TL494, PWM controller, dead time control problem, internal offset voltage seems too high

arie.van.baren

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Mar 26, 2001, 8:24:33 AM3/26/01

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TL494CN

Problems with DTC circuit in the TL494

The circuit is regulating well.
However:
At max power, the dutycycle of the signal is not 97%, as stated by the
specifications from Texas Instruments, but only 88%. Specs and Application
Report "Designing Switching Voltage regulators with TL494" from Texas
Instruments.
At max power, due to the DTC comparator (pin 4 connected to ground)
dutycycle goes to max 88%; the active time is 35.5 micro sec, the not activ
time is 4.5 micro sec.
By connecting DTC input to - 0.5V the dutycycle is brought to 97%.
So it seems that the 0.1V internal offset voltage at the DTC comparator
input is 0.6V in stead of 0.1V.

Circuit is used as current source into an electromagnet coil.
Electromagnet coil is powerd by pnp tansistor collector and ground Through
sense resistor, the emitter of the pnp is connected to 15V. The transistor
basis is activated by Q1 collector (pin 8).
Error amplifier 1 is used as integrator. (set signal to pin 1, C=470p
between pin 3 and pin 2)
Current sense signal from sens resistor is connected to pin 1 via 10k.
Resistor RT to ground is 47k
Capacitor CT to ground is 1 n, so frequency is about 25kHz. ( T = 40micro
sec).

Is there anybody who knows or recognizes the problem?
Please send me the solution are information of recognition.

Friendly greetings
Arie van Baren

Robert

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Mar 26, 2001, 11:06:41 AM3/26/01

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"arie.van.baren" wrote:

> TL494CN
>
> Problems with DTC circuit in the TL494
>
> The circuit is regulating well.
> However:
> At max power, the dutycycle of the signal is not 97%, as stated by the
> specifications from Texas Instruments, but only 88%. Specs and Application
> Report "Designing Switching Voltage regulators with TL494" from Texas
> Instruments.

Take a look at the *data* sheet: the "TYPICAL" maximum duty cycle is 90% with
no min/ max specification given. Your measurement is close enough.

http://www-s.ti.com/sc/psheets/slvs074b/slvs074b.pdf

>
>
> Is there anybody who knows or recognizes the problem?

There is no problem.

>
> Please send me the solution are information of recognition.

Huh?

>

Genome

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Mar 28, 2001, 12:29:02 PM3/28/01

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"arie.van.baren" <a...@enraf-nonius.nl> wrote in message
news:99nfpb$bj8$1...@news1.xs4all.nl...

> TL494CN
>
> Problems with DTC circuit in the TL494
>

> Friendly greetings
> Arie van Baren
>
>
>
>

What are you trying to do?

DNA

nimi...@gmail.com

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Oct 21, 2015, 6:42:09 AM10/21/15

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I have tl494 in I ball amps in which I get 5 vsb & power on signal perfectly. But no output at 5 12 3.3etc
In pin4 tl494 I get 3.3 voltage what does it mean????? Please guide me .
How to check drive of push pull & ct rt oscillator.??????

legg

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Oct 21, 2015, 9:24:01 AM10/21/15

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The TL494's minimum operating supply voltage is 7V.

It has no internal undervoltage lock-out; supply current and pin
characteristics are undefined at start-up or when its supply voltage
is low.

Dead time control (DTC) pin 4 is an input that you are expected to
control, normally grounded for minimum deadtime.

RL