Driver IC for single-coil latched Relais - Page 1
Forum section: electronics / repair

author: Calvin
author_rank: Regular Contributor
timestamp: April 30, 2019, 06:04:22 am
content: Hi,I´m in search for a Driver IC for single-coil latched Relais.I know that when Panasonic Relais still were SDS, that they offered small IC drivers for their latched relais.But today I can´t find this type of driver anymore.To be precise ... I need a driver for (from one up to four) 12V relais TX2S-L-12 with a directly switched or activating input (no SPI, µC or other coded input), supplied by a single positive 12V rail.At the time I´m using a diode/cap/trans circuit which works fine so far, but the ´dead time´ between switching states is sometimes just too long.Thanks in advanceCalvin

author: pbarton
author_rank: Frequent Contributor
timestamp: April 30, 2019, 08:25:55 am
content: Here is a suitable circuit, but not a driver IChttp://oatleyelectronics.com/files/K231Bnotes.pdfAlsohttps://www.velleman.eu/downloads/29/vma331_a4v02.pdf

author: wolfp
author_rank: Contributor
timestamp: April 30, 2019, 10:48:47 am
content: What about a 12V H-bridge driver?Wolfgang

author: pbarton
author_rank: Frequent Contributor
timestamp: April 30, 2019, 05:25:19 pm
content: Would either of these do? SN754410NE or L293D (you didn't specify a relay coil current).

author: mariush
author_rank: Super Contributor
timestamp: April 30, 2019, 05:33:59 pm
content: Wouldn't it be feasible to use a small microcontroller + linear regulator (12v->3.3v-5v) to power the microcontroller, and a couple of transistors/mosfets for each relay, or something like ULN2003 (to control 12/24v/whatever with a small voltage from the micro) ?

author: floobydust
author_rank: Super Contributor
timestamp: May 01, 2019, 08:08:16 pm
content: You can use mosfet driver IC's as an H-bridge, likeTPS2812family. Those have push-pull outputs and enable pins, 8-pin package.OP could possibly use a row/column matrix to drive many latching relays.

author: Calvin
author_rank: Regular Contributor
timestamp: May 02, 2019, 06:07:47 am
content: Hi,thank You so much for Your suggestions.Unfortunately none of it looks like a real alternative to my prob.The H-bridges require some kind of pulse generation and inversion of the incoming dc-signal (either 0V or 12V from a mechanical switch) to generate the required two input signals to the driver and hence that's output pulse.Let me explain the situation a bit more.A dc-Voltage (open, 15V) is switched by a mechanical switch onto the pulse-generating circuit (2Diodes, 1Transistor, 1R, 1C).The circuit generates the positive pulse when 15V is switched on an a negative going pulse when the switch opens.I can fudge a bit with the Cap value to reduce the ´deadtime´.So far the circuit worked flawlessly, apart from the (minor) prob, that the repition rate of switching events has a lower limit of a few 100 msec, which I liked to be lower.Compared to the actual circuit in use both alternatives appear to be more effort in parts number count, real estate and cost.So it´d be nice if there were a dedicated IC around fulfilling the above described action .... there had been, but they seem to have vanished nowadays.regardsCalvin

author: Ian.M
author_rank: Super Contributor
timestamp: May 02, 2019, 08:11:24 am
content: As mentioned above the easiest option if you need more than one of these would be one of the many H-bridge ICs + a MCU. If you want a minimum parts count solution (only two ICs and three passives), Microchip have some 'HV' 8 bit PIC microcontrollers, with on-chip 5V shunt regulators. To run from a 12V supply, just add a dropper resistor and a decoupling cap. For 12V input compatibility, use another resistor to limit the input current to <1mA and let the upper internal protection diode clamp it to Vdd (only acceptable on pins that don't have analog capability). SeePIC12HV609 datasheet

author: Calvin
author_rank: Regular Contributor
timestamp: May 02, 2019, 10:48:41 am
content: Hi,thanks, but I´m hopeless with MCUs.regardsCalvin

author: Ian.M
author_rank: Super Contributor
timestamp: May 02, 2019, 01:03:53 pm
content: Well that severely limits your options and vastly increases the cost and component count compared to a MCU based solution.You may be able to get aCD4098dual monostable to do what you want, Configure one half as a positive edge triggered non-resettable monostable and the other half as a negative edge triggered non-resettable monostable, triggered by the same input signal. Beef up its Q outputs with a complimentary pair emitter follower on each to get enough drive for the relay coil wired between them. You will need to debounce the switch to get a suitable trigger signal for the 4098. Ideally use a SR flipflop with a SPDT switch, common to ground and NO and NC contacts to S and R with pullup resistors.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: May 02, 2019, 01:13:16 pm
content: Can you use the relay output, either the main contacts or a second set of contacts for feedback?Without it you would have to size the length of the pulse conservatively and hope that the relay switched. Personally, I try to avoid "hope" in my designs...

author: Calvin
author_rank: Regular Contributor
timestamp: May 03, 2019, 06:00:08 am
content: Hi,thank alot so far.I´m familiar with the more complex solutions to the prob.As I was asked for options to an existing design the room for maneuvre is rather small, since the layout and general ´structure´ should be conserved as much as possible.So that´s why I was looking for a IC that provides for the required functionality as a standalone device.If it were a completely new design I´d probabely opt for the MCU/H-Bridge.Think I´ll have to stick with the existing circuit and optimize the parts values.regardsCalvin

author: Psi
author_rank: Super Contributor
timestamp: May 03, 2019, 06:46:12 am
content: Could maybe do it with a two channel mosfet gate drive IC, or any push pull buffer.Put the relay across the output of 2 channels.Then invert one of the inputs and use some series caps to make it transition into a state with both outputs the same after the initial surge through the cap.

author: Ian.M
author_rank: Super Contributor
timestamp: May 03, 2019, 10:11:55 am
content: Using a latching relay without a feedback contact severely constrains the possible solutions. To guarantee to set/reset it you need to apply a pulse of the min. duration specced in its datasheet(which I'll call 'min_t' ). That means for every switch transition, you must generate a pulse of width min_t of the appropriate polarity. However if another transition occurs during the time min_t the pulse is active, the next pulse must be deferred. There's no way simple RC delays can do this. It could be done with a whole mess of monostables, clocked flipflops, edge detectors and logic gates in front of a H-bridge or dual N-MOSFET driver, but you aren't going to fit that in the space the dedicated IC took up.The best option due to the space constraint would be to bite the bullet and use a MCU + H-bridge. If you cant 'hack' simple MCU programming, contract it to someone that can. Using modern SMD parts it should be possible to fit them on a daughterboard with the same footprint as a DIL package IC.