what's the worst that can happen if you feed a 555 timer too low of a voltage?

[engineheat]

I want to use a low power CMOS 555 timer to do PWM to slow down a DC motor. My power source is only 1.5V AA so that's less than the recommended Vcc of the 555, which is 2V minimum. This also result in a voltage to the motor less than the rate voltage.

I wonder if there are any dangers to powering the 555 and in turn the motor at a lower voltage than recommended? What's the worst that can happen aside from things not doing anything or performing poorly?

Thanks

[cncjerry]

I don't think the 555 will even oscillate at that voltage.  Breadboard it and check it out.  There might be a 3.3V version but I don't think that will run at that voltage either.  To answer your question, it will be like turning it off.  A motor that is designed to run at a certain voltage will depending on the motor, draw more current for a given HP and turn more slowly at a lower voltage.

[tsman]

TLC551 will run down to 1V.

[Brumby]

A motor that is designed to run at a certain voltage will depending on the motor, draw more current for a given HP and turn more slowly at a lower voltage.

There is also the possibility that the motor will simply stall and not turn at all.  In such a state, expect the current draw to rise ... and all the issues that can arise from that.

[floobydust]

What are you using for a PWM switch to drive the motor? I'd guess a BJT. How much motor current?

The TLC551 only has 1mA/-0.3mA output current running off 2V and less 0.1mA/-0.01mA on 1V power.
The output-stage mosfets don't have much gain at low voltages.

[Zero999]

To answer the original question: what's the worst that can happen if you feed a 555 timer too lower voltage?

Smoke! If the voltage drops below 0V, too far into negative territory, it'll smoke. 

Of course you're not doing that. If the voltage is under 2V it might work, but there's no guarantee.

Another issue is the voltage will drop, as the battery discharges under load, so your circuit should work down to around 0.8V, to extract most of the energy from the battery.

It's possible to make a PWM circuit, which will work at these low voltages. A Schmitt trigger and comparator would do the job and suitable ICs are available which will work down to near 0.8V. The only trouble is they're surface mount.

Here's a schematic. I've not selected the component values, which will depend on the desired frequency and what's available. It will also need a couple of transistors to drive the motor, which will depend on how much power it uses.


http://www.ti.com/lit/ds/symlink/sn74auc1g14.pdf
https://docs-emea.rs-online.com/webdocs/1396/0900766b81396eb3.pdf
http://www.ti.com/lit/ds/symlink/tlv3691.pdf