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It doesn't need one. As an emitter follower, it'll only take the current that it needs. Besides, the LM358s output is current limited to around 20-30ma anyway. kemo0o will need to use a darlington if he wants 1A output.Boncuk said:no pity with the poor transistor? Give it a base resistor too.
kchriste said:Well, you've converted the current from the DAC to a voltage with an op-amp and resistor. Do you want a voltage source output or a current source type output? ie: what do you need 1A for? It could be as simple as this, if you don't need high frequency response:
kchriste said:What are going to use the circuit for? Anything from DC to a few hundred Hz should be fine. I depends on the amount capacitance on the output and how fast you want it to respond especially when trying to lower the output level. This is because the output, while it can source plenty of current via the transistor, cannot sink much via the 1k resistor.
blueroomelectronics said:Sounds like it's time to upgrade to PIC or AVR that support hardware PWM. Your antique 89S52 is pretty limited.
It will work OK. Since a motor is an inductive load, I've added a diode to the original diagram posted above. Your original PWM method is better and generates less waste heat.kemo0o said:so what about it ?? is it fine or No ? <<>> because i want to apply it about one or two days to use it
kemo0o said:i know that PWM is better than this way but
i want the motor start at low speed then by the time it increase its speed
i tried to do it by PWM but i failed
so i made it to control the motor
thanks alot << kchriste>> and all member help me
Boncuk said:Using PWM has a lot of advantages. First you don't step up the motor, it will increase rpm with pulse length. You can use PWM with an astable oscillator and varying pulse lengths.
Wire a 555 accordingly and hook up an N-Channel Power MosFet. The circuit is much cheaper than using a converter and you don't have the disadvantage of very limited torque when starting at low rpm.
This circuit can be done within 30 minutes. The frequency varies slightly with pulse width. Pot position is near 100%. Shortest pulse width 2.5microseconds, longest pulse = steady DC.
Boncuk