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TNY288 not switching

Posted by: kumarshiva on

Hi

we have designed high voltage input SMPS for our design(MOSFET in series with TNY288) . specification as follows.

input :450Vdc - 750Vdc
output : 24V/0.05A and 5V/1A.

voltages on different pins of TNY288
pin-1 EN : 2.4V
pin2 BP/UV: 5.85V
pin4 Drain : 450V

Regards
kumar

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Comments

Submitted by PI-Jedidiah on 07/02/2019

Hi,
Can I request to have a clear schematic attachment? Maybe clear enough to read the components values?
Regards,
Jedidiah

Submitted by PI-Jedidiah on 07/09/2019

Hi Kumarshiva,
Based from your schematic, you have Q1 connected to Drain pin which is initially open at the start. The schematic of TNY288 is that it's drain pin should be directly connected to the primary winding so that during start-up, BP will be charge by the path from Input Bulk capacitors to primary winding then to drain tap inside the TNY.
You will see in the block diagram of TNY datsheet that Drain pin is directly connected to a regulator then to BP pin. BP pin needs to charge up for the IC to power-up and send start-up pulses.
Regards,
Jedidiah