TL 494 Basic Questions and Misunderstanding

[Reactance]

Hi I’m new to the TL 494 IC and my preference is for research and my interest in high power DIY CAR audio amplification as well as commercial CAR power supply design like the rockfordfostgate brands they so commonly found in 90% CAR amplifier SMPS I thought I will ditch the SG 2535 IC for now

Questions & Misunderstandings

There are 2 error amplifiers, are they used for PWM control ?or a cut off when a voltage exceeds a predefined voltage, like a comparator? And error amp2 usage would be a current sensor or even a temperature sensor?

Is PWM control only allowed on the DTC Pin 4 of the chip are there other ways of doing it? If so how?

Are most CAR SMPS driven with a 1:1 PWM 50%ON 50%OFF duty cycle or do there duty cycle vary according to the load?

Is it a must that the TL 494 require totem pole gate drivers in a push pull configuration to be present ? I have witnessed some CAR audio amplifiers never use this technique, or are it dependent on the gate drive, output voltage, and stability that it is introduced?


Thanks guys I will add more as I investigate and conduct research.



Thank you in advance and thank you all for keeping this forum alive!

[Eva]

Both error amplifiers, as well as the DTC pin, have the ability to clamp the duty cycle. The one imposing the lower duty cycle limit dominates. These error amplifiers may be employed to limit output voltage (regulation) and current.

Almost all amplifiers work with a fixed duty cycle resulting in an unregulated output.

The outputs of the TL494 can either source or sink current depending on the way they are connected, but they can't do both things at the same time. Since totem pole drive is always required for MOSFET gates, an external transistor, diode and resistor combination is usually employed (on each output) to pull down the gate as soon as the TL494 stops pulling it up.

[Reactance]

Thanks for the quicky reply

Can i get some examples on this please ?

[Mooly]

Like this
http://focus.tij.co.jp/jp/lit/an/slva001d/slva001d.pdf
This IC was used a lot in TV/VCR equipment in the 1980's.

[Reactance]

Thank you
Mooly,

Strange i was under the impression that the error amp was used to completely shut down the chip, not adj the pwm, the example show single ended config, is the example true for push pull configurations ?

[Mooly]

Hi Reactance,
Sorry I am no expert on SMPS design. I have worked on lot, mainly high voltage types and so on fault finding etc but thats a different thing.

[Reactance]

I guess diagrams like this didnt give enough information on the subject.

[Reactance]

I’m still unable to adjust the PWM of the TL 494 using one of its error amplifiers
Only the DTC PIN 4 allows me to adjust the pwm if i adjust the voltage from 0V to 3.3V I get 3% to about 50% control in a push pull layout, the reason why im not using the DTC Pin 4 is my soft start circuit is configured to control the PWM at start up and sensing logic sits there and future sensing will control shut down on PIN4 example temp sensor logic.


I don’t have a picture at hand but here is my layout of the two error amplifiers,

PIN 15 = VRef (+5V)
PIN 16 = GND
PIN 1 = 0 v~ 2.5v adjust
PIN 2 = ½ Vref 2.5 v

When varying from 2.5 to 0 or 2.5 to 0v on PIN 1 the PWM Just shuts down and back up when approximately 1v or so, but never adjusts the PWM

[Reactance]

Both error amplifiers, as well as the DTC pin, have the ability to clamp the duty cycle. The one imposing the lower duty cycle limit dominates. These error amplifiers may be employed to limit output voltage (regulation) and current.

Eva Im not 100% with you can u please elaborate ?

[Reactance]

Anyone ?