If you followed exactly the bipolar SGS example, apparently everything is ok. a) You should use the diodes. b) Check again all connections and possible "invisible short circuits" at your circuit board. Don't assume everything is ok just because you did it by yourself. When I have a problem and can't find it, I go back to the basics, checking grounds, VCC's, logic levels, every single connection, check pin by pin in sequence, as if it was done by somebody else with an error in purpose to test you, suspect everything, don't assume things are correct. Changes of having a wrong connection, bad assembly or short circuit somewhere is just 99.99%, with 1 in 10 thousand for a bad chip (except if you fried it). c) You can also try to use a 100 Ohms 10 Watts resistor, or use a 100 to 200 Watts (115Vac) normal incandescent lamp in place of the motor, and repeat the measurements. The 200 Watts lamp should represent a resistance around 60 Ohms when lit, something less when not complete warm, mainly for DC supply, probably will drain around 1 Amp from the 30Vdc supply. If you are afraid to force too much the L298, use a 100 W, or even a 60W lamp instead. Wagner. soon lee wrote: > > ----- Original Message ----- > From: Wagner Lipnharski > > Wagner wrote > > > If you are driving a transistor connected to ground, it means the motor > > has one lead to VCC, than it seems to be an under driving situation. > > This should be the reason why your voltmeter shows the same voltage no > > matter which pwm signal you use. The transistor is not switching > > completely to ground. Why don't you show a simple schematic about this > > driving design? > > > > Wagner > > the circuit that i have use is actually the circuit that is found in > appication note for L298/L293 (bi-direction) > the only thing thing i did not follow is tha used of diode at the output and > the others all the same > > thanks for your help > > regards