undervoltage lockout for flyback powersupply input

[Eeyore]

Also, note that the ripple on +V will be attenuated about 37.5dB by
the divider on the non-inverting input of the comparator.

Oh puh-leeze !

That's obfuscation of the very worst sort !

You're a damn clot as ever.

Graham

 

[John Fields]

Oh puh-leeze !

That's obfuscation of the very worst sort !

You're a damn clot as ever.

 

[legg]

---
Not necessarily, since that depends on the amplitude and frequency
of the ripple and how long it takes +V to get through the 75V
threshold, neither of which the OP specified.

Also, note that the ripple on +V will be attenuated about 37.5dB by
the divider on the non-inverting input of the comparator.

As will the voltage being measured. If the low frequency ripple on the
HV rail were only 5%, loaded, you'd want a window around the detection
points to overcome this.

If inrush limiters are thermally dependant, you'd also have to account
for supply droop as these heated up to their low resistance state, in
order to avoid loaded motorboating at low line. A simple slow start
circuit is seldom able to account for relatively long thermal time
constants.

HF ripple and pin signal noise is another issue, but the principal is
the same in most power electronic circuits.

RL

 

[Jamie Morken]

.FROM +V>---+----------------+
. |5%,2W |1%
. [150K] [7.5M]
. | |
. +----------------|-----+ TO Q3 BASE
. | | | |
. | | 5 |
. +--[909K]--+-----|---4|-\LT1716 C
. | 1% | | | >1----[100K]--B 2N3904
. |K |1% +---3|+/ 5% E
. [LN4040] [100K] |1% 2 |
. |10V | [100K] | |
. | | | | |
.GND>-------+----------+-----+-----+-----------------+

---
Better yet:


.FROM +V>---+----------------+
. |5%,1W |1%
. [300K] [7.5M]
. | |
. +----------------|-----+
. | | |
. | | 5
. +--[909K]--+-----|---4|-\LT1716
. | 1% | | | >1----> TO Q3 BASE
. |K |1% +---3|+/
. [LM4040] [100K] |1% 2
. |10V | [100K] |
. | | | |
.GND>-------+----------+-----+-----+

Hi,

Q3 can't shut the circuit off once it is started as it is powered from
the 235uH coil and Q3 shuts off once that coil is powering the UC3843.

cheers,
Jamie

 

[legg]

Q3 can't shut the circuit off once it is started as it is powered from
the 235uH coil and Q3 shuts off once that coil is powering the UC3843.

As Abott said to Costello;

" Who's on first."

An undervoltage lock-out is one of the circuit sections that must be
functional under any hot application. At present you are defeating the
purpose of the built-in UVLO circuitry in the 384x by using Q3 as
presently configured.. To shut down the circuit you would have to
defeat both Q3 and the 384x.

RL