1.5A peak current for 200ms with DC-DC converter using MP2560 DC-DC converter ?

Thread Starter

mishra87

Joined Jan 17, 2016
645
That circuit will deliver 2.5A, so should easily provide 1.5A for 200ms.
What's the concern?
Hi,

This is a very good question,

My requirement is to limit output current to 500mA @ 12V. So we don not want continuous current more that 500mA.
Now my question is:
1. How do we limit current for 500mA
2. How do we meet requirement for 1.5A peak for 200ms.

regards,
 

BobTPH

Joined Jun 5, 2013
2,255
You cannot limit the current to 500 mA @12V. If the load wants more than 500mA at 12V you must reduce the voltage.

Your requirements do not make much sense. If you are limiting the current to 500mA, how does it get to be 1.5A? If you are allowing it to go over 500 mA for 200 ms then limit the current, when does it start allowing peak current again?

Bob
 

Thread Starter

mishra87

Joined Jan 17, 2016
645
You cannot limit the current to 500 mA @12V. If the load wants more than 500mA at 12V you must reduce the voltage.

Your requirements do not make much sense. If you are limiting the current to 500mA, how does it get to be 1.5A? If you are allowing it to go over 500 mA for 200 ms then limit the current, when does it start allowing peak current again?

Bob
I think that the challenge
Output current has to be limited for 500mA and same time it should able to supply 1.5A for 200ms.
How this could be implemented ?
 

crutschow

Joined Mar 14, 2008
24,325
Output current has to be limited for 500mA and same time it should able to supply 1.5A for 200ms.
How this could be implemented ?
That circuit has no provision for a current limit adjustment, so you would have to add an external circuit.

What is the purpose of the 500mA current limit?
Is it just for short-circuit protection or will it continuously need to limit to 500mA (for what load)?
 

Alec_t

Joined Sep 17, 2013
10,902
An external circuit could provide an adjustable current limit and a 200mS timer could adjust that limit. For a given load the voltage would have to change in sympathy with the limit.
What would start the timer?
 

crutschow

Joined Mar 14, 2008
24,325
An external circuit could provide an adjustable current limit and a 200mS timer could adjust that limit.
My approach would be to have a 500mA current-limit circuit with a 200ms delay before it becomes active.
The circuit could then provide the 1.5A, 200ms pulse (or any pulse up to the 2.5A inherent limit of the converter) after which the current is limited to 500mA.
 
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Thread Starter

mishra87

Joined Jan 17, 2016
645
My approach would be to have a 500mA current-limit circuit with a 200ms delay before it becomes active.
The circuit could then provide the 1.5A, 200ms pulse (or any pulse up to the 2.5A inherent limit of the converter) after which the current is limited to 500mA.
Yes, That is probably good approach.
Could you let me know that how to do this ?
How could this be achieved and what kind of external component needs to be added.

Regards,
 

Thread Starter

mishra87

Joined Jan 17, 2016
645
Hi,

The specification says.

Vout(min) : 11V
Vout(max): 12V
Constant current @12vdc : 500mA
The application is to disconnect the load on over current condition.

Regards,
 

crutschow

Joined Mar 14, 2008
24,325
How could this be achieved and what kind of external component needs to be added.
I have an approach that uses two transistors, three resistors, and a capacitor.
But it won't work for a short circuit load, if that's something you need to protect against.
However, the circuit could be modified to handle that condition.
The application is to disconnect the load on over current condition.
So do you want the converter to shut off when an overcurrent occurs, or just limit the current to 500mA.
Those are two quite different ways to handle an overcurrent.

If you tell us more about the exact application and load we can likely give better solutions without having to play a game of 20 questions. ;)
 
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Alec_t

Joined Sep 17, 2013
10,902
The specification says.
Vout(min) : 11V
Vout(max): 12V
Constant current @12vdc : 500mA
Specification of what? Is that the spec of a ready-built constant-current supply? If so, you won't be able to get a 1.5A 200mS pulse out of it directly; but a capacitor charged by it could provide a hefty current pulse.
 

BobTPH

Joined Jun 5, 2013
2,255
My approach would be to have a 500mA current-limit circuit with a 200ms delay before it becomes active.
The circuit could then provide the 1.5A, 200ms pulse (or any pulse up to the 2.5A inherent limit of the converter) after which the current is limited to 500mA.
So it allows exactly one high current pulse and then limits forever? If not what resets it to allow the next pulse?

The problem needs better specification.

Bob
 

Thread Starter

mishra87

Joined Jan 17, 2016
645
I have an approach that uses two transistors, three resistors, and a capacitor.
But it won't work for a short circuit load, if that's something you need to protect against.
However, the circuit could be modified to handle that condition.
So do you want the converter to shut off when an overcurrent occurs, or just limit the current to 500mA.
Those are two quite different ways to handle an overcurrent.

If you tell us more about the exact application and load we can likely give better solutions without having to play a game of 20 questions. ;)
Hi Guys,

Thanks for your reply and suggestion.
Sorry for late reply.

It is not only limit the current but shut down the load in case of Over-current/Short circuit protection.
Device has to work at 500mA current only but yes it should source 1.5A peak for 300mS.

I got two ideas to do it.

1. Use current measurement circuit (1mohm in GND) line and then amplify it and give signal to MCU ADC. MCU adc take decision to shut the load in case of OC/SC. One DO from MCU will be connected to enable pin of DC DC converter.
For 1.5A peak requirement mcu will not read data for first 300ms.

Pros : Cost effective solution and 20 cent only.
Cons: Response time is more

2. Use of any e-fuse like TPS25921LDR (https://www.mouser.in/Search/Refine?Keyword=TPS25921LDR)
Faster response time but costly.


Could anybody suggest and other requirement?

Thanks again,
Regards
 

crutschow

Joined Mar 14, 2008
24,325
1. Use current measurement circuit (1mohm in GND) line and then amplify it and give signal to MCU ADC. MCU adc take decision to shut the load in case of OC/SC. One DO from MCU will be connected to enable pin of DC DC converter.
For 1.5A peak requirement mcu will not read data for first 300ms.

Pros : Cost effective solution and 20 cent only.
Cons: Response time is more
You only need to respond in 300ms.
What response time a problem? :confused:
 

crutschow

Joined Mar 14, 2008
24,325
I don't think so.

Could you suggest any other solutions ?
You don't think so what?
Sorry I still don't understand what response time problem you think you have using the MCU as a detector.

Edit: So when you shutdown the converter after an overload, how and when will you restart it?
 
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