DigiTan
New Member
I'm in need of advice on what type of MOSFET I should use to switch off current from two battery supplies.
Basically, I've got this plan for a 6V regulator. The regulator output feeds to the supply of a graphing calculator that would normally use AAA batteries. I want to augment the original batteries with a second bank of AA cells. I've done this by linking both battery groups in parallel through a Schottky barrier pair to prevent backward current from the strongest battery set.
Then I added a regulator/TVS so that a wall adapater can be used as a third source. This also runs in parallel with the batteries and uses the same Schottyky barrier.
**broken link removed**
To maximize battery life, I want to completely shut of current from both battery groups whenever the adapater source is present. I used a relay in my previous version, however the switching time caused transients that could reset the calculator under certain conditions.
I want to replace the relay entirely. I've heard of depletion-mode MOSFETs being compared to normally-open switches, and this is exactly the type of behavior I need.
My questions are: will a depletion MOSFET in series with Battery supply 1 and 2 provide the switching I want without the need for a negative voltage supply? And will it have a very low transconductance when it is supposed to allow current from the batteries? I'm thinking the MOSFETs would go in series with D3 and D4 on the diagram?
Basically, I've got this plan for a 6V regulator. The regulator output feeds to the supply of a graphing calculator that would normally use AAA batteries. I want to augment the original batteries with a second bank of AA cells. I've done this by linking both battery groups in parallel through a Schottky barrier pair to prevent backward current from the strongest battery set.
Then I added a regulator/TVS so that a wall adapater can be used as a third source. This also runs in parallel with the batteries and uses the same Schottyky barrier.
**broken link removed**
To maximize battery life, I want to completely shut of current from both battery groups whenever the adapater source is present. I used a relay in my previous version, however the switching time caused transients that could reset the calculator under certain conditions.
I want to replace the relay entirely. I've heard of depletion-mode MOSFETs being compared to normally-open switches, and this is exactly the type of behavior I need.
My questions are: will a depletion MOSFET in series with Battery supply 1 and 2 provide the switching I want without the need for a negative voltage supply? And will it have a very low transconductance when it is supposed to allow current from the batteries? I'm thinking the MOSFETs would go in series with D3 and D4 on the diagram?