Yes... The pic solution is not for this project, no more pins available, but I'll look at that solution you suggested Mauricio Jancic Janso Desarrollos Microchip Consultant Program Member (54) 11-4542-3519 info@janso.com.ar www.janso.com.ar >>-----Original Message----- >>From: pic microcontroller discussion list >>[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Robert Monsen >>Sent: Thursday, July 29, 2004 4:01 PM >>To: PICLIST@MITVMA.MIT.EDU >>Subject: Re: [EE:] Discrete challenge >> >>You need a dead-man's switch. >> >>Use a retriggerable monostable. The trigger is the high side >>of the mosfet being high (suitably protected from high >>voltages.) The time constant must be larger than any expected >>PWM 'on' time. >> >>The relay is closed when the output from the monostable is >>high. If the monostable ever goes low, the relay opens. >> >>Make sure the thing starts when you first wiggle the mosfet. >> >>You could also do this with another PIC pin, monitoring the >>high side of the mosfet, of course... pic pin set to >>interrupt on low-to-high transition right before turning off >>the MOSFET. If it doesn't happen in n cycles, use another pin >>to turn off a relay. >> >>Regards, >> Bob Monsen >> >>----- Original Message ----- >>From: "Mauricio Jancic" >>To: >>Sent: Thursday, July 29, 2004 10:09 AM >>Subject: [EE:] Discrete challenge >> >> >>> Hi, >>> I basically have a FET which has a PWM signal on it's gate. >>> This >>FET >>> controls the speed of a DC motor, which runs on 300 VDC. >>> The gate Voltage is 7.5V, but there is a 18V supply >>available. >>Also, >>> in some point I have the PWM signal with 5.1V >>> >>> The FET drives the motor on the low side, meaning this that >>> the motor is continuously connected to V+ and the FET switches GND. >>> >>> What I need? Well, when the FET is destroyed it >>conducts 100% >>> and the motor goes up to 15000 RPM, being this very >>dangerous for the >>operator. >>> I need a discrete circuit that operate a RELAY which enable >>the motor >>> ONLY when the PWM is present and (before, in time, of the >>PWM) the FET >>> was not conducting. >>> >>> >>> >>> Mauricio Jancic >>> Janso Desarrollos >>> Microchip Consultant Program Member >>> (54) 11-4542-3519 >>> info@janso.com.ar >>> www.janso.com.ar >>> >>> -- >>> http://www.piclist.com hint: To leave the PICList >>> mailto:piclist-unsubscribe-request@mitvma.mit.edu >> >>-- >>http://www.piclist.com hint: To leave the PICList >>mailto:piclist-unsubscribe-request@mitvma.mit.edu >> -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu