1 amper half wave constant current source

[nima_1981]

hi my friend.
I need half wave constant current source for grounded load
Resistance of load is under 1 ohm
my oscillator output voltage is near 2 Volt peek to peek
any one have idea for that ,
Thanks

 

[crutschow]

Not enough info.

Do you have a sine-wave source of 1Vpk and you want to drive a 1 ohm load with a half-wave of that giving somewhere in the neighborhood of 1A?

What is the frequency of the wave?

Does the load have to be grounded?

 

[nima_1981]

Not enough info.
Do you have a sine-wave source of 1Vpk and you want to drive a 1 ohm load with a half-wave of that giving somewhere in the neighborhood of 1A?
Yes i have i sin wave source 1 Vpk and i want flow 1 Amp to a resstor that is grounded .

What is the frequency of the wave?
1Khz
Does the load have to be grounded?

yes Its grounded

 

[crutschow]

Do you need a true constant current source where the current is constant at 1A even if the load is much less than 1 ohm?

 

[nima_1981]

Do you need a true constant current source where the current is constant at 1A even if the load is much less than 1 ohm?

exactly yes

 

[crutschow]

That requires a high-side constant-current circuit to drive a grounded load which can get somewhat complex. Are you able to buy modern rail-rail type op amps where you are (since "Ocean Mind" isn't on Google Maps)?

 

[crutschow]

Below is the sim of a constant current source consisting of a high-speed rail-rail op amp and a P-MOSFET driver. Is that what you want? It is shown generating a peak current of 1A for loads of 0.1Ω, 0.5Ω, and 1Ω. The half-wave current occurs on the negative half of the input sine-wave but I don't see that as a problem.

 

[KlausST]

Hi,

in my understanding constant current means DC.

This is not possible with any frequency.
Do you mean that the averaged current (or RMS current) is constant? Then it makes sense.

Klaus

 

[FvM]

If you replace the term "constant current source" by "current source", you have the right name for what the OP wants and what crutschow suggested...

 

[crutschow]

If you replace the term "constant current source" by "current source", you have the right name for what the OP wants and what crutschow suggested...

Current Source is indeed the proper name for the circuit I made and what I assumed the OP wanted.

 

[crutschow]

Below is the sim of a current source with a differential DC input as compared to the single-ended AC coupled input of my design in post #7. Again it shows a 1A peak current for loads of 0.1Ω, 0.5Ω, and 1Ω It also is able to use a common LM324 or LM358 single-supply op amp. The sim has the lower input (In-) grounded but it can be used to accept a differential input in conjunction with the In+ input, or used as a inverting input with the In+ input grounded.

Note that R1 should be a 1W resistor.

 

[nima_1981]

thankss
but i have a question we have positive Voltage for load why use p-channel ???
p-channel use for negative Voltage is that right ???

 

[crutschow]

thankss
but i have a question we have positive Voltage for load why use p-channel ???
p-channel use for negative Voltage is that right ???

No. It just has to have the drain more negative than the source (the source more positive than the drain). If you look at my circuit you will see that the output ( transistor drain) is always more negative than the transistor source, satisfying the polarity requirement for a P-MOSFET.

Since the load must be connected to the drain for this type of constant current circuit, then a P-MOSFET is required when the load is grounded with a positive supply. An N-MOSFET could be used if the load can float.

 

[nima_1981]

Thanks you very much.

But one other question?
Is this design, MOSFET drivers do not need?
Basically, when we use MOSFET drivers?

 

[crutschow]

Thanks you very much.

But one other question?
Is this design, MOSFET drivers do not need?
Basically, when we use MOSFET drivers?

You either need a MOSFET or a BJT to control the 1A current. But MOSFET's are more accurate since the BJT collector current would differ from the emitter current (be in error) by the value of the base current (which flows through the emitter but not the collector). Also the op amp would likely not be able to supply the required base current to generate 1A of collector current with a BJT so you would need a Darlington stage.

Edit: I forgot to note that the MOSFET should be a logic-level type if the supply voltage is less than 10V. Also it's maximum power dissipation is approximately equal to the supply voltage times 0.5A so the transistor needs to be on a heatsink.

 

[nima_1981]

You either need a MOSFET or a BJT to control the 1A current. But MOSFET's are more accurate since the BJT collector current would differ from the emitter current (be in error) by the value of the base current (which flows through the emitter but not the collector). Also the op amp would likely not be able to supply the required base current to generate 1A of collector current with a BJT so you would need a Darlington stage.

Edit: I forgot to note that the MOSFET should be a logic-level type if the supply voltage is less than 10V. Also it's maximum power dissipation is approximately equal to the supply voltage times 0.5A so the transistor needs to be on a heatsink.

Did I need to add is a Darlington after op-amp In your design ??because LM324 Can not Deliver 1 A ??

 

[crutschow]

Did I need to add is a Darlington after op-amp In your design ??because LM324 Can not Deliver 1 A ??

No, the circuit works as shown. The MOSFET carries the current. The LM324 just controls its gate-source voltage to regulate the current. Do you understand how transistors work?

 

[nima_1981]

OK , that's my mistake sorry . and thanks again my friend .

 

[D.A.(Tony)Stewart]

exactly yes

In order to provide 1A constant current from a 1Vp 1kHz source, the voltage source must have an ideal 0Ω impedance and the load must be low enough resistance to demand it.

Generally with such low voltages , you have no margin to maintain such current. In any case the source resistance must be much lower than the load to supply enough voltage to deliver 1A

If all you want is a 1A current limiter, this is not constant for a sine voltage.

Pls advise. What is the purpose?
What is the real source & load impedance ?

 

[crutschow]

In order to provide 1A constant current from a 1Vp 1kHz source, the voltage source must have an ideal 0Ω impedance and the load must be low enough resistance to demand it.

Generally with such low voltages , you have no margin to maintain such current. In any case the source resistance must be much lower than the load to supply enough voltage to deliver 1A
...............................

You are talking about a voltage source, but this is a current source. For a current source the effective dynamic output impedance should be as high as possible (in other words the output current should be unaffected by the load impedance). With the circuit shown the dynamic output impedance is in the megohm region due to the negative feedback and the load being in the MOSFET drain (the drain has an inherently high impedance). It will deliver a current proportional to the input voltage into a dead short or any resistance up to the clipping point.