Author Options:

Using a hall effect sensor with TL494 pulse width modulator. Answered

I have an electric billy cart with a dead controller board. I constructed the kit circuit below to replace the dead board and it works well enough for the job except for one small problem. The throttle on the billy cart utilizes a hall effect device and not a pot. The billy cart also has a handbrake with a switch that closes when applied. I use this with a resistor to discharge C2 and pull pin 4 (inhibit) high. This ensures a gentle start (as the capacitor slowly charges through the 100k resistor) if the brake is released with the throttle advanced. The output range of the throttle is 950 mV to 4.1 V if VREF (5V) is used as the supply. (I'm dropping it in in place of the pot.) 4.1 V is sufficient to achieve the maximum 90% duty cycle of the chip, but 950 mV leaves me with a minimum duty cycle of about 21%, and of course a motor that won't stop. Will changing the divider ratios 20k/2k2 & 47k/47k be sufficient to get me zero speed or am I going to have to do something more exotic? Thanks in advance.


hey.Rasputin 182, can you explain about system of TL494 and BC639,BC640 ? I just study about electric. so can you help me?

The answer is simple enough. Their purpose is to ensure a fast rise and fall time on the gates of the MOSFETs. The faster these devices turn on and off the less heat they have to dissipate when switching heavy loads.


10 years ago

Hi, my name is Raul. I was looking at your PWM and I wondered if you could help me build a PWM to make it work at around 20000 and 30000 cycles per second(20khz), it needs to be rotary too, it means that it needs to change polarity in every cycle. I can't find something like this in the market and I don't know much about electronic. I realy need help or some orientation please! I will appreciate!

That's great, sorry about not seeing this until now, but happy you got it to work :-)

Solved. An AA cell to provide a -ve 1.5 V rail. And a 7805 because the reference regulator choked on the extra current the hall sensor drew at the higher voltage. Sensor between -ve rail and +5v.