AC switch with 2 mosfets

[Adam Seychell]

I'm looking for a simple and cheap way of driving two mosfets in
series with sources tied together. I need to convert logic signal from
a microcontroller and make it control a isolate AC switch (30 VAC 50Hz
@ 4A). Switching frequency is about 2 Hz, and will power a heater
element.

How about a 555 timer driving the a small toroid transformer at 500kHz
with secondary as shown. The reset pin of the 555 can then be used to
signal the AC witch.


1:2 |
----- 10nF |
| |----||---#|| |\| D
|555 | #||#--o--| |-o---G
| | GND---#||# | |/| | S
----- ||# | 4.7k |
||# | | |
||#---------o-----o
|| | | |
| 4.7k |
| |/| | S
--| |-o---G
|\| D
|
|

 

[John Larkin]

I'm looking for a simple and cheap way of driving two mosfets in
series with sources tied together. I need to convert logic signal from
a microcontroller and make it control a isolate AC switch (30 VAC 50Hz
@ 4A). Switching frequency is about 2 Hz, and will power a heater
element.

How about a 555 timer driving the a small toroid transformer at 500kHz
with secondary as shown. The reset pin of the 555 can then be used to
signal the AC witch.


1:2 |
----- 10nF |
| |----||---#|| |\| D
|555 | #||#--o--| |-o---G
| | GND---#||# | |/| | S
----- ||# | 4.7k |
||# | | |
||#---------o-----o
|| | | |
| 4.7k |
| |/| | S
--| |-o---G
|\| D
|
|

Photovoltaic opto-couplers are cool, too. They typically generate
maybe 9 volts DC, but are rather slow, as the output current is low.

Or a triac?

John

 

[CBarn24050]

I'm looking for a simple and cheap way of driving two mosfets in

series with sources tied together. I need to convert logic signal from
a microcontroller and make it control a isolate AC switch (30 VAC 50Hz
@ 4A). Switching frequency is about 2 Hz, and will power a heater
element.

A power inverter I'm repairing has just such a device, they use a dc-dc
converter (nme1212d). If you only have 5v you could use a nme0512d instead.

 

[Walter Harley]

I'm looking for a simple and cheap way of driving two mosfets in
series with sources tied together. I need to convert logic signal from
a microcontroller and make it control a isolate AC switch (30 VAC 50Hz
@ 4A). Switching frequency is about 2 Hz, and will power a heater
element.

The usual way of doing that is to use a solid-state relay. Any special
reason you're trying to avoid that?

 

[Winfield Hill]

Adam Seychell wrote...

I'm looking for a simple and cheap way of driving two mosfets in
series with sources tied together. I need to convert logic signal from
a microcontroller and make it control a isolate AC switch (30 VAC 50Hz
@ 4A). Switching frequency is about 2 Hz, and will power a heater
element.

How about a 555 timer driving the a small toroid transformer at 500kHz
with secondary as shown. The reset pin of the 555 can then be used to
signal the AC witch.


1:2 |
----- 10nF |
| |----||---#|| |\| D
|555 | #||#--o--| |-o---G
| | GND---#||# | |/| | S
----- ||# | 4.7k |
||# | | |
||#---------o-----o
|| | | |
| 4.7k |
| |/| | S
--| |-o---G
|\| D
|
|

Connect both n-channel FET gates together, and use just one diode
to rectify your 500kHz ON pulse train.

Alternate opto schemes include using a PVI1050, see IR's DT 94-5,
or an optocoupler, see their DT 94-12.