demonstrations and experiments. Plus a twist at the end that proves that the "Capacitance multiplier" is perhaps one of the most mis-named circuits of all time.

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[Trent-trnx]

Brilliant, Dave. Wish you did more of this content. Bring back fundamentals Friday!

[FotatoPotato]

Wow, this video just saved my ass... I had 350mv ripple on a crappy power supply at work and it was messing with some of my testing and this circuit got rid of it all! Thanks so much Dave! You're a real life saver!

[herbybey]

Nice explanation, Dave. There is a trap for young players here. If the input voltage ripple amplitude exceeds Vbe-Vce~=0.6V, this circuit doesn't work properly anymore, because the collector voltage drops too close or even below the emitter voltage. At that point, only the base current makes it to the output and there is no current gain anymore. An additional resistor across the capacitor can be used as a voltage divider to solve this issue. This will lower the base voltage, which lowers the emitter voltage, and allows the input voltage to drop lower before there is no current flowing from the collector to the emitter. I ran into this problem with a low power, high voltage boost converter that had more than a volt of ripple.

[tylerhernandez]

5 years later and this circuit just pulled my nearly 200 mV of output ripple voltage to just over 5 mV after a little playing around with various capacitor and resistor values. Absolute gem of a circuit and these videos help us young players immensely as we fall into trap after trap going into actual circuit design rather than just the books. Brilliant, absolutely brilliant content!

[caltech-wirewizard]

@EEVblog Hey Dave, I LOVE your videos! Hands-down... the best in electronics on YouTube! I benched this circuit IDENTICALLY as shown including values for components. (I even used a mini breadboard) to DUPLICATE “EXACTLY” what you used in the video. I used a Switch Mode Power Supply configured for 5v. (Just as you showed in the video). However, I couldn’t replicate your ripple results.

COMPONENTS:
Switch Mode Power Supply Volts: 5.00 (5.001v Actual Output) – Measured using:
Keysight 3458A - 30min+ warm-up
Keysight U1271A

R1 (Base Resistor) = 1k - 1/2watt - 1% (996.83 Actual) - Measured using:
Siglent SDM3055 - recently calibrated - 30min+ warm-up
Keysight 3458A - 30min+ warm-up

C1 = 470uF 35v (486uF Actual) - Measured using:
Siglent SDM3055 - recently calibrated - 30min+ warm-up
Keysight U1271A

RL (Load Resistor) = 270 - 1/2watt - 1% (269.94 Actual) - Measured using:
Siglent SDM3055 - recently calibrated - 30min+ warm-up
Keysight U1271A

Q1 = BD137 – (not a BD137G)

BD137:
R1 Voltage = 57.593mV = 0.057593v (Verified with the above 3 Multimeters)
RL Voltage = 4.2747v (Verified with the above 3 Multimeters)

I1 = 57.78uA = .00005778A
IL = 15.83mA = .01583574A

hFE: 274.069574

Of course, it smoothed out the ripple nicely. However, my ripple numbers are considerably higher than yours. I used a Keysight DSOX2012A to take the measurements. (Essentially the same O-Scope you used in your video). – I wish we had the ability to attach photos here on YouTube. One thing I would like to point out that when I measured, I used a ‘M’ BNC Oscilloscope Probe Adapter & a “Pomona” ‘F’ BNC to Banana-to-Hook Test Leads on the Oscilloscope Probe. This is the best possible connection to give the “FAIREST” test possible so that external Transients were not introduced and won’t skew the measurements. This is why I didn’t use the supplied Oscilloscope Probe “Ground Wire” to Alligator clip.

Ripple PRIOR: (Raw Power Supply output)
Pk-Pk: 40.92mV

Ripple w / “Capacitance Multiplier”:
Base Resistor R1 = 1k (996.83 Actual)
Pk-Pk: 17.64mV

Base Resistor R1 = 10k (10080 Actual)
Pk-Pk: 36.17mV (Pk-Pk went up, (by DOUBLE) NOT Down)

Using the EXACTLY the same parts & essentially the same oscilloscope to take the measurements, how were you able to reduce the Ripple down to: ~ 2.5mV Pk-Pk? Something doesn’t add-up here.

BTW, I agree with you, I don't like the term "Capacitance Multiplier" either. It's really just an RC Filter.

[gjforeman]

Thanks, Dave, for all your efforts. I retired in 2013 after 34 years on the road in the US and Canada as a Biomedical Field Service Engineer. Like many old guys, I have a pretty decent wood shop, but I got to looking at my pile of electronics stuff, collecting drifts of sawdust, and decided to get back into it. Your videos are a great help, renewing what I used to know, and learning new stuff as well. A great help in keeping the old brain cells moving.

[chamrog]

This type of video, where one "building block" is explained in detail is my favorite.

[tocsals]

s. 578 in The Art of Electronics :)
And if the ripple is in the MHz range, you can add a ferrite bead to the base lead of the transistor.

[tomgeorge]

Hi Dave, great video.
I used to service electronic engine analysers many, many years ago.
One brand of analyser, proudly made in Sydney, use the capacitor multiplier in its pos and neg supplies to the scope display.
They used a 15inch TV B/W picture tube with magnetic deflection. The scope did not run at TV scan frequencies but swept at 10Hz up to over 1kHz. So the load caused by the deflection circuitry, apart from being quite large, was also not of constant frequency.
The multiplier circuit work a treat and was made up of 4700uF and good old 2N3055 and MJ2955.

[td]

Dave is a knowledgeable teacher. This is one of his more direct and precise tutorials. Informative and enjoyable.

[pcproa]

For years I have been using 3 different names for this circuit among my colleagues.

1. Capacitor Clipper
2. Ripple Clipper

and my personal favourite:
3. Ripple Cripple (May not pass PC 'certification')

[dhpbear]

12:30 - This circuit also provides a soft-start as C charges on power-up

[Cynthia_Cantrell]

In telephony, this circuit ( Rb, C, Darlington Q, and Re) are used as an "electronic inductor." (Re is the load resistor - RL in Dave's circuit). If you measure *AC* impedance from V+ to ground, (or do the math for this circuit) you'll find that at low frequencies, this impedance is Re - which is typically small. At high frequencies, the impedance is Rb, which is larger. In-between, the impedance goes up at 20db/decade - the same slope as an inductor.

This assumes you are below the frequency where Miller capacitance is a problem - above that frequency, the impedance will start dropping again.

This circuit was used to replace the inductance of the ringer coil when newer phones came out. The phone lines were specified to require a certain amount of inductance across the leads when on-hook. When big mechanical ringers were replaced with electronic ones, they still had to keep that inductance in the circuit - hence the "electronic inductor" circuit came to be. The effective inductance of this circuit only needed to appear in the audio band.

When using this circuit for ripple reduction, I've heard it referred to as a "rip-red, " i.e. short for "ripple reducer." In that case, Re is replaced with the load you're reducing the ripple to.

[allaheadflank]

I don't think the phrase "Half a bee's dick" has gotten NEARLY as much use as it deserves

[DJFixNYC]

we usually just hire an intern to watch the scope with one hand on the regulator's Vout control. They've gotta have good reflexes though. And coffee.

[kloneo]

Hands down the most informative long-term active channel with both great insight in complicated stuff but also content for a beginner like me.

[apbosh]

So good you could do one for each day of the week. Methodical Monday, Tuition Tuesday, Whiteboard Wednesday, Theory Thursday, Fundamentals Friday, Strap in Saturday and Sod off it's Sunday. Thanks for all the great content.

[orhanuzunoglu]

Not only very good teacher, also you are very very very very gooood teacher.... Thanks all of your works!!

[abowyer]

I used these (BJT implementation) for the power supply rails feeding VCOs in PLL synthesizer applications many years ago to reduce oscillator modulation due to power supply rail ripple/noise, thus improving phase noise in the design situation.

[hoofheartedicemelted]

Dave I have the early stages of dementia and you should have lost me in the first 5-10 minutes of the video, but had me right up to the end m8. That speaks volumes about the effectiveness of your teaching. This was nothing short of fascinating, and as it happens it's a small piece of the puzzle I'm trying to figure out and put together in a correct way so that it actually works. Liked and Subscribed sir. Thank you.