A question about PWM IC's

[Crystaleyes]

Re: A question about PWM IC's

Just a note on the source resistor, it should be a non-inductive type once you do the final repair. Also without a load on the power supply, the circuit may start but be in burst mode until a load is placed on the secondary. This is a complex, green mode ic, and the circuit operates at high frequency. The whole circuit is fairly simple as the ic does a lot of the work, I suspect and hope the ic should fix the smps.

Just a note on the source resistor, it should be a non-inductive type once you do the final repair. Also without a load on the power supply, the circuit may start but be in burst mode until a load is placed on the secondary. This is a complex, green mode ic, and the circuit operates at high frequency

Nice one for the heads-up on those points.

I was unware on 'non-conductive' resistors, so that is for sure good to know.

There are three different ones here, two are wire-wound, one a fat, green 5W affair and the other looking like a wire-wound carbon.
The third is a square-edged, white ceramic axial, 2W

Looking into it, some non-inductive resistors have an extra yellow band, which none of these have. I'll see if I can't get back to the shops today.

[Crystaleyes]

Re: A question about PWM IC's

As a last thing I can point you to in understanding this circuit and others is this site.

https://training.ti.com/pulse-width-...pwm-converters

I find the free ti training course offer a good fundamental understanding.

Cool.

Thank you for your patience.

[sam_sam_sam]

Re: A question about PWM IC's

As a last thing I can point you to in understanding this circuit and others is this site.

https://training.ti.com/pulse-width-...pwm-converters

I find the free ti training course offer a good fundamental understanding.

Thanks for posting this website link for this type of information
Very informative information

[keeney123]

Re: A question about PWM IC's

Thanks for posting this website link for this type of information
Very informative information

I once took an amplifier source from them for free. At the time they actually gave you a test and they graded it. So, your welcome.

[R_J]

Re: A question about PWM IC's

Nice one for the heads-up on those points.

I was unware on 'non-conductive' resistors, so that is for sure good to know.

There are three different ones here, two are wire-wound, one a fat, green 5W affair and the other looking like a wire-wound carbon.
The third is a square-edged, white ceramic axial, 2W

Looking into it, some non-inductive resistors have an extra yellow band, which none of these have. I'll see if I can't get back to the shops today.

Most non-inductive resistors have a black band as the last band

In this case I would just use a metal oxide type resistor, like a MOSX2CT52RR12J 0.12Ω/2watt from digikey

[Crystaleyes]

Re: A question about PWM IC's

Most non-inductive resistors have a black band as the last band

In this case I would just use a metal oxide type resistor, like a MOSX2CT52RR12J 0.12Ω/2watt from digikey

The shops were all shut on saturday due to Carnival, but are you saying that this will cause the unit to fail?
Digikey is a long way from here and the 40 USD postage is too much, so it'll have to be something else, at least for now, until I get back to Europe.

The new chip is installed, and only the source resistor remains.

Can the PSU not be switched on for a short period of time, just to verify, or is it absolutely critical to use non-inductive resistors on the source of the switching Mosfets?

[R_J]

Re: A question about PWM IC's

Any resistor should be ok for the source resistor, being such a low value I doubt there would much inductance in even a wire wound resistor. So you should be ok.
The part number I gave was from digikey KOA Speer electronics, but any supplier should be able to provide a suitable resistor

[keeney123]

Re: A question about PWM IC's

The shops were all shut on saturday due to Carnival, but are you saying that this will cause the unit to fail?
Digikey is a long way from here and the 40 USD postage is too much, so it'll have to be something else, at least for now, until I get back to Europe.

The new chip is installed, and only the source resistor remains.

Can the PSU not be switched on for a short period of time, just to verify, or is it absolutely critical to use non-inductive resistors on the source of the switching Mosfets?

So here is an insight to wire wound resistors.

https://eepower.com/resistor-guide/r...und-resistor/#

[Crystaleyes]

Re: A question about PWM IC's

A quick update.

I replaced the Ic and used a 0.12 ohm ceramic resistor and switched it on.

No 24V DC output and no frequency on the gate pin of the IC.

Unfortunately I had been using hooks to measure the FET voltages and even though it was switched off, I hadn't waited for the filter caps to discharge before removing them which shorted it out, so until I get a replacement FET there is not a lot else to report.

All invaluable lessons, although I am now short of ideas on resolving this.

This PSU is not really so important, so I may just take the experience learnt and move on, if a replacement FET does nothing new.

[Crystaleyes]

Re: A question about PWM IC's

So here is an insight to wire wound resistors.

https://eepower.com/resistor-guide/r...und-resistor/#

Thanks.

Classic quote from the first page seems to sum up my situation perfectly


“The way to succeed is to double your failure rate.”

- Thomas J. Watson

[keeney123]

Re: A question about PWM IC's

Thanks.

Classic quote from the first page seems to sum up my situation perfectly


“The way to succeed is to double your failure rate.”

- Thomas J. Watson

One of my teachers once quoted Thomas Edison on inventing something new. "It's 1% genius and 99% persistence."
Edison tried thousands of experiments to come up with the light bulb. He categorized everything he did. One of those things was the foundation for a vacuum tube.
My teacher was one of the people who made the first transistor computer that Westinghouse paid $2 million to develop.