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JUAN DELA CRUZ
10-21-2008, 02:37 AM
Hi guys.. I've a trouble using SG3525 PWM controller IC..

Here are my questions..

1. What is the formula needed to calculate the Osc. frequency (not shown in the datasheet attached) ?

2. The frequency of the OUTPUT A (pin 11) & OUTPUT B (pin 11) is ½ the OSC. Output (pin 4) frequency ?

3. How can shutdown the SG3525? ...by holding SHUTDOWN (pin 10) "high" ?

Thank you

JUAN DELA CRUZ
10-21-2008, 06:18 AM
Hi guys.. I've a trouble using SG3525 PWM controller IC..

Here are my questions..

1. What is the formula needed to calculate the Osc. frequency (not shown in the datasheet attached) ?

2. The frequency of the OUTPUT A (pin 11) & OUTPUT B (pin 11) is ½ the OSC. Output (pin 4) frequency ?

3. How can shutdown the SG3525? ...by holding SHUTDOWN (pin 10) "high" ?

Thank you ^_^

jpanhalt
10-21-2008, 10:29 AM
The datasheets do not show a simple formula to use. You have to go to Figures 1 and 2 from which oscillator timing for various resistances and capacitors can be determined graphically.

Pin 10 is shutdown; alternatives are described on page 2.

The datasheets for the Linear equivalent are the same.

John

JUAN DELA CRUZ
10-22-2008, 04:14 AM
The datasheets do not show a simple formula to use. You have to go to Figures 1 and 2 from which oscillator timing for various resistances and capacitors can be determined graphically.

Pin 10 is shutdown; alternatives are described on page 2.

The datasheets for the Linear equivalent are the same.

John

Thank you sir for th info... ^_^

One more thing Sir ....is the output frequency of pin 11 (OUTPUT A) & pin 14 (OUTPUT B) is ½ the OSC. OUTPUT (pin 4) ? Thank you

bertus
10-22-2008, 05:47 AM
Hello,

The flip-flop will divide the clock frequency by 2.
The latch will deliver the pulse width.

Greetings,
Bertus

Bill_Marsden
10-22-2008, 06:07 AM
I don't have much to add (I was asked offline) but page 4 on your pdf file was interesting, looks like a practicle guide to use. Interesting chippie though, I could see trying to use it myself.

JUAN DELA CRUZ
10-22-2008, 06:17 AM
Hello,

The flip-flop will divide the clock frequency by 2.
The latch will deliver the pulse width.

Greetings,
Bertus

I don't have much to add (I was asked offline) but page 4 on your pdf file was interesting, looks like a practicle guide to use. Interesting chippie though, I could see trying to use it myself.

Thank you for both of you.. ^_^

How about the exact/ right formula in calculating the output frequency ?

...I need a 50HZ/ 60Hz output ƒ

bertus
10-22-2008, 06:26 AM
Hello,

In the datasheet the shutdown is done by connecting the shutdown-pin to Vref using a 2K resistor.
An other possibility is holding the softstart pin low via a 5 K resistor.

Greetings,
Bertus

JUAN DELA CRUZ
10-22-2008, 06:34 AM
Hello,

In the datasheet the shutdown is done by connecting the shutdown-pin to Vref using a 2K resistor.
An other possibility is holding the softstart pin low via a 5 K resistor.

Greetings,
Bertus

Thank you sir.. ^_^

1. How can I do that "automatically".. I mean to SHUTDOWN the SG3525 at a voltage for about approx. 11.8V ? Do I need an op-amp voltage comparator to detect the battery voltage (Sg3525 supply) variation from 13.8V to 11.8V ?

2. How about the exact/ right formula in calculating the output frequency ?
...I need a 50HZ/ 60Hz output ƒ @ OUTPUT A & B (pins 11/14)
..and a 100Hz / 120Hz @ OSC. Output (pin 4)

Bill_Marsden
10-22-2008, 06:58 AM
The problem is there are no formula's. I don't know if this means it isn't predictable enough, or if it was just too complex to list. If the freq is X2 whatever you actually need then you'll probably need to figure out a charge time and discharge time from Figure 1 and Figure 2 that will give you the freq you need. In other words, use the charts to calculate values, and it won't be a symetrical square wave.

You'll probably have to breadboard one to pin the values down for real, and even then use variable parts (such as variable resistors).

The shutdown as I interpret it assumes a ground, a high voltage level shuts it down. I'm not sure of it though.

JUAN DELA CRUZ
10-22-2008, 11:37 AM
How can I calculate the values of RT & CT needed to have a 100Hz/ 120Hz output from the Pin 4 (Osc. output) using these charts.

I need some assistance here 'coz I'm an undergraduate... didn't know the relation between the charge/ discharge time to the output frequency ^_^

Thank you

Bill_Marsden
10-22-2008, 12:20 PM
My best guess (and it is a guess) is to break it down. The charge time plus the discharge time should equal the period.

If you want 100Hz the period is 10ms, 10000 μs. Figure 1 shows using a .1μF cap this should be around 150KΩ to 180Ω. The discharge is going to be small no matter what, so go for 470Ω for 180μs.

10000μs + 180μs = 10180μs, which should work out to 98Hz.

Again, this is a guess. Never used the chippie.

JUAN DELA CRUZ
10-22-2008, 12:31 PM
My best guess (and it is a guess) is to break it down. The charge time plus the discharge time should equal the period.

If you want 100Hz the period is 10ms, 10000 μs. Figure 1 shows using a .1μF cap this should be around 150KΩ to 180Ω. The discharge is going to be small no matter what, so go for 470Ω for 180μs.

10000μs + 180μs = 10180μs, which should work out to 98Hz.

Again, this is a guess. Never used the chippie.

Thank you Mr. Bill ^_^

Hmmmm... I'm quite confuse. How about for 120Hz Osc. output?

bertus
10-22-2008, 12:48 PM
Hello,

The cycletime = 1 / frequency.
For 120 Hz => 1/120 = 8.333 mSec = 8333 μSec.
So look in your graphics for the resistor value with a capacitor of 0.1 μF.

Greetings,
Bertus

JUAN DELA CRUZ
10-22-2008, 12:48 PM
I've noticed that the discharge time is affected by RD (DISCHARGE resistor) shown in the second chart. That is, I think should be connected to CT & DISCHARGE pins. So, the discharge time and the charge time is independent to each other. That is, the charge time is controlled by RT & CT... and th DISCHARGE time is dependent to the value of RD (Discharge resistor) and CT. What do you think ?

bertus
10-22-2008, 01:04 PM
Hello,

I think you should add the charge- and discharge- time to calculate the cycletime.
I think it is a sawtooth generator with seperate charge and discharge resistors.

Greetings,
Bertus

JUAN DELA CRUZ
10-22-2008, 01:19 PM
I think the formula in calculating the Osc. output ƒ is 1.44 / RT (in ohm) x CT (in Farad)...
So, for OUTPUT A & B ƒ = 0.7 / RT x CT

I based it in a given tested oscillator output frequency in the SG3525A datasheet. Here (http://forum.allaboutcircuits.com/attachment.php?attachmentid=4962&d=1224681451) is the portion of the SG3525A datasheet.

JUAN DELA CRUZ
10-22-2008, 01:42 PM
So, I think using this formula..

ƒ = 1.44 / RTxCT

RT = 120kΩ, & CT = 0.1µF ..for 120Hz Oscillator output frequency

RD (discharge resistor) must have a low resistance for faster discharge..
I chose 100Ω (for approx. 25µS discharge time) using the same value of CT (0.1µF)

What do you think sir?

bertus
10-22-2008, 02:27 PM
Hello,

I think your calculations are correct.
Keep in mind that a capacitor can have a tolerance up to 20 %.
The resistor also takes part in the tolerance question, depending on the type you use.

Greetings,
Bertus

SgtWookie
10-22-2008, 02:35 PM
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.

bertus
10-22-2008, 06:36 PM
Hello,

I have looked for the timing formula and found it in a datasheet from ST.

Greetings,
Bertus

jpanhalt
10-22-2008, 08:03 PM
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

JUAN DELA CRUZ
10-22-2008, 11:31 PM
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
10-22-2008, 11:42 PM
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".

JUAN DELA CRUZ
10-22-2008, 11:50 PM
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

JUAN DELA CRUZ
10-22-2008, 11:56 PM
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
10-23-2008, 12:10 AM
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.

JUAN DELA CRUZ
10-23-2008, 07:53 AM
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.

Sir, how about a Ceramic capacitor with the same tolerance (±5%) ?

"Hey you" Stud DUDE... (http://www.aaroncake.net/forum/topic.asp?TOPIC_ID=7784&whichpage=2):D ...just kiddi'n

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

jpanhalt
10-23-2008, 09:26 AM
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

JUAN DELA CRUZ
10-23-2008, 12:37 PM
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..

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

Thank you

Audioguru
10-23-2008, 02:01 PM
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
10-23-2008, 06:25 PM
Hello,

More on capacitor technology can be found here.
http://www.educypedia.be/electronics/capacitors.htm
One example is the stability versus temperature.

Greetings,
Bertus

bertus
10-24-2008, 07:08 AM
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

JUAN DELA CRUZ
10-24-2008, 07:15 AM
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
10-24-2008, 07:18 AM
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

JUAN DELA CRUZ
10-24-2008, 07:26 AM
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

bertus
10-24-2008, 07:39 AM
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

JUAN DELA CRUZ
10-24-2008, 07:48 AM
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?

bertus
10-24-2008, 07:56 AM
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

JUAN DELA CRUZ
10-24-2008, 08:09 AM
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 (http://forum.allaboutcircuits.com/attachment.php?attachmentid=4990&stc=1&d=1224890158) ?
How many voltage must be at the -ve input (pin 1) ?

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

bertus
10-24-2008, 09:39 AM
Hello,

I think that you have connected it correctly.
If the output goes to high, the pwm will be cut as the output of the error amplifier goes low.
As far as i can see the input voltages of the error amplifier is max Vref.

Greetings,
Bertus

PS you don't have to say sir, I am just a service engineer and no professor.

JUAN DELA CRUZ
10-24-2008, 12:37 PM
Hello,

I think that you have connected it correctly.
If the output goes to high, the pwm will be cut as the output of the error amplifier goes low.
As far as i can see the input voltages of the error amplifier is max Vref.

Greetings,
Bertus

PS you don't have to say sir, I am just a service engineer and no professor.

To be an Engineer is my dream.. ^_^ . Unfortunately I didn't finish my study in college. But I'am still lucky because there are educational forum like this (AAC) that have a lot of generous members that assist me. For this reason, I can say that they are better than a real professor ^_^ .

So, can I call you Mr. Bertus ? ...or dude ^_^ ?
'Coz audioguru said that "SIR" are for the knight of the Queen.
Anyway, for me SIR can be the short term for Mister (Mr.) ^_^ as a sign of courteousness.

Back to the Topic...

So, my feedback ckt. is seemed correct ^_^

For the SHUTDOWN.. what do you think is the needed voltage for the SHUTDOWN (pin 10) to be activate ? ...Vref also? If so, if the voltage applied in Shutdown pin is less than the Vref (5.1V) the output A & B is high and when a 5.1V is applied to the shutdown pin the output A & B is LOW?

Thank you

bertus
10-24-2008, 12:46 PM
Hello,

Just call me Bertus.
For the shutdown you van use an inverting comparator.
So Vref on the + input of the comparator.
A volatage divided signal from the battery to the - input.
The output of the comparator can be connected to the shutdown-pin via a 2 K resistor.

Greetings,
Bertus

JUAN DELA CRUZ
10-24-2008, 12:51 PM
Bertus,

I need to turn-off the SG3525 when the battery voltage is LOW (11.8V).
So, do you think I will need a external op-amp as a voltage comparator to detect when the battery voltage is discharge (11.8V) ?

*I need to turn-off the Sg3525 "automatically".

Thank you

bertus
10-24-2008, 12:58 PM
Hello,

Yes, the error amplifier is already in use for regulating.

Greetings,
Bertus

JUAN DELA CRUZ
10-24-2008, 01:06 PM
Bertus, ..just call me Juan ^_^

So, I will use an EXTERNAL Op-amp.. which op-amp do you think is suited in this application?

The EXTERNAL op-amp + input should be connected also to Vref (pin 16) of the SG3525? ..and the - input is connected to the voltage divided from the battery...

Do you think I will need a positive feedback (hysteresis) for the EXTERNAL op-amp as a voltage comparator?

BTW, 5.1V at the SHUTDOWN pin is "Output ON" ..and less than 5.1V at the SHUTDOWN pin is "Output OFF" ?

Thank you

bertus
10-24-2008, 01:14 PM
Hello,

If the voltage on the shutdown-pin is higher than ca. 0.8 Volt the sg will stop pulsing.
See part of datasheet.

Greetings,
Bertus

JUAN DELA CRUZ
10-24-2008, 01:23 PM
Bertus,

So, higher than 0.8V to the SHUTDOWN (pin 16) the SG3525 is OFF ?

bertus
10-24-2008, 01:26 PM
Juan,

As you see in the table, typ. 0.8 Volts , max. 1 Volt.

Bertus

Tahmid
07-02-2009, 12:08 PM
Grounding pin 8 will also shutdown SG3525.