How to design a over power protect circuit???

[tryagain]

My device output voltage 0~20A,and current 0~2A,Now I need require over power limition. When output power over 20-22W,need to generate a hign level signal to this device.
Now, how can i to design this circuit.I need a simple circuit to realize it.

 

[Fom]

DC power, AC average power or AC peak power?

 

[tryagain]

It is DC output.

 

[ramesh]

Find Power=VxI by measuring both voltage and current. If needed you can scale down suitably this factor and use crowbar protection circuit to sense this and shutdown the power supply output.

 

[tryagain]

Hi,ramesh,thanks you.
But what is "crowbar protection circuit"

 

[goodboy_pl]

if your device is a power supply, this protection can be made with voltage and corrent limiting at the same time, i.e. a voltage regulator with current limiter (constructed with a feedback network from the output current).
in this way the current is limited to a defined value (this value can be cahnged.)
but if u want to control the power of a circuit, multiplier is the best soultion also some OTAs can be used for this perpuse!

crowbar is used to protect the ckt. against over voltage and is only on/off control method which is not suitable for several applications.

BEST!

 

[tryagain]

My device is not a power supply,so I can not use your first method.
for multiplier,special multiplier is expensive,and if i use general way to made a multiplier with op,it is too complexity.
I need a simple circuit to implement it,I don't need high precision.

 

[cherrytart]

maybe you can let heat be your wattage indicator, like a resettable thermal fuse mounted on the heatsink that shutsdown the supply if open, or a thermal resistor that pulls an enable pin low when its hot enough

 

[rauol]

What do you want to measure Power VxI or only current. if it is only current you can use a low value resistor as a shunt and a small amplifier to amplify the signal followed by a camparator to give a signal.
it would cost you less than doller.

if you want to measure power may be try using analog multipliers etc..

 

[ramesh]

Analog multiplier is more expensive than todays Microcontrollers with on chip 8-channel analog multiplexer, low speed analog-to-digital converter and a comparator. It will be cheaper and more versatile especially for power supply control units, to use such Microcontrollers to compute the power (VxI) and control the power supply unit. Please see Atmel's ATmega128 or other devices in this RISC microcontroller family for inexpensive applications.

 

[rauol]

8) Using microprocessor in real time application can be trickey but a good solution. There are some ICs from analog devices which are used in domestic power meter application, i think it may be possible to measure power using the same.