Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

invisible Resistance value

Status
Not open for further replies.
hameeds01

hameeds01

Advanced Member level 2
Joined
Aug 23, 2005
Messages
599
Helped
75
Reputation
156
Reaction score
41
Trophy points
1,308
Location
Islamabad Pakistan
Activity points
4,540
i have a transformerless suppply composed of following components capacitor,Resistance, Bridige and a 5 volt zener diode, input voltage 110 volt output 5 volts but the current is unknown, the problem is that the resistance tha is connected in series with non polar capacitor has burnt away now how i can read the resistance value as there is nothing left behind??
this supply is used to run a small contolling circuit having 10 LED + a 5 volt small Relay
 

In circuits like yours this resistor mainly works like a thermal fuse.
It’s value is usually 1/20>to>1/10 of the impedance of the bipolar capacitor at 50(or 60) Hz.
For example, if the capacitance is 330nF – that’s an equivalent of 9.5kohm (at 50Hz), you may use a 1kohm resistor rated for, I’d say, 1W ..

Rgds,
IanP
 

28_1256991386.gif
 

The 1.5µF capacitor limits the current in the loop to roughly 50mA, so it should be something like 150Ω to 220Ω rated for 1W and the value is not critical ..

Rgds,
IanP
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top