Hi folks,
the SAP 15N and SAP15P devices are really good but a SOA protection must be included due to the weakness of the 0.22R resistors that easily blows if a short occurs. Normally the resistor blows first than the transistor 😀.
In attach you can found the schematic of a robust power amplifier developed by myself and a generic description of its functionality.
Amp description
The differential pair uses a current tail circuit and a current mirror active load that provides high open loop gain.
The output swing of the first stage is limited in order to avoid cliping with high slew rate signals (we can check this with square wave).
The diff pair uses high value emitter resistors in order to increase the linearity of this stage and to provide stability with a very smal miller capacitor, providing a a good slew-rate.
Regards 🙂
the SAP 15N and SAP15P devices are really good but a SOA protection must be included due to the weakness of the 0.22R resistors that easily blows if a short occurs. Normally the resistor blows first than the transistor 😀.
In attach you can found the schematic of a robust power amplifier developed by myself and a generic description of its functionality.
Amp description
The differential pair uses a current tail circuit and a current mirror active load that provides high open loop gain.
The output swing of the first stage is limited in order to avoid cliping with high slew rate signals (we can check this with square wave).
The diff pair uses high value emitter resistors in order to increase the linearity of this stage and to provide stability with a very smal miller capacitor, providing a a good slew-rate.
Regards 🙂
Attachments
This looks like nice work but the SAP15 pair have been obsolete more than 10 years and whilst these certainly had a problem with their internal emitter resistors, it was eliminated in the STD03 pair. As the STD types are the only type still available from authorized sellers, it makes sense to use these in new designs.
SAP darlingtons were good for sound quality and I appreciate the time and effort in this protected design but there is always a high risk to buying "pulls" or alleged genuine parts from unauthorized sellers. As time passes, supplies either become absurdly expensive or they are fakes of one type or another.
Whether we are repairers of broken amplifiers or builders of the new design, the question over genuine parts remains so I would modify the design to suit the currently available Darlingtons and just verify that it does work as specified.
SAP darlingtons were good for sound quality and I appreciate the time and effort in this protected design but there is always a high risk to buying "pulls" or alleged genuine parts from unauthorized sellers. As time passes, supplies either become absurdly expensive or they are fakes of one type or another.
Whether we are repairers of broken amplifiers or builders of the new design, the question over genuine parts remains so I would modify the design to suit the currently available Darlingtons and just verify that it does work as specified.
Your power dissipation is rather high as the transistors have a maximum dissipation of 125Watts at 50 C.
I would use at least 2 pair of them at that rail voltage. Also it's worth using the STD03 pair instead - you just need external emitter resistors. They are otherwise identical.
Yeah you are completly right!
The SAP devices are really good but obsolete 🙁
Even using ST03, probably after some years they will be removed from the market...
Considering this, in my new Board I have done some modifications to allow use the SAP, STD or a general purpose darlington devices, MJ11015 and MJ11016, and a VBE multiplier with BD139 as example 😀 See the pics.
Thanks by the feedback!
Hugo Ribeiro
The SAP devices are really good but obsolete 🙁
Even using ST03, probably after some years they will be removed from the market...
Considering this, in my new Board I have done some modifications to allow use the SAP, STD or a general purpose darlington devices, MJ11015 and MJ11016, and a VBE multiplier with BD139 as example 😀 See the pics.
Thanks by the feedback!
Hugo Ribeiro
Attachments
Yeah, with 4ohms and under high temperature, even with the protection, maybe I have a problem. You are right, 125Wrms will the maximum power dissipated in the device for an output of 250Wrms (voutmax=vsupply). I have made the design for this hipotetic case and considering low temperature with a huge heatsink 😀
For high temperature conditions we need a cooler. The other option is to use the amp with a more reduced output power... 200Wrms or 150Wrms.
Thanks by the feedback!
Hugo Ribeiro
For high temperature conditions we need a cooler. The other option is to use the amp with a more reduced output power... 200Wrms or 150Wrms.
Thanks by the feedback!
Hugo Ribeiro
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