Help me to design constant current circuits.

[paulsingam]

Hi,.....
I need to design a constant current circuit for our product. its a LED driver circuit. 350ma circuit is required, voltage nearly 65v. how can i design this?

 

[bmandl]

Current source - Wikipedia, the free encyclopedia

 

[samiurrehman]

i think you can design current mirror circuit, which is quiet easy to design and provides accurate current as per desires. The voltage can be catered for by controlling the reference resistance.
Plz search current mirror currents.

 

[leebluer]

try boost converter

 

[ashishsahu.iiit]

I assume with constant current you mean, current constant with process, voltage and temperature. There are a few ways to achieve this as,
1) Design a constant voltage source, band-gap or you may want to scale-up the band-gap voltage using an error amplifier and pass device. Then use this voltage to generate constant current, using resistor (external or internal). Mirror this current to get your current source.
Also you may want to go for process trimming to increase the accuracy.
2)Another method would be designing a band-gap circuit, then using the IPTAT, ICTAT and adding them you can get a nearly constant current with temperature. The design can have process trimming.
3) Yet another way could be, generating a VPTAT (again designing a band-gap circuit) and then applying this VPTAT across MOS transistor operating in linear region. Please note, a mos transistor operating in linear region will have resistance across it proportional to temperature. Thus applying VPTAT/R_mos, where R_mos is proportional to temperature, you would get a fairly temperature compensated current source. As usual use current mirrors to mirror the current.

 

[rk433]

You can design a very good current source or sink by using bandgap & resistor
i.e vbg / r .
In the above equation, band gap is constant but resistor varies a lot. to minimize the resistor variation across temperature, use two resistors (one with positive temp. coefficient & another one with negative temp. coefficient) , you will get good current across temperature. For process variation use trimming.

Bye

 

[checkmate]

Too many IC designers around.
Use an opamp to control the current through a high-voltage N-Channel FET and resistor in series. The voltage drop of the resistor is fedback to the inverting input of the opamp. Provide a reference voltage into the non-inverting input of the opamp. Whether you use a voltage divider or voltage reference IC depends on your required accuracy.
The current is given by Vref/R.