36w dimmable driver
Sir,
we are in to develop a 36w dimmable driver with the help of DER286. We use LNK 409G. We need your help to design a bleeder ckt for triac dimming. We use 4A scr and 130ohm/3w resistor for active damper. What should be the value for
bleeder capacitor and resistor? We tried 220nf with 450 ohm , but dimming is not ok. Again with 330nf & 330ohms , gives better dimming. Power factor should not fall below 0.9. Please suggest values for bleeder components.
Thanks
SDM
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Hi,
thanks for your guidance. We made a 36w dimmable driver using the same components as per der286 with a SCR DAMPER (130ohms damper) and a bleeder ckt with 330nF, 330ohms. Transformer design as per PIXLs designer using PQ2625. Output is 50V/0.7A. We get 49.9V /0.7A at 100V input.
But the problem is current 700ma(at 100V) is increasing slowly without changing the input. After 30mins from starting, current increased from 700 to 725ma for the same input 100v. We provide a heat sink with 50mmx15mmx2mm size. Without heat sink IC goes shut down within 2minutes. Can you please help us to rectify this problem. Also fyi damper resistor is giving more heat up to 60deg. Current through damper resistor measured 10mA. Is it a normal value?
Thanks
SDM
Hi SDM,
For 36W output level definitely you need a heatsink.Make sure to watchout the output diode temperature too.
Output current variation is due to the temperature drift of the other components(diodes, capacitance and inductance plus leakage) ,the load itself and the IC.
You need to consider the damper power rating at 90degreees conduction angle of the triac. This is at this point the input capacitance absorbs highest peak current. As such you need to balance the effective input capacitance and the damper resistor. Always monitor the input current during tuning.
Do you plan to pot the whole system? If you are going to pot it, normally the averall device temperature will go down by 20deg approximate.
Regards,
PI-Jono
Hi SDM,
You are in a correct direction to add SCR damper and and a bleeder to convert DE-286 into a dimmable design. These are the key items to watch out:
1. SCR damper timing should be around 1mS. Make sure that the input current is not ringing down to zero to avoid unwanted turn-off of the triac. The resistor (130ohms) should be adjusted depending on the ringing. Very high resistance will create noise and ringing upon SCR turn-on and too low resistance will sharpen the input current. Tune it accordingly.
2. RC bleeder is usually good for around 220nF and 510 to 1000 ohms. This is needed to avoid unwanted turn-off of the triac, monitor the input current and make sure it does not reach zero during triac conduction. It is more efficient to place it before the bridge but it can also be placed after the bridge in order to maintain above 0.9PF.
Regards,
PI-Jono