Author Topic: Ripple current / voltage, what is too much?  (Read 5194 times)

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Offline mvs

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Re: Ripple current / voltage, what is too much?
« Reply #25 on: October 26, 2018, 05:25:26 pm »
You need to add some load. Try to set R4 to 10 Ohm.
 

Offline T3sl4co1l

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Re: Ripple current / voltage, what is too much?
« Reply #26 on: October 26, 2018, 05:27:24 pm »
For a 976k (5uA) load?

For a circuit that looks like it's made for, I guess a few amperes maximum load?

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Offline FriedMuleTopic starter

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Re: Ripple current / voltage, what is too much?
« Reply #27 on: October 26, 2018, 05:32:59 pm »
I am trying to reach 500mA-1MA 2V-10V

Ohm law, right?

10V / 0.500 = 20Ohm?

It looks much more realistic:-)

What do you say?
« Last Edit: October 26, 2018, 05:38:13 pm by FriedMule »
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Offline not1xor1

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Re: Ripple current / voltage, what is too much?
« Reply #28 on: October 27, 2018, 07:00:12 am »
I am trying to reach 500mA-1MA 2V-10V

Ohm law, right?

10V / 0.500 = 20Ohm?

It looks much more realistic:-)

What do you say?

your circuit just doesn't make sense
1) the source voltage is too low (5V peak)  |O
  you must take into account:
  a) drop through the rectifier and ripple at the levelling capacitors (how much depends on the current)
  b) gate-source voltage must be higher than the Vgs threshold (how much depends on the current)
  c) drop through the regulator (how much depends on the current)

just use any voltage regulator IC for you first experiments, but read other people posts, study and experiment before trying to design any complicated circuit
 

Offline FriedMuleTopic starter

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Re: Ripple current / voltage, what is too much?
« Reply #29 on: October 27, 2018, 07:03:38 am »
Thank you a lot, I'll happy for all your help:-)
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Offline cowana

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Re: Ripple current / voltage, what is too much?
« Reply #30 on: October 27, 2018, 07:07:52 am »
Your current flowing through R4 is absolutely tiny - which means the capacitors are all basically sitting at full charge, and having to supply significant energy during the 'off' portion of the input waveform.

How does it look if you change the value of R4 to 10 ohms?
 

Offline FriedMuleTopic starter

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Re: Ripple current / voltage, what is too much?
« Reply #31 on: October 27, 2018, 07:11:17 am »
If I change the R4 to other then 20Ohm, I only get a flat line to the picho Ohm.

I am trying to change inV to 20V and see what happens:-)
« Last Edit: October 27, 2018, 07:17:43 am by FriedMule »
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Offline r0d3z1

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Re: Ripple current / voltage, what is too much?
« Reply #32 on: October 30, 2018, 10:15:39 am »
it's a good question, the LED don't like ripple but it will be hard to find such a parameters in the DS

then may be they like tea with both lemon and milk like the young Mr Feynman  :-DD

oh yes, and maybe they like play bongos like Mr. Feynaman  ;)
 

Offline spec

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Re: Ripple current / voltage, what is too much?
« Reply #33 on: October 31, 2018, 08:15:43 am »
I am trying to learn how I determine max allowable power supply ripple for flawless functioning of a component, out from a datasheet, because I can't seem to find out.

+FriedMule

As some of the other members have indicated, afraid you are asking the wrong question here. What you need to determine is what noise plus ripple (N+R) does my particular application require.

For example, if you were just turning a 12V relay on, a 12V supply line with a N+R of 2V would be acceptable.

But if you were building an an audio preamplifier using an operational amplifier you may need a 12V supply line with no more than 100uV N+R.

There is one component where the ripple voltage is fundamentally important. The ripple voltage across a capacitor creates a ripple current through the capacitor. The ripple current causes internal heating and if the ripple current rating of a capacitor is exceeded the capacitor can be damaged. This aspect is most important in the case of power supply reservoir capacitors.

In electronic engineering there are basic design rules (BDR), which everybody uses. For example, to decouple an opamp you would use 100nF low ESR capacitors. You do not generally work out what value capacitor to use because in most cases 100nF will be fine.

Likewise with power supplies. In most cases a mains transformer-bridge rectifier- reservoir capacitor raw supply is adequate for the input to a three terminal regulator, like the LM317 or LT1086. And providing that you use the components specified in the datasheet, you will have a stabilized supply line more than adequate for most circuits, especially if you add the extra capacitors to increase the regulators performance as shown in the data sheet.

Typically, the output supply line from a medium price linear bench power supply would have a maximum N&R of 10mV, so that gives you an idea of the amount of N&R that is generally acceptable.

If you do have a circuit that requires very low N&R supply lines, an often used approach is to fit another low noise regulator running from the supply line of the first regulator. Also local decoupling is used.

There are many factors that affect N&R: layout, especially the 0V line, component type, screening ...

That ends the cracker barrel advice. But I hope you can move on and enjoy your electronics without worrying anymore about ripple. :)
« Last Edit: October 31, 2018, 09:55:10 am by spec »
 
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