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If I put 5v in a 5v voltage reg, will 5v come out? Answered

What kind of voltage drop should I expect if I put 5v in a 5v reg?

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Goodhart (author)2009-09-19

According to the spec sheet for a 7805 regulator ; with a 7v-20v input, you will get a 4.75v-5.25v output (min-max). Below this and the regulator drops out.

Now, this doesn't mean that voltage will no longer flow, but that regulation is no longer occurring. That is, the regulator is not holding the specified voltage range, and any internal resistance will degrade the voltage out, and any ripple current control, etc. will no longer be controlled.

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mhkabir (author)Goodhart2009-09-19

Is he using a 7805 based regulator???

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Goodhart (author)mhkabir2009-09-20

I only gave that as an example.

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steveastrouk (author)Goodhart2009-09-19

Tsk Tsk. VOLTAGE NEVER FLOWS.

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Goodhart (author)steveastrouk2009-09-19

Voltage is never static either ;-)

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Laserman595 (author)2009-09-19

Almost, around 4-4.5v. If 5v does come out it will fluctuate, according to the 7805 voltage regulator schematic a constant 5v will come out ,if a constant 7.5-20v is supplied.

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seandogue (author)2009-09-19

A switching regulator? Perhaps. But you will lose power. A linear? nope.

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mhkabir (author)2009-09-18

For 5v in, you would get about a two volt voltage drop due to regulator electronics dissipating about 1.93 volts as heat.so 3v out . By the way, what regulator are you talking about??They use different chips, so more/less dropping in output.Most regulators work satisfactorily with a 9v in to compensate with all drops in output. To 'regulate' the voltage AND make the current smooth, the drop is necessary to maintain smooth flow of current.The heat from the chip is because of the voltage drop. Good Luck Kabir

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steveastrouk (author)mhkabir2009-09-19

Good answer, but bear in mind that a linear regulator doesn't get warm because it is dropping VOLTS, it drops it because current is being drawn as well, and the current drawn x voltage dropped power is dissipated in the regulator - if there is a lot of current, it will be warmer than if there is a little. Steve

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AndyGadget (author)2009-09-19

As mhkabir says, you need to supply more than 5V to get a regulated 5V output. Any less than it needs and you'll lose all regulation. The common 7805 type needs at least 2V 'overhead' to work properly. There are low dropout types (such as the LM2954) which only need 0.5V above the regulated voltage.

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orksecurity (author)2009-09-18

At a guess, I'd expect about 4 to 4.5 volts out.

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