hi jo,
This is one draft option.
Replace the 2N2222 with your opto's, also not included the solenoid snubber diodes etc...

E

Updated:
Added the opto's etc ...

 

I have been guided before that using MOSFETS for fast frequency switching(like PWN) is not recommended as it reduced the life of the MOSFET in use.

MOSFETs are built to switch fast. In almost every power supply there is a MOSFET switching 100,000 times a second. They do this all day long. And switching 1000 times a second like my example is not fast at all. I have built power supplies where the MOSFET runs at 2,000,000 times a second.

Option 1) Switching power supplies are very efficient. It could take 12V at 1A and make 6V at 1.9A. For one solenoid (12V at 250mA, 6V at 125mA, but with a switching supply the 12V will only see 62mA) I could build a switching power supply that has a input pin. So the computer controls the voltage. The power supply for the solenoid could be set to 12V or 5V by software. Most of the time the supply will be at 5V or 4V but when you want to turn on another solenoid set the supply to 12V, turn on, wait 1mS then set the supply back to 5V. I think you can go from 250mA/solenoid to 60mA solenoid.

Option 2) Because solenoids average out the current sent to them you can switch on/off fast to save power. Using the OE pin on the HV595 you can turn off the current for a short amount of time and save power. Each (MOSFET, Diode, Solenoid) all act just like a switching power supply (MOSFET, Diode, Inductor or coil). Drive the OE pin to off for 2mS then on for 1mS will cut the current to 1/3.

 

hi,
Checking power options, this SMPS unit would give 5V from 12Vdc source.
What is the current rating of the existing 12Vdc power supply.?

https://www.ebay.co.uk/itm/DC-DC-9A-300W-Step-Down-Buck-Converter-Module-Power-Supply-Voltage-Regulator-CY1/303414463759?_trkparms=aid=555018&algo=PL.SIM&ao=1&asc=20131003132420&meid=724507e98ddf41deae598ee3c7af26c4&pid=100005&rk=3&rkt=12&mehot=lo&sd=164025442051&itm=303414463759&pmt=1&noa=0&pg=2047675&_trksid=p2047675.c100005.m1851

Thank you, will check it out. currently im using 12V 10Amp SMPS

 

hi,
If the SMPS has a conversion efficiency of approx 85% [ which is typical] , the 12V at 10A should be OK to drive the SMPS.
E

 

MOSFETs are built to switch fast. In almost every power supply there is a MOSFET switching 100,000 times a second. They do this all day long. And switching 1000 times a second like my example is not fast at all. I have built power supplies where the MOSFET runs at 2,000,000 times a second.

Option 1) Switching power supplies are very efficient. It could take 12V at 1A and make 6V at 1.9A. For one solenoid (12V at 250mA, 6V at 125mA, but with a switching supply the 12V will only see 62mA) I could build a switching power supply that has a input pin. So the computer controls the voltage. The power supply for the solenoid could be set to 12V or 5V by software. Most of the time the supply will be at 5V or 4V but when you want to turn on another solenoid set the supply to 12V, turn on, wait 1mS then set the supply back to 5V. I think you can go from 250mA/solenoid to 60mA solenoid.

Option 2) Because solenoids average out the current sent to them you can switch on/off fast to save power. Using the OE pin on the HV595 you can turn off the current for a short amount of time and save power. Each (MOSFET, Diode, Solenoid) all act just like a switching power supply (MOSFET, Diode, Inductor or coil). Drive the OE pin to off for 2mS then on for 1mS will cut the current to 1/3.

Thank You so much for your knowledge, much obliged.

Your Option 1) "but when you want to turn on another solenoid set the supply to 12V, turn on, wait 1mS then set the supply back to 5V. " This is the main issue. I do have a solenoid that works on 12V with ~120mA current. But same is the treshhold voltage for this too. They need 12V for 1ms then 4V to remain ON.

Your Option 2) Wouldn't controlling OE pin to 1/3 time ON state also hamper the output of all the other solenoids controlled through that perticular hc595? then the same problem of turning another solenoid , would require 12V.

 

hi,
If the SMPS has a conversion efficiency of approx 85% [ which is typical] , the 12V at 10A should be OK to drive the SMPS.
E

ok Eric. Im still studying your circuit Sir .

 

hi jo,
This is one draft option.
Replace the 2N2222 with your opto's, also not included the solenoid snubber diodes etc...

E

Updated:
Added the opto's etc ...

Respected Eric,
Deeply appreciate your kind efforts towards helping me. Will try this circuit out.
Thank You Sir for your efforts and time and guidance!

 

hi jo,
I guess you will build just one driver as a proving circuit.
I will be interested in seeing your test results and any modifications.

As you have used opto-isolators in your design, I assume that you want isolation between the MCU and the drivers,
so the 0V connections I have shown will need to be changed.
E

 

Dear Eric and Ronsimpson,
I am using STM32G474 with 43 PWN pins to control 36 solenoid outputs, that are independently controlled. To operate any solenoid, a full 100% PWM signal would be sent at 12V. This will ON the solenoid. Then a PWN of about 33.3% PWN of 12V i.e. ~ 4V will be sent to save on power and heat to keep them on. The switching is done through the same IRFZ44n MOSFET. My only concerns are here under.

1) I hope the controller supports the operation of 36 outputs independently. all of them work without affecting the operation of the rest outputs.

2)Another issue is that, under volting the solenoid coil through PWN signals is causing a high pitch noise(low volume). The mechanical components are removed then also the noise persists. The noise doesnt come if i give a linear power supply of 4V.

Kindly advice.
Thank you

 

The nasty audible noise is going to be a problem with a PWM solution, unless you drive them above 15-20 khz.

This noise is caused by magnetostriction of the magnetic materials and the windings themselves buzzing away under magnetic forces- very hard to quench this.

 

Dear Eric and Ronsimpson,
I am using STM32G474 with 43 PWN pins to control 36 solenoid outputs, that are independently controlled. To operate any solenoid, a full 100% PWM signal would be sent at 12V. This will ON the solenoid. Then a PWN of about 33.3% PWN of 12V i.e. ~ 4V will be sent to save on power and heat to keep them on. The switching is done through the same IRFZ44n MOSFET. My only concerns are here under.

1) I hope the controller supports the operation of 36 outputs independently. all of them work without affecting the operation of the rest outputs.

2)Another issue is that, under volting the solenoid coil through PWN signals is causing a high pitch noise(low volume). The mechanical components are removed then also the noise persists. The noise doesnt come if i give a linear power supply of 4V.

Kindly advice.
Thank you

The noise part has been taken care of.
Kindly guide if STM32G474 is the correct MCU selection for the work?
There are 2 cases :

CASE 1:
These are the list of 6 PWN signals of 12 V that are in use.
1) 100% i.e 12V equivalent
2) 75% i.e 9V equivalent
3) 50% i.e 6V equivalent
4) 41.66% i.e 5V equivalent
5) 33.3% i.e 4V equivalent
6) 25V% i.e 3V equivalent
There are 36 Outputs.
1) 1 output would only receive 3V to 5V equivalent PWN signa, which ever is called for
2) 1 Output would only receive 6V to 12V equivalent PWN signal, which ever is called for
3) 34 Outputs receive 100% or 33.3% PWM independently. First 100% for 100ms to turn on then 33.3% to remain ON.



CASE 2:
I can even work with 2 PWM signals
1) 100%
2) 33.3%
This will be used for 34 outputs. Outputs receive 100% or 33.3% PWM independently. First 100% for 100ms to turn on then 33.3% to remain ON.



Are any of the cases possible?