Motor speed contol using h bridge

[electroniccrazy]

Hi,

Below is a link which shows a servo pulse to PWM converter, this circuit can be used with the H bridge circuit in this website which i have built and tested and im happy to say that it works!, however this circuit is even more complicated than the last, can anyone tell me how this works?,all i understand is that this circuit will take the output pulses from a reciever then feed in PWM signals into the H bridge circuit. everything in between is a bit hard to understand. shown below is the link and the second link is to the circuit diagram.

http://www.bobblick.com/techref/projects/sv2pwm/sv2pwm.html

http://www.bobblick.com/techref/projects/sv2pwm/sv2pwmsc.pdf

thankyou!

 

[Skogsgurra]

Hi,

Why not ask Bob?

In the meantime, I'll try to step through the schematics - more fun than a crossword puzzle.

The pulses enter J1. A 1000 us pulse represents -100%, a 1500 us pulse is zero and a 2000 us pulse is +100%

The 74C14 schmitt inverter inverts the signal so that you have +5V when no pulses present and pulses going to GND after the inverter.

The GND pulses go to three different places. Let's start at the bottom:

D1/R4/C7/U1C make a fast-on/delayed-off circuit. U1C-6 goes high as soon as a pulse is received and stays high about 200 ms after pulses disappear. The signal closes the analogue switches that activate the U1E and U1D control signals. The J2 output is zero (H bridge off) when the switches are open.

C1/R1/U1B make a pulse detector and an inverter. Output from U1B controls analogue switch U3D so that it closes during the length of an incoming pulse. Resistors R2/R8 and capacitors C2/C3 always start from +5V and gets charged towards GND when U3D is closed. Short pulses -> high voltage and long pulses -> low voltage. This is the analogue voltage that controls the output PWM duty cycle.

U1F inverts the pulses and controls the next gate, U3A. This gate works as an S/H together with C8/C9. This means that the voltage is kept locked on the capacitors when the switch is open (that is when the new voltage is formed on C2/C3) and it is only when the new voltage level has been reached (switch U3D opens and U3A closes)that it is transferred from voltage follower U2B to capacitors C8/C9. This makes the control voltage stable between pulses.

U2D and its associated resistor/capacitor network make up a classic triangle wave generator. R3/C5/C6 make an integrating negative feed-back and R5/R6/R7 create a positive feed-back that keep the U2D output locked in either state (high or low) until the negative feed-back "catches up" and switches the opamp over to the other state. This goes on as long as there is a supply voltage.

The triangle wave is compared to the DC control voltage on C8/C9. There are two comparators; one for the "plus" switches and one for the "minus" switches. Plus and minus meaning positive and negative output from the bridge diagonal.

The comparison is not a direct one, the triangle signal is level adjusted and there is also a differential voltage added to create a little time between the output signals to prevent "cross conduction" in the H-bridge.

There's more to say about this circuit. But I leave like this. Hope you can find out the finer details on your own.