PWM selection for higher amperage

[Boosted67]

Again with this lol

So I’m finding plenty of PWM setups. The ones where I can adjust both duty cycle and freq, have a low power tolerance. I shouldn’t need all 850ma to operate the solenoid but that’s its requirement. Dual adjustability unit I have only seen a capability of 30ma. The PWM I find that can handle anything more, the Hz is already predetermined in all the units I’m finding. Is there anywhere or a company I can find to set me up w one that can do it all? Or am I overlooking something?

 

[KlausST]

Hi,

PWM is pulse width modulation....it has nothing to do with current.

If you need high current then feed the PWM signal to a Mosfet, bjt, half bridge, full bridge, or any suitable driver IC.

I don't know where your 850mA and 30mA values come from. Also we don't know about voltage, duty cycle range, frequency range....

Klaus

 

[c_mitra]

Or am I overlooking something?

Yes!

Please tell us the objective, motivation and the thinking behind the setup. What is the purpose?

 

[schmitt trigger]

This is a wide-open question.

The key to receiving an educated and meaningful forum answer, is to ask an educated and meaningful question in the first place.

 

[summitville]

Please post a ULR to the exact device that you a currently looking at.
This will allow us to better understand your PWM requirements, and advise accordingly.

 

[Boosted67]

Looks like a non logic mosfet will do what I need. Maybe
Trying to control a solenoid. Fully activated it draws 850ma. It’s a PWM to ground. But the controllers I see that control duty cycle and Hz independently, the signal is only good for 30ma.

So if a mosfet is voltage based only so I don’t need to worry about the Hz control. I can control the ground on the solenoid thru source and drain it seems. But a mosfet is is resistance based where the solenoid is designed for PWM. Under my operation the solenoid will only be operated for 1 millionth of the duration of it’s life like this. Not sure resisting the ground instead of PWM should scare me

 

[c_mitra]

Under my operation the solenoid will only be operated for 1 millionth of the duration of it’s life like this. Not sure resisting the ground instead of PWM should scare me

I think you just need a mosfet driver for the solenoid and not a PWM signal. Solenoids are mechanical devices and cannot respond fast and they must not be driven with a PWM signal.

You need a high current to get the stuff activated and then you can reduce the current to hold it on to the current state. You reduce the current very low (or shut off) to release it.

Why do you need a PWM signal for this?

 

[Boosted67]

These solenoids are designed to be driven by PWM, and are not simple on/off driven. Fuel pumps in cars now a days are done the same way for pump life. So basically the solenoid is always fed positive current it is controlled by PWM on the ground side.
I need the PWM to precisely control the solenoid’s position. Simply switching it off and on defeats my purpose.

If a mosfet is voltage driven and I need the mosfet’s transfer to be variable, wouldn’t I want a PWM to control the voltage to the mosfet?
Errors for the solenoid happen at 175Khz+ or under 100khz. But idk the targeted kHz, or a straight PWM might be easier to control the ground

 

[KlausST]

Hi,

You don't give requested informations....especially not to posts#3, #4, #5
we mainly see your assumptions...wrong assumptions.

A MOSFET is voltage driven means:
The output (drain, source) state of the MOSFET depends on the voltage between gate and source V_gs.
The MOSFET may be OFF, in linear operation, or ON.
For PWM you want ON and OFF (while you want to avoid lossy linear region)

The MOSFET datasheet tells you which V_gs levels you need for the MOSFET to work properly.

designed to be driven by PWM, and are not simple on/off driven

A PWM is ON and OFF... thus - in my eyes - you contradict yourself.

Looks like a non logic mosfet will do what I need.

I don't agree. To me it looks like a logic level MOSFET is what you need. And a free wheeling diode.

You talk about solenoid, pump, and position. A bit confusing.
If you want to control the position --> maybe you want to control the solenoid's (average) current --> maybe by changing the (average) voltage --> maybe by controlling the duty cycle of a PWM.
A lot of "maybe".

Errors for the solenoid happen at 175Khz+ or under 100khz. But idk the targeted kHz, or a straight PWM might be easier to control the ground

I don't get what this means at all.
It seems you have some information that you hide. Maybe you have a datasheet? ..or you did some tests already? With which hardware? Maybe unsuitable hardware? What do the waveforms look like?
"Errors happen" isn't a meaningful information at all. Without knowing what you expect and what you see instead.
It could mean a 0.1% value mismatch ... up to "the circuit explodes".

Klaus

 

[Boosted67]

Don’t take my questions as assumptions. I’m taking what’s posted and trying to google and do some of my own leg work as not to be lazy. But I have almost zero experience in this field so take it a little easy. I’m try my best not to just say “gimme.”

I don’t contradict myself. The solenoid is not meant to be operated as fully open or closed. It makes more sense if you snip more from the quote than you did. The solenoid is operated as is, by PWM. The solenoid is not on/off operated.

Yes a PWN signal is off and on. But the average which I need will operate the solenoid somewhere in the middle of fully open and closed.

I don’t have most of the info. All I could really find was it takes 850ma to fully open and the controlling ecu will throw a code if the frequency to operate the solenoid goes outside 100-175Khz. This I did assume, would be my targeted area, average voltage still unknown.

Did I read wrong or is a logic mosfet for 5v low voltage like an arduino?


As easily as I can try to bridge the communication gap here: I have a solenoid I am hijacking. It already has its own 12v signal all the time. I’d like to manipulate the ground, so I have more control of the solenoid than simply on and off.

 

[KlausST]

Hi,

it is a fact, that PWM is ON OFF only. There is no inbetween.
A PWM is defined by: frequency, duty cycle, HIGH (ON) level, LOW (OFF) level.
So if you drive a solenoid with PWM it is driven ON/OFF only. --> please use a scope to show the PWM waveform to verify this.

Now it depends what you connect to the PWM signal.
* A scope shows ON / OFF voltage
* a resistor shows ON / OFF, voltage as well as current
* a capacitor will show current peaks.
* an inductive load will show ON / OFF voltage (square wave) but will smooth the current. You may see some DC current with some current ripple.

Your solenoid is an inductive load. Independent of duty cycle the voltage will show ON/OFF. In your case 0V/12V.
Only if you low pass filter the voltage (with extra circuit) you may see that the average voltage is about: 12V x duty_cycle

The solenoid current is (due to it´s inductivity) already low pass filtered. Thus the solenoid current will be about: 850mA x duty_cycle

****
"Average" can be of any waveform. 6V average may come from 6V DC, from 60V ON/OFF PWM with 10% duty cycle ..and it may come from 12V with 50% duty cycle.
Average is a mathematical function... to define "average" in detail you need to specify the averaging time.
Often "averaging" is made with low pass filters. They are defined by: cutoff frequency, filter order and filter type.

****

Did I read wrong or is a logic mosfet for 5v low voltage like an arduino?

Logic level means: The "drive" voltage = gate-source-voltage (V_gs) is in logic level range. Mabye 5V, for details you need to consult the datasheet.
But even a "logic level MOSFET" may have higher or lower drain-source-voltage (V_DS). This depends on circuit and needs to be within datasheet specifications.

Klaus

 

[Boosted67]

I understand how PWM works for the most part. Would it make more sense of my intention if I said “open or closed” for the solenoid? I’m not referencing the voltage to the solenoid, but it’s operation. The circuit can be on/off because of duty cycle, but that doesn’t mean the solenoid is operational. I need it to operate between completely open and completely closed.

850ma x duty cycle is how I assumed the 30ma signal generator maximum load wasn’t going to cut it from my first post.

 

[KlausST]

Hi,

How can we help you?
What do you expect from us?

Klaus

 

[c_mitra]

Would it make more sense of my intention if I said “open or closed” for the solenoid? I’m not referencing the voltage to the solenoid

Does the solenoid (under current discussion) have in between states other than open or closed (say 20% open or 50% closed etc continuous operation) - say a continuously variable open state (say 1-100%)?

Does the state of the solenoid depend on the average voltage (or current) in some known fashion (say the voltage applied is proportional to the degree of opening state)?

Do you plan to use the solenoid working at a low frequency (say 1s on and 9s off) and you want to see the average response over long time (say 10 sec; the solenoid follows the PWM in that case)?

Does the solenoid respond to high frequency on/off cycles? (there is mechanical inertia to consider)- a pump motor may not start with a 10% duty cycle of a PWM voltage with rated voltage.

You need to clarify and give more details.