Fuse alarm schematic help 1

[mcgyvr]

See attached schematic for a fuse alarm circuit. This product uses 2 types of fusing. If only F1 blows the relay is energized, if only fuse 2 blows the relay is energized and D3 illuminates. The problem comes when fuse 1 and fuse 2 have blown. Due to the drops from the transistors/diodes fuse 1 signal is at a higher voltage so D3 doesn't illuminate until F1 has been cleared. (please excuse the bottom LED of D3 it is not in use for this example and my utterly basic knowledge of circuits) I would essentially like to add something (simple if possible of course) between F1 pin 2 and the relay pin 1 to drop the voltage a few volts to let F2 signal be the controlling voltage. or any other ideas would be welcome. Simply adding a 3.7v zener off F1 pin 2 works perfect for one polarity but this product also needs to operate from a positive or negative supply voltage. Also R2/Q1,2/D1-D3 are all included in the fuse holder cartridge and cannot be modified. Any ideas welcome...

 

[VEBill]

Couldn't this sort of function be accomplished using only relays?

 

[mcgyvr]

umm no
A visual indication is required/included on F2 already (purchased part with R2,Q1/2,D1-3 built into its housing). It needs to illuminate when blown and it does with only when its the only blown fuse. F1 has a mechanical arm that extends providing its visual indication so that part is taken care of.

 

[amptramp]

1) How does F1 work, i.e., is there a connection from pin 1 to pin 2 if the fuse blows.

2) Does D3 include 2 LEDs back to back, one LED and one diode back to back, or what?

 

[VEBill]

If one zener works perfectly, then put two in series. Subtract Vf(zener) from the 3.7 volts.

If that doesn't work, then use steering diodes or a bridge rectifier to sort out the zener.


What limits the current through LEDs D3?

 

[mcgyvr]

1) How does F1 work, i.e., is there a connection from pin 1 to pin 2 if the fuse blows.
Yes when F1 blows the mechanical arm connects pin 1 to 2

2) Does D3 include 2 LEDs back to back, one LED and one diode back to back, or what?
D3 is a bi-polar led.

Ve1bll, D3's current is limited by the relays coil resistance.
I will try the 2 in series...

 

[mcgyvr]

VE1BLL, 2 zeners in series did the trick... Thanks.