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[SOLVED] Short circuit protection for IR2153

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Salvu

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Hello everyone
I need to include a short circuit protection for my new smps for amplifier using an IR2153 driving a couple of IRF740 in half bridge. Input voltage is 230vac. output voltage 40-0-40. Transformer is an ETD 39. Power around 500-600 watts.

I already winded a small 15mm core for this purpose and the ratio is 80:1 bifilar.

I need a simple but efficient circuit to pull down pin 3 of the IR2153 in adequate time in the event of short circuit and will latch till I reset.


My supply consists of a constant current start up circuit with 2 transistors with a current of 10mA at 10 volts. Then when the trafo starts oscillation and the auxiliary supply comes on and providing 13volts stabilised with a zener diode.

I am not sure if i should use an SCR or a mosfet for this purpose.

Any schematic will be very helpful.

regards, Salvu
 

d123

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Hi,

Without any numbers it's not so easy to suggest what might fit best. Simple but efficient could be a single BJT open collector, accurate maybe not so much... One option is a comparator (open collector with pull-up output), an adjustable voltage reference and a sensing resistor - assuming anything above a specific known amount of current means there is a problem so the circuit would require shutdown.
 
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KlausST

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Hi,

Use
* A shunt
* maybe an amplifier
* a comparator
* a DFF with async Clear (D=1, Clk=PWM, Clr = comparator output, Q= IR2153_enable) like LVC1G175
(I didn't check signal polarities)

This gives a cycle by cycle current limit.
* overcurrent disables driver = switches Mosfets high impedance
* a rising PWM edge re-enables driver
You may use a seperate reset signal to the DFF_clk instead of the PWM. Then you have latching overcurrent limit with seperate reset.

Klaus
 
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Salvu

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I have found this circuit and I am trying to adopt it. I can see that it is a current limiter. This I need as well as charging the secondary caps might trip the overload protection hence with this will cater for both charging the secondary caps safely and also starting the supply on load. I would like to know if this will function in time in the event of a dead short on the output.

The circuit has a constant current source in the input which will wait for the bulk cap to charge to 170 volts thus then starts charging the 47uf cap near pin 1 and when the threshold voltage is reached approximately 9 volts oscillation from the chip starts.
As oscillation starts the secondary caps starts charging and the current is limit by the set point on the preset to limit current to approximately 5amps. The relay in the input across the 15 ohm NTC resistor will close to minimize loses.

The current limiter works on the basis of reading the ripple on the line hence the AC voltage is rectified and this feeds the base of the transistor tied with pin 3. When the ripple settles to a lower value there will not be enough to drive the base of the transistor hence oscillation on the chip starts again and runs the smps continuously.

I guess this is more simple than using a current transformer.

Your opinion is greatly appreciated

What I need to know is with the R/C values shown what will be the rise time to pull pin 3 to ground.


Best regards, Salvu
 

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KlausST

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Hi,

I'm confused..
What do you want?
A short circuit protection for a mosfet?
Or a current limiter for the load?

Klaus
 

d123

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Hi,

Looks like a great circuit, beyond my level. Doesn't the BJT datasheet provide rise time info., as well as the IR2153 regarding delay and turn off? Or are you referring to the 10k and 1nF around pin 3? 10k * 1nF is 10mS to get to 2/3rds VCC or whatever comes out of pin 2.
 

Salvu

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Hi,

I'm confused..
What do you want?
A short circuit protection for a mosfet?
Or a current limiter for the load?

Klaus

Sorry Klaus, if I was a bit misleading. I am really looking for some kind of protection that protects the fets. What really I was considering is having something that works as a limiter and also shuts down in due time in the event of a short on the output. My circuit does not shut down but hiccup in the event of an overload. It will switch on and off keeping the output at a safe average current. What I don't really know if it is fast enough during a dead short or maybe the stress on the fets during this hiccup will finally damage them ending in blowing up.

Regarding the RC network I was referring to is how the limiter is sensing the load and the trigger finally to the BJT pulling pin 3 to ground. BJT it is an mpsa 42. as I forgot to detail it. Will it react fast enough?

I included a small inductance in the output so that the fets do not see a dead short during start up and also helps the transformer a bit to to straggle a lot during heavy load.

Considering what I said what is your opinion?

regards, Salvu
 

Salvu

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Hi,

Looks like a great circuit, beyond my level. Doesn't the BJT datasheet provide rise time info., as well as the IR2153 regarding delay and turn off? Or are you referring to the 10k and 1nF around pin 3? 10k * 1nF is 10mS to get to 2/3rds VCC or whatever comes out of pin 2.

Hi d123, I was referring to if the reaction of the limiter was fast enough during an overload and even a dead short.

Regards, Salvu
 

Salvu

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Hi d123, I was referring to if the reaction of the limiter was fast enough during an overload and even a dead short.

Regards, Salvu

Well I experimented a bit and trimmed out some resistor values. I ended up with a current limiter and works very well. The advantages I found where:-
1) It limits the current during charging secondary caps. (IR2153 has no soft start)
2) Can start up smps on nearly full load (600W) Max power I got was 700 watts
3) No need to reset during overload.
4) If overload is continuous the current drops to half the maximum in my case about 4.5 amps.
5) Limiter can be set not to overload the amplifier it is driving (from 1.5 to 10 amps)

IMG_0591.jpgIMG_0586.jpgIMG_0575.jpgIMG_0576.jpg

In the pics above The smps is designed for 45-0-45 at 600-700 watts.
input ac voltage 227 ac
input current 3.52 amps
output voltage 78.3
output current 9.4 amps output power 736 watts

Limiter operates at 9.5 amps

Wave forms taken across primary winding No load and full load

regards,

Salvu
 

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