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You need current limiting resistors in series with Q9 and Q10 collectors.ikalogic said:Okay here is what i came up with ..
**broken link removed**
now, the 2 transistors i added Q9 and Q10 are to perform a logic task.
Probably a few tens to hundreds of nanoseconds, depending on what type of transistors you use, how much excess base current you drive them with, and the impedance of the turn-off circuit.Ron H, you may notice that all transistors are 'active turn off'
i know the 2 extra transistors may cause some micro seconds of delay...
Do what you want. I think the safety factor is built in to the datasheet. Excessive base current means additional turn-off time.Now you can also notice i didn't fixe the value of the base resistors of the TIPs (Rt) .. i am leaving it open for suggestions.
I still beleive that injecting smothing like 40 mA in the base of the TIPs through 1/5 watt 220 Ohm resistors would be better (Ron H, i just viewed the data sheet. and if my collector current jumps to 5A, i'll need 20 mA of base current to maintain the collector current.., if i multiply this by 2, as a factor of safety i'll get a fare 40 mA.. what do you think?)
Yep, and he would only have to level shift at the inputs (assuming the inputs come from a 5V logic system), or maybe not at all.audioguru said:A 74LS00 logic high output can supply a minimum output voltage of 2.7V with a 0.4mA load. The 470 ohm resistors in series with some of the transistors are a (2.7V- 0.7V)/470= 4.3mA load which is 10 times higher. I don't think the gate is suitable for driving NPN transistors. An ordinary Cmos CD4011 with a 12V supply would have a much higher output current.
ikalogic said:ok, now how can i test the performance of the h bridge when its done?
with a high power resistor? , with a motor and stalling the rotor?
is there any sites which does this?
Styx said:what kind of control do you have? current-loop?
audioguru said:A 74LS00 logic high output can supply a minimum output voltage of 2.7V with a 0.4mA load. The 470 ohm resistors in series with some of the transistors are a (2.7V- 0.7V)/470= 4.3mA load which is 10 times higher. I don't think the gate is suitable for driving NPN transistors. An ordinary Cmos CD4011 with a 12V supply would have a much higher output current.
Yes, but the max supply current is only 50ma so you can't have all 4 gates with 25mA each simultaneously.ikalogic said:the 74HC00 seems to me like a real problem solver, with its +/- 25mAcurrent sink/source at 5v... right?
since only half of the h-bridge is on at once, i'll need only 2 channels, then, the 74hc00 will power the 2n2222 and the 2n2907 transistors, with a base current of about 8 mA each.. so its really ok i guess..audioguru said:Yes, but the max supply current is only 50ma so you can't have all 4 gates with 25mA each simultaneously.
Also, the 74HC00 has Cmos-level inputs and needs a pullup resistor to work from TTL signals. The 74HCT00 has TTL-level inputs so works fine with TTL-level signals.
Ron H said:You don't need 8mA of base current. Accepted practice for a saturated transistor is to set Ib=Ic/10.
ikalogic said:what do you mean by current loop..?? you mean closed loop?
Styx said:yes, if you want to do stall-tests you will need something to control the current
ikalogic said:EDIT: ooops after re-reading what you wrote.. i think i got it wrong.. well i absolutely want more information about this.. for what purpose de we need to control the current while making a stall test? shouldn't the current rises? shouldn't we just measure it? what do you mean by control in that case?
Hero999 said:To get the stall current just measure the resistance of the motor with a multimeter and use ohms law to calculate the current.
Nigel Goodwin said:Not so much 'control' as 'limit' the stall current will be MANY times the normal running current - without any limit it may well destroy things.