RF board power supply

[disisku_22]

Hi all,
for one of my RF project, I have to provide 5 volts supply to RF transceiver module witch operates in 868MHz, due to space constraints i have go for resistor to step down the 230 volts power supply to 5 volts(without using transformer) and convert to DC 5/3.3 volts by using rectifier.

1. can i go for the resistor option to step down 230volt to power up the RF board? if yes any precaution need to be taken care?

2. is there any other option available to power up the RF board without using transformer.

3. is there will be any 50Hz leakage interference to the RF performance?

Pls suggest for any precaution or for bets option for my above issues.

Thanks.....:-(

 

[tony_lth]

1. No, that's not safe.
3. what's your modulation scheme?
You can use transformer from AC 230V to DC 5V, then use regulator.

 

[vfone]

https://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf

 

[jayce3390]

Yes as tony_lth said, you should use a transformer AC/DC, you need a floating bias voltage supply for your RF transceiver.
Are you grounding the RF receiver with the AC power line ?

 

[disisku_22]

hi tony
1. ok, what would be main reason?
2. planned to use 2 FSK or GFSK or MSK
i can't go for transformer due to space constraints .. project customer specification.

---------- Post added at 14:49 ---------- Previous post was at 14:44 ----------


Hi..jayce3390
again.. due to space constraints...
1. if i have to go for resistor option then i don't have any choice other then grounding to ac power--- i know its not good option?
2 do you have any suggestion without transformer.

---------- Post added at 14:51 ---------- Previous post was at 14:49 ----------


hi.vfone
thanks.. i will go through this.

 

[davenn]

Hi..jayce3390
again.. due to space constraints...
1. if i have to go for resistor option then i don't have any choice other then grounding to ac power--- i know its not good option?
2 do you have any suggestion without transformer.

DO NOT, I repeat DO NOT even consider the resistor way, that is EXTREMELY dangerous and under fault conditions you risk electric shock to yourself or some other person
if it doesnt have room for full sized transformer then use a switchmode supply they are very small these days .... see some of the ones in mobile phone walls charger plugpacks

Dave

 

[tony_lth]

If you use some RC Pi power filter at output, the leakage of 50Hz should have little influence on your transciver.

 

[disisku_22]

hi all
Apart from Risk is there will be any performance affect for transceiver.. as per vfone app-note(attachment) i planned to go with capacitive power supply with RC filter at output and use 2FSK or GMSK modulation,
will i have to go for particular modulation scheme for this kind the power supply option.

waiting for ur suggestion.

 

[jayce3390]

I suggest you to use a Zener diode (and your resistor) with a treshold voltage of 5 volts at the input of the transceiver bias to regulate the voltage.

 

[tony_lth]

hi all
will i have to go for particular modulation scheme for this kind the power supply option.

waiting for ur suggestion.

FSK is good choice for anti-spurs caused by power supply. But QPSK requires more strict near-end phase noise than higher modulation, for passing the MASK.

 

[BigBoss]

Use SMPS ( Switch Mode Power Supply) if you have space constraints.1A SMPS will occupy around 3cmx3cm or less with SMD components.Nowadays, AC/DC offline converters are sold as modules and they are really small.
But do not use transformerless power supply because it will be dangerous and very noisy.

 

[disisku_22]

Hi Bigboss,
it will be great if you can share part number or supplier details, i/p 230V a c, o/p 5V d c.

 

[BigBoss]

Hi Bigboss,
it will be great if you can share part number or supplier details, i/p 230V a c, o/p 5V d c.

The simplest way to buy a low cost, miniature smps module for portable phone charger and use the circuit on your RF board or implement 1-to-1 with its components..
Very practical and straight forward..

 

[jayce3390]

Right, if you can use a phone charger, do it.

But, if you want to design your own power supply, as a starting point you can follow this topology :