Author Topic: How do I use TL494 output: Common emitter or common collector?  (Read 11973 times)

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Offline hkBattousai

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I studied TL494 datasheet carefully, but still I can't make sure of one thing (because it is not clearly stated). With what output configuration do I obtain two PWM signal with dead-time between them? Please refer to the schematics below.



Since these two configurations will give out mutually inverse pulse waveforms, one of them will yield proper dead-time while the other one will cause shoot-though. I feel that the correct configuration for my case is the common collector (emitter follower) one, but I need an experienced users confirm to get rid of my worries.

Note: The blocks represented as "Mosfet Driver" turn on their both high and low MOSFETs when their input are high, and vice versa.

Links:
TL494/TL594 Datasheet
Designing Switching Voltage Regulators With the TL494
A Simplified Power Supply Design Using the TL494 Control Circuit
 

Offline T3sl4co1l

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Re: How do I use TL494 output: Common emitter or common collector?
« Reply #1 on: July 09, 2014, 12:06:39 pm »
The emitter side output example provides active-high pulses.

Use example: http://seventransistorlabs.com/tmoranwms/Circuits_2010/12-24_Converter.png
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Offline hkBattousai

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Re: How do I use TL494 output: Common emitter or common collector?
« Reply #2 on: July 09, 2014, 12:10:56 pm »
I have found another example circuit here.



This one also takes the driving pulses from the emitters.
 

Offline GK

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Re: How do I use TL494 output: Common emitter or common collector?
« Reply #3 on: July 09, 2014, 12:17:15 pm »
The NPN emitter follower outputs of the TL494 can actually sink current as well as source it, even so they are not supposed to be used that way. I found this out by accident when I once hastily bread boarded a buck SMPS with a TL494 after only skim reading the datasheet. I drove the gate of the moderately beefy N-ch MOSFET directly from the emitter follower outputs (paralleled). Switching frequency was 60kHz and it worked fine.

There is a TI applications note on the use of the TL494 which details the internal schematic. If you study the schematic for the emitter follower outputs it is clear how the follower outputs can both sink and source current. However I would not bet on it for long term reliability!
« Last Edit: July 09, 2014, 12:20:41 pm by GK »
Bzzzzt. No longer care, over this forum shit.........ZZzzzzzzzzzzzzzzz
 


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