What is this component?

[HighPower]

Hi all, this is my first post on the forum. I have a relay controller PCB (that uses a 555 timer) and I am in the process of drawing the circuit diagram for it. The trouble is that I have no idea what the little blue component is. It only has two leads. I'm guessing it could be two components in one. It has 47nS marked on the side of it.

Cheers

 

[ericgibbs]

hi,
Its a 47nF capacitor

Post the circuit when you have finished drawing it, we can double check.

 

[HighPower]

Thanks for your reply. The marking on it is definitely 47nS but I believe you when you say that it is a 47nF capacitor. I have attached the full circuit diagram. Component C6 is the capacitor we are discussing. As you will see, the circuit contains a relay that controls a fuel pump in a car. The design should be such that the relay will only energise if terminal 15 is at 12V and terminal 31b is receiving pulses from the ignition coil. I actually don't understand the circuit if I'm honest.

Can I be cheeky and ask one further question? Can anyone tell from the diagram whether the circuit allows the relay to 'prime' the fuel pump? I mean should the relay energise for a second or two when the circuit is first switched on, whether or not ignition pulses are being received? I imagine there would need to be a capacitor and resistor (CR delay) somewhere to make this happen.

Cheers

 

[DerStrom8]

Thanks for your reply. The marking on it is definitely 47nS but I believe you when you say that it is a 47nF capacitor.
Cheers

Sometimes, a capacitor only says, for example, 47n, which means 47nF. The S may be a type or some other spec of the capacitor.

 

[MikeMl]

Re your schematic: There is something wrong with Diodes D3/D4.

C6 is just a power supply bypass so it is not critical at all.

 

[colin55]

Diodes D3/D4 produce a 90v zener and diode rectification.

 

[MikeMl]

Diodes D3/D4 produce a 90v zener ...

I'll buy that.

... and diode rectification.

How does a symmeteric network rectify? Clamp, yes, but rectify, no.

 

[ericgibbs]

Its a clamping circuit, reverse voltage breakdown.

 

[Mr RB]

I have tested and measured 1N4148 Vr breakdown on a number of occasions, it's usually about 150v.

That schematic should show D3 as a zener diode I believe, as the voltage on the top of D3 won't get very high at all in operation.

I would also check the resistors around the threshhold and trigger pins on the 555, and the pin labelling. Something looks to be not right on that schematic.