Hello,
I am trying unsuccessfully to drive the n-mosfets in my H-bridge inverter. I am using the PIC18f252 together with two IR21844 MOSFET drivers. After programming the PIC with the Pickit2 programmer, the PIC responds well when out of its application circuit (that is when disconnected from the drivers). In fact CCP1 and CCP2 output pins are almost exactly like on the MPLAB Sim interface. When connected to target circuit, the pins stop working and all go high. I thought the PIC is not able to supply the current demanded by the drivers; so I tried inserting, progressively, resistors of 22 Ohm, 33 Ohm, 100 Ohm and 1kOhm. With the first two, the result is exactly similar to when the pins are directly connected to the drivers. With the others, the pin voltage does not get to the driver input at all. Just a straight 5-volt on the driver input (one end of the resistor) but with the desired signal on the other end of the resistor (the PIC-facing end).
Furthermore, thinking it was an issue with the Mosfet driver, I used a 50kHz function generator (in TTL mode) and the driver responded wonderfully. I do not want to draw hasty conclusions, but Ineed to know if there is an issue with the 18f252 and what possible solution(s) to apply. I have spent sleepless nights on this matter and given that I have bought a packet of 18f252s I would greatly appreciate your rapid reply.
Thanks. Edwin
I am trying unsuccessfully to drive the n-mosfets in my H-bridge inverter. I am using the PIC18f252 together with two IR21844 MOSFET drivers. After programming the PIC with the Pickit2 programmer, the PIC responds well when out of its application circuit (that is when disconnected from the drivers). In fact CCP1 and CCP2 output pins are almost exactly like on the MPLAB Sim interface. When connected to target circuit, the pins stop working and all go high. I thought the PIC is not able to supply the current demanded by the drivers; so I tried inserting, progressively, resistors of 22 Ohm, 33 Ohm, 100 Ohm and 1kOhm. With the first two, the result is exactly similar to when the pins are directly connected to the drivers. With the others, the pin voltage does not get to the driver input at all. Just a straight 5-volt on the driver input (one end of the resistor) but with the desired signal on the other end of the resistor (the PIC-facing end).
Furthermore, thinking it was an issue with the Mosfet driver, I used a 50kHz function generator (in TTL mode) and the driver responded wonderfully. I do not want to draw hasty conclusions, but Ineed to know if there is an issue with the 18f252 and what possible solution(s) to apply. I have spent sleepless nights on this matter and given that I have bought a packet of 18f252s I would greatly appreciate your rapid reply.
Thanks. Edwin