fast switching BJT or MOSFET

[electricshock]

WHICH DEVICE IS FASTER OUT OF BJT , MOSFET ,IGBTs and SCRs for fast switching. is it possible to have solid state relays which can switch 220 V ac.

 

[electricuwe]

Switching speed of most devices (for all of the devices you mentioned) is also a function of the drive cicuit.

If an approbiate driver is used the switching speeds are (from fast to slow)

Mosfet
IGBT
BJT
SCR

There are several types of solid state relais available on the market. Small ones using Mosfets and larger devices (up to 100 A) using thyristors. But keep in mind that such device are not intended for fast switching (compared to the characterisic of the semiconductor device)since solid state devices use special driving circuits!

 

[nbucska]

Solid State relays are slow switching : they wait for the next 0-crossing and swith at 0 voltage to reduce noise.

Why do you need speed ? <nbucska@pcperipherals.com>

 

[electricshock]

thanks friends
i would like to discuss it bit more..
off to on time for typical transistor relays is 5-15 microseconds ie transistor when used as a switch it takes approximately this much time. now as electricuwe has pointed out this time also finds lots of variation depending upon driver ckt and device.anyway the timing is much faster as compared to electromechanical relays irrespective of the device. so nbusca, microsecond order of time is o.k for me to operate a device which should close within 25 millisecond.
a related queery is.. transistor when used as a switch can handle dc voltage only in the output ie. one can easily connect a dc operated relay. can any one of the solid state devices listed above operate a load which runs on 220 v . for example a 220V AC relay?

and ofcourse when these devies are used in converters and choppers , switching times might be putting limitations on max. switching frequencies attainable apart from other factors?

 

[electricuwe]

There are solid state relais available using two Mosfets in back to back connection to switch ac, but unfortunately I do not remember the manufacturer.

Solid state relais are not intended for the use in choppers or converters. Slow switching leads to high switching losses when used at high swicthing frequencies. Use the basic device (Mosfet, IGBT, BJT) together with a suitable driver for such applications.

 

[electricshock]

hi friends
i have managed to get solid state relays which provide potential free contact at the output rated for 220 V AC, 5 A but circuit details are not available. i am curious as normally we ar concerned with sourcing and sinking logic in transistor switches whereas in above case all that stuff is imaterial.

 

[electricshock]

this solid state relay should be using SCRs

 

*For the slow speeds you're asking MOSFETs are the easiest to drive.
*A simple way of using a unipolar device for AC current is to embed it in a bridge rectifier, ie. connect it to the &quot;rectified&quot; side, and then the AC side will open an close both ways.
*A nice drive method is photovoltaic. You can buy optocouplers (agilent, toshiba) that have a stack of photodiodes on the secondary side that produce enough voltage to drive a MOSFET.

Complete &quot;photovoltaic relays&quot; are produced by folk like teledyne relays and clare.