W
Walter Harley
- Jan 1, 1970
- 0
I need to switch two 9v batteries (forming a bipolar supply) on and off,
with the following requirements:
- very low current drain, particularly when OFF.
- control by whether a sense line is grounded or open. (I've shown a
switch, but this could also be the open collector of a micropower
comparator.)
Here's what I came up with. The MOSFETs are by Supertex, little TO92 things
with around 0.5 ohm Rds(on) that cost less than $1. In simulation this
works nicely (except that I had to use a VP2206 model instead of VP3203,
since Supertex don't provide a VP3203 model). I haven't actually built it
yet.
Am I missing something? Is it really this simple?
It scares me a little that when it's on, the N-channel MOSFET is seeing Vgs
= 19v (for fresh, 9.5v batteries). The rated max is 20v. Should I put a
Zener diode in series with the collector of the 2N3906?
VP3203
----------o-------+^+--- LOAD+
V+ | |||
| ===
| ___ |
o-|___|-o
POWER | 10MEG |
_/ | ___ |
.-o/ o-----|___|-o
| | 10k |
=== | .-.
GND | | |10MEG
| | |
| '-'
/|
|
___ |
.-|___|--o
| 10MEG |
| ===
V- | |^| VN3205
-o--------+|+------------ LOAD-
created by Andy´s ASCII-Circuit v1.22.310103 Beta www.tech-chat.de
with the following requirements:
- very low current drain, particularly when OFF.
- control by whether a sense line is grounded or open. (I've shown a
switch, but this could also be the open collector of a micropower
comparator.)
Here's what I came up with. The MOSFETs are by Supertex, little TO92 things
with around 0.5 ohm Rds(on) that cost less than $1. In simulation this
works nicely (except that I had to use a VP2206 model instead of VP3203,
since Supertex don't provide a VP3203 model). I haven't actually built it
yet.
Am I missing something? Is it really this simple?
It scares me a little that when it's on, the N-channel MOSFET is seeing Vgs
= 19v (for fresh, 9.5v batteries). The rated max is 20v. Should I put a
Zener diode in series with the collector of the 2N3906?
VP3203
----------o-------+^+--- LOAD+
V+ | |||
| ===
| ___ |
o-|___|-o
POWER | 10MEG |
_/ | ___ |
.-o/ o-----|___|-o
| | 10k |
=== | .-.
GND | | |10MEG
| | |
| '-'
2N3906 |-----'
/|
|
___ |
.-|___|--o
| 10MEG |
| ===
V- | |^| VN3205
-o--------+|+------------ LOAD-
created by Andy´s ASCII-Circuit v1.22.310103 Beta www.tech-chat.de