*SG3525: Pin Connections

jpanhalt

Joined Jan 18, 2008
11,087
The fly in the ointment is that Discharge time varies with Rd (deadtime) as shown in Figure 2. For example, for a 2-uS discharge time, Ct varies by an order of magnitude. If Rd is kept at zero, then one can probably calculate a simple relationship, as is shown for similar chips. The LM3524 oscillator is simply 1/RC.

John
 
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Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Thank you guys.. ^_^


@ bertus

Sir, what type of capacitor (low tolerance?) as the CT is suitable in this application ?

..and thank you for this great info.. ^_^

 

Audioguru

Joined Dec 20, 2007
11,248
A metalized plastic film capacitor is availabe in a 5% tolerance for a low price.
In the Orient they are called a "green cap" and the letter J is 5% tolerance.
A 0.1uF, 5% is labelled "104J".
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
I think that you can attempt to derive a formula all that you wish, but at best "your mileage will vary".

I looked at a datasheet I downloaded from ST Microelectronics. It doesn't have a formula either; two separate charts for charge and discharge times.

The recommended oscillator frequency range is from 100Hz to 400kHz. You are attempting to operate this IC at the extreme lower end of the recommended range.

I suspect that the charge/discharge response curves will tend to vary significantly over temperature when you're running the IC at nearly minimum or nearly maximum frequencies. You will have to verify operation by testing.

It wasn't designed to be a precision oscillator; merely oscillate in a ballpark range.

It sounds to me like you're trying to build a UPS or inverter. That isn't what the IC was designed for. It was designed for use as a building block in a DC-DC switching power supply.
Sir, you are right I will use it to make a linear type Modified Sine wave inverter (together with a NOR gate to make a stepped-square wave).

I think by using a SG3525 PWM Controller IC in making a simple type invertor project (even the IC chosen isn't design for making an inverter accrdg. to you) , voltage regulation can be achieve just like in a DC-DC switching power supply. I'am planning to use the internal error amplifier of Sg3525 to adjust the output voltage of my simple invertor project (low ƒ) in accordance with battery voltage variation (i.e. from 13.8V to 11.8V).
Do you think its achievable? Thank you


The fly in the ointment is that Discharge time varies with Rd (deadtime) as shown in Figure 2. For example, for a 2-uS discharge time, Ct varies by an order of magnitude. If Rd is kept at zero, then one can probably calculate a simple relationship, as is shown for similar chips. The LM3524 oscillator is simply 1/RC.

John
Sir, I think the RD is also used so that OUTPUT A & B never "ON" at the same time.. so, RD must NOT kept at ZERO?
Thank you
 
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Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
A metalized plastic film capacitor is availabe in a 5% tolerance for a low price.
In the Orient they are called a "green cap" and the letter J is 5% tolerance.
A 0.1uF, 5% is labelled "104J".
Hi Audioguru.. ^_^

A metalized plastic film capacitor have a the same characteristics as the MYLAR (polyester-film) capacitor? ...'coz I saw some MYLAR with a label just like this "104J".. or a metalized plastic film capacitor is more stable?

BTW, do you think I can use the error amp. of SG3525 for voltage regulation? ...I mean to compensate for battery voltage variation. And I will use SG3525 together with a Logic gate to have a stepped-square wave. I think using this IC, "shoot-through" can be prevent..Thank you
 

Audioguru

Joined Dec 20, 2007
11,248
A metalized plastic film capacitor have a the same characteristics as the MYLAR (polyester-film) capacitor? ...'coz I saw some MYLAR with a label just like this "104J".. or a metalized plastic film capacitor is more stable?
A Mylar capacitor uses a metalized polyester fim made by Dupont. Other plastics companies also make the same plastic film but call it a different name.

BTW, do you think I can use the error amp. of SG3525 for voltage regulation? ...I mean to compensate for battery voltage variation. And I will use SG3525 together with a Logic gate to have a stepped-square wave. I think using this IC, "shoot-through" can be prevent.
I didn't look at its datasheet but I think the SG3525 is about the same as a TL494.
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
A Mylar capacitor uses a metalized polyester fim made by Dupont. Other plastics companies also make the same plastic film but call it a different name.


I didn't look at its datasheet but I think the SG3525 is about the same as a TL494.
Rich (BB code):
Sir, how about a Ceramic capacitor with the same tolerance (±5%) ?
"Hey you" Stud DUDE... :D ...just kiddi'n

..how about a Ceramic capacitor with the same tolerance (±5%) ?
 
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jpanhalt

Joined Jan 18, 2008
11,087
Sir, I think the RD is also used so that OUTPUT A & B never "ON" at the same time.. so, RD must NOT kept at ZERO?
I did not say RD should be zero. I was referring to the original datasheet that showed typical frequencies with RD set to zero. As I recall, the previous posts didn't mention what value you were considering for RD either.

The new formula seems to take RD into account, but I suspect you will need to do empirical adjustments to get your intended frequency.

John
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Hi guys.. ^_^

I will use the ERROR Amp inside the Sg3525 to compensate for battery voltage variation (i.e. from 13.8V to 11.8V) to regulate the output voltage of my invertor ckt. And here is my design attempt..
Please check it.. ^_^



...Or do you think I will need a feedback from the output ?


Thank you
 

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Audioguru

Joined Dec 20, 2007
11,248
Sir, how about a Ceramic capacitor with the same tolerance (±5%) ?
I am not a SIR because I was not knighted by the old Queen.:)
An NPO ceramic capacitor is accurate and temperature stable but their value goes as high as only about 100pF.
I have never seen a 0.1uF ceramic capacitor that is temperature stable and never seen one with a tolerance less than ±20% which is no good for an inverter's oscillator.
 

bertus

Joined Apr 5, 2008
22,270
Hello,

I think your circuit will not regulate.
You are not looking at the wanted voltage to be regulated.
You have created some kind of shutdown circuit now.

Greetings,
Bertus
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Hello,

I think your circuit will not regulate.
You are not looking at the wanted voltage to be regulated.
You have created some kind of shutdown circuit now.

Greetings,
Bertus
Thank you Sir.. ^_^

Is there a way of regulating the output voltage using SG3525 ?
...through feedback from the output? How?
 

bertus

Joined Apr 5, 2008
22,270
Hello,

You must detect the output voltage and feed it back to the error amplfier.
What is the output voltage you want to make?

Greetings,
Bertus
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
So, I will need a feedback from the output of the transformer (low ƒ).. (i.e. 230Vrms Output).
Do you think the +ve input of the error amp must be connected to the Vref (pin 16)?


BTW, I will use a 12V battery to power the inverter. As the battery voltage discharges from 13.8V to 11.8V the output voltage of my low ƒ-type modified sine wave invertor decreases. So, I think I need to 'sense" the voltage variation from the battery. Something that will narrow the output pulse when the battery is charge (13.8V) and widen the output pulse when the battery is nearly discharge (11.8V). So that, the output voltage from the low ƒ transformer is "stable".

Thank you
 
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bertus

Joined Apr 5, 2008
22,270
Hello,

Take a look at the drawing of comparators i attached.
For "regulating" you could also "misuse" the softstart pin.
A higher voltage will give a broader pulse.
You should put a resistor in line with the softstart pin.

Greetings,
Bertus
 

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Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Thank you Sir.. ^_^

Which one should I use ^_^ ? INVERTING comparator or NON-Inverting ?

...Do you mean I need to connect the +ve input (pin 2) to the Vref (pin 16) and then use feedback from the output to the -ve to regulate the output. BTW, what is Max. voltage that the input of the error amp can handle?
Please explain it (elaborate) because I'm an undergraduate ^_^ Thank you
 

bertus

Joined Apr 5, 2008
22,270
Hello,

You must compare the battery voltage to a deriviate of the output voltage to regulate.
You can do this with an extra winding on the transformer, rectify the voltage from this winding and put an elco on it to obtain a DC voltage that follows the output voltage.
This DC voltage can be used to regulate the output.
(you quit often see this is smps systems).

Greetings,
Bertus
 

Thread Starter

JUAN DELA CRUZ

Joined May 27, 2008
121
Hello,

You must compare the battery voltage to a deriviate of the output voltage to regulate.
You can do this with an extra winding on the transformer, rectify the voltage from this winding and put an elco on it to obtain a DC voltage that follows the output voltage.
This DC voltage can be used to regulate the output.
(you quit often see this is smps systems).

Greetings,
Bertus
You mean something like this ?
How many voltage must be at the -ve input (pin 1) ?



I used another transformer from the output of the M-sinewave invertor
 

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