I need help creating a transistor circuit for delay

inwo

Joined Nov 7, 2013
2,419
Reset times can be controlled in any of the circuits.

You might as well go with the newer fet design.
I don't have a simulator and too lazy to do math.

Alec_t , what is purpose of D3?

Do you have to protect fet drive?
From high voltage or spike?

I don't do fet's yet. :D
 

inwo

Joined Nov 7, 2013
2,419
Hello and thank you again!

Those Versa-Timers I cannot seem to find a price for one. 2" square seems a bit large?

inwo, would you have any idea on the reset time for those darlington circuits? Thank you! Reset time is controlled LS1 (pilot lite) or resistor.
Start with 5k if you don't want an led or lamp indicator.

Yes, 3 and possibly 5 coils at 16.7mA each. At such a low current, a 2n2222 should work alone.

iimagine, I like the prospect of very low power consumption for the circuit to activate. What kind of FET's or device is that do you propose I look for? Quick reset time? Thank you!

Alec_t, Very well displayed! I like the low part count and release time on that, it appears less than half a second.

I am enjoying all these proposals! Keep it fun for yourselves also, no losing sleep or family time here! Simple, functional and some versatility is my thoughts

Scott
None of the circuits will use much current.
The fet and transistor circuits are almost identical.
The fet can use a larger charging resistor and hence a smaller cap.
The zener in the base circuit allows a higher threshold so it should be about a wash.

Use circuit in #6 for power on delay without switch. Ignore ground. Works rail to rail.
 

Alec_t

Joined Sep 17, 2013
11,538
Alec_t , what is purpose of D3?
It prevents the gate voltage rating from being exceeded.
Do you have to protect fet drive? From high voltage or spike?
Yes. Each relay should have a free-wheel diode across it.
I don't have a simulator
Get one! Very useful. LTspice is a free downlaod from Linear Technology, and the Yahoo LTS User Group has libraries of sim models for free download.
 

Thread Starter

*synonymous*

Joined Nov 29, 2013
35
How about this mod of the circuit in the other thread:-
I am assuming that about any FET with similar characteristics can be subbed into place for the 7805? I don't remember my last SMD soldering skill coming out too super... I also appreciate the small capacitor in this design, thanks again!

Scott
 

Thread Starter

*synonymous*

Joined Nov 29, 2013
35

Alec_t

Joined Sep 17, 2013
11,538
I am assuming that about any FET with similar characteristics can be subbed into place for the 7805?
The FET you linked to doesn't have similar characteristics. Its Rds_on resistance is on the high side at ~10 Ohms. However, if the total current draw for the bank of relays is no more than, say, 100mA you should be ok. The FET dissipation would then be ~100mW.
If you can source that FET cheaply then it's worth a try, and would avoid the need for an external zener.
 
Top