Hi nix
LM35DT it is a precision temperature sensor in TO-220 package for perfect mounting on heatsink. It is more accurate and less expensive from the usual bi-metal thermal breakers with fixed temp. trip point, thus it is more flexible as well.
The output of LM35 it varies according to its junction temperature by: 1mV / degC. That means, if its junction temp is 50degC its output is exactly 0,5V. The max output is 1V at 100degC.
You can use LM35 in conjuction with 2 comparators to: 1) Deactivate the output relay for disconnecting the load from the output, if the temp of heatsink exceeds e.g. 80degC when a cooling fan is faulty. For this purpose, you may set a trip point in one of the inputs of comparator at 0,8V with the aid of a voltage reference implemented from a voltage divider. 2) Manage the speed of cooling fan in 2 levels i.e. half speed and full speed. For this purpose, you can do the same as above by setting the trip point of one of the inputs of the second comparator at 0,5V (corresponding to 50degC).
For comparator use, i preffer the dual LF353.
But all above, it is only a part of the whole story of a protection circuit for an amplifier. You have to study first of all, how a comparator is operating. For example: Its (+) input it is tied in a voltage refference of 0,8V and its (-) input it is connected in the output of LM35. As long as the output of LM35 it is bellow 0,8V the output of comparator remains in Hi state (which is equal to the supply voltage of comparator). When the output of LM35 goes equal to 0,8V then the output of comparator goes in Low state (which is equal to 0V). These two states, can manage the coil of a relay to open or close its contacts .
Fotios
LM35DT it is a precision temperature sensor in TO-220 package for perfect mounting on heatsink. It is more accurate and less expensive from the usual bi-metal thermal breakers with fixed temp. trip point, thus it is more flexible as well.
The output of LM35 it varies according to its junction temperature by: 1mV / degC. That means, if its junction temp is 50degC its output is exactly 0,5V. The max output is 1V at 100degC.
You can use LM35 in conjuction with 2 comparators to: 1) Deactivate the output relay for disconnecting the load from the output, if the temp of heatsink exceeds e.g. 80degC when a cooling fan is faulty. For this purpose, you may set a trip point in one of the inputs of comparator at 0,8V with the aid of a voltage reference implemented from a voltage divider. 2) Manage the speed of cooling fan in 2 levels i.e. half speed and full speed. For this purpose, you can do the same as above by setting the trip point of one of the inputs of the second comparator at 0,5V (corresponding to 50degC).
For comparator use, i preffer the dual LF353.
But all above, it is only a part of the whole story of a protection circuit for an amplifier. You have to study first of all, how a comparator is operating. For example: Its (+) input it is tied in a voltage refference of 0,8V and its (-) input it is connected in the output of LM35. As long as the output of LM35 it is bellow 0,8V the output of comparator remains in Hi state (which is equal to the supply voltage of comparator). When the output of LM35 goes equal to 0,8V then the output of comparator goes in Low state (which is equal to 0V). These two states, can manage the coil of a relay to open or close its contacts .
Fotios
Yes, you are right nix.
In the schematic that i posted, included the basic protections which used as well in many Hi-Fi power amplifiers. These are the clamping diodes in output, the zobel network and the output inductor and the VI limitter. For a high power amplifier for PA use, these protections are not enough. An extra protection circuit it is indispensable. This circuit, in modern PA amplifiers, does not includes only the standard DC and thermal protection of the past years. It is a quite sophisticated computer, which computes each moment the state in the output of amplifier and compares the input - output signal. If detects an abuse, then reacts by activating either an input limitter or deactivating the output relay.
Many well known brands have passed from my workbench for service. I had the luck to study a lot of different versions of protection computers. Each constructor uses its own scheme. After the long time of the study of these circuits, and when i had understand: "why is monitored this point?" and: "how reacts this device when is activated?" then i proceeded in the design of a circuit of mine invention. These circuits does not have any relation with audio schemes, these are servo-controllers and have relation with automation circuits. Because i had enough expertise in such type electronics, the design of a new was a relativelly easy work to me.
Fotios
In the schematic that i posted, included the basic protections which used as well in many Hi-Fi power amplifiers. These are the clamping diodes in output, the zobel network and the output inductor and the VI limitter. For a high power amplifier for PA use, these protections are not enough. An extra protection circuit it is indispensable. This circuit, in modern PA amplifiers, does not includes only the standard DC and thermal protection of the past years. It is a quite sophisticated computer, which computes each moment the state in the output of amplifier and compares the input - output signal. If detects an abuse, then reacts by activating either an input limitter or deactivating the output relay.
Many well known brands have passed from my workbench for service. I had the luck to study a lot of different versions of protection computers. Each constructor uses its own scheme. After the long time of the study of these circuits, and when i had understand: "why is monitored this point?" and: "how reacts this device when is activated?" then i proceeded in the design of a circuit of mine invention. These circuits does not have any relation with audio schemes, these are servo-controllers and have relation with automation circuits. Because i had enough expertise in such type electronics, the design of a new was a relativelly easy work to me.
Fotios
Hi fotios i want speaker protection circuit with function of LM35dt pls help KHALSAAUDIOCENTER@YAHOO.COM THANKS
so so fine
Thank you guys for your kind words. You are very polite.
@ zakzak: Your improvements and modifications on the current circuit are very good. Indeed, the lot of decoupling capacitors on the supply rails it is unnecessary. Your modification it is right. Congratulations for your success, because this project it is very difficult. 2SA1943 - 2SC5200 looks very good in output stage.
I wish you enjoy with this amplifier.
@ andrewlebon: It was my pleasure to offer my help in you and in any one he asked me. Thank you for your greetings and for your thanks.
Best regards to all
Fotios
@ zakzak: Your improvements and modifications on the current circuit are very good. Indeed, the lot of decoupling capacitors on the supply rails it is unnecessary. Your modification it is right. Congratulations for your success, because this project it is very difficult. 2SA1943 - 2SC5200 looks very good in output stage.
I wish you enjoy with this amplifier.
@ andrewlebon: It was my pleasure to offer my help in you and in any one he asked me. Thank you for your greetings and for your thanks.
Best regards to all
Fotios
hi fotios are you fine?
i need some your help;i want to replace(mj15024/25) with( mil21193/94) any changes need to protection ciricut?
any changes need if i runed dirty harry with 92v?
thank you for every think
The MJL21193/194 are more or less the same devices as the MJ15024/25..
MJL3281/1302 are way better..
Hi zakzak, thanks for your interesting to me (this question at the begining of each post "are you fine?" is placed usually and only from people which live around the Mediterranean see like Greeks). I am fine from health, hope the same for you.
By some way, wahab remark it is right. There is of course, a significant difference between MJL21193-94 and MJE15024-25. You may see at the datasheet of these devices. The SOA curve of MJL21193-94 shows e.g. for Vce=80V a maximum Ic=2.5A instead this of MJ15024-25 shows for the same Vce=80V a maximum Ic=3.5A. In MJL21193-94 datasheet as well, you can see at the preliminary text the note: High SOA:2.25A, 80V, 1 Second. Instead in datasheet of MJ15024-25 is referred: High Safe Operating Area (100% Tested) - 2A @ 80V. This indicates that MJ15024-25 are more strong than MJL21193-94. And this is reasonable not only because the TO-3 metal case which is used in MJ15024-25, but as well the difference in fabrication between these devices. Each designer has its own philosophy. PA amplifiers suffers heavy abuse during operation. Using MJL21193-94 in output you have to visit the service, say, each 1 year for replacing destroyed output transistors. Using MJ15024-25 in output, the time of possible service is extended, say, at 5 years at least. So the choice is yours. If you wish to use MJLs in output, the only that i have to suggest you it is to add another one pair in the output. The issue it is to keep the Ic per each device lower than 1,5A (regardless of the load connected in output). Can you make some calculations? For 92V supply, the MJ15024-25 SOA shows a max Ic=1,3A approximately. For a load of 4 ohms, that means Ic = 92Vp/4Ohms = 23Ap which is theoretical only. Because 92Vp^2/4Ohms = 2116Wp = 1496Wrms. In practice, a power transformer of 1,5KW/2 X 92V under such load will drop down its output voltage at 80V approximately (i talk for low frequencies, bellow 150 Hz) and thus you will have Ic = 80Vp/4Ohms = 20Ap/device. To keep the Ic = 1,5Ap we need 20/1,5 = 13 transistors per rail, or 26 transistors total. That is unrealistic! For this reason we use the VI limiter circuit, which restricts instantly (during heavy loading of output transistors from music bass frequencies) the drive signal of output transistors, allowing thus the use of 9 to 10 pairs as much (i talk for MJ15024-25, for MJL you have to add two pairs more to feel safe).
As for MJL3281/1302 instead are far better in audio performance than MJ15024-25 and MJL21193-94, but their SOA indicates a Ic = 1,2A approx. at 80V. In the preliminary of their datasheet, it is referred clearly that are designed for 100W Audio Frequency. Consequently, their use in the output stage of a PA amplifier it is not suitable, unless you will include 20 to 25 pairs in output! Moreover their extended bandwidth up to 30MHz it makes them very delicate in any abuse (e.g. reactive loading) caused from PA speakers. For home use up to 100W are unsurpassed. For PA amplifiers, as i have mentioned already, the use of MJL3281/1302 as main drivers in triple Darlington output schemes (like this of Dirty Harry) it is a must.
Finally, i have a question to you zakzak: What have in your mind to build with so high supply rails of 92V each one? Maybe it is preferable to share this power in two units?
Regards
Fotios
By some way, wahab remark it is right. There is of course, a significant difference between MJL21193-94 and MJE15024-25. You may see at the datasheet of these devices. The SOA curve of MJL21193-94 shows e.g. for Vce=80V a maximum Ic=2.5A instead this of MJ15024-25 shows for the same Vce=80V a maximum Ic=3.5A. In MJL21193-94 datasheet as well, you can see at the preliminary text the note: High SOA:2.25A, 80V, 1 Second. Instead in datasheet of MJ15024-25 is referred: High Safe Operating Area (100% Tested) - 2A @ 80V. This indicates that MJ15024-25 are more strong than MJL21193-94. And this is reasonable not only because the TO-3 metal case which is used in MJ15024-25, but as well the difference in fabrication between these devices. Each designer has its own philosophy. PA amplifiers suffers heavy abuse during operation. Using MJL21193-94 in output you have to visit the service, say, each 1 year for replacing destroyed output transistors. Using MJ15024-25 in output, the time of possible service is extended, say, at 5 years at least. So the choice is yours. If you wish to use MJLs in output, the only that i have to suggest you it is to add another one pair in the output. The issue it is to keep the Ic per each device lower than 1,5A (regardless of the load connected in output). Can you make some calculations? For 92V supply, the MJ15024-25 SOA shows a max Ic=1,3A approximately. For a load of 4 ohms, that means Ic = 92Vp/4Ohms = 23Ap which is theoretical only. Because 92Vp^2/4Ohms = 2116Wp = 1496Wrms. In practice, a power transformer of 1,5KW/2 X 92V under such load will drop down its output voltage at 80V approximately (i talk for low frequencies, bellow 150 Hz) and thus you will have Ic = 80Vp/4Ohms = 20Ap/device. To keep the Ic = 1,5Ap we need 20/1,5 = 13 transistors per rail, or 26 transistors total. That is unrealistic! For this reason we use the VI limiter circuit, which restricts instantly (during heavy loading of output transistors from music bass frequencies) the drive signal of output transistors, allowing thus the use of 9 to 10 pairs as much (i talk for MJ15024-25, for MJL you have to add two pairs more to feel safe).
As for MJL3281/1302 instead are far better in audio performance than MJ15024-25 and MJL21193-94, but their SOA indicates a Ic = 1,2A approx. at 80V. In the preliminary of their datasheet, it is referred clearly that are designed for 100W Audio Frequency. Consequently, their use in the output stage of a PA amplifier it is not suitable, unless you will include 20 to 25 pairs in output! Moreover their extended bandwidth up to 30MHz it makes them very delicate in any abuse (e.g. reactive loading) caused from PA speakers. For home use up to 100W are unsurpassed. For PA amplifiers, as i have mentioned already, the use of MJL3281/1302 as main drivers in triple Darlington output schemes (like this of Dirty Harry) it is a must.
Finally, i have a question to you zakzak: What have in your mind to build with so high supply rails of 92V each one? Maybe it is preferable to share this power in two units?
Regards
Fotios
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yes i want to share this power in two units?
That is the most wise. During my career in PA audio, i did always this. For example, when i had to drive a Peavey UDH subwoofer ( a 4 port band-pass chamber driven from 4 Peavey BW speakers, 15" each one rated at 350Wrms/8Ω, thus total power 1400Wrms/2Ω) instead one monster power amplifier rated at this power, i used two Peavey CS1200X amplifiers (rated at 2 Χ 650Wrms/4Ω each one) to drive 2 speakers each one.
Regards
Fotios
Sorry for a mistake: I used NOT two Peavey CS1200X but only one to drive each UDH subwoofer. The UDH sub, had a 8way speakon socket in which was connected separately the 4 speakers. Thus i connected the 2 speakers of each side of UDH in parallel (4Ω load) to each one of the outputs of amplifier.
Yes, you can do this because the VI limiter it helps in such instances. Because it senses the output current via the resistors summing network, if you remove 2 devices from each rail, then you will remove and the emitter resistors and the sensing resistors. Thus, the trip point of VI limiter will be changed to keep the max allowable current per output transistor again at 1.5Ap. In such way it works the VI limiter. I made some PA amplifiers with only 3 pairs in output working under +/-68V supply rails and i had no problem with loads down to 4Ω.
Fotios
thank you
Reilly you are a kind man .if you need any help in medicine (i am doctor)and any think i,ll help.sorry my English not good
Thank you zakzak for your kind words and for your polite offer. I will keep it in my mind
. As for English, i am a little better from you. That is, we are illiterate from English . But i can understand what you write, and you can understand what i write. Consequently, there is no reason for us to be worried .Greetings from Greece
Fotios
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