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TPS7A4700 low noise LDO regulator PCB

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dziki

Member
Joined 2014
K i n g p i n said:
I finished the 5V version and here are the results (50ohm load gives 100mA).
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An externally hosted image should be here but it was not working when we last tested it.

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Click to expand...

Hello,
Nice one :)

Just 1 question, as there is an output for the cable, isn't that the problem if a one use a long cable ?
It seems to me that Ales said that the cable for the DC output should be as short as possible.

PS
2nd question : How long (max.) can be a cable between this Regulator's DC output and the device to be supplied ?
 
mravlca

mravlca

Member
Joined 2009
dziki said:
Hello,
Nice one :)

Just 1 question, as there is an output for the cable, isn't that the problem if a one use a long cable ?
It seems to me that Ales said that the cable for the DC output should be as short as possible.

PS
2nd question : How long (max.) can be a cable between this Regulator's DC output and the device to be supplied ?
Click to expand...

If you are using longer cable to the powered device, sensing wires are recommended to be used. Sensing wires and power wires must be connected together on the connector that goes into the device. Of course you will not be reaching same noise levels as with short cable.

Best Regards,
Aleš
 
D

diymax62

Member
Joined 2004
Hello AudioH,

have you used them both for +12v and +5v DDAC power supply? Is there any problem about the heating (I've bought a double board one)?

Have you tried the original DDDAC power supply scheme? Are the Aleš's regulator better (or, at least, equal) than the original one?

Best regards,

Massimo
 
mravlca

mravlca

Member
Joined 2009
Back in stock are also power supplies for Raspberry pi.
Price for the one with Meanwell psu is 45€. Without it the price is 35€.
 

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rickmcinnis

Member
Joined 2006
Just ordered a plus/minus kit from EBAY.

Thanks for offering this. Much simpler and, I suspect, better than the TI Evaluation Kit.

I am confused by your power transformer sizing advice.

If this was used to size for a 5 VDC output I come up with a result of approx 4.5 VAC instead of the approx 5.2 VAC the manual states.

What am I getting wrong?

Please let me know.

Thanks and take care,
 
K i n g p i n

K i n g p i n

Member
Joined 2012
streamingplaza.com
rickmcinnis said:
I am confused by your power transformer sizing advice.

If this was used to size for a 5 VDC output I come up with a result of approx 4.5 VAC instead of the approx 5.2 VAC the manual states.
Click to expand...
4,5Vac or also 5,2Vac is very low for 5Vdc output, or you should use a very big capacitor for low ripple voltage, otherwise the ripple will getting below the working voltage of the regulator, but a very big capacitor will give you other problems with very big ripple currents on power on.
I use a 6Vac transformer, after rectifying and smoothing with a 4700uF it will give you around 8 to 8,5Vdc for input, this will give you around 2V headroom.
 
K i n g p i n

K i n g p i n

Member
Joined 2012
streamingplaza.com
Calculation at 4,5V

Transformer: 4,5V
Load: 50 ohm
Ampere: 1A max
Rectifier Voltage: 1,1V
Usec = secundairy voltage transformer (1,41 x Utransformer)
Uc1 = Voltage across smoothing capacitor = 1,4(load) x Usec, this is your input voltage for the regulator.

Formula:
Uinput-regulator minimal = 5 + 1 = 6V
Uc1: ((1,41 x Utransformer) - 1,1) x 1,4 = 6,34V
Your max ripple voltage = 6,34 - 6 = 0,34V

That's not gonna work.


Calculation at 5,2V

Transformer: 5,2V
Load: 50 ohm
Ampere: 1A max
Rectifier Voltage: 1,1V
Usec = secundairy voltage transformer (1,41 x Utransformer)
Uc1 = Voltage across smoothing capacitor = 1,4(load) x Usec, this is your input voltage for the regulator.

Formula:
Uinput-regulator minimal = 5 + 1 = 6V
Uc1: ((1,41 x Utransformer) - 1,1) x 1,4 = 7,56V
Your max ripple voltage = 7,56 - 6 = 1,56V

If you choose a ripple voltage of 1V you need at least a smoothing capacitor of 10.000uF
Ripple current at switch on will be very high and 1V ripple is very tight if you consider that you mains power of 230V will fluctuate 10%.


Calculation at 6V

Transformer: 6V
Load: 50 ohm
Ampere: 1A max
Rectifier Voltage: 1,1V
Usec = secundairy voltage transformer (1,41 x Utransformer)
Uc1 = Voltage across smoothing capacitor = 1,4(load) x Usec, this is your input voltage for the regulator.

Formula:
Uinput-regulator minimal = 5 + 1 = 6V
Uc1: ((1,41 x Utransformer) - 1,1) x 1,4 = 8,96V
Your max ripple voltage = 8,96 - 6 = 2,96V

Ripple voltage ~ 2V will give you a smoothing capacitor of 4700uF.

An externally hosted image should be here but it was not working when we last tested it.



An externally hosted image should be here but it was not working when we last tested it.
 
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