Buck converter with recycling timer (fixed timer)

Thread Starter

Kdonald525

Joined Jan 6, 2019
10
Hello, I am looking for a basic circuit design that has a DC input voltage range of 30-42V and an output voltage of 9.5 Volts at less than 1 amp current draw. I need the 9.5 volts on a timer that goes to zero volts and then immediately back to 9.5 volts. This has to repeat every 7 seconds continuously.

I have a controller that won't work correctly unless it sees the 9.5 volts go to zero then back to 9.5 for 7 seconds. It is only at zero volts for less than 1 second.

Thanks
 

crutschow

Joined Mar 14, 2008
30,463
You could use a buck converter such as this to get the 9.5Vdc out from the 30-42V input.
Then you could add a P-MOSFET high-side switch to turn the output voltage on and off, using a 555 timer.
(Do you need a circuit diagram for that?)

Turning the converter on and off for this purpose is problematic.

What is the tolerance on the timing?
 

Thread Starter

Kdonald525

Joined Jan 6, 2019
10
You could use a buck converter such as this to get the 9.5Vdc out from the 30-42V input.
Then you could add a P-MOSFET high-side switch to turn the output voltage on and off, using a 555 timer.
(Do you need a circuit diagram for that?)

Turning the converter on and off for this purpose is problematic.

What is the tolerance on the timing?
Hi, thanks for responding. I think if it's within a second it should still be fine. When you say it's problematic, do you mean if I only used a converter without the mosfet?

I would need a diagram of what you are recommending if that's possible...

Thanks
 

crutschow

Joined Mar 14, 2008
30,463
I think if it's within a second it should still be fine. When you say it's problematic, do you mean if I only used a converter without the mosfet?
Yes.
I would need a diagram of what you are recommending
Ok.
Below is the LTspice simulation off a 555 astable circuit driving a P-MOSFET high-side driver, which should do what you want:
R2 adjusts the MOSFET output OFF time, and R3 adjusts the ON time (higher resistance increases the times).
The P-MOSFET can be just about any with a 12V, 5A or greater rating.
.
What is the nature of the load?

1654888356750.png
 

Papabravo

Joined Feb 24, 2006
19,023
Hi, thanks for responding. I think if it's within a second it should still be fine. When you say it's problematic, do you mean if I only used a converter without the mosfet?

I would need a diagram of what you are recommending if that's possible...

Thanks
A DC-DC converter will exhibit transient behavior at startup and shutdown. You would have to take special care in the design of such a DC-DC converter to make sure that the transients do not affect the operation of the circuit with the unusual timing requirements.
 

Thread Starter

Kdonald525

Joined Jan 6, 2019
10
Yes.
Ok.
Below is the LTspice simulation off a 555 astable circuit driving a P-MOSFET high-side driver, which should do what you want:
R2 adjusts the MOSFET output OFF time, and R3 adjusts the ON time (higher resistance increases the times).
The P-MOSFET can be just about any with a 12V, 5A or greater rating.
.
What is the nature of the load?

View attachment 269177
The 9.5V is going to a scooter controller (from a lithium battery bms) - it appears to be giving the controller this voltage as some sort of "check" to let the controller know the battery is ok. If this wire is disconnected the battery symbol on the display blinks and the scooter no longer works until it's reconnected. I did just try to give the controller a constant 9.5 volts via buck converter and it works fine still. I'm not sure why the original is pulsing to zero every 7 seconds...
 
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