use of PWM

Hi I have created a schematic for a project that will enable me to operate the solenoids on a valve unit. I would now like to add a PWM to allow the use of a duty cycle but I am not sure how to do this, any guidance would be appreciated.

Many thanks

I have attached the draft schematic for information.

Regards
Woollster

Why do you need PWM for establishing a duty cycle? Is this for a 'peak-and-hold' type of energisation such as is used for fuel injectors? Or do you simply want to energise the solenoids repeatedly at varying intervals?

My plan is to energise the solenoids repeatedly at varying intervals? I am not clear on the use of PWM's as you may have guessed.

Thank you for your response.

I think the choice is between :-
(1) A pulse generator which provides fixed-width pulses of just sufficient duration to actuate a solenoid and keep it actuated for the desired time, with the interval between pulses being variable. That is fairly straightforward.
(2) If saving current/power is important then the more complicated 'peak-and-hold' type of energisation would be needed during the fixed-width pulse duration, again with the interval between pulses being variable.

Hi alec_t

Thanks for your speedy reply, much apreciated.

I feel that option 1 is the best option, I now need to try and include this into my schematic which may prove more difficuult to do.

(1) A pulse generator which provides fixed-width pulses of just sufficient duration to actuate a solenoid and keep it actuated for the desired time, with the interval between pulses being variable. That is fairly straightforward.

Regards
Woollster

Ok. So now the questions :-
(a) what is the minimum time needed for a solenoid to pull in?
(b) what is the required 'hold-in' time of a solenoid?
(c) what is the required range of time interval between successive actuations of a given solenoid?
(d) will each solenoid have its own timer or are the solenoids to be actuated in a fixed sequence from a single timer?
(e) how much current does each solenoid need to switch on reliably?