Hello Everyone,

I looking for a schematic for delay on power circuit for 24VDC. I would like solve this problem with componets SMD because i nned instal samll PCB in some device. Could you help me to solve this probelm. I found some schematic but on 12VDC. This PCB must delay power on in relay but author used a THT parts. Could you help me solve this issue.

List parts:
R1 = 1o0K (Resistor to discharge C2, when power OFF)
R2 = 330K (Resistor delay)
R3= 10K
R4 = 10KR4 10K
D1 = 3V zener diode (* option)
D2 = 1N4007
D3 = 1N4148
T1 = BC547
T2 = BC557
C2 = 33uF/25V (Capacitator delay)

 

Use a 555 timer and a 12 or 15V zener, ..

 

The circuit can be used almost for 24 Volt operation:

• Change the Zener Diode D1 to a 6V2 type
  
• C2 never gets more than the Zener voltage, so 25 Volts is OK
• D2 need not be more powerful than a 1N4148
• The relay coil, of course, must be for 24 volts

 

The differences between PTH (Plated Through Hole) and SMT (Surface Mount Technology) devices is the leads. A 10KΩ resistor, whether PTH or SMT is the same thing, plus or minus the leads. Building the exact circuit you show in SMT is as straight forward as using PTH. There are more advantages using SMT than just size. Smaller circuits are (for one thing) less vulnerable to unwanted interference from stray AC signals. There are other considerations as well. But for a simple circuit like the one posted, SMT's advantage will be size.

 

Could someone explain the purpose of D1 and D3? Just trying to understand the circuit completely....

 

D3 is to turn off transistor T1 by pulling the base to 0.7V at switch on, D1 is the Zener clamp diode that sets the charge reference voltage on C2 and the turn on voltage for T1, this charges up and then T1 turns on turning T2 on..

 

Thanks, Dodgy!