Minimize Ripple in Rectifier by Waveform, Polarity, Bridge-Type, Inductor, Trafo?

[john-boom]

In a rectifier and RC filter, which combination of waveform, bi-polarity, inductor/cap, and transformer-type will give the least ripple in the output?

My source is 100 kHz AC supplying a transformer. I have control over the supply voltage, wave shape, and polarity, over the transformer type, and over the rectifier / filter design. This question is about how to minimize ripple through selection of those parameters.

My load wants 5V @ 3A (after the filter).

Assume there is no regulator involved. Just AC source, transformer, rectifier, filter. This isn't for safety. My source is already isolated from mains. This is for operational needs.

Ie, how is ripple affected by:

• - an AC source that goes negative on the troughs, vs an AC source that only goes positive, never below 0v?
• - sine vs square source?
• - pulse transformer vs non-pulse transformer?
• - full-bridge vs half-bridge?
• - Use an inductor in the filter? Or just a cap?

ChatGPT says:
To achieve the least ripple in the output of a bridge rectifier and RC filter:

• - Use a bipolar AC source (e.g., a sine wave) rather than a unipolar one, as it results in a higher ripple frequency. [specifically, 2 x f-in]
• - Use a sine wave input rather than a square wave for a smoother, more manageable ripple. [specifically, no harmonics]
• - Use a standard non-pulse transformer designed for power applications rather than a pulse transformer. [i need to understand more]
• - Use a full-bridge rectifier instead of a half-bridge rectifier to take advantage of the higher ripple frequency produced by using both halves of the AC waveform. [specifically, 2 x f-in]

 

[davenn]

an AC source that goes negative on the troughs, vs an AC source that only goes positive, never below 0v?

Well, ALL AC signals have positive and negative parts of their cycle, unless there is some purposely added offset ... usually a DC offset

sine vs square source?

Yeah, sine, as GPT said, a square wave is full of and will generate many harmonics

pulse transformer vs non-pulse transformer?

personally, not sure whar to suggest there

full-bridge vs half-bridge?

Full Bridge leads to better rectification and easier to smooth

Use an inductor in the filter? Or just a cap?

Inductors help as well, specially for higher current supplies

For most PSU's, I have ever build, less than 10A, I have never used inductors
In general, I have only used them, and also in commercial PSU's, on PSU's greater than 20A


cheers
Dave

P.S. ... ohhh and the general rule of thumb is, 1000uF per 1A of current

 

[WHONOES]

Is whatever you are driving intolerant to ripple? If so, what is it?

 

[AnalogKid]

You want a full-wave output from the rectifiers. This can be done either with a non-center-tapped secondary and a full bridge, or a center-tapped secondary and only two diodes. The latter is slightly more efficient, but a center-tapped transformer (and yours almost certainly will be a custom design) is more expensive. The cost difference will be more than the savings from two fewer diodes. How much is the extra efficiency worth?

After that, a cap, a choke, and a cap. This will reduce the output ripple with very little power loss and zero active components. The choke and the second cap form a low-pass filter, so bigger is better.

ak

 

[danadak]

I know you stated no regulator but they have high ripple rejection (representative part) :

---

Caps, for bulk caps Polymer Tants excellent (OS-CON is Polymer) :

---

Pay particular attention to allowed C ESR specs in datasheets, if present. Newer types, especially
LDOs, have min ESR requirements to maintain stability.

Regards, Dana.

 

[crutschow]

There a "swinging chokes" made for power supplies that have a high inductance an low currents, so the inductor doesn't "drop out" between half-cycles, which otherwise would increase the output ripple volage at those low currents.