Lytswitch modificaions for 100mA to 200mA

Hello Friends,

I am Building a circuit by taking the application example from LTYSWITCH-7 from the Power Integrations.

Now i want to make the some changes accordingly.

Changes are
When input voltage range:85-135VAC, the ic should provide me a constant current of 80mA

When input voltage range:150-210VAC, the ic should provide me a constant current of 160mA

Now by looking at the datasheet VFB Pin if we provide a 280mv to that pin it will regulate the current

Now i want to process the shunt signal and accordingly make the chnage in current.

How it can be accomplished.
My thoughts are attached but having problem to do the same.


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https://www.google.co.in/url?sa=t&r...load=1&usg=AFQjCNH-qJ2-LyYzPui93smtjf_He4q45Q

Not impossible but tricky. The circuit runs on rectified but 'raw' DC, the final filtering to produce constant clean DC is from C6.

The current limit is set by R3 and R4 so you need to add another resistance in parallel but only when the voltage across C2 exceeds a certain threshold. The AC input voltages will be RMS so you need to decide the equivalent DC level at which the new components come into effect before going further. The IC is really designed for dimmable LED lighting so bear in mind that the waveform from most dimmer controls, if thats what you are using, will come from a trailing edge phase triggered triac so even if the average power is reduced, the peak voltage may still be high and enough to fool a simple comparator circuit.

Brian.

Brian

I have developed the window comparator for voltages

and Inverting amplifier for the current sensing with the gain of 15-20 by the potentiometer.

Does it gives problem..??

I'm not sure why you need the amplifier.

To set the output current to 80mA, the sense resistance can be 1 Ohm in parallel with 30 Ohms (=0.96774 Ohms total) when ideally it should be 0.96875 Ohms.
To set it to 160mA switch in an additional 1 Ohm across the others to give 0.4918 Ohms total when ideally it should be 0.484375 Ohms.

With care you can use a low Rds MOSFET to switch the addition resistance across the sense resistors but be careful to account for it's own resistance and to keep the gate voltage high enough during zero crossing periods.

Brian.

Hi,

it´s less critical to use two 0.5 Ohms resistors in series and feedback the signal of ONE or from TWO 0.5Ohms resistors with an analog switch.
..because the analog switch doesn´t need to carry the load current.

Use low_inductive resistors. No wire_wound.

Klaus

Hi..

1) We will have to vary the current from 60mA-100mA by using pot..

2) We will have to vary the current from 160mA-200mA by using pot..

With the analog switch, we will able to vary the current for that i am using amplifier with Variable feedback resistor (pot)

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Hi..

1) We will have to vary the current from 60mA-100mA by using pot..

2) We will have to vary the current from 160mA-200mA by using pot..

With the analog switch, we will able to vary the current for that i am using amplifier with Variable feedback resistor (pot)

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Ok...
So far i calculated the shunt required..

To limit 180mA=0.388ohm
to limit 140mA=0.500 ohm

To limit 80mA=0.875 OHM
TO Limit 60 mA=1.16 OHM

So for first case, for keeping variation i will 0.5ohm and one parallel pot of 30ohm(Which can be varied from 2 ohm to 30ohm) and give the variation from 0.487OHM to 0.400 ohm.. Similarly in case 1.16 to 0.875 ohm...

Now the question is which analog switch is available and reliable..

I am not thinking of relay at this stage..

I want some analog switch which can be perform operation by giving a signa 0 and 1 From window Comparator..

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Except relay what we can use on that Analog switch part..??

Hi,

did you read my post#5?
With the new informations I´d use 0.772 Ohms and 0.388 Ohms in series.
Power supply - 0.772 Ohms - 0.388 Ohms - LytSwitch
Use two low ohmic pots (10R ... 100R) across the 0.772 Ohms resistor.
Connect both wipers to NC and NO of an analog switch.
Connect COM of the analog switch to FB of the LytSwitch.
The range of each pot is 60...180mA, you only have to adjust them correctly.

Klaus

Yes..
Klauss

I have used one Analog switch last 6 month ago..

But i was failing..

Hi,

isn´t an analog switch as easy/difficult as a relay?

Klaus

Analog switch is difficult..

and i dont want to use relay

Hi,

Analog switch is difficult..

Click to expand...

Could you be more specific?

The only "real" difference I see is, that an analog switch needs a DC supply voltage that is wider than the expected signal voltage.

Same or similar is: (You need to take care about with both analog switch as well as relay)
* switch ON threshold voltage
* switch OFF threshold voltage
* signal voltage range
* ON resistance
* OFF resistance / leakage currents
* signal overvoltage protection
* overcurrent protection
* switching times
...

Klaus

Also bear in mind that the analog switch needs it's own power rail, it should be possible to create one from the existing rectified AC using a resistor / Zener and suitably sized reservoir capacitor but beware that there will be a start up time before the switch is operative so the 'wrong' current may be produced for a moment.

Brian.

Earlier i used this part..
https://www.ti.com/lit/ds/symlink/sn74lvc1g3157.pdf

Which was continuously failing..

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Earlier i used this part..
https://www.ti.com/lit/ds/symlink/sn74lvc1g3157.pdf

Which was continuously failing..

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Earlier i used this part..
https://www.ti.com/lit/ds/symlink/sn74lvc1g3157.pdf

Which was continuously failing..

Hi,

Come on. You are an experienced user. You should know how a forum works. --> give useful informations.

Why it was failing?
How did you recognize it?
Show us your circuit.
Give informations like supply voltage, logic input voltage levels, analog signal levels, load..

How else do you think we can give helpful answers?

Klaus

Hi.. I have developed the same on proto board and it is regulating by Fixing the FB Resistor.

Now i take the VFB(Pin) for Amplifieng it gives unbalanced output (Constant current is not following)-> Output voltage is Varyng.

I think dues to connection to amplifier circuit,it creates noise on the FB Pin and not maintaining CC Loop.

Can anyone tell me how i can vary the current by putting the 2 different shunts or with one shunt so that it can give 100mA or 200mA Constant current.

I have checked the SPDT Switches but they are not rated for 200mA Continuous current.

Thanks
Marx

Hi,

Post#5, post#7?

Klaus

Hello All,

was out for few days.
here i have developed the circuit with the Mosfet at each shunt and i can now switch the Current 100mA to 200mA and vice versa by switching M1 and M2 Accordingly.

i need help in selecting mosfet..??
which mosfet will be good N-MOS OR P-mos and how it can be connected.

Kindly help me.

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pls find the attached images as per my thinking