circuit design problem

[dspcan]

there are two working condition for the circuit:
a.when the controller give 'test' signal, the circuit should provide stable 200mA current.
b.when the controller give 'open' signal, the circuit should provide stable 5A current.
the 'bad' circuit had been designed has two seperate circuits for the two situations,which uses more transistors and op,I wonder if there's such circuit that can provide the two choices simultaneously?

 

[Roff]

there are two working condition for the circuit:
a.when the controller give 'test' signal, the circuit should provide stable 200mA current.
b.when the controller give 'open' signal, the circuit should provide stable 5A current.
the 'bad' circuit had been designed has two seperate circuits for the two situations,which uses more transistors and op,I wonder if there's such circuit that can provide the two choices simultaneously?

Probably, but you have not given nearly enough information.

1. What are the voltage levels of the "open" and "bad" signals?
2. What power supply voltages do you have available?
3. What is the nature of the load (impedance, voltage, etc.)?

 

[dspcan]

Probably, but you have not given nearly enough information.

1. What are the voltage levels of the "open" and "bad" signals?
2. What power supply voltages do you have available?
3. What is the nature of the load (impedance, voltage, etc.)?

--------------1. the voltage of the signal is 5V
2. 24V
3. the load just like a resistor, when the circuit is 'open' the load voltage is equal to the power supply ,24V

 

[Roff]

--------------1. the voltage of the signal is 5V
2. 24V
3. the load just like a resistor, when the circuit is 'open' the load voltage is equal to the power supply ,24V

So when you get an 'open' signal, you just want to apply the full 24V supply voltage to the load, which draws 5A at 24V. When the 'test' signal is applied, you want 200mA applied to the load. Is this correct?
Are 'test' and 'load' mutually exclusive, or can both be present at the same time?

 

[dspcan]

So when you get an 'open' signal, you just want to apply the full 24V supply voltage to the load, which draws 5A at 24V. When the 'test' signal is applied, you want 200mA applied to the load. Is this correct?
Are 'test' and 'load' mutually exclusive, or can both be present at the same time?

--------------'test' and 'load' mutually exclusive,they are proveded at different time

 

[Roff]

Does the switch need to be between the positive side of the 24V supply and the load, or can it/should it be in the negative leg? Is one side of the supply designated as Ground?

 

[dspcan]

Does the switch need to be between the positive side of the 24V supply and the load, or can it/should it be in the negative leg? Is one side of the supply designated as Ground?

-----------------------
that is not required. as you wish

 

[Roff]

It will require at least 2 MOSFETs, an op amp, a resistor, and a capacitor. Is that any less parts than you now have?
Or maybe someone else has a simpler solution.

 

[dspcan]

yes,roff,but how to provide two working conditions for such circuits?

 

[dspcan]

yes, Roff, but how to provide two different working conditions for such circuit? by changing the input voltage level of the amp to exert different voltage to the mosfets?

 

[Roff]

Here's the general configuration. Some of the values are yet to be determined.
Can you use surface mount parts?
Do you have access to a good supplier like Digikey, Mouser, etc.?
Does this require rapid switching, or is it essentially static? Rapid switching will require MOSFET drivers.
Is your 5V supply stable enough to be the reference for the 200mA current source, as drawn? If not, a voltage reference will be required.

 

[dspcan]

so ,it seems to be a very detailed design, and I just need a simple method to complete the circuit layout as far as possible, no matter it is a mosfet or transistor, I want a 'smart' switcher to exert required current to the load according to my command.

 

[Roff]

so ,it seems to be a very detailed design, and I just need a simple method to complete the circuit layout as far as possible, no matter it is a mosfet or transistor, I want a 'smart' switcher to exert required current to the load according to my command.

Hopefully someone else can help you with layout software. You apparently know how to finish the circuit design. Let us know how it works.

 

[dspcan]

thanks ,ROFF. and I have an idea after I had read your suggestion. I think one constant current source that is sensitive to the input voltage will accomplish such task. which I just need are: op-07, irf540 and one sample resistor as the voltage feedback to op07. and the input voltage can be adjustable accord to the microcontroller's D/A, and the irf540 should be in saturation