03-08-2014, 03:53 PM
Wall wart and desktop computer FETs have a lot more gm than audio FETs in the region of 10 amps per volt with a gate that looks like a capacitor to the driver.
A linear regulator by its nature has 100% feedback with a little bit subtracted as the load increases.
SMPSU FETs run into darlington territory straight away and the ripple rejection will increase accordingly.
The driver will have lower gm due to it being driven at a very low drain currant but will still have a gm of an amp or so per volt. This is the variable mu region of the FET but with the huge overall loop gain this can largely be ignored. One from a small wall wart would be best here. The main currant pass FET is best from a computer power supply for the larger heat sink tab.
Modern LDO three terminal regulators have FETs in them and they allow you to reduce the capacitor value on the unregulated input in order to keep the power dissipation down without poor ripple rejection. The things use the extra gm to save heat in the gaps in the incoming ripple while the load voltage stays in spec.
A high voltage PSU is on my to do list but it is quite a way back in the queue.
A linear regulator by its nature has 100% feedback with a little bit subtracted as the load increases.
SMPSU FETs run into darlington territory straight away and the ripple rejection will increase accordingly.
The driver will have lower gm due to it being driven at a very low drain currant but will still have a gm of an amp or so per volt. This is the variable mu region of the FET but with the huge overall loop gain this can largely be ignored. One from a small wall wart would be best here. The main currant pass FET is best from a computer power supply for the larger heat sink tab.
Modern LDO three terminal regulators have FETs in them and they allow you to reduce the capacitor value on the unregulated input in order to keep the power dissipation down without poor ripple rejection. The things use the extra gm to save heat in the gaps in the incoming ripple while the load voltage stays in spec.
A high voltage PSU is on my to do list but it is quite a way back in the queue.
