InnoSwitch4-CZ & ClampZero - Enabling A New Class of Mobile Device Chargers Watch Now
Solution Finder

AC DC converter TOP246P

Posted by: alex_ on Wed, 03/03/2021

Hello,

I want to convert 85-265 TO 24V 1A the below I use schematic. but I do not know why the drain voltage is not goes down to 0V. For Testing the circuit I use 120V dc as input voltage. The chip keep auto-restarting and drain voltage varies between 120V DC to 100V instead of 0V. I do not know maybe something limits the drain current and does not let TOP246P's drain goes its voltage to 0V. Please help

Log in or register to post comments

Comments

Submitted by PI-csbabu on Wed, 03/03/2021

Top switch has soft-start feature that limits the current during start-up. The peak current limit is increased gradually to max value within 10ms soft-start time.
Please check the transformer polarity and magnetizing inductance. If Lmag is too low, the current hits peak limit within short duty cycle and switch may not turn-on fully. Does M-pin connected to Source? Please share the design sheet and transformer datasheet .

Submitted by alex_ on Wed, 03/03/2021

This circuit already worked for more than 5 years(So transformer polarities is Ok). The M pin connected to source(as I read datasheet it means bypassing some features like under voltage, over voltage) should I connect it to mega ohm resistor and then M pin.

I find out some something because the drain voltage go down from 120V just around 15 voltage as a result it makes small voltage 0.5V in secondary which is not enough for turning ON TL431 and my VC pin of top246p waveform is Auto restarting and the is low frequency wave that can be seen by oscilloscope.

And I checked the transformer by oscilloscope and signal generator(Sine wave). Primary applied peak voltage is 10V as a result axillary is 1.4V and secondary is 2.5V

Submitted by PI-csbabu on Wed, 03/03/2021

Hi Alex,
The waveforms are not so clear. Do you have current probe measure drain current? Have you tried replacing the part with new one ?

Submitted by PI-csbabu on Wed, 03/03/2021

Hi Alex,
The waveforms are not so clear. Do you have current probe measure drain current? Have you tried replacing the part with new one ?

Submitted by alex_ on Wed, 03/03/2021

Hello PI-csbabu,

There is no current prob but possible that I solder 3 ohm series resistor for measuring the current.
and also I attached vdrain zoomed(Those 10V peak to peak)

Attachment Size
pi-1600x12002x_scale-2-2sp0430t.png 560.96 KB
Submitted by alex_ on Wed, 03/03/2021

Hello PI-csbabu,

There is no current prob but possible that I solder 3 ohm series resistor for measuring the current.
and also I attached vdrain zoomed(Those 10V peak to peak)

Attachment Size
pi-1600x12002x_scale-2-2sp0325t-module.png 583.79 KB
Submitted by PI-csbabu on Fri, 03/05/2021

Hi Alex,

Please connect RC across the capacitor C4 at control pin. The R =6.8 ohm and C=47 uF. During the startup this capacitor is charged by drain voltage and helps to start unit properly.

Submitted by KattiMini on Tue, 05/04/2021

Hi...use AC rather than DC power source and all ought to be alright, may be that you killed a ton of parts in the circuit meanwhile, however on the off chance that you assemble another circuit it should work.

Best case just the TOP264 is the lone thing that passed on, in spite of the fact that your comment on the exchanging proposes that it has interior security systems.....

you may likewise have murdered the transformer, did it or does it get hot ?

pcb assembly quote online