SOA versus peak current limiter
That is not a VI limiter, it is a peak current limiter. A safe area of operation limiter tracks the SOA of the output stage. That means near no output the current is limited to a few amps. When near the power supply the limiter allows full current through the transistor. In this way the output stage is actually protected. I use a single slope limiter as that is enough to track and protect a good device. Multi-slope limiter is not usually required.
A peak current limiter limits the peak current only so if the output is at a low level and a fault condition occurs the current is to high to protect the transistor with that voltage across the device. If there is no limiter and the amp is very stable the peak current can be briefly very high and clear the short. With the peak current limiter the output transistor is forced into secondary breakdown and fails immediately. Hence the name- always fail blow up the amp.
That is not a VI limiter, it is a peak current limiter. A safe area of operation limiter tracks the SOA of the output stage. That means near no output the current is limited to a few amps. When near the power supply the limiter allows full current through the transistor. In this way the output stage is actually protected. I use a single slope limiter as that is enough to track and protect a good device. Multi-slope limiter is not usually required.
A peak current limiter limits the peak current only so if the output is at a low level and a fault condition occurs the current is to high to protect the transistor with that voltage across the device. If there is no limiter and the amp is very stable the peak current can be briefly very high and clear the short. With the peak current limiter the output transistor is forced into secondary breakdown and fails immediately. Hence the name- always fail blow up the amp.
Keep the car from becoming unexpectedly squirrely when stepping on the throttle. Turn the switch and be ready for it. Drowsy driving and leave the limit on for ease of operation. This is why.
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I've used these output devices with good results, they are fairly well known for audio (if not purposely designed for such applications even ?) and have a very good reputation - but of course, like other things in life, it's how you use them that matters.
sumaudioguy - are you sure about the squirrely throttle ? the instant response from the engine is a function of it's torque and not the horsepower (they are related of course) so as far as I can see the limiter doesn't help too much.
sumaudioguy - are you sure about the squirrely throttle ? the instant response from the engine is a function of it's torque and not the horsepower (they are related of course) so as far as I can see the limiter doesn't help too much.
I would like to know with two 25-0-25V 8 amp transformer if i run the amp in a bridge mode on 8E how much power would the original circuits produce.....................
and how can the bass response of the amp be increased although the amp is sounding very nice just wanted to know if i wanted to use them as subwoofer amps what needs to be done????
regards sekhar
and how can the bass response of the amp be increased although the amp is sounding very nice just wanted to know if i wanted to use them as subwoofer amps what needs to be done????
regards sekhar
is this possible that i replace the TIP3055 in the given circuit with IRFP250............
wat changes r needed??????
QUASICOMPLEMENTARY
wat changes r needed??????
QUASICOMPLEMENTARY
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Fun ride??
Sorry bad wordage- how about unexpected tire slippage. Have you ever owned a super car and driven it when very tired? I sneezed hard one time and looked down and had been going 30 and now was going 80... big oops on a surface street.
Sorry bad wordage- how about unexpected tire slippage. Have you ever owned a super car and driven it when very tired? I sneezed hard one time and looked down and had been going 30 and now was going 80... big oops on a surface street.
How about just putting modern fast BJT into this circuit? That is easy. Use good fast BJT and fast switching electrolytic everywhere. Is this a bad idea? It sure is easy to do!
How about Mouser supplies these KSC2690A KSA1220A 2 amp driver and MJL1302A MJL3281A 17amp outputs. I do not know about the BD139 BD140- specs are good but lower voltage and smaller SOA. I would only use one set of outputs and not parallel 2. In the past have used a lot of Panasonic FM caps from Digikey but there are many other good caps.
it's about time you did some of your own research.
Try this.
25Vac gives ~35Vdc.
25-0-25Vac gives ~+-35Vdc.
The maximum peak of a continuous output signal must be below 35Vpk
The maximum is likely to be between 2V and 10V below the supply rail voltage depending on the design and on the loading.
Let's assume a very good PSU feeding a very good amplifier. +-35Vdc will result in 33Vpk ( = 66Vpp = 23.4Vac) into the load.
If the load is 4r0 then the maximum power is 23.4^2 / 4 = 136W.
bridging a pair of these very good PSUs and very good amps will allow a maximum output of twice the power into twice the load resistance, i.e. 272W into 8r0.
Now look at a low current capacity PSU feeding a less than good power amp..
For this poor design, as far as power delivery is concerned, the maximum peak of a continuous output signal will be about 10V below the supply rails, about 25Vpk ( = 50Vpp = 17.68Vac) into the load.
Again for a 4r0 load, the maximum power will be 17.68^2 / 4 = 78W.
The bridged pair will deliver 156W into 8r0.
The range of output powers from your bridged pair run off 25Vac transformers is very roughly from 156W to 272W into 8r0.
This says nothing about the amps ability to drive a reactive speaker load and also says nothing about the amps reliability. It is simply a statement about power.
Now go and find sources that can confirm the calculations and the assumptions given in this explanation. Do not accept it as fact. Find corroboration or prove to yourself it is wrong.
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Thanks andrew for ur reply .......... I had a Doubt if by bridging i get 272w rms on an 8E wat is the use of bridging i can seperately drive two 4E load and get the same output and save the hassle ......... I read it some where that by bridging all most 4 times the power is avaiable if PSU is good enough........ & aint the effiency of class AB amp need to be included in the calculation........
CALculation according to me
P=25*25/ 4
=156.25W
Efficiency of class AB amp = 70% roughly
So,
70% of 156.25=109W
Correct me if I am wrong
Regards
Sekhar
Yes. If you bridge two amps, you get double the voltage across the load. Since power is voltage squared / load, doubling the voltage gives you 4 times the power, in the same load. Nothing to do with amp efficiency.
BUT, (there's always a but), since the double voltage also doubles the current, the amp has to deliver double the current in the same load. So for the amp it LOOKS like he has half the load. Therefor, if you bridge an amp with 8 ohms load, make sure the amp can handle 4 ohms load.
jd
yes, thanks for corroboration.
A bridged pair delivers double the power into double the load resistance.
Indeed. The important thing is that the output voltage doubles. Now you have several choices:
- keep the original load: the output will quadruple, BUT the amp 'sees' half the original load;
- double the load: the output power doubles, but the amp still 'sees' the original load.
jd
sorry, I cannot agree on this.
All amps I have ever measured deliver a lower output voltage when the load resistance is reduced. If the output voltage drops then the power cannot be pro rata.
eg, 20Vpk into 8r0 is equivalent to 25W
dropping to 19Vpk into 4r0 is equivalent to 45.1W
Doubling the power into double the load resistance gives 90.2W into 8r0.
That is not the same as quadruple the power by bridging.
The example is for an amplifier that loses 0.45dBV into half load resistance.
An amp that loses 1dBV into half load resistance would appear to do even worse than falling short of quad power. If the amp drops 1.5dBV into half load resistance then throw it in the bin, it's not worth listening to.
Erm .....no ...... that's Logarithmic
It's not clinical or totally prescriptive but a basic rule of thumb is
For a given dBA... 10Watts..... to double that you need 100Watts.... to double again 1000Watts.... to peel the paint from your house 10000Watts - to remove your bum and stick it on your forehead 100000Watts ......to turn you inside out and have you make nothing but rude noises for the rest of your days, 1000000Watts ......and so on
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