I constructed a test prototype of the circuit in Al's link.
I dont have the 555 ic's as yet so I am feeding the control voltage straight into the Darlington circuit.
But I was not impressed with the load control and voltage stability.
I am looking for around 1 Amp supply at 12 volt. But with various test resistors I am getting the following results.
Initial voltage on smoothing cap 17.8v
full voltage on output 13.2v no load.
47R load 240mA @ 11.3v
22R load 450mA @ 10v
12R load 750mA @ 9v
4.3R load 1300mA @ 5.5v at this load the protection circuit has cut in.
So no real voltage stability.
I am now thinking of using a mosfet transistor for the final control, I believe these have a far better loss and lower resistance when in conducting state than the 2N3055 transistor used in my prototype.
This is the basic circuit I am now considering.
But I am confused by the 2 diodes in the variable resistor circuit. What are these for.
But I would like to add the inertia function of the first speed control circuit, and overload protection as well.
The variable resistor would be used to set the final max speed.
I am thinking to use a 7815 regulator for the initial supply for the motor and mosfet circuit, then feed that to the 7805 to get the supply for the 555 PWM controller.
If I was going to use a R C combination to build up the 555 control voltage slowly where would I connect this into the variable resistor circuit.
Thanks
Mike
I dont have the 555 ic's as yet so I am feeding the control voltage straight into the Darlington circuit.
But I was not impressed with the load control and voltage stability.
I am looking for around 1 Amp supply at 12 volt. But with various test resistors I am getting the following results.
Initial voltage on smoothing cap 17.8v
full voltage on output 13.2v no load.
47R load 240mA @ 11.3v
22R load 450mA @ 10v
12R load 750mA @ 9v
4.3R load 1300mA @ 5.5v at this load the protection circuit has cut in.
So no real voltage stability.
I am now thinking of using a mosfet transistor for the final control, I believe these have a far better loss and lower resistance when in conducting state than the 2N3055 transistor used in my prototype.
This is the basic circuit I am now considering.
But I am confused by the 2 diodes in the variable resistor circuit. What are these for.
But I would like to add the inertia function of the first speed control circuit, and overload protection as well.
The variable resistor would be used to set the final max speed.
I am thinking to use a 7815 regulator for the initial supply for the motor and mosfet circuit, then feed that to the 7805 to get the supply for the 555 PWM controller.
If I was going to use a R C combination to build up the 555 control voltage slowly where would I connect this into the variable resistor circuit.
Thanks
Mike
