Fast DC solid state relay - Page 1
Forum section: electronics / projects

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: March 16, 2012, 11:43:51 pm
content: For specific timing tests of output driver diagnostics, I'd need some kind of very fast switching (solid state) relay with low on-resistance (definitely below 0.1Ohm).In a nutshell, I'd like to apply e.g. a 500µs short circuit to ground, open load or short circuit to power condition on low side driver outputs and also on high side driver outputs. Since the outputs have full diagnostic capabilities, they will switch off quickly in case of critical overcurrent (within a a few microseconds), but for this short time, the short circuit current will be pretty high (let's say like 30A or even more).While I think I could probably use an N-channel logic level FET (e.g. IRLIZ 44N) controlled by a signal generator with an according offset/amplitude, I'd like to use a more solid solution for a couple or reason. E.g. I'd like to control the switch with a 0V/5V signal without the need to adjust the offset for the specific test case. And honestly there is no time to design and test a circuit. I'd need a solid product that's just working and that's easily available. Price is not so much of a problem. This is neither for private stuff nor for mass production.Anyway, I searched around a little and found FET based solid state relays designed to switch a DC voltage, namely the Hongfa HFS33 and the Crydom D1D40. However, according to the datasheets, these are too slow for my application. E.g. the the HFS33 defines turn-on/off times of 500µs and the D1 100µs/1ms. I could live with turn-on/off times of around 100µs, but not much more.So are there faster DC solid state relays available?Ok, I found the HDD-6V20E and HDD-1V50E from Power-IO. Unfortunately, there don't seem to be available over here in Europe...

author: Rufus
author_rank: Super Contributor
timestamp: March 17, 2012, 01:28:40 am
content: SSRs are generally LEDs shining on PV cells driving the gates of back to back MOSFETs so the weak gate drive makes them inherently slow.Seems to me you just need an N channel MOSFET with floating gate drive, if it is manual then what is wrong with a button, 555 timer and 9v battery? If it needs to be automated then maybe an off the shelf isolated RS232 interface would drive the gate hard enough (one that requires a power supply, line powered ones are likely to be wimpy).

author: Ajahn Lambda
author_rank: Regular Contributor
timestamp: March 17, 2012, 07:35:03 am
content: You'd be much further ahead using a MOSFET with an appropriate gate driver.500µs -> 2 kHz100µs -> 10 kHzNeither of those frequencies are even in the neighborhood of 'fast' for a MOSFET, nor even a BJT (which you could use to drive the MOSFET gate).

author: eevblogfan
author_rank: Frequent Contributor
timestamp: March 17, 2012, 11:08:18 am
content: heylook at this one :http://www.fairchildsemi.com/ds/FD/FDP032N08.pdf3.2mOHM , 75VDs , and crazy amount of current capabilities (235A with infinite heat sink,940A pick )335nS turn off time (typ)well , with the appropriate circuit , no one is going to win that oneand you should buy it within 15 Hr , here >http://www.ebay.com/itm/Power-MOSFET-FDP032N08-235A-75V-3-2m-Lo-Gate-Charge-/170802629373?pt=LH_DefaultDomain_0&hash=item27c4a14afd#ht_2671wt_902cheers

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: March 17, 2012, 11:35:37 am
content: Dunno if I need such monsters and unfortunately, the shipping costs to Europe will partly destroy the bargain, but thanks for the recommendation.Anyway, I'd still need a fast gate driver for the N-channel FET. I figure something like aIRS2117should do.Any (other) recommendations?BTW: while searching around, I also stumbled over the FairchildFOD3180which I could use as gate driver for the FET. Although it's isolated via optocoupler, it's specified up to 250kHz switching speed with delay rise/times in the ns or low µs range.It costs around 4€ and would add a certain protection for the input stage.Opinions on this?

author: Short Circuit
author_rank: Frequent Contributor
timestamp: March 17, 2012, 12:51:45 pm
content: Or something like this;http://www.analog.com/en/interface/digital-isolators/adum1233/products/product.htmlUp to 5MHz, but output current only 100mA, so you'd need a fairly low capacitance mosfet