Testing Top246YN
I have a Top246YN in three terminal mode trying to determine whether it works.
My Setup:
48v supply with 300mA capacity
LED and 10k resistor to test the drain current
47uF cap attached to the control line and negative side to neutral
10k and series 100k pot supplying current to control
Everything seems to work just fine, the led turns on and as i increase the current to the control pin the led dims as if the duty cycle is being reduced. I has a look at the control line voltage and the shunt kicks in and holds the line at ~5.8V. The problem is that even if i dont give the control line current the thing still runs. I have even tried adding a pull down resistor. What do you think is going on? The reason the IC was pulled in the first place was that it seemed to not be feeding back in a stable manner. Any ideas?
Thanks in advance
Comments
Right, when the device starts up its internal supply charges the control pin/attached RC circuit to 5.8v to begin soft start. Yet if no external feedback is applied before the RC circuit reaches 4.8v autorestart begins. Autorestart should then put the device in a low power mode and attempt to restart the device with a frequency of eight times the RC time constant. My problem is that, in testing the device as described above, when no external feedback is applied the device continues to run. I am wondering if this could be caused by damage to the control pin.
Hi,
Yes, if there is no external feedback to the control pin, means it is open loop. the capacitor on the CONTROL pin discharges towards 4.8 V. At 4.8 V, auto-restart is activated which turns the output MOSFET off and puts the control circuitry in a low current standby mode. The high-voltage current source turns on and charges the external capacitance again. A hysteretic internal supply under-voltage comparator keeps VC within a window of typically 4.8 V to 5.8 V by turning the high-voltage current source on and off.
Just wondering when you say "no external feedback is applied the device continues to run", what does it really mean? Would you be possible to check the drain current using a current probe instead of LED, then we really know what happened. Did you test another TOP or you only tested one IC?
i think i have the same problem can you give me your schematic to verify one thing
Hi.
The reason that you see a 5.8V on the control pin is because there is a internal shunt regulator in the TOP246YN. As long as you put a voltage over 7V or so into the drain pin, you will get 5.8V on the control pin. You can find the detail in the data sheet of Top swith.
Hope this answer your question.