PSU Capacitors

[oxfordjon]

Hi everybody,

I am building a simple +5 -5 volt power supply to use with IR detector
circuit's on a model railway layout, it uses a 12v transformer, diodes, 7805
and 7905 VR's, etc but requires a couple of electrolytic capacitors that are
marked on the shematic as 220MF, I cannot find any on the web from my usual supplier's, I'm not very good when it comes to capacitor conversion
can anyone tell me the equivelent in Uf, Pf or Nf.

Any help would be appreciated.

 

[audioguru]

220MF is an incorrect way to say 220 microfarads, or 220uF.
Use 0.1uF ceramic discs for the 100nF caps.

 

[oxfordjon]

Thank you

Thank you very much Uncle $crooge for your help, can I be really cheeky
and ask 2 more questions ?..... could you convert the component values for me in the circuit to work from a 12v supply.
And finally I have another circuit that need's a MPS3904 transistor, Radio Shack ref 276-2016, I can't find any reference to a MPS3904 transistor here in the UK and our equivalent to RS is Maplin Electronics.

Sorry to be a pain, Hope you can help.

John

 

[eblc1388]

Re: Thank you

could you convert the component values for me in the circuit to work from a 12v supply.

You need to change both R1 value from 470 to 1K for the circuit to operate at 12V. No other changes required.

And finally I have another circuit that need's a MPS3904 transistor, Radio Shack ref 276-2016, I can't find any reference to a MPS3904 transistor here in the UK and our equivalent to RS is Maplin Electronics.

A transistor has many different attributes that is important for it to function correctly in a particular circuit.

Luckily for your application of driving LED, only two of the attributes are vital. Just look up any transistor such that:

1. a small NPN type, case TO-92 as the original (not as big as TO-3 2N3055)

2. It has Vceo >30V or simply quoted as V >30V

3. (desirable) cheapest will do

 

[audioguru]

Re: Thank you

could you convert the component values for me in the circuit to work from a 12v supply.

What circuit? The IR detector circuit is designed to work from a 12VDC/300mA AC adapter.

I have another circuit that need's a MPS3904 transistor, Radio Shack ref 276-2016, I can't find any reference to a MPS3904 transistor here in the UK and our equivalent to RS is Maplin Electronics.

Any little NPN transistor will work: 2N3904, 2N2222 or BC547. The pins are reversed on a BC547.

 

[oxfordjon]

Thank you

Thank you both very much for your help