Output ripple.

[Anarchist420]

Is there a general formula(s) for amount of acceptable output ripple? If so, what is it/are they?

What's the maximum acceptable amount of output ripple, for say, my monitor (Apple LED Cinema 24 in) or would it be undefined?

They list its max power consumption, but I've never heard a display maker advertise their monitor's power circuitry was great nor have I ever heard a reviewer mention the quality of a monitor's insides.

 

[C1]

It has been a long ass time ago since I completed my 3 year basic electronics home study course from RCA Institutes (remember them?), but yes, there is a measure for ripple. In fact, the VOM that I built as part of that course had a special section in it with its own input jack just for measuring ripple in dc current. There is also a standard equation that is an index for ripple (dont remember the details - too long ago). Basically, any ripple passed a diode (ie, was rectified) and charged a capacitor. On the meter. the ripple showed as a needle deflection (d'Arsonval Wesson).

You most likely will not find the specification for allowable ripple with you monitor's PS, but if it gets too large my guess is that you would see it as noise and/or brightness flicker. If you are concerned about it, then a likely cure is to replace the PS smoothing capacitors (might even use a bit larger ones).

 

[Anarchist420]

It has been a long ass time ago since I completed my 3 year basic electronics home study course from RCA Institutes (remember them?), but yes, there is a measure for ripple. In fact, the VOM that I built as part of that course had a special section in it with its own input jack just for measuring ripple in dc current. There is also a standard equation that is an index for ripple (dont remember the details - too long ago). Basically, any ripple passed a diode (ie, was rectified) and charged a capacitor. On the meter. the ripple showed as a needle deflection (d'Arsonval Wesson).

You most likely will not find the specification for allowable ripple with you monitor's PS, but if it gets too large my guess is that you would see it as noise and/or brightness flicker. If you are concerned about it, then a likely cure is to replace the PS smoothing capacitors (might even use a bit larger ones).

Thanks🙂 Nothing wrong with my monitor's PS; I just wanted to know what how many mv of ripple is to be expected from a computer monitor's power supply.

 

[PsiStar]

Every device using DC power has different tolerance for ripple. A properly designed DC power supply would just enough margin to be within that tolerance but not necessarily too much to keep cost down.

In other words, "it depends".

 

[Modelworks]

There is ripple and then there is regulation. Ripple is what you get when there is not enough filtering on the conversion from AC to DC, that should be below 1% . Regulation is how tight the tolerance is between the reference voltage and the output, a general rule is 5% for most applications. If you convert 120VAC to 10VDC and only use a 10uf cap for filtering powering a 100ohm load you will have a lot of ripple. If you then take that power and feed it to a regulator you will have ripple in the supply but regulation can still be within range. There is an old term for it ,' AC in the DC'.

You can solve ripple with more filtering where as regulation can be harmed by adding more filtering. If you place a large capacitor on the output of a voltage regulator then you increase the time it takes for the regulator to adjust for changes in the load.

 

[Anarchist420]

There is ripple and then there is regulation. Ripple is what you get when there is not enough filtering on the conversion from AC to DC, that should be below 1% . Regulation is how tight the tolerance is between the reference voltage and the output, a general rule is 5% for most applications. If you convert 120VAC to 10VDC and only use a 10uf cap for filtering powering a 100ohm load you will have a lot of ripple. If you then take that power and feed it to a regulator you will have ripple in the supply but regulation can still be within range. There is an old term for it ,' AC in the DC'.

You can solve ripple with more filtering where as regulation can be harmed by adding more filtering. If you place a large capacitor on the output of a voltage regulator then you increase the time it takes for the regulator to adjust for changes in the load.

Is there anyway to get the best of both (<= 1/8 ripple and <= 3% regulation)? Would that involve any sacrifices?

I know that 120 VAC input gives worse output ripple than VDC input, but does DC input have worse regulation or does it have good regulation in addition to good ripple?

I hope this wasn't a stupid topic.

 

[Modelworks]

Is there anyway to get the best of both (<= 1/8 ripple and <= 3% regulation)? Would that involve any sacrifices?

I know that 120 VAC input gives worse output ripple than VDC input, but does DC input have worse regulation or does it have good regulation in addition to good ripple?

I hope this wasn't a stupid topic.

DC , like from a battery, has no ripple because it doesn't use AC as the source.
AC as a source can be made very close to a DC source with enough filtering. Regulation comes in a lot of different forms. The most accurate form is one that uses a feedback wire. To power a load you would connect the load to the + and - of the power supply and then you attach a third wire , the feedback wire, to the + of the load. What this allows is the regulator to sense the voltage at the end of the wire and adjust the voltage to match the requirements as accurately as possible negating any effect the resistance of the wire would have between the regulator and the load.

You can have extremely low ripple in the source and excellent regulation the only downside are cost of the parts.

 

[PsiStar]

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I know that 120 VAC input gives worse output ripple than VDC input, but does DC input have worse regulation or does it have good regulation in addition to good ripple?

Depends if the output voltage is higher or lower. The easy case is when the voltage is lower. Anything from a simple voltage divider (poor regulation) to 3 terminal regulator to more complex circuits as modelworks mentions.

If the output voltage is higher, then the input DC has to be switched or made into some kind of AC with all of the issues mentioned.

The design of a power supply requires some knowledge of the load. If the load is fixed such as your monitor is, then the design of a power supply's requlation & ripple is easier. If the supply is expected to handle a wide variety of unspecified loads design gets more interesting and expensive depending on the expectations. Unspecified loads means that assumptions are made about the range of loads versus just anything.

You can imagine the difference between the supply for your monitor versus 1.8 VDC supplying 100 Amps to a processor array in which some processors can be put in sleep mode but able to be switched back on in a few clock cycles.

In short, "Is there anyway to get the best of both (<= 1/8 ripple and <= 3% regulation)? Would that involve any sacrifices?" ... yes, just send money and wait.

 

[uclabachelor]

Is there a general formula(s) for amount of acceptable output ripple? If so, what is it/are they?

What's the maximum acceptable amount of output ripple, for say, my monitor (Apple LED Cinema 24 in) or would it be undefined?

They list its max power consumption, but I've never heard a display maker advertise their monitor's power circuitry was great nor have I ever heard a reviewer mention the quality of a monitor's insides.

Unless it's specified in the power supply, no.

If you were designing the power supply, then you would be provided with that figure as part of the design requirements.

If you're trying to look for that figure on consumer products, you'll never find it unless you have access to engineering specs.