TNY274 UV lockout

For the Power supply to stat switching at power up = 180VAC, you can use the EN/UV pin. See TNY274 data sheet page 4 “ Line Under Voltage Sense Circuit” to show you how to implement the UV function.

For the power supply to stop switching at Vin =230 Volts, you can use the BP/M pin to implement the OV shutdown.

See figure 14 of the data sheet. Connect R3 to the High voltage DC buss and adjust R3 and VR2 to shut down the controller when VAC =230VAC. You do not need to use R8. When Vin = 230 , the zener will conduct and the current into the BP/M pin should be = 6.5mA (ISD of data sheet)

Thanks. I see I was a bit confusing in my description.

Basically I want the PSU to stop switching when AC input
falls below 180V again. But i guess this is exactly how the
UV pin works?

Martin

Update:

I have tested the TNY278 using the PI eval board RD-91.

If I install a resistor R5 I can easily control the start-up voltage. No problems. My actual concern is that when voltage is ramped DOWN the switcher keeps switching all the way down to like 50VAC. I MUST stop switching when input AC falls below say 170V, with a configured UV at 180V. Is this possible someway?

Thanks.

Hello Having a similar problem was this every answered?

Looks like the site was spammed :(
Anyhow.
How does the chip lockout on a low voltage brownout?
(If it doesn't, can you indicate as such?)
Regards,
Brendan

Any help from Power Integrations?

Thank you for using Power Integration Products

The EN/UV pin Line Undervoltage functions only when

" During power up or when the switching of the power MOSFET is disabled in auto-restart, the current into the EN/UV pin must exceed 25 μA to initiate switching of the power MOSFET."
From datasheet page 4.

During normal operation the IC is fully bias. EN/UV pin monitors the current which the Internal Power Mosfet Turns-on or off. During normal operation this current is above the 25uA limit of the Line undervoltage.

At normal operation the IC is fully bias and lowering the input voltage will not lower down the EN/UV pin current to less than 25uA. The IC will monitor the EN/UV pin current to turn-on or off the Power FET. The EN/UV pin current for turn-on -off Power FET is high as compare to the Line undervoltage EN/UV pin current.

Thank you for responding but the answer is somewhat confusing.
It appears that:
If I power a unit up and it goes above 180V the unit will start functioning. If I bring the voltage down below 180 the unit continues to operate. (This is NOT undervoltage protection)

From a logical end-user standpoint this is not how an IC should work. If I go undervoltage the driver/controller should protect itself and the MOSFET from getting into a bad/brownout state.

What are some design suggestions to get the TNY274 to perform this function? I am sure the designers of the chip would have included a way to do this.

Best Regards,
Brendan

Hi Brendan

The specs does not state "Line undervoltage protection".
The specs just specifies "Line Undervoltage".
The Line undervoltage function is define on the datasheet page 4 "Line Undervoltage Sense Circuit"
The IC Ilimit function or peak current protection protects power supply during Brown-out condition.

Thanks

Regards

PI-Chloe

Hello PI-Chloe.
Can you explain how the IC protects during brown out?

Hi Brendan

Datasheet page 6 Figure 12 and Figure 13 shows power down condition.
Page 7 explains the power down condition.

When input voltage is lowered down, the power fet current will increase.
The IC will protect itself by terminating switching cycle when the DRAIN current reaches the current limit of the device. Meaning, the IC will not allow excessive current to flow to the power fet. It is always limited by the current limit parameter of the IC.

Thanks

Chloe.