ucd 25 watts to 1200 watts using 2 mosfets

[SERGIODS]

The there the circuit's designer finds this one in forums electronic and down after original them de4jo the link or lace :
http://www.forosdeelectronica.com/f31/ampli-highend-clased-ucd-25w-1250wrms-solo-2-mosfets-n-24854/

[Tekko]

Heres a simulation of what im gonna try when the MAX913's arrives.

[savu]

Tekko,

Hold down ALT key and then click on R14

regards,
savu

[PeterCharles]

Originally Posted by Baldin

OK. Changed a few components, and skipped the big capacitor in the input ...

Now it starts up every time, but only with a load (speaker or 8 ohm resistor).
Switching freq is 235 kHz

Because I had to remove the big cap there is 0,6 V DC on the output .... need to find a solution ... any suggestions??

Also need ot find a way to make it start without the load ...

Otherwise it seems quite good for a breadboard circuit

And I think it is an improvement over the original ........

Hi Baldin,

Just had a look at your schematic and breadboard amplifier. Amazing what can be done on breadboard!

In your circuit the bootstrap capacitor is larger (47uF) than the main supply decoupling capacitor (10uF). Having read through most of the International Rectifier site they recommend that the supply side capacitor C11 should be around 10 times larger than the bootstrap capacitor C14 between VB and VS which is charged through the high speed bootstrap diode.

Try swapping these two capacitors around and let us know whether it makes any difference. Might not, if a very good power supply is used as capacitors above about 4.7uF might not make a huge difference.

PeterCharles.

[Baldin]

Hi PeterCharles

I have not dis-asembled the circuit yet ... so I'll try it .... if it still works

Please point to where IR writes this ..... not sure at all why this should be recommended (what significance the relative size difference should make)

BR Baldin

[gogowatch]

Hello Baldin,

1. IR Application Note AN978-b HV Floating MOS-Gate Driver ICs, page 16
2. Laszlo Balogh, Design And Application Guide For High Speed MOSFET Gate Drive Circuits, page 27

Both mentioned the size of bootstrap and bypass capacitor size.

Cheers,
WK Lai

[PeterCharles]

Baldin,

Will see if I can find this info at some point, but will try and explain how they described the workings of the bootstrap capacitor circuit.

When the amplifier is first switched on the power supply charges capacitor at pin VCC first, then charges the Bootstrap Capacitor at pin VB through a high speed bootstrap rectifier D4. This sequence is quite important for the correct startup operation of the amplifier.

If the first capacitor is only 10uF it's charge will try to charge the 47uF Bootstrap capacitor rapidly through the diode and it would struggle to do so because the charge in the 10uF capacitor is smaller than the charge the 47uF capacitor can hold. Like trying to fill one's kettle quickly with a cup!

If the capacitor at VCC is large enough then it will hold enough charge for the Low side Driver stage and also enough charge to send to the High side driver stage and Bootstrap capacitor (through the diode) The diode prevents the bootstrap capacitor from becoming discharged by the larger capacitor at VCC when there is a large demand for charge from IR2110.

Some designers use totally independent power supplies for the High side and Low side driver stages to avoid these problems with Bootstrapping.

Hope it makes sense that the bootstrap capacitor should be smaller (easier to keep it topped up from the bigger capacitor)

PeterCharles

[Tekko]

So this saga continues, heres the daughter board with the MAX913 on it:


Yeah i know the layout isent that great but it was my first ever smd job and after all none of the long traces carry more than audio signals so it should be ok, atleast for a prototype.

[savu]

Any new news on the amp Tekko?

[Tekko]

Still waitin fer those MAX913 samples.