Exo
Active Member
Hello again ppl,
The circuit below is a motor driver using a H-bridge. Current is measured using resistor R1 and divided by R2, R3 and R7. This way we can use R3 to set the working point of transistor Q1 roughly between 0.9A and 5.3A.
When Q1 is triggered C13 will provide a small delay (to filter out little crap) and then the set reset (made up by IC4A and IC4B) is reset causing the H-bridge to shutdown by taking the enable signal away.
This all works great using a resistor as a load, but when trying with an actual motor causes problems.
I was testing with a very small unloaded motor wich only draws 35mA when running and i need to crank R3 all the way up to 4A or the motor isn't allowed to start by the SC protection.
Now i realize that a motor will need a larger startup current, but a 35mA motor requiring a 4A startup current is something i don't believe (hard to measure).
So, Any of u guys know what might be causing the protection to switch off so fast. To my belief the protection should never act when using such a small motor cause i dont believe it actually uses that much current for starting, more something like 250mA.
But like said, with a resistive load it works :?
The circuit below is a motor driver using a H-bridge. Current is measured using resistor R1 and divided by R2, R3 and R7. This way we can use R3 to set the working point of transistor Q1 roughly between 0.9A and 5.3A.
When Q1 is triggered C13 will provide a small delay (to filter out little crap) and then the set reset (made up by IC4A and IC4B) is reset causing the H-bridge to shutdown by taking the enable signal away.
This all works great using a resistor as a load, but when trying with an actual motor causes problems.
I was testing with a very small unloaded motor wich only draws 35mA when running and i need to crank R3 all the way up to 4A or the motor isn't allowed to start by the SC protection.
Now i realize that a motor will need a larger startup current, but a 35mA motor requiring a 4A startup current is something i don't believe (hard to measure).
So, Any of u guys know what might be causing the protection to switch off so fast. To my belief the protection should never act when using such a small motor cause i dont believe it actually uses that much current for starting, more something like 250mA.
But like said, with a resistive load it works :?