want to raise current up

[kemo0o]

Hey

i have built dac Simple circuit by 0808 IC
when i enable all inputs it gives me the refrence voltage (( that's OK))


the problem is the current

is there any way to raise the current ??? to reach 1 A or higher

the schematic is attached

 

[kchriste]

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:
EDIT: Added diode for inductive load:

 

[Boncuk]

Hi kchriste,

no pity with the poor transistor? Give it a base resistor too.

Boncuk

 

[kchriste]

no pity with the poor transistor? Give it a base resistor too.

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.

 

[Roff]

A big heat sink will be needed, though.

 

[kemo0o]

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:

thanks for your reply it is very nice solution but what about your opinion that if i don't want high frequency

 

[kchriste]

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.

 

[kemo0o]

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.

i am going to control motor speed by the change in o/p voltage because when i used PWM @ ATMEL 89s52 i used Software that switch on/off the motor very fast speed i get the speed 50% when i used it .

so here i found that i could control Volt value So i can control the speed by varying the volt

so what about it ?? is it fine or No ? << >> because i want to apply it about one or two days to use it

 

[blueroomelectronics]

Sounds like it's time to upgrade to PIC or AVR that support hardware PWM. Your antique 89S52 is pretty limited.

 

[kemo0o]

Sounds like it's time to upgrade to PIC or AVR that support hardware PWM. Your antique 89S52 is pretty limited.

I believe that But i have Built all program on it So i can't change it Now

After i finished this project i will upgrade my Future on AVR

 

[kchriste]

so what about it ?? is it fine or No ? << >> because i want to apply it about one or two days to use it

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]

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]

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

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

 

[kemo0o]

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

Nice idea

but can i apply it with microprocessor AVR
if i can do with it send me the proteus file and code if you can coz i am
AVR BEGINNER
it seems that i will convert the project to AVR