24
votes
Accepted
If cost can be ignored, is a higher-value capacitor for ripple suppression always a good choice?
A high value capacitor will cause a current surge when the device is first switched on. The capacitor needs to charge from 0 volts to whatever the circuit voltage is, in a very short time.
In extreme ...
- 19.5k
16
votes
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Ripple voltage filtering capacitor
I've included a snapshot, of sorts, so that you can see what's happening better:
On the main diagram, I expanded out a rectangle and placed it over to the right side so that you might see a little ...
- 78.3k
14
votes
If cost can be ignored, is a higher-value capacitor for ripple suppression always a good choice?
A large value capacitor needs to be charged. A very large capacitor will, at best, take a long time to charge assuming a safely current limited power source, and at worst reduce the life of the ...
- 169k
12
votes
Accepted
Capacitor multiplier does not remove ripple
The all important component that is missing is in the red box below: -
Taken from the EDN article linked by OP.
You have to have the resistor in the red box to bias the base at a few volts below the ...
- 465k
11
votes
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Full wave rectifier with a high DC offset voltage?
No, you can't do that. If you have 5V peak-to-peak riding on top of 100V dc then two of the rectifier diodes will always be forward biased. The other two diodes will see a combined reverse voltage ...
- 31.6k
8
votes
Difference Between RMS noise and PSRR in an LDO
The noise is internal to the LDO and is always on the output whether you power it directly from an SMPS, a battery, or the most perfect noiseless voltage source.
The PSRR is how well the LDO can stop ...
- 56.9k
8
votes
Accepted
Does voltage ripple matter to a relay driven by a transformer?
It won't matter. The relay will pull in when the applied V reaches 9 V. A higher voltage will make it pull in somewhat faster, but that doesn't matter in most applications.
You don't need an 'RC' ...
- 19.4k
8
votes
Bridge rectifier circuit with a step-up transformer
Your supply is 60 Hz and, your primary inductance is 5 μH <-- that is a massive problem on a supply voltage that peaks at 120 volts: -
5 μH at 60 Hz has an impedance of 1.88 milli ohms and, will ...
- 465k
7
votes
Accepted
Large capacitors "producing more I²R heating"?
For a given average current, drawing it in short bursts creates more heating in a resistor than a smooth flow. The reason for this is that current is averaged over time but power is equal to current ...
- 56.6k
7
votes
Capacitor as a ripple filter in the rectifier circuit - difference in charging and discharging time
The time constant for charging and discharging is same. How can charging for a small amount allows it to discharge for such a long time.
No, they are not the same. The capacitor charges from the ...
- 8,567
7
votes
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LTSpice voltage source understanding
No.
Your top plot is in the frequency domain and is called a frequency Bode plot. Notice the axes. X is frequency in decades, and Y is output voltage ( somewhere on top of C1) relative to 1V in ...
- 7,567
7
votes
Accepted
Very high ripple at the output of my converter
It isn't ripple as such; it's overshoot. The part of your circuit that regulates the output voltage to (circa) 750 volts is a little unstable. You need to probably increase the phase margin possibly ...
- 465k
6
votes
Accepted
Ringing/Noise on smps output while BJT turns on
You didn't provide the all-important schematic, so we first have to guess at your circuit, then guess at the cause.
Bad scope probe grounding. Make sure the ground lead of the scope probe is ...
- 314k
6
votes
LM350 not reducing the ripple
Notice in the TI datasheet, line regulation is spec'ed with \$V_{in}-V_{out}\ge 3\ {\rm V}\$. With 11.5 V at input and 8.4 V at output, you just barely meet that requirement.
Possibly the input ...
- 131k
6
votes
Capacitor multiplier does not remove ripple
This should be a comment, but I needed to include a picture:
There are two different kinds of noise on the purple trace. Before trying to design a filter to get rid of this noise, it is important to ...
- 79.5k
6
votes
Accepted
Capacitor sizing for known current load
I would use an easier approach: the capacitor is only needed to act as buffer for the high-current spikes. Just get the duration of the (biggest) spike (t_duration) and the height of the (biggest) ...
- 10.7k
6
votes
Capacitor as a ripple filter in the rectifier circuit - difference in charging and discharging time
The charging and discharging happen through two separate paths, controlled by the rectifier. The charging path has a very low impedance compared to the discharge path (i.e., different time constants), ...
- 175k
6
votes
Flyback converter design using UC3843
I looked at the circuit proposed by TI around the UC3843 and it is truly a Rube Goldberg Machine, especially for the feedback arrangement. Below are the points to look at and correct for a reliable ...
- 22.7k
5
votes
Accepted
Designing a small footprint DC/DC converter
The SW copper pour sticks out too much beyond L1 pin. This does not improve current carrying capacity much but increases noise.
The footprints for capacitors look rather small. Did you cut the voltage ...
- 12.9k
5
votes
Accepted
Why is an inductor rather than a capacitor used to smooth switch mode regulators
In a switching regulator (buck, boost, buck-boost etc.) the inductor isn’t there to smooth the output. It’s there to store and release energy in a controlled way. The input switch will ‘charge’ the ...
- 55k
5
votes
Accepted
Ripple rejection of capacitance multiplier when compared to linear regulators
1 - Why the Capacitance Multiplier has a better response ‘filtering’
the higher frequencies
The very low quiescent current of the MCP1700 suggests that \$gain \times bandwidth\$ product is not ...
- 26.7k
5
votes
Accepted
Bridge rectifier circuit with a step-up transformer
If I were to have to design this on a PCB, what are some tips that I need to follow?
Creepage distances - keep them conservative. 8mm spacing for 1000V would be a good bet I think.
Are there some ...
5
votes
Accepted
Understanding ripple in oscilloscope
As said by @Tim Williams and @Justme, be careful when making oscilloscope measurements with low resolution. In some cases, voltage peaks don't exist, they're artifacts.
Here's a naive measurement (...
- 1,284
5
votes
How much charging ripple voltage is allowed while charging a LiFePO4 battery?
The datasheet for the battery tells you to use constant current in section 4.1: The "Standard Charge" means charging with constant current 0.5C. So that's what you should do. Charging ...
- 4,146
5
votes
Accepted
Inductor magnetic field collapses during switching?
The spikes that you're seeing on the scope trace aren't actually present across the 47µF output capacitor. Instead, what's happening here is that the magnetic field produced by the circuit couples ...
- 20k
4
votes
Rectifier ripple voltage formula
There is a mass of online help to aid calculating this. This one at Hyperphysics is particularly complete with a calculator provided.
- 21.8k
4
votes
Why am I getting this oscilloscope reading? (Half wave rectifier)
Your vertical scale is 20mV-per-division, which is FAR too sensitive. Try a scale voltage of 5V-per-division.
Note the zero-volt symbol at lower left. It is pointing down, indicating that zero volts ...
- 26.7k
4
votes
If cost can be ignored, is a higher-value capacitor for ripple suppression always a good choice?
The larger the capacitor the worse the power factor and the higher the peak current in the rectifier.
This can be largely mitigated by adding a choke between the rectifier and the capacitors.
- 34.6k
4
votes
Accepted
How does the inductor current ripple influence a switch-mode power supply?
The main tradeoffs are as follows:
Higher inductor ripple:
Pros:
Smaller inductor size, better transient response to load step and release.
Cons:
Higher core and AC losses therefore lower efficiency, ...
- 24.1k
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