Ucd for s/woofer appln

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#63
Pls tell me whether the following current sense / protection design is correct....

Trip power 275W avg into 3.6 ohms
Trip current = sqrt (275/3.6) = 8.74 A RMS
Trip voltage = 750mV
CS resistor = 750mV/8.74 = 86mohm

But my MOSFET is only 32m Ohm 🙁
 
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#65
Overcurrent protection like the sc protection in regulator circuits.

When sense voltage > 0.7 V, a bjt turns on etc. and shuts down the amp.

If I use 86mohm cs resistor, wont i lose a significant power in it?
Even though my mosfet will be 32mohm, will I not lose efficiency (because of much larger CS resistor)?
 
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#66
newvirus2008 said:
Overcurrent protection like the sc protection in regulator circuits.

When sense voltage > 0.7 V, a bjt turns on etc. and shuts down the amp.

If I use 86mohm cs resistor, wont i lose a significant power in it?
Even though my mosfet will be 32mohm, will I not lose efficiency (because of much larger CS resistor)?
Click to expand...

Where you are going to put the current sense resistor and how will you make the bjt to shutdown the amp?

Post the circuit..😕
 
#67
Ok I picked this off the UM10155 from Philips........ 🙂

I want my circuit to protect my speaker in case of large DC at output or permanent short to supply rails (Due to blown MOSFET or otherwise).

What will be my value of CS resistor? UM10155 uses 50mOhm each.
The HI side logic signal is referred to GND.
Should refer it to power GND (COM) and combine the signals (OR) to SD pin of IR2110.

Thanks.
 

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#68
newvirus2008 said:
Ok I picked this off the UM10155 from Philips........ 🙂

I want my circuit to protect my speaker in case of large DC at output or permanent short to supply rails (Due to blown MOSFET or otherwise).

What will be my value of CS resistor? UM10155 uses 50mOhm each.
The HI side logic signal is referred to GND.
Should refer it to power GND (COM) and combine the signals (OR) to SD pin of IR2110.

Thanks.
Click to expand...

You can use this circuit with same value resistor.
COM is not power GND, its just a negative rail which is reference for the gate driver chip.
In the protection circuit both bjt collectors from HI & LO side sensing have their reference to GND which is actually power gnd a.k.a centre midpoint of power supply.

Update your knowledge on level shifting of various potentials.
 
#71
Will post schematic of protection soon.

I am planning to get an 8A transformer with

1) 32 - 0 - 32 V (45V for power)
2) 11 - 0 - 11 V (15V for small signal, protection etc.)
3) 21 - 0 - 21 V (-30V for 4070, IR2110)

Can I use the -30V obtained by rectifying +/- 21 V as +15V referred to -45V (COM) for the gate drive?

If yes, across which voltages should I put the filter capacitor for this -30V?

Across 0V & -30V or across -45V & -30V?

Thanks.
 
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#72
I hate spoon feeding

newvirus2008 said:
Will post schematic of protection soon.

I am planning to get a 8A transformer like

1) 32 - 0 - 32 V (45V for power)
2) 11 - 0 - 11 V (15V for small signal, protection etc.)
3) 21 - 0 - 21 V (-30V for 4070, IR2110)

Can I use the -30V obtained by rectifying +/- 21 V as +15V referred to -45V (COM) for the gate drive?

If yes, across which voltages should I put the filter capacitor for this -30V?

Across 0V & -30V or across -45V & -30V?

Thanks.
Click to expand...

You need:

32-0-32 for power
15-0-15 for preamp and you need to regulate it also using 15V regulators
0-15 for IR2110, this also need to be regulated and referenced to -Ve power rail.
 
#80
Ordered the MOSFETS and ferroxcube core. Finished with PCB. Now i would like to calculate my inductor.

I have ordered the TN 23/24/7-4C65 toroid.
L=27uH, Al = 87n, N = 18.

But how do i know whether it saturates or not ?
My RMS current 8A. core mag length = 55.8mm
 
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