killingtime
- Nov 21, 2011
- 2
- Joined
- Nov 21, 2011
- Messages
- 2
Hello,
I've received a batch of bt169d (nxt semi) thyristors from farnells. The datasheet specifies 4mA latching current (anode to cathode), and yet I cannot get the device to latch below 80mA. Above 80mA it behaves like a thyristor would (remove th gate current and the current still flows between a->c).
Circuit is simple:
cathode tied to ground.
anode tied to 1K ohm, tied to +12v
gate tied to central wiper of a 10K pot. Pot legs tied to 0v and 12v.
I've had 10mA into the gate (way above the gate threshold), and it still doesn't latch.
I have to add additional resistors in paralle with the 1k to get the current above 80mA.
Either NXP have sent out a bad batch of thyristors, or I'm missing something.....
Anyone help?
Just put 'bt169d nxp' into google. 1st non sponsored link back takes you to the datasheet.
Thanks.
***EDIT***
OK,
On further investigation, it would appear that the device will latch below 80mA, but only if the gate goes to high impedance after switch on (instead of to 0V). If you send the gate to 0V below 80mA, the thyristor turns off again.
As a workaround, I can place a diode in series with the gate ...... but can someone please confirm that this is normal behaviour for a thyristor?
I thought you could ground the gate ater exceeding the latching current without interrupting the anode - cathode current flow?
Thanks.
I've received a batch of bt169d (nxt semi) thyristors from farnells. The datasheet specifies 4mA latching current (anode to cathode), and yet I cannot get the device to latch below 80mA. Above 80mA it behaves like a thyristor would (remove th gate current and the current still flows between a->c).
Circuit is simple:
cathode tied to ground.
anode tied to 1K ohm, tied to +12v
gate tied to central wiper of a 10K pot. Pot legs tied to 0v and 12v.
I've had 10mA into the gate (way above the gate threshold), and it still doesn't latch.
I have to add additional resistors in paralle with the 1k to get the current above 80mA.
Either NXP have sent out a bad batch of thyristors, or I'm missing something.....
Anyone help?
Just put 'bt169d nxp' into google. 1st non sponsored link back takes you to the datasheet.
Thanks.
***EDIT***
OK,
On further investigation, it would appear that the device will latch below 80mA, but only if the gate goes to high impedance after switch on (instead of to 0V). If you send the gate to 0V below 80mA, the thyristor turns off again.
As a workaround, I can place a diode in series with the gate ...... but can someone please confirm that this is normal behaviour for a thyristor?
I thought you could ground the gate ater exceeding the latching current without interrupting the anode - cathode current flow?
Thanks.
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