Adjustable PWM control without software?

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chico

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I would like to have a PWM control (for a fan) that has 2 PWM outputs.
One Output when: pin 1 NAND pin 2 is high (0 0 or 1 0 or 0 1)
Another output when: pin 1 AND pin 2 are high. (1 1)

I can get two different signals with AND and NAND gates but I dont know what sort of IC i would want to be running my signals to (if it exists).

Maybe i would need 2 different PWM ICs and switch between them?
or maybe the AND/NAND signals would control voltage divider circuits to a voltage controlled PWM controller IC (does that exist)?


Thank you in advance
 
If you want the 2 fans to run at different speeds you would need two PWM's.
 
You could use a voltage controlled PWM circuit such as this. It requires a triangle-wave generator which he references in the article.

You would just use a voltage divider to generate the control voltage with two parallel resistors in the bottom leg of the divider. You switch one of the resistors in and out of the circuit with the logic signal driving a transistor used as a switch (collector to bottom of resistor, emitter to common).
 
There are no voltage controlled PWM ICs? I cant find any.

ronv said:
If you want the 2 fans to run at different speeds you would need two PWM's.
Click to expand...

nope I want one fan with 2 PWM "modes", so i can switch duty cycle.
 
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You could start with a basic PWM fan speed controller like this one. Then just think about modifying the R1 configuration. There are any number of ways to go about it. However, if the fan will only ever see two speeds there are simpler ways to go about it.

What is the fan voltage and current?

Ron
 
chico said:
There are no voltage controlled PWM ICs? I cant find any.



nope I want one fan with 2 PWM "modes", so i can switch duty cycle.
Click to expand...

Not sure what your looking for but, I found this on crutschows site he suggested.

It also uses the 555 as PWM.

**broken link removed**
 
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Switching regulator ICs use PWM and you could likely use one of them for your purposes. But you'd have to understand how they work so you could adapt it for your use.
 
Im getting through all the posts but ill start with this one.


The fan is pretty beastly and I have to use it. It is 3A at 48V and has PWM control. If you were thinking of having a potentiometer or soemthing control the voltage to it i think the current is too much. If anything I could use a regulator with a heatsink to change the voltage thats why i thought PWM would be easier.

I just did a google on Switching Regulators pulling this one up. Is this what you mean crutschow ?

DC to DC Regulator and BuckBoost
Click to expand...
whoa thats getting complicated, ill stick to this simpler stuff.

what do you guys think of using the logic to switch between a part like this. I would have 2 different chips and switch back and forth.
 
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No, the circuit I linked to is a simple PWM circuit based on a 555 and is a common circuit. The circuit is driving a IRFZ 46N MOSFET whicgh would easily handle a 48 vo9lt 4 amp fan load. What I would suggest a modification of the D1, D2 and R1 portion (duplicate it) so based on logic either of two adjustable preset speeds could be selected. That was what my link and suggestion was all about. Using a 555 with literally several additional parts.

I have not used the MCP1630-E/MS you linked to so really can't comment on using a set of them.

Ron
 
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I would suggest using the 555 circuit that ron suggests, but use a 556 timer (one for each pwm state), then the nand*and logic inputs can go to the reset pins on the 556
 
Here is a way to use one 555 with two selectable PWM duty cycles. It uses a 4066 analog switch to select either of two pots that control the duty cycle of a 555.

A logic high on the appropriate input selects that pot. The pot not selected must be at a logic low (0V).
(Note: The logic high must be equal to the supply voltage).

Note that the maximum 4066 supply voltage is 15V.
 
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Regarding the above (and attached). Wouldnt changing the R1 pot (now R11 and R12 in my schematic) just change the frequency not the duty cycle?
The whole circuit is based on how fast the C1 resistor charges and discharges but its the same circuit so wouldnt the duty cycle be 50% all the time?
EDIT: Never mind the above i realized my mistake

Is there a suggested frequency to run this at?

Also is the below how you thought i would integrate the logic?
 

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One question, this circuit is based on the fact that the output pin of a 555 timer can sink and source current but I dont see that mentioned in any of the data sheets im looking at, is it a typical 555 timer thing?

Also just to make sure, the output PWM signal is a pull high that is forced low (sinked) by the discharge pin right, just want to make sure i understand this properly.
 

The 555 timer can source or sink 200 mA. I should mention the standard 555 as in NE555 variety:

Features
Direct replacement for SE555/NE555
Timing from microseconds through hours
Operates in both astable and monostable modes
Adjustable duty cycle
Output can source or sink 200 mA
Output and supply TTL compatible
Temperature stability better than 0.005% per °C
Normally on and normally off output
Available in 8-pin MSOP package

Taken from this data sheet.

I would build the circuits using the values shown in the first link I posted. That should get you going. Just use 2 pots and run with that. I would do the switching exactly as crutschow mentions using a CD4066 quad bi lateral switch.

Ron
 
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