7809 voltage regulator for 12V 2A SMPS Power Supply

Hi

Moonwalker_M said:

Is this a better combination than a buck converter at the output?

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I´m not sure what you are asking for.
What does "a better combination than a buck converter" mean?
And what does "better" mean?
An 7809 has benefits and drawbacks. So it may be "better" in some regard and "worse" in some regard.

Moonwalker_M said:

I'm kind of confused about connecting the 7809 to ground.

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What is the confusion. GND is GND. The GND of the 7809 needs to be connecte to the GND of the meter and needs to be connected to the GND of the 12V supply.

Moonwalker_M said:

Can you advise me on the value of in / out capacitors?

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My advice: Read the datasheet.
And this advice is not meant ironically. No electronics designer can have all datsheet informations of all parts in mind.
If it´s my job: Even for the standard 7809 I´d open the latest datasheet for the latest informations of the manufacturer.

Klaus

Take note of the advice Klaus gives!

However, looking at the DE-5000, it probably only needs about 20mA to operate so yes, you can use a 7809 and although an SMPS will work, it is probably overkill and not economical. GND pin should go to the negative side of the battery connector but you must observe the rules about capacitors at each side of the regulator, they are important and you risk damaging the meter if you don't fit them as advised in the data sheet.

Do be cautious though, when running from a battery the whole thing is 'floating' electrically but if you use an external power source you could be grounding one side of the supply. It won't stop it working but be careful if the probes are used on components on a board which has a different power source or you could short them together.

Brian.

Hi,

betwixt said:

Do be cautious though, when running from a battery the whole thing is 'floating' electrically but if you use an external power source you could be grounding one side of the supply.

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Good point.

Hint: medical power supplies have defined/reduced leakage currents against earth-ground.
There are even cheap power supplies that meet medical power supply specifications.

Klaus

betwixt said:

Take note of the advice Klaus gives!

However, looking at the DE-5000, it probably only needs about 20mA to operate so yes, you can use a 7809 and although an SMPS will work, it is probably overkill and not economical. GND pin should go to the negative side of the battery connector but you must observe the rules about capacitors at each side of the regulator, they are important and you risk damaging the meter if you don't fit them as advised in the data sheet.

Do be cautious though, when running from a battery the whole thing is 'floating' electrically but if you use an external power source you could be grounding one side of the supply. It won't stop it working but be careful if the probes are used on components on a board which has a different power source or you could short them together.

Brian.

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Thank you for the answer.

The original power supply for the device is also SMPS (not linear) as an alternative to the 9V battery. The device also has a dedicated input for 9V power supply. As far as I understood "ground" in this case is the negative (external) part of the input 12V connector. I hope I got it right. The SMPS is connected to 220V (LIVE + NEUTRAL), there is no connection to ground in the literal sense of the word.
According to the datasheet, the regulator 7809 does not need capacitors if it is installed in the power supply housing, so I might try to mount it that way.

Bojan

According to the datasheet, the regulator 7809 does not need capacitors if it is installed in the power supply housing

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Then I would strongly advise you looked at a different data sheet!
The physical placement of the 7809 isn't too important but the capacitors MUST be there and MUST be wired close to the pins. It's an electrical requirement, not a mechanical one. If you omit them you run the risk of the regulator output being unstable and if it goes over-voltage, possibly damaging the meter.

Brian.

betwixt said:

Then I would strongly advise you looked at a different data sheet!
The physical placement of the 7809 isn't too important but the capacitors MUST be there and MUST be wired close to the pins. It's an electrical requirement, not a mechanical one. If you omit them you run the risk of the regulator output being unstable and if it goes over-voltage, possibly damaging the meter.

Brian.

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Thanks again. No, I have no problem setting up capacitors, I just relied on this information.

Moonwalker_M said:

there is no connection to ground in the literal sense of the word.

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In electronics, ground usually refers to circuit common, not earth ground.

Why not use a 9V adapter, such as this?

crutschow said:

In electronics, ground usually refers to circuit common, not earth ground.

Why not use a 9V adapter, such as this?

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It looks okay, there are a lot of positive reviews. I can find 9V power supplies in my country as well, but I'm afraid I will run into something of poor quality. Unfortunately the cost of ordering the "original" power supply is half the price of the device. "Original" because it does not actually exist on the official DER DE-5000 website as an option. I do not know if such an identical power supply from TPLINK (9V, 0.6A) would be appropriate?
I mean new, not burnt.

Hi,

some more information:
Datasheet says:

Although no output capacitor is need for stability, it does improve transient response

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* not needed for stability means: the regulator does not oscillate on it´s own when the capacitor is missing
* improve transient response means: When the load current changes rapidly (microcontroller, LED ON/OFF, motor...) then the voltage may fluctuate and even ring. It needs time for the voltage to stabilize. For a measurement equippment you want quiet, smooth , stable supply.

Datasheet says:

Required if regulator is located an appreciable distance from power supply filter.

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... or "far from the power supply"T this may be centimeters. Usually it´s good design to place the capacitor in millimeter distance to the IC.

The reason is "impedance".

Klaus

to answer you qu: 10uF on the input, 1uF on the o/p - it will work fine for 20mA out, a good idea to bolt or glue the tab to something flat - isolated - just to dissipate that small amount of heat generated ....

Easy peasy said:

to answer you qu: 10uF on the input, 1uF on the o/p - it will work fine for 20mA out, a good idea to bolt or glue the tab to something flat - isolated - just to dissipate that small amount of heat generated ....

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Do you suggest electrolytic or ceramic capacitors?

In this application it isn't too important. I would suggest tantalum electrolytics give best 'bang for your buck', they have excellent performance, long life and small size. Keeping them close to the regulator pins is more important than the exact type.

Brian.

Hi,

if you have: use ceramics, especially at the output.
Did you read the datasheet? Follow it´s recommendation. It´s usually the most reliable information.

Standard electrolytics suffer from high ESR and reduced lifetime (compared to ceramics). If electrolytics, then I recommend low_ESR types.

Klaus

KlausST said:

Hi,

if you have: use ceramics, especially at the output.
Did you read the datasheet? Follow it´s recommendation. It´s usually the most reliable information.

Standard electrolytics suffer from high ESR and reduced lifetime (compared to ceramics). If electrolytics, then I recommend low_ESR types.

Klaus

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I agree that it is always best to follow the manufacturer's instructions, but the fact remains that this regulator dates back to 1970. Its primary function was to stabilize/lower voltage from a battery or linear power supply. Unfortunately SMPS have different characteristics, presence of noise and ripple. I could also find this data in newer datasheets:

- An input capacitor is required if the regulator is placed more than 3 inches from the power supply filter. A 0.33-µF
capacitor on the input is suitable for most applications
- TI recommends a minimum load capacitance of 0.01-µF to limit high-frequency noise.
- The linear regulator input supply must be well regulated and kept at a voltage level to not exceed the maximum
input to output voltage differential allowed by the device. The minimum dropout voltage (VIN - VO) must be met
with extra headroom when possible to keep the output well regulated. A 0.33-µF or higher capacitor must be
placed at the input to bypass noise.

It is a pity that no datasheet specifies which types of capacitors can or can not be used. At least I did not notice such information.